TWI489682B - Active material for lithium secondary battery, electrode for lithium secondary battery, lithium secondary battery and fabricating method thereof - Google Patents

Description

Active material for lithium secondary battery, electrode for lithium secondary battery, lithium secondary battery, and method of producing the same

The present invention relates to an active material for a lithium secondary battery, a lithium secondary battery using the active material for a lithium secondary battery, and a method for producing the same.

Previously, LiCoO ₂ was mainly used as a positive electrode active material in a lithium secondary battery. However, the discharge capacity is about 120 mAh/g to 130 mAh/g.

A material which forms a solid solution of LiCoO ₂ and other compounds is known. It has a crystal structure of α-NaFeO ₂ type, and Li[Co _1-2x Ni _x Mn _x ]O ₂ (0<x≦1/2) which is a solid solution of three components of LiCoO ₂ , LiNiO ₂ and LiMnO ₂ has been produced in 2001. Published in the year. A lithium secondary battery using LiNi _1/2 Mn _1/2 O ₂ or LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ as an example of the above solid solution as an active material has a discharge capacity of 150 mAh/ g~180mAh/g, better than LiCoO ₂ .

Non-Patent Document 1 to Non-Patent Document 4 propose three kinds of Li[Li _1/3 Mn _2/3 ]O ₂ , LiNi _1/2 Mn _1/2 O ₂ and LiCoO ₂ having an α-NaFeO ₂ type crystal structure. A solid solution of the ingredients. This material can be expressed as Li[Li, Mn, Ni, Co]O ₂ , in LiCoO ₂ having an α-NaFeO ₂ type crystal structure, in the site where Co exists, Li exists in addition to the transition metal. . Therefore, a higher discharge capacity can be expected, and in Non-Patent Document 1 to Non-Patent Document 4, a discharge capacitance of about 180 mAh/g to 200 mAh/g is reported.

However, an active material for a lithium secondary battery having a larger discharge capacity is sought.

An attempt to replace a part of a transition metal site of a transition metal compound used for a positive electrode active material for a lithium secondary battery with a different element, and examples of other active materials such as LiMn ₂ O _{4 having a} tetragonal spinel structure are numerous. A lot of research has been done. However, the effect of replacement of different elements is different for various active substances, and it is self-evident in the technical field that it is completely difficult to predict whether the effects exhibited by different materials are similarly exhibited in the case of other materials. .

Non-patent document 5 describes that a part of Co of LiCoO ₂ is replaced by Mg, and as a result, the electron conductivity at room temperature is increased (see Fig. 2 (Fig. 2)), but the discharge capacity is lowered by the addition of Mg (see Fig. 6, Fig. 8).

Non-Patent Document 6 discloses that a part of transition metal sites of LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ corresponding to a solid solution of three components of LiCoO ₂ , LiNiO ₂ and LiMnO ₂ are replaced by Mg, and as a result, a transition metal site of LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ corresponding to a solid solution of LiCoO ₂ , LiNiO ₂ and LiMnO ₂ is replaced by Mg. Still the discharge capacitance is reduced (see Fig. 8).

Non-Patent Document 7 discloses that Li[Li _0.15 Ni, which is a solid solution corresponding to two components of Li[Li _1/3 Mn _2/3 ]O ₂ and LiNi _1/2 Mn _1/2 O ₂ , is replaced by Mg. A part of the transition metal sites of _0.275 Mn _0.575 ]O ₂ results in an increase in the capacitance retention rate accompanying the charge and discharge, but the initial discharge capacity is still lowered (see Fig. 2). In addition, the reported discharge capacitance does not exceed 200 mAh/g (refer to the figure).

Further, Patent Document 1 describes "a positive electrode active material in which Li[Mn _c Ni _d Co _e Li _a M" _b ]O ₂ (M" is selected from the group consisting of B, Mg, Al, Ti, V, Cr, At least one element selected from the group consisting of Fe, Cu, and Zn, d≦c+e+a+b, c+d+e+a+b=1, 0≦a≦0.05, 0≦b≦0.05, The composite oxide represented by 0.2≦c≦0.5, 0.02≦e≦0.4) is used as a main component, and the positive electrode active material is characterized in that the specific surface area obtained by the Brunauer-Emmett-Teller (BET) method is 0.3 m. ² / g or more and 1.5 m ² /g or less, having an X-ray diffraction pattern attributable to the space group R3 / m, and a diffraction peak at 2θ = 44.1 ± 1° with respect to 2θ = 18.6 ± 1° The relative intensity ratio of the radiation peak is 0.6 or more and 1.1 or less, and the half width of the diffraction peak at 2θ=18.6±1° is 0.13° or more and 0.20° or less, and 2θ=44.1±1°. The invention has the invention that the half-height width of the diffraction peak is 0.10° or more and 0.17° or less, and the particle diameter is 3 μm or more and 20 μm or less (see Patent Application No. 6). It is also disclosed that the relative intensity ratio is set to be Positive electrode activity of 0.6 or more and 1.1 or less Quality, can provide a non-aqueous electrolyte secondary battery with good high rate discharge performance and good charge and discharge cycle performance (paragraph [0031] ~ paragraph [0032]); but does not disclose, using Mg as M" When the above-mentioned relative intensity ratio of the active material of a specific composition is within a specific range, the discharge capacity is remarkably improved, and when the full width at half maximum of the active material of the active material using Mg as the specific composition of M" is within a specific range, high rate discharge Significantly improved characteristics.

Patent Document 2 describes "a positive electrode active material containing a composition formula of Li _a Mn _0.5-x Ni _0.5-y M _x+y O ₂ (where 0 < a < 1.3, -0.1 ≦ xy ≦ 0.1, M is Li a composite oxide represented by an element other than Mn or Ni. (Application No. 1 of the patent application), and a positive electrode active material according to the second aspect of the invention is characterized in that the M is selected from the group consisting of Al, At least one element of the group consisting of Mg and Co and the coefficient in the above composition formula satisfies the composite oxide of the following relationship (0.05≦x<0.3, 0.05≦y<0.3, -0.1≦xy≦0.02,0) <a < 1.3, x + y < 0.5). According to such a configuration, a positive electrode active material capable of producing a nonaqueous electrolyte secondary battery having high rate discharge performance and high charge and discharge cycle performance and high energy density can be formed. 6th page from the bottom to the seventh row - page 7 and 4th row), "The positive electrode active material of the fifth application patent is characterized in that the total pore volume of the above composite oxide is ... or less, and CuKα is used. The relative intensity ratio of the diffraction peak at 2θ=44.1±1° of the powder X-ray diffraction pattern relative to the diffraction peak at 2θ=18.6±1° In particular, it is possible to form a positive electrode active material capable of producing a nonaqueous electrolyte secondary battery having high rate discharge performance and charge/discharge cycle performance and high energy density (high discharge capacity). The fourth embodiment of the present invention is characterized in that: the positive electrode active material of the sixth aspect of the invention is characterized in that the specific surface area of the composite oxide is ... or less, and CuKα ray is used. The relative intensity ratio of the diffraction peak at 2θ=44.1±1° of the powder X-ray diffraction pattern to the diffraction peak at 2θ=18.6±1° is 0.65 or more and 1.05 or less. A positive electrode active material capable of producing a nonaqueous electrolyte secondary battery having high rate discharge performance and excellent charge/discharge cycle performance and high energy density (high discharge capacity) (page 9, line 4 to line 10), but not It is revealed that the discharge capacity is remarkably improved when the above relative intensity ratio of the active material using Mg as a specific composition of M is within a specific range.

Further, the positive electrode active material of the seventh aspect of the invention is characterized in that the full width at half maximum of the diffraction peak at the above 2θ: 18.6±1° is 0.05° or more and 0.20° or less, and the above 2θ: 44.1±1 The half-height width of the diffraction peak at °° is 0.10° or more and 0.20° or less. According to this configuration, it is possible to form a high energy density (high discharge capacity) and charge and discharge cycle performance. An excellent positive electrode active material for a nonaqueous electrolyte secondary battery (page 9, line 11 to line 16), but does not disclose a half height of the above-mentioned diffraction peak of an active material using Mg as a specific composition of M When the width is within a specific range, the high rate discharge characteristics are remarkably improved.

Patent Document 3 discloses an active material for a lithium secondary battery containing a solid solution of a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure, and the active material for a lithium secondary battery is characterized in that The composition ratio of Li, Co, Ni, and Mn contained in the above solid solution satisfies Li _1+1/3x Co _1-xy Ni _y/2 Mn _2x/3+y/2 (x+y≦1, 0≦) y, 1-xy=z), in the triangular phase diagram of Li[Li _1/3 Mn _2/3 ]O ₂ (x)-LiNi _1/2 Mn _1/2 O ₂ (y)-LiCoO ₂ (z) system Where (x, y, z) is present at point A (0.45, 0.55, 0), point B (0.63, 0.37, 0), point C (0.7, 0.25, 0.05), point D (0.67, 0.18) , 0.15), point E (0.75, 0, 0.25), point F (0.55, 0, 0.45), and point G (0.45, 0.2, 0.35) are represented as the values of the on-line or inner range of the octagonal ABCDEFG. Further, the intensity ratio of the diffraction peaks of the (003) plane and the (104) plane obtained by the X-ray diffraction measurement is I(003)/I(104)≧1.56 before charge and discharge, and I(003) at the end of discharge. In the invention of the first aspect of the invention, "a method for producing a lithium secondary battery, wherein the maximum reaching potential of the positive electrode during charging is 4.3 V (vs. Li/Li+) The following charging method A method for producing a lithium secondary battery according to claim 9, which comprises the steps of: performing over 4.3 V (vs. Li/Li+) and being 4.8 V or less (vs. Li) The invention in which the potential change occurring in the positive electrode potential range of /Li+) reaches at least the charging of the relatively flat region (Patent No. 10) is additionally described as "in the prior active matter, due to the generation of such disorder ( Since the phase of the disorder does not cause the smooth movement of Li ions from the Li layer, it is considered that the reversible capacitance is also affected. In contrast, in the active material of the present invention, since I(003)/I(104)≧1.56, The generation of the disorder phase is extremely small, and it is generally considered that an excellent discharge capacity can be obtained" (paragraph [0068]); as an example, the diffraction peaks of the (003) plane and the (104) plane obtained by X-ray diffraction measurement are also disclosed. The active material for lithium secondary batteries having an intensity ratio of I(003)/I(104)=1.77 before charge and discharge, I(003)/I(104)=1.67 at the end of discharge, and a discharge capacitance of 225 mAh/g However, the active material does not contain Mg and is not disclosed in the above relative activity of the active substance containing a specific composition of Mg. When the intensity ratio is within a specific range, the discharge capacitance is remarkably improved.

In addition, the lithium secondary battery using the solid solution described in Patent Document 3 as an active material has a problem that a capacitor at a high rate of discharge cannot be obtained as in the comparative example described later.

Patent Document 4 describes "a layered structure having a chemical composition of Li _a Ni _x Mn _y Co _z O _2+b (x+y+z=1, 1.00<a<1.3, 0≦b<0.3). Lithium ‧ nickel ‧ manganese ‧ cobalt composite oxide, the diffraction peak angle 2θ of the (003) plane and the (104) plane of the Miller index hkl using the powder X-ray diffraction of the CuKα ray The diffraction peaks have a half-height width of 0.18° or less, and the diffraction peak angles 2θ of the (108) plane and the (110) plane are 64.40° and 65.15, respectively. And above, and the half-height widths of the diffraction peaks of the respective surfaces are all 0.18° or less (the first paragraph of the patent application); and the Miller index of the powder X-ray diffraction using the CuKα ray is also described. The diffraction peak angle 2θ of the (003) plane and the (104) plane of hkl is less than 18.65° and 44.50°, respectively, and the phase interval is reduced, the diffusion of lithium ions is suppressed, and the charge and discharge characteristics are deteriorated. When the half-height width of the diffraction peak is greater than 0.18°, the crystal growth may be insufficient and the composition variation may be large, so that the charge and discharge characteristics are deteriorated (paragraph [0017]), but not Relational characteristics shown in (003) plane diffraction peak and the (104) plane half width (FWHM) and the high-rate discharge.

Patent Document 5 describes "a positive electrode active material characterized by containing a half-height width of an X-ray diffraction peak which is attributable to a space group R-3m and corresponding to a (104) plane in a range of 0.06 to 0.15. Lithium-containing metal composite oxide particles having an average value of the shape factor SF1 calculated by the following formula (1) in a range of more than 1 and 3.3 or less. (" Patent Application No. 1) Further, it is disclosed that the crystal structure of the lithium-containing metal composite oxide particles belongs to the space group R-3m, and the full width at half maximum of the X-ray diffraction peak corresponding to the (104) plane is in the range of 0.06° to 0.15°. In the case of internal, a high discharge load characteristic (high rate discharge characteristic) can be obtained; and if the full width at half maximum exceeds 0.15°, the crystallinity of the lithium-containing metal composite oxide is lowered and it is difficult to obtain high high rate discharge characteristics (paragraph [ 0025]); however, there is no description about the inclusion of Mg in the lithium-containing metal composite oxide, and it is not suggested that the half-height width of the diffraction peak of the lithium-containing metal composite oxide containing Mg is set to a specific range. High rate discharge characteristics are significantly improved.

Patent Document 6 describes that "addition of a dissimilar element to LiNi _1/3 Mn _1/3 Co _1/3 O ₂ of the present invention exhibits an additional function, and electron transfer can be made by the addition of magnesium. Sexually improved" (paragraph [0077]); it is also disclosed that Li[Li _x (Ni _1/3 Mn _1/3 Co _1/3 ] _1-x ]O ₂ can be used to increase the lithium atomic ratio (wherein , the oxide represented by 0≦x≦0.3), the nickel manganese cobalt composite oxide obtained by mixing the composite oxide obtained by coprecipitation with lithium hydroxide in a dry manner and calcining at 1000 ° C belongs to a layer structure R3m Hexagonal system (paragraphs [0028] to [0030]); however, it has not been suggested that when magnesium is contained as a solid solution component in the nickel manganese cobalt composite oxide, the discharge capacity is remarkably improved, and the high rate discharge characteristics are remarkably improved.

Patent Document 7 discloses a lithium nickel manganese-cobalt composite oxide powder for a lithium secondary battery positive electrode material, which is composed of a crystal structure belonging to a layered structure, and has a composition of the following formula (I). It is expressed that Li[Li _z/(2+z) {(Li _x Ni _(1-3x)/2 Mn _(1+x)/2 ) _(1-y) Co _y } _2/(2+z) ] O ₂ ...(I)

(Where, 0.01≦x≦0.15, 0≦y≦0.35, 0.02(1-y)(1-3x)≦z≦0.15(1-y)(1-3x))” (Scope 6 of the patent application) Invention; and reveals that it is important that the amount of Li is within a slightly richer range of stoichiometric composition, whereby battery performance (especially rate characteristics or output characteristics) is improved (paragraphs [0014] and [0015]) However, it has not been suggested that when the lithium nickel manganese cobalt composite oxide is a specific composition containing magnesium, the discharge capacity is remarkably improved, and the high rate discharge characteristics are remarkably improved.

In addition, the positive electrode active material for a lithium secondary battery described in Patent Document 1 to Patent Document 7 is not assumed to be Li[Li _1/3 Mn _2/3 ]O ₂ , LiNi _1/2 Mn _1/2 O ₂ , or LiCoO _{2 .} And a solid solution of the four components of the LiMg _1/2 Mn _1/2 O ₂ , the non-patent document 5 to the non-patent document 7 are not included in the case where the positive electrode active material as described above contains Mg and satisfies the relative strength ratio. According to the records, it is impossible to expect an increase in discharge capacitance.

[Previous Technical Literature]

[Non-patent literature]

[Non-Patent Document 1] Electrochim. Acta, vol. 51, page 5581-5586, 2006.

[Non-Patent Document 2] J. Power Sources, vol. 146, page 598-601, 2005.

[Non-Patent Document 3] J. Electrochem. Soc., vol. 152, no. 1, page A171-A178, 2005.

[Non-Patent Document 4] Mater. Lett., vol. 58, page 3197-3200, 2004.

[Non-Patent Document 5] J. Electrochem. Soc., vol. 144, page 3164-3168, 1997.

[Non-Patent Document 6] Solid State Ionics, vol. 178, page 849-857, 2007.

[Non-Patent Document 7] J. Mater. Chem., vol 13, page 319-322, 2003.

[Patent Literature]

[Patent Document 1] Japanese Patent No. 4320548

[Patent Document 2] WO 2002/086993 A1

[Patent Document 3] WO 2009/063838 A1

[Patent Document 4] Japanese Patent No. 4216669

[Patent Document 5] Japanese Patent No. 2003-178756

[Patent Document 6] Japanese Patent No. 2003-17052

[Patent Document 7] Japanese Patent No. 2006-253119

The present invention has been made in view of the above problems, and an object of the invention is to provide an active material for a lithium secondary battery having a large discharge capacity and high rate discharge characteristics, and a lithium secondary battery using the active material for a lithium secondary battery.

The technical concept of the configuration and effects of the present invention will be described. Among them, the mechanism of action includes presumption, and its correctness does not limit the present invention. Further, the present invention can be embodied in other various forms without departing from the spirit or essential characteristics thereof. Therefore, the embodiments or experimental examples described below are merely illustrative and not restrictive in all respects. Further, variations or modifications of the equivalent scope of the claims are all within the scope of the invention.

A material having an α-NaFeO ₂ type crystal structure and exhibiting Li[Li, Mn, Ni, Co]O ₂ should pay attention to the valence of each metal element present at the transition metal site. In other words, when a material which can be expressed as Li[Li, Mn, Ni, Co]O ₂ is synthesized, the composition ratio of Li, Co, Ni, and Mn which are metal elements contained in the raw material is not arbitrarily set, but is present in The ratio of each metal element is set under the condition that the valence of each metal element at the transition metal site becomes Li ¹⁺ , Mn ⁴⁺ , Ni ²⁺ , Co ³⁺ , and the X-ray is used in the material thus synthesized. When a substance having a half-height width of a diffraction peak in a specific range is used as an active material for a lithium secondary battery, a high discharge capacity can be exhibited.

The condition that the valence of each metal element becomes Li ¹⁺ , Mn ⁴⁺ , Ni ²⁺ , and Co ³⁺ can be assumed by considering Li[Li _1/3 Mn _2/3 ]O ₂ , LiNi _1/2 Mn _1/2 A solid solution of three components of O ₂ and LiCoO ₂ is provided. That is, by considering xLi[Li _1/3 Mn _2/3 ]O ₂ -yLiNi _1/2 Mn _1/2 O ₂ -(1-xy)LiCoO ₂ (where x>0, y>0, x+ y<1), and arbitrarily select x and y, theoretically, the valence of each metal element present in the transition metal site of the α-NaFeO ₂ type crystal structure is Li ¹⁺ , Mn ⁴⁺ , Ni ²⁺ , Co ³⁺ .

The active material for a lithium secondary battery of the present invention is characterized by containing Mg, but at this time, it is also necessary to pay attention to the valence of the metal element present at the transition metal site. That is, the ratio of each metal element is set under the condition that the valence of each metal element present at the transition metal site becomes Li ¹⁺ , Co ³⁺ , Ni ²⁺ , Mn ⁴⁺ , and Mg ²⁺ . The effects of the invention are remarkably exhibited.

Here, when setting the Mg ratio under the conditions of maintaining Li ¹⁺ , Mn ⁴⁺ , Ni ²⁺ , Co ³⁺ , and Mg ²⁺ , several ideas can be employed. The first idea is to replace the Ni ²⁺ _1/2 Mn ⁴⁺ _1/2 moiety constituting the envisioned LiNi _1/2 Mn _1/2 O ₂ by Mg ²⁺ _1/2 Mn ⁴⁺ _1/2 The method of setting the Mg ratio by thinking is described in detail in the present specification as Example 2-1 to Example 2-6. The second idea is to replace [Li _1/3 Mn _2/3 ] ³ constituting the envisioned Li[Li _1/3 Mn _2/3 ]O ₂ by [Mg _1/2 Mn _1/2 ] ^{3+ +} partial thinking method set Mg ratio, and to be specific details as an example of the specification of examples 2-7 to 2-10. The third idea is to think of a method of setting the Mg ratio based on the idea of replacing Co ³⁺ by [Mg _1/2 Mn _1/2 ] ³⁺ . Also think of a method of repeatedly applying 2 or 3 of these ideas.

When using any of the above ideas, it can be understood that the condition that the valence of each metal element becomes Li ¹⁺ , Mn ⁴⁺ , Ni ²⁺ , Co ³⁺ , Mg ²⁺ can be assumed by considering Li [Li _1/3 Mn _2/3 A solid solution of four components of O ₂ , LiNi _1/2 Mn _1/2 O ₂ , LiCoO ₂ and LiMg _1/2 Mn _1/2 O ₂ is provided. That is, by envisioning a solid solution xLi[Li _1/3 Mn _2/3 ]O ₂ -yLiNi _1/2 Mn _1/2 O ₂ -zLiMg _1/2 Mn _1/2 O ₂ -(1-xyz)LiCoO ₂ (x>0, y>0, z>0, x+y+z<1) and arbitrarily select x, y and z, which can theoretically exist in the transition metal sites of the α-NaFeO ₂ type crystal structure The valence of each metal element is Li ¹⁺ , Co ³⁺ , Ni ²⁺ , Mn ⁴⁺ , and Mg ²⁺ .

If the above formula xLi[Li _1/3 Mn _2/3 ]O ₂ -yLiNi _1/2 Mn _1/2 O ₂ -zLiMg _1/2 Mn _1/2 O ₂ -(1-xyz)LiCoO _{2 is} deformed, Then, Li _1+(x/3) Co _1-xyz Ni _y/2 Mg _z/2 Mn _{(2x/3)+(y/2)+(z/2)} O ₂ can be obtained by the intention. Here, the present invention is an active material for a lithium secondary battery comprising a solid solution of a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure, and the active material for a lithium secondary battery is characterized by: The composition ratio of the metal element contained in the above solid solution satisfies Li _1+(x/3) Co _1-xyz Ni _y/2 Mg _z/2 Mn _{(2x/3)+(y/2)+(z/2 ) (x> 0, y>} 0, z> 0, x + y + z <1), having an X-ray diffraction pattern attributable to the space group P3 ₁ 12, and has more than 200mAh / g discharge capacity.

As shown in the comparative example described later, even if the active material satisfies the composition ratio of the metal element and has an X-ray diffraction pattern that can be attributed to the space group P3 ₁ 12, the discharge capacity may be 200 mAh/g or less. In the present invention, the active material is limited to an active material having a discharge capacity of more than 200 mAh/g obtained by a charge and discharge cycle test described later.

In order to make the above-mentioned active material have a discharge capacity of more than 200 mAh/g, the influence of the calcination temperature is large, and the solid solution of the lithium transition metal composite oxide satisfying the composition ratio of the above metal elements is at a temperature exceeding 900 ° C, for example, 920. Calcination at a temperature above °C can obtain an active material having a discharge capacity of more than 200 mAh/g. When the calcination temperature exceeds 1000 ° C, an active material having an X-ray diffraction pattern attributable to the space group P3 ₁ 12 may not be obtained, and therefore it is preferably 1000 ° C or lower.

In the present invention, it has been found for the first time that when the solid solution of the above-mentioned Mg-containing lithium transition metal composite oxide is made into an active material having a large discharge capacity of more than 200 mAh/g, the high rate discharge characteristics are remarkably improved.

From the viewpoint of satisfying the composition ratio of the above-described metal element and having an X-ray diffraction pattern attributed to the space group P3 ₁ 12, for example, the (003) plane obtained by X-ray diffraction measurement 114) When the intensity ratio of the diffraction peak of the surface is I ₍₀₀₃₎ / I ₍₁₁₄₎ ≧ 1.15, and/or the half-height of the diffraction peak of the (003) plane is 0.15° or less, and (114) plane When the half-height of the diffraction peak is 0.25 or less, the discharge capacitance exceeds 200 mAh/g.

In general, when a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure is synthesized by a calcination step, and an elemental composition ratio is obtained by chemically analyzing the actually obtained compound, it is actually known that There is a slight (about 5%) change in the composition calculated from the composition ratio. It is to be understood that the present invention may be carried out without departing from the technical spirit or main characteristics thereof, and should not be construed as a substance obtained by synthesis, which is not in the scope of the present invention only because the composition is not strictly consistent with the above composition formula. . In particular, regarding the amount of Li, it is known that it is easily volatilized in the calcination step. Further, the coefficient of the oxygen atom may vary depending on the synthesis conditions and the like, and is not strictly limited to 2, and should not be construed as being in the range of the present invention due to oxygen deficiency. Further, in the present invention, the coefficient of oxygen is not defined in the above formula in which the metal element composition ratio is specified.

Further, the active material of the present invention may contain an element other than Li, Co, Ni, Mn, Mg, or O. When an element other than Li, Co, Ni, Mn, Mg, or O is contained, the active material of the present invention is also required. Among the elements constituting the above solid solution, the valences of Li, Co, Ni, Mn, and Mg satisfy the valence conditions of Li ¹⁺ , Co ³⁺ , Ni ²⁺ , Mn ⁴⁺ , and Mg ²⁺ , respectively. Furthermore, the amount of Li in the active material changes with the charge and discharge of the battery, and the valence of the transition metal also changes, but the active material taken by the battery whose self-charge and discharge depth is unknown may be inductively coupled. In the case of an inductively-coupled plasma (ICP) luminescence spectrometry, an X-ray diffraction measurement, an oxygen amount analysis, or the like, the ratio of the metal element containing Li when the active material is synthesized is known, and therefore, it can be determined whether the active material belongs to The technical scope of the present invention.

Here, a powder in which a mixture of LiCoO ₂ powder, LiNi _1/2 Mn _1/2 O ₂ powder, Li [Li _1/3 Mn _2/3 ]O ₂ powder, or the like is simply prepared cannot be regarded as "the present invention". Solid solution". Since the peak positions corresponding to the respective lattice constants observed in the X-ray diffraction measurement of the individual materials of the materials are different, if the simple mixture is subjected to X-ray diffraction measurement, each of the obtained products can be obtained. The diffraction pattern corresponding to the single product.

Here, by selecting a value of a range of 1/3<x<2/3 as x, the synthesized material can exhibit relative relative use as an active material for a lithium secondary battery. Higher discharge capacitance is preferred. The value of x or y can be appropriately selected in consideration of which battery characteristics are desired in the battery for which the active material for a lithium secondary battery is to be used. The value of z is related to the amount of Mg. However, as shown in the later example, even if the amount of Mg is extremely small, the effect of increasing the discharge capacity is remarkably exhibited as compared with the case where Mg is not contained. On the other hand, since Mg does not change the valence even if it is charged and discharged, the excess is not useful, and it is preferably not excessively contained. The expression of the effect of the present invention when the value of z is variously changed is different depending on the value of x or y. Therefore, the value of x and y to be used is determined according to the design of the battery, and then the value of x and y is then determined. According to the above technical idea, the value of z is changed, and an appropriate value of z can be used. In order to increase the discharge capacity, it is preferably 0 < y < 2 / 3 and 0 < z < 0.3.

As described above, the active material for a lithium secondary battery contains a solid solution of a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure, and the composition of the metal element contained in the solid solution The ratio satisfies Li _1+(x/3) Co _1-xyz Ni _y/2 Mg _z/2 Mn _{(2x/3)+(y/2)+(z/2)} (x>0, y>0, z >0, x+y+z<1)", which can exhibit high discharge capacitance; in the present invention, in order to significantly improve discharge capacitance and high rate discharge characteristics, the lithium transition metal composite oxide is solidified. The solution has an X-ray diffraction pattern attributable to the space group P3 ₁ 12 such that the intensity ratio of the diffraction peaks of the (003) plane and the (114) plane obtained by the X-ray diffraction measurement is I (003) / I (114) ≧ 1.15, and/or the half-height width of the diffraction peak of the (003) plane is 0.15° or less, and the full width at half maximum of the diffraction peak of the (114) plane is 0.25° or less.

Furthermore, the X-ray diffraction pattern of the above solid solution of the present invention can be attributed to the space group P3 ₁ 12, but it is not impossible to belong to the space group R3-m. At this time, the diffraction peak of the (114) plane attributed to the space group P3 ₁ 12 must be referred to as "the diffraction peak of the (104) plane" when it belongs to the space group R3-m. Here, regarding the expression of the space group, "R3-m" should originally be marked with a short bar (-) on "3", but this description is expressed as "R3-m" for convenience. .

When the active material for a lithium secondary battery of the present invention is used, a charging method in which the maximum reaching potential of the positive electrode during charging is 4.3 V (vs. Li/Li ⁺ ) or less is used, and a sufficient discharge capacitor can be taken out for production. In the lithium secondary battery, it is important to provide a charging step in which the characteristic behavior of the active material for a lithium secondary battery of the present invention is taken into consideration in the production step of the lithium secondary battery. In the same manner as the active material for a lithium secondary battery described in Patent Document 3, the active material for a lithium secondary battery containing Mg of the present invention is also used for a positive electrode and continuously charged at a constant current. As will be described later, in the range of the positive electrode potential of 4.3 V to 4.8 V, a region where the potential change was relatively flat was observed for a relatively long period of time.

Here, the present invention is a method for producing a lithium secondary battery, which is a method for charging the lithium secondary battery using a charging method in which the maximum reaching potential of the positive electrode during charging is 4.3 V (vs. Li/Li ⁺ ) or less. The manufacturing method is characterized by comprising the steps of: performing a potential change occurring in a positive electrode potential range exceeding 4.3 V (vs. Li/Li ⁺ ) and being 4.8 V or less (vs. Li/Li ⁺ ) to at least relatively relatively Charging of flat areas.

Here, the charging of the initial charge and discharge step before the completion of the battery must be performed until at least the potential flat region is reached. The potential flat area is relative Longer (e.g., above 100 mAh/g) continues, so it is preferred to continue charging as much as possible through the process. In addition, when the end point of the potential flat region is observed due to an increase in potential or the like, the charge termination condition may be set accordingly, and the current value may be attenuated to a set value by constant current constant voltage charging, and may be set to Charge termination condition.

According to the present invention, it is possible to provide an active material for a lithium secondary battery having a large discharge capacity and excellent high-rate discharge characteristics.

The above and other objects, features and advantages of the present invention will become more <RTIgt;

A method of producing the active material for a lithium secondary battery of the present invention will be described.

The active material for a lithium secondary battery of the present invention can be obtained basically by the following means: for a metal element (Li, Mn, Co, Ni, Mg) constituting the active material, such as a composition of a target active material (oxide) The raw materials contained are adjusted and calcined. Among them, regarding the amount of the Li raw material, it is expected that a part of the Li raw material in the calcination disappears, so an excess of about 1% to 5% is added.

When an oxide of a target composition is produced, a so-called "solid phase method" in which a salt of each of Li, Co, Ni, Mn, and Mg is mixed and calcined is known, or Co, Ni, and Mn are prepared in advance in one particle. A coprecipitated precursor of Mg in which a Li salt is mixed and a "coprecipitation method" of calcination is carried out. In the synthesis process by the "solid phase method", in particular, it is difficult to uniformly dissolve Mn with respect to Co and Ni, and it is difficult to obtain a sample in which each element is uniformly distributed in one particle. At present, attempts have been made to solid-dissolve Mn in a part of Ni or Co by a solid phase method (LiNi _1-x Mn _x O _{2 ,} etc.) in the literature, etc., but it is easier to select the "coprecipitation method". A homogeneous phase is obtained at atomic level. Therefore, the "coprecipitation method" is employed in the examples described later. Further, a preferred method for producing such a precursor is described, for example, in Patent Document 2.

In making a coprecipitated precursor, it is extremely important to make the solution in which the coprecipitate precursor is to be obtained an inert environment. The reason is that Mn is easily oxidized in Co, Ni, Mn, and Mg, and it is difficult to produce a coprecipitated hydroxide in which Co, Ni, Mn, and Mg are uniformly distributed in a divalent state, and thus atoms of Co, Ni, Mn, and Mg are formed. The uniform mixing of the levels tends to be insufficient. Particularly in the composition range of the present invention, since the Mn ratio is higher than the Co and Ni ratios, it is more important to make the solution inert. In the latter example, the inert gas is bubbling in an aqueous solution to remove dissolved oxygen, and the reducing agent is simultaneously added dropwise.

The method of adjusting the precursor for the above calcination is not limited. The Li compound, the Mn compound, the Ni compound, the Co compound, and the Mg compound may be separately mixed, or a hydroxide containing a transition metal element may be coprecipitated in a solution and mixed with the Li compound. In order to produce a uniform composite oxide, a method of mixing and calcining a coprecipitated compound of Mn, Ni, Co, and Mg with a Li compound is preferred.

The preparation of the coprecipitated hydroxide precursor is preferably a compound obtained by uniformly mixing Mn, Ni, Co, and Mg. Wherein, the precursor is not limited to hydroxide, and besides, as long as it is carbonate or citric acid A poorly soluble salt in which an element such as a salt is uniformly present at an atomic level can be used in the same manner as the hydroxide. Further, a precursor having a larger bulk density can also be produced by using a crystallization reaction or the like using a coupling agent. At this time, since the active material having a higher density and a smaller specific surface area can be obtained by mixing with the Li source and calcining, the energy density per unit electrode area can be improved.

Examples of the raw material of the coprecipitated hydroxide precursor include manganese oxide, manganese carbonate, manganese sulfate, manganese nitrate, manganese acetate, and the like. Examples of the Ni compound include nickel hydroxide, nickel carbonate, nickel sulfate, and nickel nitrate. Examples of the Co compound include cobalt sulfate, cobalt nitrate, cobalt acetate, and the like. Examples of the Mg compound include magnesium sulfate, magnesium nitrate, and magnesium acetate.

The raw material for producing the above-mentioned coprecipitated hydroxide precursor may be used in any form as long as it can form a precipitation reaction with an aqueous alkaline solution, and it is preferred to use a metal salt having a high solubility.

The active material for a lithium secondary battery of the present invention can be suitably produced by mixing the above-mentioned coprecipitated hydroxide precursor with a Li compound and then heat-treating it. It can be suitably produced by using lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate or the like as a Li compound.

The choice of calcination temperature is extremely important in obtaining an active material with a significantly increased discharge capacitance.

As set forth below, by setting the calcination temperature to 920 ° C to 1000 ° C, "the composition ratio of the metal element contained in the solid solution satisfies Li _1+(x/3) Co _1-xyz Ni _{y / 2} Mg _{z / 2} Mn _{(2x/3)+(y/2)+(z/2)} (x>0, y>0, z>0, x+y+z<1) solidification of lithium transition metal composite oxide The solution has an X-ray diffraction pattern attributable to the space group P3 ₁ 12, and the intensity ratio of the diffraction peaks of the (003) plane and the (114) plane obtained by X-ray diffraction measurement is I ₍₀₀₃₎ /I ₍₁₁₄₎ ≧ 1.15, the discharge capacitance is significantly improved.

When the calcination temperature is too high, the obtained active material disintegrates with the oxygen release reaction, and the phase specified by the monoclinic Li[Li _1/3 Mn _2/3 ]O ₂ type other than the hexagonal crystal of the main phase is not There is a tendency to form a solid solution phase and it is observed by phase separation. Such a material is less preferable because the reversible capacitance of the active material is greatly reduced. This material observed impurity peaks around 35° and around 45° on the X-ray diffraction pattern. Therefore, it is important that the calcination temperature is set to a temperature lower than the influence of the oxygen release reaction of the active material. The oxygen release temperature of the active material is substantially 1000 ° C or more in the composition range of the present invention. However, depending on the composition of the active material, the oxygen release temperature is slightly different. Therefore, it is preferred to confirm the oxygen release temperature of the active material in advance. In particular, since it is confirmed that the amount of Co contained in the sample increases, the oxygen release temperature of the precursor shifts to the low temperature side, so care must be taken. Regarding the method of confirming the oxygen release temperature of the active material, in order to simulate the calcination reaction process, a mixture of the coprecipitated precursor and LiOH‧H ₂ O may be supplied to the thermogravimetric analysis (DTA-TG measurement), but the method may determine the machine. The platinum used in the sample chamber is corroded by the volatilized Li component and damages the machine. Therefore, it is preferred that the composition which has been crystallized to some extent by a calcination temperature of about 500 ° C in advance is subjected to thermogravimetric analysis.

On the other hand, when the calcination temperature is too low, the crystallization does not sufficiently proceed, and the intensity ratio of the diffraction peaks of the (003) plane and the (114) plane obtained by the X-ray diffraction measurement is I ₍ as in the comparative example described later). ₀₀₃₎ /I ₍₁₁₄₎ <1.15, the discharge capacitance is reduced, so it is not good. In the present invention, the calcination temperature must be set to at least 900 °C or higher. Sufficient crystallization is important to reduce the impedance of the grain boundaries and promote smooth lithium ion transport. The method of discriminating the degree of crystallization can be exemplified by visual observation using a scanning electron microscope. When the positive electrode active material of the present invention is observed by a scanning electron microscope, when the sample synthesis temperature is 800 ° C or lower, the sample is formed of primary particles of a nanometer order, but is further crystallized by further increasing the temperature of the sample synthesis. At a micron level, large primary particles accompanied by an increase in electrode characteristics are obtained.

On the other hand, another standard indicating the degree of crystallization is the full width at half maximum of the X-ray diffraction peaks described above. In the present invention, in order to improve not only the discharge capacitance but also the high rate discharge characteristics, it is preferable that the half-height width of the diffraction peak of the (003) plane is 0.15 or less in the X-ray diffraction pattern attributed to the space group P3 ₁ 12 . And the half-height width of the diffraction peak of the (114) plane is 0.25 or less. The full width at half maximum of the diffraction peak of the (003) plane is preferably 0.14° to 0.15°, and the full width at half maximum of the diffraction peak of the (114) plane is preferably 0.23° to 0.25°.

In order to make the half-height width of the diffraction peak of the (003) plane 0.15° or less and the half-height width of the diffraction peak of the (114) plane to be 0.25° or less, it is necessary to increase the firing temperature.

As described above, the calcination temperature is preferably different depending on the oxygen release temperature of the active material, and it is difficult to set the calcination temperature in a preferred range, but it is preferably 900 ° C to 1050 ° C, more preferably 920 ° C to 1000 ° C, It can play a high level of performance.

The full width at half maximum of the diffraction peak is the amount of deformation indicating the degree of mismatch of the crystal lattice, and the crystallite size as the minimum domain. According to one factor, in order to distinguish the degree of crystallinity according to the full width at half maximum, it must be separately grasped. The inventors confirmed by analyzing the full width at half maximum of the active material of the present invention that the sample synthesized at a temperature of 800 ° C or lower was deformed in the crystal lattice and synthesized at a temperature higher than the temperature. The deformation can be almost removed. Further, the size of the crystallites becomes larger in proportion to the increase in the synthesis temperature. Therefore, the composition of the active material of the present invention is also almost free of lattice deformation in the system, and is intended to form particles having a sufficiently grown crystallite size, whereby a good discharge capacity can be obtained. Specifically, it is preferable to use a synthesis temperature (calcination temperature) in which the amount of deformation affecting the lattice constant is 1% or less and the crystallite size is increased to 150 nm or more. By molding the active materials into electrodes and performing charge and discharge, changes due to expansion and contraction are also observed, and it is preferable that the crystallite size is maintained at 130 nm or more in charge and discharge. That is, by selecting the calcination temperature as close as possible to the oxygen release temperature of the above-mentioned active material, an active material having a reversible capacitance significantly large can be obtained.

The nonaqueous electrolyte used in the lithium secondary battery of the present invention is not limited, and a nonaqueous electrolyte generally used for a lithium battery or the like can be used. Examples of the nonaqueous solvent used for the nonaqueous electrolyte include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, and ethylene carbonate. a cyclic ester such as γ-butyrolactone or γ-valerolactone; a chain carbonate such as dimethyl carbonate, diethyl carbonate or carbonate methyl group; methyl formate a chain ester of methyl acetate, methyl butyrate or the like; tetrahydrofuran or a derivative thereof; 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxy ethane, 1,4-dibutoxyethane, methyl diglyme, etc. Ethers; acetonitrile, benzonitrile and other nitriles; dioxolane and its derivatives; ethylene sulfide, sulfolane, sultone And a derivative thereof, or the like, or a mixture of two or more of them, but is not limited to the solvents.

Examples of the electrolyte salt used for the nonaqueous electrolyte include LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiSCN, LiBr, LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr, An inorganic ion salt containing one of lithium (Li), sodium (Na), and potassium (K) such as KClO ₄ or KSCN; LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN(CF ₃ SO ₂ )(C ₄ F ₉ SO ₂ ), LiC(CF ₃ SO ₂ ) ₃ , LiC(C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , (CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃ H ₇ ) ₄ NBr, (nC ₄ H ₉ ) ₄ NClO ₄ , (nC ₄ H ₉ ) ₄ NI, maleic acid-(C ₂ H ₅ ) ₄ N((C ₂ H ₅ ) ₄ N-maleate), benzoic acid-(C ₂ H ₅ ) ₄ N((C ₂ H ₅ ) ₄ N- Benzoate), phthalic acid-(C ₂ H ₅ ) ₄ N((C ₂ H ₅ ) ₄ N-phthalate), lithium stearyl sulfonate, lithium octyl sulfonate, lithium dodecylbenzene sulfonate, etc. These ionic compounds may be used singly or in combination of two or more kinds.

Further, by using LiBF _{4 in} combination with a lithium salt having a perfluoroalkyl group such as LiN(C ₂ F ₅ SO ₂ ) ₂ , the viscosity of the electrolyte can be further lowered, so that the low-temperature characteristics can be further improved, and the self-inhibition can be further suppressed. Discharge is more ideal.

Further, a normal temperature molten salt or an ionic liquid can also be used as the nonaqueous electrolyte.

Regarding the concentration of the electrolyte salt in the nonaqueous electrolyte, in order to reliably obtain a nonaqueous electrolyte battery having high battery characteristics, it is preferably from 0.1 mol/l to 5 mol/l, more preferably from 0.5 mol/l to 2.5 mol/l. .

The material of the negative electrode is not limited, and may be arbitrarily selected as long as it can precipitate or occlude lithium ions. For example, a titanium-based material such as lithium titanate having a spinel crystal structure represented by Li[Li _1/3 Ti _5/3 ]O ₄ or an alloy material such as Si or Sb or Sn-based material may be mentioned. , lithium alloy (lithium-niobium, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and lithium metal alloys such as Wood's metal), lithium composite Oxide (lithium-titanium), antimony oxide, and other examples: alloys capable of occluding and releasing lithium, carbon materials (for example, graphite, hard carbon, low-temperature calcined carbon, amorphous carbon) and many more.

The powder of the positive electrode active material and the powder of the negative electrode material preferably have an average particle size of 100 μm or less. In particular, in order to improve the high output characteristics of the nonaqueous electrolyte battery, the powder of the positive electrode active material is preferably 10 μm or less. In order to obtain a powder in a specific shape, a pulverizer or a classifier can be used. For example, a mortar, a ball mill, a sand mill, a vibratory ball mill, a planetary ball mill, a jet mill, a counter jet mill, a vortex jet mill or Sieves, etc. At the time of pulverization, wet pulverization in which an organic solvent such as water or hexane is present may be used. The classification method is not particularly limited, and dry or wet types such as a sieve or an air classifier are used as needed.

The positive electrode active material and the negative electrode material which are main constituent components of the positive electrode and the negative electrode have been described in detail above, and the positive electrode and the negative electrode are excluded from the above. In addition to the main constituent components, a conductive agent, a binder, a tackifier, a filler, or the like may be contained as another constituent component.

The conductive agent is not limited as long as it is an electron conductive material that does not adversely affect the battery performance, and may generally include natural graphite (scaly graphite, flaky graphite, earthy graphite, etc.), artificial graphite, carbon black. , acetylene black, Ketjen black, carbon whisker, carbon fiber, metal (copper, nickel, aluminum, silver, gold, etc.) powder, metal fiber, conductive ceramic material, etc. One or a mixture of conductive materials.

Among these, from the viewpoint of electron conductivity and coatability, the conductive agent is preferably acetylene black. The amount of the conductive agent added is preferably from 0.1% by weight to 50% by weight, particularly preferably from 0.5% by weight to 30% by weight based on the total weight of the positive electrode and the negative electrode. In particular, when acetylene black is pulverized into ultrafine particles of 0.1 μm to 0.5 μm, the amount of carbon required can be reduced, which is preferable. The mixing method of the ingredients is physical mixing, and it is desirable to uniformly mix. Therefore, it is possible to mix a powder mixer such as a V-type mixer, an S-type mixer, a crusher, a ball mill, or a planetary ball mill in a dry or wet manner.

As the above-mentioned binder, a thermoplastic resin such as polytetrafluoroethylene (PTFE), polyvinylidene difluoride (PVDF), polyethylene or polypropylene, or an ethylene-propylene-diene terpolymer ( One or two of rubber-elastic polymers such as ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber, etc. The mixture on it. The amount of the binder added is preferably from 1% by weight to 50% by weight, particularly preferably from 2% by weight to 30% by weight based on the total weight of the positive electrode and the negative electrode.

The filler may be any material as long as it does not adversely affect the battery performance. Generally, an olefin-based polymer such as polypropylene or polyethylene, amorphous cerium oxide, aluminum oxide, zeolite, glass, carbon or the like can be used. The addition amount of the filler is preferably 30% by weight or less based on the total weight of the positive electrode negative electrode.

The positive electrode and the negative electrode are suitably produced by kneading the above-mentioned main constituent components (the positive electrode is a positive electrode active material and the negative electrode as a negative electrode material) and other materials into a mixture, and mixing it with N-methyl-pyrrolidinone (N-methyl-pyrrolidinone) After the organic solvent such as toluene or the like, the obtained mixed solution is applied to a current collector which will be described later in detail, and is pressure-bonded at a temperature of about 50 ° C to 250 ° C for about 2 hours. Heat treatment. The above coating method is preferably, for example, roll coating, screen coating, doctor blade method, spin coating, bar coater using an applicator roll or the like ( The means such as bar coater) is applied to any thickness and arbitrary shape, but is not limited thereto.

The separator is preferably used alone or in combination with a porous film or a nonwoven fabric exhibiting excellent high rate discharge performance. The material constituting the separator for a non-aqueous electrolyte battery is, for example, a polyolefin resin represented by polyethylene or polypropylene, or a polymer represented by polyethylene terephthalate or polybutylene terephthalate. Ester resin, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, partial a vinyl fluoride-tetrafluoroethylene copolymer, a vinylidene fluoride-trifluoroethylene copolymer, a vinylidene fluoride-fluoroethylene copolymer, a vinylidene fluoride-hexafluoroacetone copolymer, a vinylidene fluoride-ethylene copolymer, A vinylidene fluoride-propylene copolymer, a vinylidene fluoride-trifluoropropene copolymer, a vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, a vinylidene fluoride-ethylene-tetrafluoroethylene copolymer, or the like.

The porosity of the separator is preferably 98 vol% or less from the viewpoint of strength. Further, from the viewpoint of charge and discharge characteristics, the porosity is preferably 20 vol% or more.

Further, as the separator, for example, acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinyl pyrrolidone, polyvinylidene fluoride or the like may be used. A polymer gel composed of a polymer and an electrolyte. When a nonaqueous electrolyte is used in a gel state as described above, it is preferable in terms of an effect of preventing liquid leakage.

Further, when the separator is used in combination with a polymer gel as described above, the porous film or the nonwoven fabric is preferably used in combination with the polymer gel. That is, by forming a film of a solvophilic polymer having a thickness of several μm or less on the surface of the polyethylene microporous film and the surface of the microporous membrane, and maintaining the electrolyte in the pores of the film, the solvophilic polymer A gel is formed.

In addition to polyvinylidene fluoride, the solvophilic polymer may be a polymer obtained by crosslinking an acrylate monomer such as an oxiranyl group or an ester group, an epoxy monomer, or a monomer having an isocyanate group. Things and so on. The monomer may be subjected to a crosslinking reaction using heat or ultraviolet rays (UV) in combination with a radical initiator, or using an active light such as an electron beam (EB).

The configuration of the lithium secondary battery is not particularly limited, and a cylindrical battery, a square battery, a flat battery, or the like having a positive electrode, a negative electrode, and a roll-shaped separator can be exemplified.

[Example 1]

(Example 1-1)

The manganese sulfate pentahydrate, the nickel sulfate hexahydrate, the cobalt sulfate heptahydrate, and the magnesium sulfate heptahydrate are dissolved in the ion exchange so that the elements of Co, Ni, Mn, and Mg become a ratio of 12.5:17.438:68.75:1.312. A mixed aqueous solution was prepared in water. At this time, the total concentration was 0.667 mol/l, and the volume was 180 ml. Then, 600 ml of ion-exchanged water was prepared in a 1 L (liter) beaker, and maintained at 50 ° C using a hot water bath, and 8 N of NaOH was added dropwise thereto to adjust the pH to 12.0. Argon gas (Ar) was bubbled in this state for 30 minutes, and the dissolved oxygen in the solution was sufficiently removed. The inside of the beaker was stirred at a number of revolutions of 700 rpm, and the mixed aqueous solution of the above sulfate was added dropwise at a rate of 3 ml/min. In the meantime, the temperature was kept constant using a hot water bath, and 8 N NaOH was intermittently added dropwise, thereby keeping the pH constant. At the same time, 50 ml of a hydrazine aqueous solution having a concentration of 2.0 mol/l as a reducing agent was added dropwise at a rate of 0.83 ml/min. After the completion of the dropwise addition, the mixture was allowed to stand still for 12 hours or more while the stirring was stopped, and the coprecipitated hydroxide was sufficiently grown.

Further, in the above procedure, if the dropping rate of each solution is too fast, a uniform precursor cannot be obtained at the elemental level. For example, when the drop acceleration is set to 10 times the above speed, the element distribution in the precursor becomes significantly uneven. Further, when the active material is synthesized using such a non-uniform precursor, the distribution of the elements after the firing is also uneven, and sufficient electrode characteristics cannot be exhibited. Incidentally, when LiOH‧H ₂ O, Co(OH) ₂ , Ni(OH) ₂ , MnOOH, or Mg(OH) _{2 is} used as a raw material powder by a solid phase method, it is more uneven, so it is not preferable. .

Then, the coprecipitated product was taken out by suction filtration, and dried at 100 ° C in an air atmosphere under normal pressure using an oven. After drying, it was pulverized in a mortar having a diameter of about 120 mmφ for several minutes so as to have a uniform particle diameter to obtain a dry powder.

It was confirmed by X-ray diffraction measurement that the dry powder was a single phase of the β-Ni(OH) ₂ type. Further, it was confirmed by EPMA measurement that Co, Ni, and Mn were uniformly distributed.

Lithium hydroxide monohydrate powder (LiOH‧H ₂ O) was weighed in such a manner that the amount of Li of the metal element (Ni+Mn+Co+Mg) satisfies the composition formula of Example 1-1 of Table 1 and was mixed. A mixed powder is obtained.

Then, the mixed powder was subjected to pellet molding at a pressure of 6 MPa. The amount of the precursor powder supplied to the pellets was determined in such a manner that the weight of the synthesized product was 3 g. As a result, the formed pellets had a diameter of 25 mmφ and a thickness of about 10 mm to 12 mm. The pellets were placed in an alumina boat having a total length of about 100 mm, placed in a box-type electric furnace, and calcined at 1000 ° C for 12 hours in an air atmosphere at normal pressure. The internal dimensions of the box-type electric furnace were 10 cm in the longitudinal direction, 20 cm in width, and 30 cm in depth, and electric heating wires were placed between the intervals of 20 cm in the width direction. After the calcination, the switch of the heater was turned off, and the alumina boat was placed in the furnace to be naturally placed and cooled. As a result, the temperature of the furnace drops to about 5 hours later. At about 200 ° C, the subsequent cooling rate is slightly slower. After a day and night, it was confirmed that the temperature of the furnace was 100 ° C or less, and then the pellets were taken out and pulverized to a uniform particle size using a mortar.

With respect to the obtained active material, the composition was Li _1.2 Co _0.1 Ni _0.139 Mg _0.011 Mn _0.55 O ₂ , and as a result of measurement of the crystal structure of the Cu(Kα) bulb by powder X-ray diffraction, α-NaFeO was confirmed. _The type ₂ hexagonal crystal structure is the main phase, and a diffraction peak near 20° to 30° visible in the monoclinic crystal of the Li[Li _1/3 Mn _2/3 ]O ₂ type is partially observed. The crystal structure analysis of all the diffraction rays by the Rietveld method is very consistent with the crystal structure model attributed to the space group P3 ₁ 12 .

The area of the diffraction peak of the (003) plane is obtained from the diffraction peak at 2θ: 18.6±1°, and the area of the diffraction peak of the (114) plane is obtained from the diffraction peak at 2θ: 44.1±1°. The intensity ratio (area ratio) I ₍₀₀₃₎ / I _{(114) of the} two diffraction peaks was calculated, and the result was 1.41.

In addition, the "crest intensity" refers to the integrated value of the numerical value obtained by the X-ray detector counting the X-ray amount, and therefore corresponds to the "area" in the peak appearing in the X-ray diffraction pattern. However, when there is no difference in the width of the peaks to be compared or the width of the peaks is very narrow, it is only necessary to compare the heights of the peaks, and here, not only the heights of the peaks but also the areas are compared.

Further, the full width at half maximum of the diffraction peak of the (003) plane was obtained from the diffraction peak at 2θ: 18.6±1°, and found to be 0.14°, which was obtained from the diffraction peak at 2θ: 44.1±1° (114). The full width at half maximum of the diffraction peak of the face is 0.23°.

Further, Rietveld analysis is performed on the data of the X-ray diffraction pattern on a computer, in which the crystallization parameters contained in the Gaussian function and the Lorentz function are refined, and the crystallization parameters obtained according to the above are The lattice deformation and crystallite size were calculated separately, and the crystallite size was 180 nm.

(Example 1-2~Example 1-5)

The active material of the present invention was synthesized in the same manner as in Example 1-1, except that the calcination temperatures (980 ° C, 960 ° C, 940 ° C, and 920 ° C) shown in Examples 1-2 to 1-5 of Table 1 were changed.

The results of the X-ray diffraction measurement were the same as in Example 1-1, and it was confirmed that the hexagonal crystal structure of the α-NaFeO ₂ type was the main phase, and the Li[Li _1/3 Mn _2/3 ]O ₂ type was partially observed. Diffraction peaks around 20°~30° visible in the slant crystal. The crystal structure analysis of all the diffraction rays by the Rietveld method is very consistent with the crystal structure model attributed to the space group P3 ₁ 12 .

In the same manner as in Example 1-1, the intensity ratio (area ratio) I ₍₀₀₃₎ / I _{(114) of the} diffraction peak was calculated, and as a result, it was 1.15 to 1.35.

(Comparative Example 1-1 to Comparative Example 1-5)

A comparative example was synthesized in the same manner as in Example 1-1 except that the firing temperatures (900 ° C, 800 ° C, 700 ° C, 550 ° C, and 1100 ° C) shown in Comparative Example 1-1 to Comparative Example 1-5 of Table 1 were changed. Active substance.

In Comparative Example 1-1 to Comparative Example 1-4, crystal structure analysis was carried out in the same manner as in Example 1-1, and as a result, an X-ray diffraction pattern attributable to the space group P3 ₁ 12 was confirmed.

Regarding Comparative Example 1-5, the space group is C2/m, which is different from P3 ₁ 12 .

In the same manner as in Example 1-1, the intensity ratio (area ratio) I ₍₀₀₃₎ / I _{(114) of the} diffraction peak was calculated, and as a result, it was 0.95 to 1.13.

(Example 1-6 ~ Example 1-9)

The composition of the metal element contained in the coprecipitated hydroxide precursor and the amount of lithium hydroxide monohydrate mixed are changed according to the composition formulas shown in Examples 1-6 to 1-9 of Table 1, and The active material of the present invention was synthesized in the same manner as in Example 1-1.

The crystal structure analysis was carried out in the same manner as in Example 1-1, and as a result, the X-ray diffraction pattern attributable to the space group P3 ₁ 12 was confirmed.

Further, the intensity ratio (area ratio) I ₍₀₀₃₎ / I _{(114) of the} diffraction peak was calculated, and as a result, it was 1.35 to 1.51.

(Comparative Example 1-6 to Comparative Example 1-9)

The active materials of Comparative Example 1-6 to Comparative Example 1-9 were set to have the same solid solution as those of Examples 1-6 to 1-9, and the calcination temperature was changed to 800 ° C, in addition to Example 1-1 was synthesized in the same manner.

The crystal structure analysis was carried out in the same manner as in Example 1-1, and as a result, the X-ray diffraction pattern attributable to the space group P3 ₁ 12 was confirmed.

Further, the intensity ratio (area ratio) I ₍₀₀₃₎ / I _{(114) of the} diffraction peak was calculated, and as a result, it was 1.12 to 1.13.

(Comparative Example 1-10 to Comparative Example 1-15)

The Mg was removed from the metal element contained in the coprecipitated hydroxide precursor, and the composition was changed to Li _1.2 Co _0.1 Ni _0.15 Mn _0.55 O ₂ and changed to Comparative Example 1-10 to Comparative Example 1-15 of Table 1. The active material of the comparative example was synthesized in the same manner as in Example 1-1, except that the calcination temperatures (1000 ° C, 900 ° C, 800 ° C, 700 ° C, 550 ° C, and 1100 ° C) were shown.

In Comparative Example 1-10 to Comparative Example 1-14, the crystal structure analysis was carried out in the same manner as in Example 1-1, and as a result, the X-ray diffraction pattern attributable to the space group P3 ₁ 12 was confirmed.

Regarding Comparative Example 1-15, the space group is C2/m, which is different from P3 ₁ 12 .

In the same manner as in Example 1-1, the intensity ratio (area ratio) I ₍₀₀₃₎ / I _{(114) of the} diffraction peak was calculated, and as a result, it was 0.94 to 1.422.

(Comparative Example 1-16)

In order to compare the properties of the active material with the substance of the present invention, a solid solution containing Li is substituted for Mg, Li _1.2 Co _0.1 Ni _0.144 Al _0.012 Mn _0.544 O ₂ .

Manganese sulfate pentahydrate, nickel sulfate hexahydrate, and cobalt sulfate heptahydrate were dissolved in ion-exchange water so that the respective elements of Co, Ni, and Mn became a ratio of 12.69:18.28:69.03 to prepare a mixed aqueous solution. At this time, the total concentration was 0.667 mol/l, and the volume was 180 ml. Then, 600 ml of ion-exchanged water was prepared in a 1 L beaker, kept at 50 ° C using a hot water bath, and 8 N NaOH was added dropwise thereto to adjust the pH to 12.0. Argon gas was bubbled in this state for 30 minutes, and the dissolved oxygen in the solution was sufficiently removed. The inside of the beaker was stirred at a number of revolutions of 700 rpm, and the mixed aqueous solution of the above sulfate was added dropwise at a rate of 3 ml/min. In the meantime, the temperature was kept constant using a hot water bath, and 8 N NaOH was intermittently added dropwise, thereby keeping the pH constant. At the same time, 50 ml of a hydrazine aqueous solution having a concentration of 2.0 mol/l as a reducing agent was added dropwise at a rate of 0.83 ml/min. After the end of the two drops, stop In the state of stirring, the mixture was allowed to stand still for 12 hours or more, whereby the coprecipitated hydroxide was sufficiently grown in the particles.

Then, the coprecipitated product was taken out by suction filtration, and dried at 100 ° C in an air atmosphere under normal pressure using an oven. After drying, it was pulverized in a mortar having a diameter of about 120 mmφ for several minutes so that the particle diameters were uniform to obtain a dry powder.

Lithium hydroxide monohydrate powder (LiOH‧H ₂ O) and aluminum hydroxide were weighed so as to satisfy the composition formula of Comparative Example 1-16 of Table 1, and mixed to obtain a mixed powder.

Next, the mixed powder was subjected to pellet molding under a pressure of 6 MPa. The amount of the precursor powder supplied to the pellets was determined in such a manner that the weight of the synthesized product was 3 g. As a result, the pellet after molding had a diameter of 25 mmφ and a thickness of about 10 mm to 12 mm. The pellets were placed in an alumina boat having a total length of about 100 mm, placed in a box-type electric furnace, and calcined at 1000 ° C for 12 hours in an air atmosphere at normal pressure. The internal dimensions of the box-type electric furnace were 10 cm in the longitudinal direction, 20 cm in width, and 30 cm in depth, and electric heating wires were placed between the intervals of 20 cm in the width direction. After the calcination, the switch of the heater was turned off, and the state in which the alumina boat was placed in the furnace was naturally placed and cooled. As a result, the temperature of the furnace dropped to about 200 ° C after 5 hours, and the subsequent temperature drop rate was slightly slower. After a day and night, it was confirmed that the temperature of the furnace became 100 ° C or less, and then the pellet was taken out and pulverized to a uniform particle size using a mortar.

With respect to the obtained active material, the composition was Li _1.2 Co _0.1 Ni _0.144 Al _0.012 Mn _0.544 O ₂ , and as a result of the powder X-ray diffraction measurement using Cu (Kα) spheres, the α-NaFeO was observed. _The type ₂ hexagonal crystal structure is the main phase. The crystal structure analysis of all the diffraction rays by the Rietveld method is very consistent with the crystal structure model attributed to the space group P3 ₁ 12 .

(Comparative Example 1-17)

In order to compare the properties of the active material with the substance of the present invention, a solid solution Li _1.2 Co _0.1 Ni _0.1395 Al _0.021 Mn _0.5395 O ₂ containing Al instead of Mg was synthesized.

The composition of the transition metal element contained in the coprecipitated hydroxide precursor and the mixing amount of lithium hydroxide monohydrate and aluminum hydroxide were changed according to the composition formula shown in Comparative Example 1-17 of Table 1. The active material of the comparative example was synthesized in the same manner as in Comparative Example 1-16.

(Comparative Example 1-18)

In order to compare the properties of the active material with the substance of the present invention, a solid solution Li _1.2 Co _0.1 Ni _0.15 Ti _0.03 Mn _0.52 O ₂ containing Ti instead of Mg was synthesized.

The composition of the transition metal element contained in the coprecipitated hydroxide precursor and the mixing amount of lithium hydroxide monohydrate and titanium oxide were changed in accordance with the composition formula shown in Comparative Example 1-18 of Table 1, and The active material of the comparative example was synthesized in the same manner as in Comparative Example 1-16.

(Comparative Example 1-19)

In order to compare the properties of the active material with the substance of the present invention, a solid solution Li _1.2 Co _0.1 Ni _0.15 Ti _0.05 Mn _0.5 O ₂ containing Ti instead of Mg was synthesized.

The composition of the transition metal element contained in the coprecipitated hydroxide precursor and the mixing amount of lithium hydroxide monohydrate and titanium oxide were changed according to the composition formula shown in Comparative Example 1-19 of Table 1, and And comparison The active material of the comparative example was synthesized in the same manner as in Example 1-16.

(Production and evaluation of lithium secondary battery)

Using each of the active materials of Examples 1-1 to 1-9 and Comparative Examples 1-1 to 1-19 as a positive electrode active material for a lithium secondary battery, a lithium secondary battery was produced in the following procedure, and battery characteristics were evaluated.

The active material, acetylene black (AB) and polyvinylidene fluoride (PVdF) were mixed at a weight ratio of 85:8:7, and N-methylpyrrolidone as a dispersion medium was added and kneaded and dispersed to prepare a coating liquid. Further, PVdF is a solution in which solid components are dissolved and dispersed, and solid weight conversion is performed. This coating liquid was applied onto an aluminum foil current collector having a thickness of 20 μm to prepare a positive electrode plate. Furthermore, all the batteries were unified in weight and thickness in such a manner that they were subjected to the same test conditions.

For the opposite electrode, in order to observe the individual behavior of the positive electrode, lithium metal was made into a negative electrode. The lithium metal is adhered to the nickel foil current collector. Among them, the capacity of the lithium secondary battery is prepared in such a manner as to be sufficiently positively controlled.

The electrolytic solution was prepared by dissolving LiPF ₆ in a mixed solvent of EC/EMC/DMC in a volume ratio of 6:7:7 at a concentration of 1 mol/l. The separator is a polypropylene microporous membrane which is surface-modified with polyacrylate to improve the retention of the electrolyte. Further, an article in which a lithium metal foil was attached to a nickel plate was used as a reference electrode. The outer casing is a metal resin composite film composed of polyethylene terephthalate (15 μm)/aluminum foil (50 μm)/metal adhesive polypropylene film (50 μm), and a positive electrode terminal, a negative electrode terminal, and a reference electrode terminal. The open end portion is exposed to the outside so as to accommodate the electrode, and the portion where the inner surface of the metal-resin composite film facing each other is a portion to be the liquid-filled hole, and the hermetic sealing is performed.

The lithium secondary battery fabricated as described above was supplied to an initial charge and discharge step of 5 cycles at 20 °C. The voltage control is all performed on the positive potential. The charging is a constant current constant voltage charging set to a current of 0.1 ItA and a voltage of 4.5 V, and the charging termination condition is set to a time at which the current value is attenuated to 1/6. The discharge was a constant current discharge set to a current of 0.1 ItA and a termination voltage of 2.0V. A rest period of 30 minutes was set after charging and after discharging in all cycles. In the lithium secondary battery of Example 1-1, at the time of the initial charging, a region where the potential change was relatively flat was observed during the period of the potential of 4.45 V from the vicinity of the self-charging amount exceeding 100 mAh/g.

Then, a charge and discharge cycle test was performed. The voltage control is all performed on the positive potential. The conditions of the charge and discharge cycle test were the same as those of the initial charge and discharge step except that the charge voltage was set to 4.3 V (vs. Li/Li+). A rest period of 30 minutes was set after charging and after discharging in all cycles. The discharge amount of the fifth cycle in the charge and discharge cycle test was recorded as "discharge capacity (mAh/g)".

Then, a high rate discharge test was performed. The voltage control is all performed on the positive potential. The conditions of the charge and discharge cycle test were the same as those of the initial charge and discharge step except that the charge voltage was set to 4.3 V (vs. Li/Li+). The subsequent discharge was a constant current discharge set to 2 ItA and a termination voltage of 2.0V. The rest time of 30 minutes was set after charging and after discharging. The ratio of the discharge capacity obtained at the time of 2 ItA to the discharge capacity obtained at a current of 0.1 ItA was recorded as "rate ratio (%)".

The calculation results of the intensity ratio (area ratio) I ₍₀₀₃₎ / I ₍₁₁₄₎ of the diffraction peaks of the (003) plane and the (114) plane, the charge and discharge cycle test results (0.1 C capacitor), and the rate ratio are shown in the table. 1 in.

[Table 1]

The composition ratio (metal element ratio) of the metal element contained in the solid solution of the lithium transition metal composite oxide is set to Li _1+(x/3) Co _1-xyz Ni _y/2 Mg _z/2 Mn _{(2x /3) +(y/2)+(z/2)} O ₂ , examples 1-1 to 1-5 are x=0.6, y=0.278, z=0.022, and examples 1-6 are x=0.51. y=0.36, z=0.04, examples 1-7 are x=0.63, y=0.12, z=0.04, examples 1-8 are x=0.54, y=0.30, z=0.06, and examples 1-9 are x=0.60. , y=0.30, z=0.02, both satisfying the above metal element ratio, having an X-ray diffraction pattern attributable to the space group P3 ₁ 12, and measuring (003) plane and (114) plane by X-ray diffraction measurement The intensity ratio of the diffraction peak is I ₍₀₀₃₎ / I ₍₁₁₄₎ ≧ 1.15, so the active materials of Examples 1-1 to 1-9 can obtain a discharge capacity of more than 200 mAh/g and a rate ratio of 65% or more. Therefore, it was confirmed that the discharge capacity was large and the high rate discharge characteristics were excellent.

The above-described metal element ratios of the active materials of Comparative Example 1-1 to Comparative Example 1-4 were the same as those of Examples 1-1 to 1-5, and had X-ray diffraction patterns attributable to the space group P3 ₁ 12, but the calcination temperature. 900 ° C, 800 ° C, 700 ° C, 550 ° C, respectively, lower than 1000 ° ~ 920 ° C of Example 1-1 ~ Example 1-5, so the intensity ratio of the diffraction peak is as small as I ₍₀₀₃₎ / I ₍₁₁₄₎ <1.15, only a discharge capacitance of less than 200 mAh/g can be obtained, and the rate ratio is also 50% or less.

Further, the above-mentioned metal element ratios of the active materials of Comparative Examples 1 to 5 were the same as those of Examples 1-1 to 1-5, and the calcination temperature was as high as 1,100 ° C, so that the intensity ratio of the diffraction peaks satisfies I ₍₀₀₃₎ /I _{( 114)} ≧ 1.15, but does not have a ray diffraction pattern attributable to the space group P3 ₁ 12, so the discharge capacitance and rate ratio are extremely low.

The above-mentioned metal element ratios of the active materials of Comparative Example 1-6 to Comparative Example 1-9 were the same as those of Examples 1-6 to 1-9, respectively, and had an X-ray diffraction pattern attributable to the space group P3 ₁ 12, but calcined. The temperature is 800 ° C, which is lower than 1000 ° C of Examples 1-6 to 1-9, so the intensity ratio of the diffraction peak is as small as I ₍₀₀₃₎ /I ₍₁₁₄₎ <1.15, and only less than 200 mAh/g can be obtained. The discharge capacitor has a rate ratio of 56% or less.

The active materials of Comparative Example 1-10 to Comparative Example 1-15 did not contain Mg, but the active material also had a solid solution of the lithium transition metal composite oxide at a calcination temperature of 1000 ° C as in Comparative Examples 1-10. The X-ray diffraction pattern attributable to the space group P3 ₁ 12, the intensity ratio of the diffraction peaks satisfies I ₍₀₀₃₎ /I ₍₁₁₄₎ ≧ 1.15, and a discharge capacitance exceeding 200 mAh/g can be obtained. However, the rate ratio was 52%, which was the same as that of the active materials of Comparative Example 1-11 to Comparative Example 1-15, and the high rate discharge characteristics were inferior. Therefore, as in the case of Example 1-1, by subjecting the active material to Mg and calcining at 1000 ° C, the discharge capacity and the high rate discharge characteristics were improved together, and as in Comparative Example 1-10, if the active material did not contain In Mg, even if the discharge capacity is increased by calcination at 1000 ° C, the high rate discharge characteristics are not improved.

Further, when Example 1-1 was compared with Comparative Example 1-10, the discharge capacity of the active material of Example 1-1 was 242 mAh/g, whereas the discharge capacity of the active material of Comparative Example 1-10 was 223 mAh. /g, it is understood that the discharge capacitance is remarkably improved by replacing a part of Ni with Mg. Such a situation in which the discharge capacitance is significantly increased by containing Mg is not predictable.

In addition, Examples 1-3 and Comparative Examples 1-10 have the same degree of discharge capacitance, but the active materials of Comparative Examples 1-10 are calcined at 1000 ° C. In contrast, the active material of Examples 1-3 is a material which is calcined at 960 ° C, and thus can be realized by obtaining Mg at a low calcination temperature in order to obtain an active material of the same degree of discharge capacity. Therefore, by using the active material of the present invention, the effect of energy supplied to the calciner at the time of calcination can be reduced.

On the other hand, when the active material containing no Mg is at a calcination temperature of 900 ° C or lower, as in Comparative Example 1-11 to Comparative Example 1-14, the intensity ratio of the diffraction peak is I ₍₀₀₃₎ /I _(114). <1.15; However, when Comparative Example 1-1 having a calcination temperature of 900 ° C was compared with Comparative Example 1-11, the discharge capacity of the active material of Comparative Example 1-1 containing Mg was 185 mAh/g, whereas The discharge capacity of the active material of Comparative Example 1-11 containing no Mg was 186 mAh/g, and Comparative Example 1-2 having a calcination temperature of 800 ° C was compared with Comparative Example 1-12 to obtain a comparative example containing Mg. The discharge capacity of the active material of 1-2 was 165 mAh/g. On the other hand, the discharge capacity of the active material of Comparative Example 1-12 containing no Mg was 166 mAh/g, so the discharge capacity was the same (calcination temperature was 700 ° C). At 550 ° C, the same level), even if a part of Ni is replaced by Mg, the discharge capacitance does not increase.

Therefore, in order to remarkably increase the discharge capacity, it is necessary to make the composition ratio of the metal element contained in the solid solution of the lithium transition metal composite oxide Li _1+(x/3) Co _1-xyz Ni _y/2 Mg _{z /2} Mn _{(2x/3)+(y/2)+(z/2)} (x>0, y>0, z>0, x+y+z<1), and need to be diffracted by X-rays The intensity ratio of the diffraction peaks of the (003) plane and the (114) plane obtained was determined to be I ₍₀₀₃₎ / I ₍₁₁₄₎ ≧ 1.15.

The solid solution of the lithium transition metal composite oxide having an active material calcined at 1000 ° C containing Al or Ti instead of Mg as in Comparative Example 1-16 to Comparative Example 1-19 has a solid solution which can be attributed to the space group P3 ₁ 12 In the X-ray diffraction pattern, the intensity ratio of the diffraction peak satisfies I ₍₀₀₃₎ / I ₍₁₁₄₎ ≧ 1.15, but a discharge capacitance exceeding 200 mAh/g cannot be obtained, and the high-rate discharge characteristics are also poor.

As described above, the active material of the present invention satisfies the composition ratio of the metal element contained in the solid solution of the lithium transition metal composite oxide to satisfy Li _1+(x/3) Co _1-xyz Ni _y/2 Mg _{z /2} Mn _{(2x/3)+(y/2)+(z/2)} (x>0, y>0, z>0, x+y+z<1)”, “has a space group attributable to "X-ray diffraction pattern of P3 ₁ 12", "The intensity ratio of the diffraction peaks of the (003) plane and the (114) plane obtained by X-ray diffraction measurement is I ₍₀₀₃₎ / I ₍₁₁₄₎ ≧ 1.15" According to the requirements, a large discharge capacity of more than 200 mAh/g can be obtained, and it is excellent in high rate discharge characteristics.

[Example 2]

(Example 2-1)

The active material having a composition of Li _1.2 Co _0.1 Ni _0.139 Mg _0.011 Mn _0.55 O ₂ was synthesized at a calcination temperature of 1000 ° C in the same manner as in Example 1-1.

The crystal structure of the obtained active material was measured by powder X-ray diffraction using a Cu(Kα) tube ball in the same manner as in Example 1-1, and it was confirmed that the α-NaFeO ₂ type hexagonal crystal structure was the main phase, and the part was confirmed. A diffraction peak near 20° to 30° visible in a monoclinic crystal of the Li[Li _1/3 Mn _2/3 ]O ₂ type was observed. The crystal structure analysis of all these ray rays by the Rietveld method is very consistent with the crystal structure model attributed to the space group P3 ₁ 12 .

In addition, the (003) plane is obtained from the diffraction peak at 2θ: 18.6±1°. The full width at half maximum of the diffraction peak was 0.14°, and the full width at half maximum of the diffraction peak of the (114) plane was obtained from the diffraction peak at 2θ: 44.1 ± 1°, and as a result, it was 0.23°.

Further, the data of the X-ray diffraction pattern is subjected to Rietveld analysis on a computer, and in the analysis process, the crystallization parameters contained in the Gaussian function and the Lorentz function are refined, and the crystal parameters obtained from the crystal parameters are respectively calculated. The lattice deformation and crystallite size, the result crystallite size is 180 nm.

(Example 2-2~Example 2-10)

The composition of the metal element contained in the coprecipitated hydroxide precursor and the amount of lithium hydroxide monohydrate mixed are changed according to the composition formulas shown in Examples 2-2 to 2-10 of Table 2, and The active material of the present invention was synthesized in the same manner as in Example 2-1.

The results of the X-ray diffraction measurement were the same as those in Example 2-1, and it was confirmed that the hexagonal crystal structure of the α-NaFeO ₂ type was the main phase, and the monoclinic form of the Li[Li _1/3 Mn _2/3 ]O ₂ type was partially observed. Diffraction peaks around 20°~30° visible in the crystal. The crystal structure analysis of all the diffraction rays by the Rietveld method is very consistent with the crystal structure model attributed to the space group P3 ₁ 12 .

Further, the full width at half maximum of the diffraction peak of the (003) plane is obtained from the diffraction peak at 2θ: 18.6±1°, and as a result, it is 0.14° to 0.15°, and the diffraction peak at 2θ: 44.1±1° is obtained. The full width at half maximum of the diffraction peak of the (114) plane is 0.23° to 0.25°.

Further, the crystallite size was calculated in the same manner as in Example 2-1, and as a result, the crystallite size was 180 nm to 200 nm.

(Comparative Example 2-1 to Comparative Example 2-4)

The Mg was removed from the metal element contained in the coprecipitated hydroxide precursor, and was changed according to the composition formulas shown in Comparative Example 2-1 to Comparative Example 2-4 of Table 2, and Comparative Example 2-1 to Comparative Example 2 were changed. -4, the active material of the comparative example was synthesized in the same manner as in Example 2-1 except that the calcination temperature was changed to 1000 ° C, 900 ° C, 800 ° C, and 700 ° C, respectively.

The full width at half maximum of the diffraction peaks of the (003) plane and the (114) plane were obtained in the same manner as in Example 2-1, and the crystallite size was calculated.

(Comparative Example 2-5 to Comparative Example 2-7)

In Comparative Example 2-5 to Comparative Example 2-7, the calcination temperature of the solid solution having the same composition as that of Example 2-2 (calcination temperature: 1000 ° C) was changed to 700 ° C, 800 ° C, and 900 ° C, respectively. The active material of the comparative example was synthesized in the same manner as in Example 2-1.

The full width at half maximum of the diffraction peaks of the (003) plane and the (114) plane were obtained in the same manner as in Example 2-1, and the crystallite size was calculated.

(Comparative Example 2-8 to Comparative Example 2-14)

Comparative Example 2-8 to Comparative Example 2-10 were set to have the same solid solution composition as in Example 2-3, Example 2-1, and Example 2-4, and Comparative Example 2-11 to Comparative Example 2-14 were set to The active material of the comparative example was synthesized in the same manner as in Example 2-1 except that the composition of the solid solution was the same as that of the example 2-7 to the example 2-10, and the calcination temperature was changed from 1000 ° C to 900 ° C.

The full width at half maximum of the diffraction peaks of the (003) plane and the (114) plane were obtained in the same manner as in Example 2-1, and the crystallite size was calculated.

(Comparative Example 2-15, Comparative Example 2-16)

For the transition metal elements contained in the coprecipitated hydroxide precursor The composition of the comparative example was synthesized in the same manner as in Example 2-1 except that the composition and the amount of the lithium hydroxide monohydrate were changed according to the composition formulas shown in Comparative Example 2-15 and Comparative Example 2-16 of Table 2. Active substance.

The full width at half maximum of the diffraction peaks of the (003) plane and the (114) plane were obtained in the same manner as in Example 2-1, and the crystallite size was calculated.

(Comparative Example 2-17)

The active material Li _1.2 Co _0.1 Ni _0.144 Al _0.012 Mn _0.544 O ₂ containing Al instead of Mg was synthesized in the same manner as in Comparative Example 1-16.

(Comparative Example 2-18)

The active material Li _1.2 Co _0.1 Ni _0.1395 Al _0.021 Mn _0.5395 O ₂ containing Al instead of Mg was synthesized in the same manner as in Comparative Example 1-17.

(Comparative Example 2-19)

The active material Li _1.2 Co _0.1 Ni _0.15 Ti _0.03 Mn _0.52 O ₂ containing Ti instead of Mg was synthesized in the same manner as in Comparative Example 1-18.

(Comparative Example 2-20)

In the same manner as in Comparative Example 1-19, Li _1.2 Co _0.1 Ni _0.15 Ti _0.05 Mn _0.5 O ₂ containing Ti instead of Mg was synthesized.

(Production and evaluation of lithium secondary battery)

Using each of the active materials of Examples 2-1 to 2-10 and Comparative Example 2-1 to Comparative Example 2-20 as a positive electrode active material for a lithium secondary battery, a lithium secondary battery was produced in the same manner as in Example 1 and evaluated. Battery characteristics.

The measurement results of the full width at half maximum, the calculation results of the crystal size, the charge and discharge cycle test results (0.1 C capacitance), and the rate ratio are shown in Table 2.

[Table 2]

Examples 2-1 to 2-6, and Comparative Examples 2-5 to 2-10 are for the solid solution xLi[Li _1/3 Mn _2/3 ]O ₂ -yLiNi _1/2 Mn _1/2 O ₂ -zLiMg _1/2 Mn _1/2 O ₂ -(1-xyz)LiCoO ₂ (x>0, y>0, z>0, x+y+z<1), based on Mg ^{2 +} _1/2 Mn ⁴⁺ _1/2 to replace the Ni ²⁺ _1/2 Mn ⁴⁺ _1/2 moiety constituting LiNi _1/2 Mn _1/2 O ₂ to satisfy the formula Li _{1+(x/3 )} Co _1-xyz Ni _y/2 Mg _z/2 Mn _{(2x/3)+(y/2)+(z/2)} (x>0, y>0, z>0, x+y+z< The method of 1) sets the composition ratio (metal element ratio) of each metal element.

With respect to Examples 2-1 to 2-6, the above metal ratio is within the range of the present invention, and the half-height of the diffraction peak of the (003) plane is 0.14° to 0.15°, and the diffraction peak of the (114) plane The full width at half maximum is 0.23°~0.25°.

The above metal element ratios of Comparative Example 2-5 to Comparative Example 2-7 were the same as those of Example 2-2, but the calcination temperatures were 700 ° C, 800 ° C, and 900 ° C, respectively, which was lower than 1000 ° C of Example 2-2, so (003 The half-height widths of the diffraction peaks of the plane are 0.31°, 0.21°, and 0.17°, respectively, which is greater than 0.14° of Example 2-2. The half-height widths of the diffraction peaks of the (114) plane are also 0.45° and 0.31°, respectively. 0.28°, which is greater than 0.24° of Example 2-2.

Further, regarding the crystallite size, Example 2-2 was 180 nm, whereas Comparative Example 2-5 to Comparative Example 2-7 were 80 nm, 110 nm, and 140 nm, respectively, and it was found that the lower the calcination temperature, the smaller the crystallite size.

The above metal element ratios of Comparative Example 2-8 to Comparative Example 2-10 were the same as those of Example 2-3, Example 2-1, and Example 2-4, but the calcination temperature was 900 ° C, which was lower than Examples 2-3 and Example 2 1. Example 2-4 at 1000 °C, so (003) The full width at half maximum of the diffraction peak is 0.16°~0.17°, which is greater than 0.14° in Example 2-3, Example 2-1 and Example 2-4. The half-height of the diffraction peak of the (114) plane is also 0.28°~ 0.29°, which is greater than 0.23°~0.24° of Example 2-3, Example 2-1, and Example 2-4.

In addition, regarding the crystallite size, Example 2-3, Example 2-1, and Example 2-4 are 180 nm to 200 nm, whereas Comparative Example 2-8 to Comparative Example 2-10 are 130 nm to 140 nm, and the crystallite size is small. .

Examples 2-7 to 2-10, and Comparative Examples 2-11 to 2-14 are similarly contemplated as solid solution xLi[Li _1/3 Mn _2/3 ]O ₂ -yLiNi _1/2 Mn _1/2 O ₂ -zLiMg _1/2 Mn _1/2 O ₂ -(1-xyz)LiCoO ₂ (x>0, y>0, z>0, x+y+z<1), based on Mg _1/2 Mn _1/2 ] ³⁺ replaces the idea of [Li _1/3 Mn _2/3 ] ³⁺ portion of Li[Li _1/3 Mn _2/3 ]O ₂ to satisfy the formula Li _{1+ (x/3)} Co _1-xyz Ni _y/2 Mg _z/2 Mn _{(2x/3)+(y/2)+(z/2)} (x>0, y>0, z>0, x+ The ratio of each metal element is set in the manner of y+z<1).

With respect to Examples 2-7 to 2-10, the above metal ratio is within the range specified by the present invention, and the half-height width of the diffraction peak of the (003) plane is 0.14° to 0.15°, and the diffraction peak of the (114) plane The full width at half maximum is 0.23°~0.25°.

The above metal element ratios of Comparative Examples 2-11 to Comparative Examples 2-14 were the same as those of Examples 2-7 to 2-10, but the calcination temperature was 900 ° C, which was lower than 1000 ° C of Examples 2-7 to 2-10. Therefore, the half-height of the diffraction peak of the (003) plane is as large as 0.16°~0.17°, and the half-height width of the diffraction peak of the (114) plane is also as large as 0.28°~0.29°.

In addition, regarding the crystallite size, examples 2-7 to 2-10 are 180 nm. ~200 nm, in contrast, Comparative Example 2-11 to Comparative Example 2-14 were 130 nm to 140 nm, and the crystallite size was small.

The solid solution satisfies the above-described ratio of the metal element, the half-height width of the diffraction peak of the (003) plane is 0.15° or less, and the half-height width of the diffraction peak of the (114) plane is 0.25° or less. The active material of 2-10 can obtain a discharge capacity of more than 200 mAh/g, compared with the active materials of Comparative Example 2-1 to Comparative Example 2-4 having the same composition as Example 2-2 except that the solid solution does not contain Mg. The discharge capacitance of 0.1C is increased. Further, the rate ratio of the active materials of Examples 2-1 to 2-10 was 58% or more, and it was confirmed that the rate ratio was remarkably improved as compared with the active materials of Comparative Examples 2-1 to 2-4, and the high rate discharge was observed. Excellent characteristics.

On the other hand, as in the case of the active materials of Comparative Example 2-5 to Comparative Example 2-14, even if the solid solution satisfies the above-described ratio of the metal element, the full width at half maximum of the diffraction peak on the (003) plane exceeds 0.15° (114). When the full width at half maximum of the diffraction peak of the surface exceeds 0.25°, only a discharge capacitance of less than 200 mAh/g can be obtained, and the rate ratio is also 54% or less, which is the same as Example 2-2 except that the solid solution does not contain Mg. In the comparative examples 2-1 to 2-4, the discharge capacity and the rate ratio (high rate discharge characteristics) of 0.1 C were not improved as compared with the active materials of Comparative Example 2-4.

Further, the full width at half maximum of the diffraction peak of the (003) plane of the active material of Comparative Example 2-1 was 0.15° or less, and the full width at half maximum of the diffraction peak of the (114) plane was 0.25° or less, that is, In the range of the invention, the discharge capacity of 0.1 C is improved as compared with the active materials of Comparative Example 2-2 to Comparative Example 2-4 in which the full width at half maximum is outside the range of the present invention, but the rate ratio is not improved. When the solid solution does not contain Mg, not only the (003) plane but also the (114) plane is reduced. The full width at half maximum of the wave peak and the high rate discharge characteristics are not improved.

Comparative Example 2-15 replaces x=0, y=2/3, and z=0 with Mg under the conditions of Li ¹⁺ , Mn ⁴⁺ , Ni ²⁺ , Co ³⁺ , and Mg ²⁺ . A part of the transition metal sites of the active material LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , specifically, results corresponding to x=0, y=0.56, and z=0.10. The calcination temperature was 1000 ° C as in the example, and the half widths of the diffraction peaks of (003) and (114) were also the same. In this case, although the valence condition can be maintained, as described in Non-Patent Document 6, the same calcination temperature, (003), and (114) are obtained as compared with Comparative Example 2-16 which is the above-mentioned active material containing no Mg. The half-height width of the diffraction peak can also be seen as a decrease in the discharge capacitance.

The half-height width of the diffraction peak of the (003) plane of the active material of Example 2-1 to Example 2-10 was 0.15° or less, and the full width at half maximum of the diffraction peak of the (114) plane was 0.25° or less. The crystallite size is also as large as 180 nm or more, and the high rate discharge characteristics are improved.

On the other hand, the active material of Comparative Example 2-2 to Comparative Example 2-14 had a large full width at half maximum, and the crystallite size was as small as 140 nm or less, and the high rate discharge characteristics were not improved.

Further, the full width at half maximum of the active material of Comparative Example 2-1 was as small as that of Examples 2-1 to 2-10, so the crystallite size was 180 nm or more, but since the solid solution contained no Mg, the high rate discharge was performed. Features are not improved.

The active material of Comparative Example 2-15 contained Mg, and the crystallite size was 180 nm or more. However, Li ^{+ was} contained in the transition metal site, and the discharge capacity and rate ratio (high rate discharge characteristics) of 0.1 C were not improved.

The active material of Comparative Example 2-16 had a crystallite size of 180 nm or more and was excellent in high rate discharge characteristics, but the transition metal site contained Li ⁺ and the discharge capacity of 0.1 C was not improved.

Therefore, in order to maintain a high discharge capacity and to improve the high rate discharge characteristics, it is preferred that the solid solution satisfies the above metal element ratio and the crystallite size is 180 nm or more.

With respect to the active material calcined at 1000 ° C containing Al or Ti instead of Mg as in Comparative Example 2-17 to Comparative Example 2-20, the solid solution of the lithium transition metal composite oxide has a group which can be attributed to the space group P3 ₁ 12 X-ray diffraction pattern, the half-height width of the diffraction peak of the (003) plane in the X-ray diffraction pattern is 0.15° or less, and the half-height width of the diffraction peak of the (114) plane is 0.25° or less, but cannot be obtained. With a discharge capacitance exceeding 200 mAh/g, the high rate discharge characteristics are also poor.

As described above, the active material of the present invention satisfies the composition ratio of the metal element contained in the solid solution of the lithium transition metal composite oxide to satisfy Li _1+(x/3) Co _1-xyz Ni _y/2 Mg _z/2 Mn _{(2x/3)+(y/2)+(z/2)} (x>0, y>0, z>0, x+y+z<1)”, “has a space attributable to The X-ray diffraction pattern of the group P3 ₁ 12 and the half-height width of the diffraction peak of the (003) plane in the X-ray diffraction pattern are 0.15° or less, and the full width at half maximum of the diffraction peak of the (114) plane is With a requirement of three elements of 0.25° or less, a large discharge capacity of more than 200 mAh/g can be obtained, and high rate discharge characteristics are remarkably improved.

[Example 3]

(Example 3-1)

The active material having the composition of Li _1.2 Co _0.1 Ni _0.139 Mg _0.011 Mn _0.55 O ₂ (the same active material as Example 2-1 in Example 2) was synthesized in the same manner as in Example 1-1.

(Comparative Example 3-1)

The active material of Comparative Example 3-1 was synthesized in the same manner as in Example 3-1 except that Mg was removed from the metal element contained in the coprecipitated hydroxide precursor (the same as Comparative Example 2-1 in Example 2). Active substance).

(Comparative Example 3-2)

The composition of the transition metal element contained in the coprecipitated hydroxide precursor and the mixing amount of the lithium hydroxide monohydrate were changed according to the composition formula shown in Comparative Example 3-2 of Table 3, and other examples were given. The active material of LiCo _0.33 Ni _0.32 Mg _0.013 Mn _0.33 O ₂ was synthesized in the same manner.

(Comparative Example 3-3)

The active material of Comparative Example 3-3 was synthesized in the same manner as in Comparative Example 3-2 except that Mg was removed from the metal element contained in the coprecipitated hydroxide precursor (the same as Comparative Example 2-16 in Example 2). Active substance).

In the same manner as in Example 2, the full width at half maximum of the diffraction peak of the (003) plane and the full width at half maximum of the diffraction peak of the (114) plane were obtained, and the crystallite size was calculated.

The active material of Comparative Example 3-2 was Li[Li _1/3 Mn _2/3 ]O ₂ (x): 0.000, LiNi _1/2 Mn _1/2 O ₂ (y): 0.641, LiMg _1/2 Mn _{1 /2} O ₂ (z): 0.026, LiCoO ₂ (1-xyz): 0.333, the half-height of the diffraction peak of the (003) plane is 0.14°, and the full width at half maximum of the diffraction peak of the (114) plane is 0.23. °, the crystallite size is 190 nm.

(Production and evaluation of lithium secondary battery)

Using each active material of Example 3-1 and Comparative Example 3-1 to Comparative Example 3-3 as a positive electrode active material for a lithium secondary battery, a lithium secondary battery was produced in the same manner as in Example 1 to evaluate battery characteristics.

(DSC measurement method)

The lithium secondary battery produced in the same order as in Example 1 and subjected to the initial charge and discharge step was subjected to a constant current constant voltage charge of 0.1 ItmA, a voltage of 4.3 V, and 15 hours.

Then, the battery was disassembled in an argon gas tank having a dew point of -40 ° C or less, the positive electrode was taken out, and the positive electrode plate was punched with a 3 mm Φ punch, and the Al foil and the mixture layer were sealed together to DSC (differential scanning). Thermal analysis) In a stainless steel pot for measurement, it was used for DSC measurement. In the DSC measurement, Al ₂ O _{3 was} used for reference, and the measurement was performed at room temperature to 400 ° C in an argon atmosphere. The heating rate was set to 5 ° C / min.

The method of filling the sample and the method of reading the peak of the heat generation are carried out in accordance with JIS K _7121-1987 (Method for Measuring Transfer Temperature of Plastics).

The charge and discharge cycle test results (0.1 C capacitance), rate ratio, and DSC heat peak temperature are shown in Table 3.

As shown in Table 3, for non-lithium-rich lithium nickel manganese cobalt composite oxide (ratio Comparative Example 3-3) The discharge capacity of the active material of Comparative Example 3-2 using Mg was deteriorated, and the thermal stability was not changed. On the other hand, the lithium-rich lithium nickel manganese cobalt composite oxide was added (Comparative Example 3) -1) The discharge capacity of the active material of Example 3-1 using Mg was increased, and the thermal stability in the charged state was also improved.

[Industrial availability]

Since the active material for a lithium secondary battery of the present invention has a large discharge capacity and excellent high-rate discharge characteristics, it can be effectively used for a lithium secondary battery such as an electric vehicle power source, an electronic device power source, or a power storage power source.

While the present invention has been described in its preferred embodiments, the present invention is not intended to limit the invention, and the present invention may be modified and modified without departing from the spirit and scope of the invention. The scope of protection is subject to the definition of the scope of the patent application.

Claims (9)

An active material for a lithium secondary battery comprising a solid solution of a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure, wherein the active material for a lithium secondary battery is characterized by: The composition ratio of the metal element satisfies Li _1+(x/3) Co _1-xyz Ni _y/2 Mg _z/2 Mn _{(2x/3)+(y/2)+(z/2)} (x>0, y >0, z>0, x+y+z<1), having an X-ray diffraction pattern attributable to the space group P3 ₁ 12 or R3-m, the (003) plane obtained by X-ray diffraction measurement 114) The intensity ratio of the diffraction peak of the face or (104) face is I ₍₀₀₃₎ / I ₍₁₁₄₎ ≧ 1.15 or I ₍₀₀₃₎ / I ₍₁₀₄₎ ≧ 1.15. An active material for a lithium secondary battery comprising a solid solution of a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure, wherein the active material for a lithium secondary battery is characterized by: The composition ratio of the metal element satisfies Li _1+(x/3) Co _1-xyz Ni _y/2 Mg _z/2 Mn _{(2x/3)+(y/2)+(z/2)} (x>0, y >0, z>0, x+y+z<1), having an X-ray diffraction pattern attributable to the space group P3 ₁ 12 or R3-m, and the (003) plane obtained by X-ray diffraction measurement The full width at half maximum of the peak is 0.15° or less, and the full width at half maximum of the diffraction peak of the (114) plane or the (104) plane is 0.25° or less. An active material for a lithium secondary battery comprising a solid solution of a lithium transition metal composite oxide having an α-NaFeO ₂ type crystal structure, wherein the active material for a lithium secondary battery is characterized by: The composition ratio of the metal element satisfies Li _1+(x/3) Co _1-xyz Ni _y/2 Mg _z/2 Mn _{(2x/3)+(y/2)+(z/2)} (x>0, y >0, z>0, x+y+z<1), having an X-ray diffraction pattern attributable to the space group P3 ₁ 12 or R3-m, the (003) plane obtained by X-ray diffraction measurement 114) The intensity ratio of the diffraction peak of the face or (104) plane is I ₍₀₀₃₎ / I ₍₁₁₄₎ ≧ 1.15 or I ₍₀₀₃₎ / I ₍₁₀₄₎ ≧ 1.15, and the diffraction peak of the (003) plane The full width at half maximum is 0.15° or less, and the full width at half maximum of the diffraction peak of the (114) plane or the (104) plane is 0.25° or less. The active material for a lithium secondary battery according to any one of the first to third aspect, wherein the solid solution of the lithium transition metal composite oxide has a composition ratio of 1/3 of a metal element. <x<2/3, 0<y<2/3, 0<z<0.3. The active material for a lithium secondary battery according to any one of claims 1 to 3, wherein the solid solution of the lithium transition metal composite oxide is Li[Li _1/3 Mn _2/3 a solid solution of four components of O ₂ , LiNi _1/2 Mn _1/2 O ₂ , LiCoO ₂ and LiMg _1/2 Mn _1/2 O ₂ . The active material for a lithium secondary battery according to any one of the first to third aspect, wherein the valence of each element of the solid solution of the lithium transition metal composite oxide is Li ^{1 +} , Mn ⁴⁺ , Ni ²⁺ , Co ³⁺ , Mg ²⁺ . An electrode for a lithium secondary battery, which comprises the active material for a lithium secondary battery according to any one of claims 1 to 3. A lithium secondary battery comprising the electrode for a lithium secondary battery according to claim 7 of the patent application. A method for producing a lithium secondary battery using a charging method in which a maximum reaching potential of a positive electrode during charging is 4.3 V (vs. Li/Li ⁺ ) or less is used to manufacture lithium as described in claim 8 A method of manufacturing a secondary battery, comprising the steps of: performing a potential change occurring in a positive electrode potential range exceeding 4.3 V (vs. Li/Li ⁺ ) and 4.8 V (vs. Li/Li ⁺ ) or less; Recharge to a relatively flat area.