KR20080063063A - Negative active material for rechargeable lithium battery and rechargeable lithium battery including same - Google Patents

Abstract

A negative electrode active material for a lithium secondary battery, and a lithium secondary battery containing the negative electrode active material are provided to improve energy density per volume, capacity, cycle lifetime and safety. A negative electrode active material comprises a lithium vanadium composite oxide represented by Li_x M_y V_z O_2+d; and a compound containing at least one element selected from the group consisting of the element of groups 2-15 which is adhered to the surface of a lithium vanadium composite oxide, wherein 0.1<=x<=2.5; 0<=y<=0.5; 0.5<=z<=1.5; 0<=d<=0.5; and M is an element selected from the group consisting of Al, Cr, Mo, Ti, W, Zr and their combination.

Description

A negative electrode active material for a lithium secondary battery and a lithium secondary battery comprising the same {NEGATIVE ACTIVE MATERIAL FOR RECHARGEABLE LITHIUM BATTERY AND RECHARGEABLE LITHIUM BATTERY INCLUDING SAME}

The present invention relates to a negative electrode active material for a lithium secondary battery and a lithium secondary battery including the same, and more particularly, to a lithium secondary battery including a lithium vanadium composite oxide negative electrode active material.

Lithium secondary batteries generally use LiCoO ₂ as a positive electrode active material, graphite as a negative electrode active material, and a nonaqueous solution as an electrolyte, and are widely used as power sources for mobile phones, digital still cameras, digital video cameras, and notebook computers. It is spreading.

As the negative electrode active material of this lithium secondary battery, various types of carbon-based materials including artificial graphite, natural graphite, and hard carbon capable of inserting / removing lithium have been applied. In the carbon-based material, graphite has a low discharge potential of about 0.2 V compared to lithium, and thus, a lithium secondary battery using a material having a low discharge potential relative to lithium as a negative electrode has a high discharge potential of 3.6 V and excellent energy density. Has

Since the graphite negative electrode active material also has excellent reversibility, it is currently most widely used in view of the long life of a lithium secondary battery.

However, since graphite has a low density (theoretical density of 2.2 g / cc), the energy density of the negative electrode using graphite as the negative electrode active material is small per unit volume, and when used in a battery, there is a problem that the capacity thereof becomes small.

In order to solve this problem, a cathode using an oxide has recently been developed. For example, as a negative electrode active material, a negative electrode active material having a composition of Li _a Mg _b VO _c (0.05 ≦ a ≦ 3, 0.12 ≦ _b ≦ 2, 2 ≦ (2c-a-2b) ≦ 5) is disclosed in Japanese Patent Laid-Open No. 2002-. 216753.

However, such a conventional oxide negative electrode active material does not exhibit sufficient energy density or capacity per volume, and thus battery performance that is satisfactory as a negative electrode cannot be obtained.

For this reason, research on an oxide negative electrode active material is actively performed now.

An object of the present invention is to provide a negative electrode active material for lithium secondary batteries having high energy density per volume, high capacity, improved cycle life and high safety.

Another object of the present invention is to provide a lithium secondary battery including the negative electrode active material.

Technical problems to be achieved by the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

In order to achieve the above object, the present invention is Li _x M _y V _z O _{2 + d} (where x, y, z, d representing the composition ratio is 0.1 ≦ x ≦ 2.5, 0 ≦ y ≦ 0.5, 0.5 ≦ z On the surface of the lithium vanadium composite oxide represented by ≤ 1.5, 0 ≤ d ≤ 0.5, M is an element selected from the group consisting of Al, Cr, Mo, Ti, W, Zr, and combinations thereof. Provided is a negative electrode active material for a lithium secondary battery to which a compound containing an element selected from the group consisting of one type of group elements and combinations thereof is attached.

The compound is preferably a compound containing an element selected from the group consisting of Zr, Mg, Al, Y and combinations thereof.

The compound is preferably selected from the group consisting of oxides, nitrides, halides, sulfides, hydroxides and combinations thereof including elements selected from the group consisting of Zr, Mg, Al, Y and combinations thereof.

The compound is preferably selected from the group consisting of yttrium oxide, zirconium oxide and combinations thereof.

The present invention also provides a lithium secondary battery comprising a positive electrode including a positive electrode active material, a negative electrode including the negative electrode active material and a nonaqueous electrolyte.

The negative electrode active material for a lithium secondary battery is a compound containing any one or two or more elements of Group 2 to Group 15 elements on the surface of the lithium vanadium composite oxide represented by Li _x M _y V _z O _{2 + d} , preferably Is a compound containing an element selected from the group consisting of Zr, Mg, Al, Y and combinations thereof, more preferably an oxide containing an element selected from the group consisting of Zr, Mg, Al, Y and combinations thereof , A compound selected from the group consisting of nitrides, halides, sulfides, hydroxides, and combinations thereof, more preferably yttrium oxide, zirconium oxide, and combinations thereof; Reactivity of the lithium composite oxide may be reduced when the lithium ion is inserted.

Therefore, the lithium secondary battery including the negative electrode active material can suppress the decomposition reaction of the nonaqueous electrolyte on the surface of the negative electrode active material at the time of lithium ion insertion.

In addition, the thermal stability of the lithium secondary battery can be improved.

In addition, since the negative electrode active material includes a lithium vanadium composite oxide represented by Li _x M _y V _z O _{2 + d} , the energy density may be increased, and the discharge potential relative to lithium may be reduced to about graphite.

Therefore, the lithium secondary battery containing such a negative electrode active material can raise the energy density per volume, and can also lengthen the cycle life.

According to the present invention, it is possible to provide a negative electrode active material for a lithium secondary battery having a high energy density per volume, a long cycle life at a high capacity, and high safety, and a lithium secondary battery including the negative electrode active material.

Hereinafter, embodiments of the present invention will be described in detail. However, this is presented as an example, by which the present invention is not limited and the present invention is defined only by the scope of the claims to be described later.

Lithium secondary battery according to an embodiment of the present invention includes a positive electrode, a negative electrode and a nonaqueous electrolyte.

In the lithium secondary battery of the present invention, the negative electrode active material included in the negative electrode includes a negative electrode active material to which a compound containing any one or two or more elements of group 2 to group 15 elements is attached to the surface of the lithium vanadium complex oxide. do. By including such an anode active material, thermal stability of the lithium secondary battery may be increased and safety may be improved.

Hereinafter, the positive electrode, the negative electrode, and the nonaqueous electrolyte constituting the lithium secondary battery of the present invention will be described in detail.

(anode)

In the lithium secondary battery of the present invention, a sheet-shaped electrode composed of a positive electrode active material capable of inserting and desorbing lithium into a positive electrode, a positive electrode mixture containing a conductive assistant and a binder, and a positive electrode current collector bonded to the positive electrode mixture can be used.

In addition, a pellet-type or sheet-type anode obtained by forming the cathode mixture in a disc shape as the anode can also be used.

The positive electrode mixture may also contain a film-forming compound. Such a film-forming compound may provide Li to the anode during supercharge in order to compensate for the initial charging and discharging efficiency, and any compound that plays a role of receiving Li again during discharge may be used. .

Examples of the positive electrode active material include a compound containing Li, an oxide, and a sulfide. Examples of the metal included may include a material containing at least one or more of Mn, Co, Ni, Fe, Al, and the like. . More specifically, LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , LiFeO ₂ , LiNi _1/3 Co _1/3 Mn _1/3 O ₂ , LiNi _0.8 Co _0.2 O ₂ , and the like can be exemplified.

Moreover, polyvinylidene fluoride, polytetrafluoroethylene, etc. can be illustrated as a binder.

Moreover, as a conductive support material, carbonide, such as carbon black, KETJEN BLACK, graphite, can be illustrated.

Moreover, as a positive electrode electrical power collector, the metal foil or the metal net which consisted of aluminum, stainless steel, etc. can be illustrated.

(cathode)

As the negative electrode, a sheet-shaped electrode made of a negative electrode material containing a negative electrode active material and a binder capable of intercalating and deintercalating lithium, and containing a conductive additive as necessary, and a negative electrode current collector bonded to the negative electrode material can be used. have.

Moreover, the pellet type or sheet | seat type electrode which formed the said negative electrode mixture in disk shape as a negative electrode can also be used.

Any one of organic and inorganic materials may be used as the binder, and any one may be used as long as the negative electrode active material can be bound by a step of dispersing or dissolving it in a solvent together with the negative electrode active material and then removing the solvent.

Moreover, what mix | blends a negative electrode active material by the process of mixing with a negative electrode active material and performing solidification formation, such as pressure formation, can also be used.

As such a binder, for example, a vinyl resin, a cellulose resin, a phenol resin, a thermoplastic resin, a heat changeable resin, or the like can be used. For example, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, styrene Resin, such as butadiene rubber, can be illustrated.

In addition to the negative electrode active material and the binder, carbon black, graphite powder, carbon fiber, metal powder, metal fiber, or the like may be added as the conductive assistant.

In addition, the negative electrode current collector may be exemplified by a metal foil or a metal mesh formed of copper.

As the negative electrode active material, a compound containing any one or two or more elements of Group 2 to Group 15 elements on the surface of the lithium vanadium composite oxide represented by Li _x M _y V _z O _{2 + d} , preferably Zr, Compounds comprising an element selected from the group consisting of Mg, Al, Y and combinations thereof, more preferably oxides, nitrides, halides, sulfides selected from the group consisting of Zr, Mg, Al, Y and combinations thereof And a compound selected from the group consisting of hydroxides and combinations thereof, more preferably yttrium oxide, zirconium oxide and combinations thereof.

Li _x M _y V _z O _{2 + d} is x, y, z and d representing the composition ratio, respectively, 0.1 ≦ x ≦ 2.5, 0 ≦ y ≦ 0.5, 0.5 ≦ z ≦ 1.5, 0 ≦ d ≦ 0.5, and M The element is a lithium vanadium composite oxide which is an element selected from the group consisting of Al, Cr, Mo, Ti, W, Zr, and combinations thereof.

The Li _x M _y V _z O _{2 + d} may provide a discharge potential and lifespan characteristic close to graphite. When the lithium vanadium composite oxide represented by the above composition formula is used, it is possible to obtain a capacity per unit volume of 1000 mAh / cc or more.

Li _x M _y V _z O _{2 + d} includes an R-3M structure in which Li and oxygen, transition metal elements, and oxygen are alternately layered. In other words, in the LiVO ₂ structure, a part of the transition metal (V) is replaced with Li to enrich Li and substituted with another third transition metal (for example, Ti, Mo, Cr, Al, etc.). , Reversible insertion / desorption of lithium is possible.

On the other hand, in the R-3M structure, the notation "-3" refers to a notation in which a bar (-) is written above "3".

That is, in the structure of LiVO ₂ , a V metal ion layer (substituted with Li and a third metal) is present at an oxygen octahedral site between oxygen ions in hexagonal closed packing. Ions are present at octahedral sites below them.

When lithium is inserted into Li ₂ VO ₂ , the structure includes a V metal ion layer (substituted with Li and a third metal), an oxygen ion layer in the next layer, and a Li layer in multiple layers. In the next layer, an oxygen ion layer is present, and the next layer is changed into a structure in which a V metal ion layer (substituted with Li and a third metal) is present.

Li _x M _y V _z O _{2 + d} is a part of the V metal ion layer that is replaced with another third metal and Li to increase lithium lattice constant, that is, the distance between a axes, so that lithium is smoothly inserted / deleted even at a low potential.

This makes the lithium layer wider and facilitates insertion / deletion of lithium in the crystal structure into which lithium is inserted.

In this way, when the insertion / extraction of the lithium becomes easy, the lithium diffusion rate during charge and discharge increases, so that the life of the battery and the efficiency during charge and discharge are improved.

In the present embodiment, the above-described change in lattice structure is used, and a lithium vanadium composite oxide having the Li _x M _y V _z O _{2 + d} composition having an optimal composition capable of smooth insertion / desorption at lithium at low potential is used.

Li _x M _y V _z O _{2 + d} is an average oxidation number of vanadium (V) in the range of + 1-valent to + 4-valent, and more preferably in the range of + 1-valent to + trivalent. In other words, the vanadium (V) of this lithium vanadium composite oxide has a redox potential when the lithium composite oxide is used as the positive electrode active material in the range of +1 to +4 valence, which is 1 V or less than that of lithium metal. On the other hand, the redox reaction couple of vanadium oxide conventionally used as a positive electrode active material is mainly + 3-valent to + 4-valent, + 4-valent to + 5-valent, and the initial redox potential is 2V or more relative to lithium metal.

In comparison with this, the redox potential of the lithium vanadium composite oxide is 1 V or less, which means that the redox reaction is possible at a very low potential of Li _x M _y V _z O _{2 + d} . In other words, when an oxide having a composition of Li _x M _y V _z O _{2 + d} is used as the negative electrode active material, the discharge voltage of the battery can be expected to show a high value.

When x, y, z and d representing the composition ratio of Li _x M _y V _z O _{2 + d} exceed the above-mentioned range, the average potential of the lithium metal becomes higher than 2.5 V, and as a result, the discharge voltage is lowered, so that x, It is preferable that y, z, and d are in the above-mentioned range.

The Li _x M _y V _z O _{2 + d} has a distance ratio (c / a axis ratio) between crystal axes before lithium insertion of 2.5 to 6.5, more preferably 3.0 to 6.2.

When the distance ratio (c / a-axis ratio) between crystal axes before lithium insertion exceeds the above-mentioned range, insertion and desorption of lithium becomes structurally difficult, and the insertion / desorption potential of lithium also increases to 0.6 V or more, thereby reducing oxygen The hysteris phenomenon, in which the potential difference between insertion and departure due to the reaction contribution becomes large, occurs, which is not preferable.

The distance ratio (c / a axis ratio) between the crystal axes after lithium insertion in the Li _x M _y V _z O _{2 + d} is 3.5 to 7.0, and preferably 4.0 to 7.0. If it is smaller than the above range, the change of the lattice due to the inserted Li is small, making it difficult to diffuse Li into the lattice, and if larger than the above range, it is difficult to maintain the crystal structure.

The Li _x M _y V _z O _{2 + d} has a theoretical density of 4.2 g / cc per unit volume, and a density per unit volume of about 3.0 g / cc or more when actually manufactured with an electrode plate. In addition, when the capacity is 300mAh / g, the theoretical capacity per unit volume is 1200mAh / cc or more, it can be seen that the actual capacity per unit volume of 900mAh / cc or more is obtained.

This is compared with a theoretical density of 2.0 g / cc per unit volume of graphite which is a conventional negative electrode active material, an actual value capacity of 570 mAg / cc per unit volume at a density of 1.6 g / cc when actually used as a negative electrode and a capacity of 360 mAh / g. The density is about 2 times better.

Subsequently, the compound attached to the surface of Li _x M _y V _z O _{2 + d} is a compound containing any one or two or more elements of Group 2 to Group 15 elements, preferably Zr, Mg, Compounds comprising an element selected from the group consisting of Al, Y and combinations thereof, more preferably oxides, nitrides and halides comprising an element selected from the group consisting of Zr, Mg, Al, Y and combinations thereof , Compounds containing an element selected from the group consisting of sulfides, hydroxides and combinations thereof, more preferably is selected from the group consisting of yttrium oxide, zirconium oxide and combinations thereof.

As described later, the compound is a method of mixing a carbonate such as Zr with Li _x M _y V _z O _{2 + d} and baking, or forming a carbonate such as Zr with Li _x M _y V _z O _{2 + d} Li raw material, M raw material and V method of raw materials at the same time, calcining the material, or a carbonate, such as Zr and Li _x M _y V along the _z O _{2 + d} to a method for integrating by the furnace Chemical Mike Li _x M _y V _z It can be attached to the surface of O _{2 + d} .

For this reason, among which the elements of Group 2 to Group 15, in particular, V (vanadium), than it is to use the large ion radius, more preferred in order to attach the compound to the surface of the Li _x M _y V _z O _{2 + d} . As an element whose ion radius is larger than V (vanadium), Y (yttrium) or Zr (zirconium) can be illustrated.

Here, "attachment" means the state which the said compound coat | covered a part of Li _x M _y V _z O _{2 + d} surface. If the entire surface of Li _x M _y V _z O _{2 + d} is covered by the compound, the insertion / desorption reaction of lithium ions to Li _x M _y V _z O _{2 + d} may be inhibited, which is not preferable. .

In addition, any element of Groups 2 to 15 constituting the compound may be infiltrated into Li _x M _y V _z O _{2+ d} in the form of invading or substituting with V or M elements.

In the inside of Li _x M _y V _z O _{2 + d} , one or two or more elements of Groups 2 to 15 are diffused to denature the crystal structure of the Li _x M _y V _z O _{2 + d} outermost surface, It may also contribute to the improvement of characteristics.

Although the surface of Li _x M _y V _z O _{2 + d} may become unstable at the time of charging and decompose the nonaqueous electrolyte as compared with graphite, as described above, Li _x M _y V _z O _{2 + d} By using the negative electrode active material having the compound attached to the surface of the non-aqueous electrolyte at the surface of Li _x M _y V _z O _{2 + d} during lithium insertion can inhibit the decomposition reaction, it is possible to increase the thermal stability.

On the other hand, the adhesion amount of the compound containing any one or two or more elements of Groups 2 to 15 to the lithium vanadium composite oxide is 0.5% by weight or more, 10% by weight or less, more preferably 0.5% by weight or more, 5 It is preferably at most% by weight, more preferably at least 0.5% by weight and at most 3% by weight. If the adhesion amount is 0.5% by weight or more, the thermal stability of the negative electrode active material can be improved. Moreover, when adhesion amount is 10 weight% or less, since the fall of the discharge capacity of a negative electrode active material is prevented significantly, it is preferable.

The negative electrode active material of the present invention is a compound having excellent thermal stability, and its calorific value is very small, from 40 mW / g to 0 mW / g. The calorific value indicates the amount of heat generated during charging and discharging of the active material, and the smaller the value, the more excellent the stability.

The said negative electrode active material is manufactured by the following three methods, for example.

The first method, to prepare a carbonate or a hydroxide, such as _{Li x M y V z O 2} + d lithium vanadium composite oxide of the composition and, Zr, Mg, Al, Y. The composite oxide, carbonate, and the like are mixed by wet or dry, and the mixture is calcined at a temperature of, for example, 400 to 1400 ° C. in a non-oxidizing atmosphere such as nitrogen and argon. In addition, baking time can be suitably changed with baking temperature. According to this method, a negative electrode active material in which oxides such as Zr, Mg, Al, and Y adhere to the surface of the lithium vanadium composite oxide is prepared.

As a method of preparing the lithium vanadium composite oxide having the Li _x M _y V _z O _{2 + d} composition in advance, first, the vanadium raw material, the lithium raw material and the M element raw material are mixed in solid phase. At this time, the mixing ratio of the vanadium raw material, the lithium raw material and the M element raw material can be appropriately adjusted in the range where the composition of Li _x M _y V _z O _{2 + d} is obtained.

As the vanadium raw material, vanadium metal, VO, V ₂ O ₃ , V ₂ O ₄ , V ₂ O ₅ , V ₄ 0 ₇ , VOSO ₄ nH ₂ O or NH ₄ VO ₃ may be used. The lithium raw material may be selected from the group consisting of lithium carbonate, lithium hydroxide, lithium nitrate and lithium acetate. As the M element raw material, a material selected from the group consisting of an oxide or a hydroxide containing a metal selected from the group consisting of Al, Cr, Mo, Ti, W and Zr can be used. Examples thereof include Al (OH) ₃ , Al ₂ O ₃ , Cr ₂ O ₃ , MoO ₃ , TiO ₂ , WO ₃ , or ZrO ₂ .

A mixture consisting of a vanadium raw material, a lithium raw material and a M element raw material is heat-treated at a temperature of 500 to 1400 ° C., preferably 900 to 1200 ° C. under a reducing atmosphere to prepare a lithium vanadium composite oxide.

At this time, when the heat treatment temperature is out of the range of 500 to 1400 ° C., impurities (for example, Li ₃ VO _4, etc.) may be formed, which is not preferable because the capacity and life of the battery are lowered due to the impurities.

The heat treatment carried out in the reducing atmosphere is carried out in a nitrogen atmosphere, an argon atmosphere, an N ₂ / H ₂ mixed gas atmosphere, a CO / CO ₂ mixed gas atmosphere, or a helium atmosphere. At this time, the oxygen partial pressure in the reducing atmosphere is preferably less than 2 × 10 ⁻¹ Pa. When the oxygen partial pressure of the reducing atmosphere is 2 × 10 ₋₁ Pa or more, the oxygen atmosphere becomes an oxidizing atmosphere, and the mixture is synthesized with another material rich in oxygen, or the oxygen water is mixed with two or more other impurities and the metal oxide is oxidized. It is not desirable to have a changed state.

As a 2nd method of manufacturing a negative electrode active material, a vanadium raw material, a lithium raw material, and a M element raw material, and carbonates or hydroxides, such as Zr, Mg, Al, and Y, are prepared. The mixing ratio of the vanadium raw material, the lithium raw material and the M element raw material is appropriately adjusted in the range where the composition of Li _x M _y V _z O _{2 + d} is obtained.

Then, these are mixed in a wet or dry manner and fired at a temperature of, for example, 400 to 1400 ° C. in a non-oxidizing atmosphere such as nitrogen and argon. On the other hand, the firing time is appropriately changed depending on the firing temperature. According to this method, a negative electrode active material in which oxides such as Zr, Mg, Al, and Y adhere to the surface of the lithium vanadium composite oxide is prepared.

In the third method, an oxide, nitride, halide, sulfide, containing a lithium vanadium composite oxide having a composition of Li _x M _y V _z O _{2 + d} and any one or two or more elements of Groups 2 to 15, Hydroxides or combinations thereof are prepared and mixed either wet or dry.

Subsequently, the mixture is treated by a mechanochemical method to physically attach the above oxides, nitrides, halides, sulfides, hydroxides, or a combination thereof to the surface of the lithium vanadium composite oxide.

In this way, a negative electrode active material having an oxide, nitride, halide, sulfide, hydroxide, or a combination thereof containing any one or two or more elements of Groups 2 to 15 on the surface of the lithium vanadium composite oxide is prepared. do.

(Nonaqueous electrolyte)

Examples of the nonaqueous electrolyte include a nonaqueous electrolyte in which a lithium salt is dissolved in an aprotic solvent.

The aprotic solvent is generally used alone or in combination with a linear carbonate. However, when mixed, the following combination examples may be mentioned.

Ethylene carbonate and dimethyl carbonate; Ethylene carbonate and methylethyl carbonate; Ethylene carbonate and diethyl carbonate; Propylene carbonate and dimethyl carbonate; Propylene carbonate and methylethyl carbonate; propylene carbonate and diethyl carbonate; Ethylene carbonate, propylene carbonate and dimethyl carbonate; Ethylene carbonate, propylene carbonate and methylethyl carbonate; Ethylene carbonate, propylene carbonate and diethyl carbonate; Ethylene carbonate, dimethyl carbonate and methylethyl carbonate; Ethylene carbonate, dimethyl carbonate and diethyl carbonate ethylene carbonate, methylethyl carbonate and diethyl carbonate; Ethylene carbonate, dimethyl carbonate, methylethyl carbonate and diethyl carbonate; Ethylene carbonate, propylene carbonate, dimethyl carbonate and methylethyl carbonate; Ethylene carbonate, propylene carbonate, dimethyl carbonate and diethyl carbonate; Ethylene carbonate, propylene carbonate, methylethyl carbonate and diethyl carbonate; Ethylene carbonate, propylene carbonate, dimethyl carbonate, methylethyl carbonate and diethyl carbonate.

The mixing ratio of the cyclic carbonate to the linear carbonate (cyclic carbonate: chain carbonate) is preferably 1:99 to 99: 1 by weight, more preferably 5:95 to 70:30, and even more preferably 10:90 to 60. : 40. When included in this mixing ratio, it is possible to provide a nonaqueous electrolyte having good electrical conductivity without compromising the charge and discharge characteristics of a lithium secondary battery.

On the other hand, as the lithium salt, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiOSO ₂ C _k F _{(2k + 1)} (k is an integer of 1 to 8), LiPF _n C _k F _(2k Lithium salt, such as _{+1) (6-n)} (n is an integer of 1-5, k is an integer of 1-8), etc. are mentioned. Lithium salts represented by the following general formula may also be used: LiC (SO ₂ R ⁵ ) (SO ₂ R ⁶ ) (SO ₂ R ⁷ ), LiN (SO ₂ OR ⁸ ) (SO ₂ OR ⁹ ), LiN (SO ₂ R ¹⁰ ) (SO ₂ OR ¹¹ ), LiN (SO ₂ R ¹² ) (SO ₂ R ¹³ ).

Here, R ⁵ to R ¹³ are the same as or different from each other, and are a perfluoroalkyl group having 1 to 8 carbon atoms. These lithium salts may be used alone or in combination of two or more thereof.

As the nonaqueous electrolyte, one obtained by mixing one of the lithium salts with a polymer such as polyethylene oxide, polyvinyl alcohol, or the like, in which the polymer having high swellability is impregnated with the aprotic solvent and the lithium salt, that is, a polymer electrolyte may be used. .

In addition, the lithium secondary battery of the present invention may include other members and the like, in addition to the positive electrode, the negative electrode, and the nonaqueous electrolyte, and may include, for example, a separator that separates the positive electrode and the negative electrode.

A separator is essential when a nonaqueous electrolyte is not a polymer electrolyte, and well-known separators, such as a porous polypropylene film and a porous polyethylene film, can be used suitably.

As described above, the negative electrode active material of the present invention is a compound containing any one or two or more elements of Groups 2 to 15 on the surface of the lithium vanadium composite oxide represented by Li _x M _y V _z O _{2 + d} , Preferably a compound comprising an element selected from the group consisting of Zr, Mg, Al, Y and combinations thereof, more preferably an element selected from the group consisting of Zr, Mg, Al, Y and combinations thereof A compound selected from the group consisting of oxides, nitrides, halides, sulfides, hydroxides, and combinations thereof, and preferably a compound selected from the group consisting of yttrium oxide, zirconium oxide, and combinations thereof; The reactivity of the lithium vanadium composite oxide at the time of lithium ion insertion with respect to a vanadium complex oxide can be reduced.

Therefore, the lithium secondary battery including the negative electrode active material can suppress the decomposition reaction of the nonaqueous electrolyte on the surface of the negative electrode active material at the time of lithium ion insertion. In addition, the thermal stability of the lithium secondary battery can be improved.

Also, since the negative electrode active material of the present invention includes a lithium vanadium composite oxide represented by _{Li x M y V z O 2} + d, it is possible to increase the energy density, the lithium compared to a discharging potential can be lowered so graphite.

Therefore, the lithium secondary battery containing such a negative electrode active material can raise the energy density per volume, and can also lengthen the cycle life.

Hereinafter, preferred examples and comparative examples of the present invention are described. However, the following examples are only preferred embodiments of the present invention and the present invention is not limited to the following examples.

"Example 1"

First, a powder of V ₂ O _{4 and} a powder of LiCO ₃ were mixed to prepare a mixed powder. At this time, the molar ratio of lithium and vanadium was Li: V = 1.1: 0.9.

Subsequently, the mixed powder was calcined at 1100 ° C. for 10 hours under a nitrogen atmosphere flowing nitrogen at a flow rate of 5 L / min to prepare a lithium vanadium composite oxide having a Li _1.1 V _0.9 O ₂ composition.

Next, 3% by weight of zirconium carbonate was added to 97% by weight of the obtained lithium vanadium composite oxide, and dry mixed, and then calcined at 1100 ° C. for 10 hours under a nitrogen atmosphere flowing nitrogen at a flow rate of 5 L / min. Thus, the negative electrode active material of Example 1 was manufactured.

Example 1, the presence of, a bar, ZrO ₂ (zirconium oxide) measured by X-ray diffraction with respect to the negative electrode active material was confirmed in. On the other hand, zirconium carbonate was not detected.

"Example 2"

A negative active material of Example 2 was prepared in the same manner as in Example 1, except that yttrium carbonate was added instead of zirconium carbonate.

Example 2 is present with respect to the negative electrode active material, as measured by X-ray diffraction bars, Y ₂ O ₃ (yttrium oxide) was confirmed in. On the other hand, yttrium carbonate was not detected.

"Example 3"

In the same manner as in Example 1, a lithium vanadium composite oxide having a Li _1.1 V _0.9 O ₂ composition was prepared.

Subsequently, 3% by weight of zirconium carbonate and 3% by weight of yttrium carbonate were added to 94% by weight of the obtained lithium vanadium composite oxide, followed by dry mixing, followed by 10 hours at 1100 ° C. under a nitrogen atmosphere flowing nitrogen at a flow rate of 5 L / min. Calcined for

Thus, the negative electrode active material of Example 3 was manufactured.

X-ray diffraction was measured on the negative electrode active material of Example 3, and the presence of ZrO ₂ (zirconium oxide) and Y ₂ O ₃ (yttrium oxide) was confirmed. On the other hand, zirconium carbonate and yttrium carbonate were not detected.

"Example 4"

A powder of V ₂ O _{4 and} a powder of LiCO ₃ were mixed to prepare a mixed powder. At this time, the molar ratio of lithium and vanadium was Li: V = 1.1: 0.9.

Subsequently, 3% by weight of zirconium carbonate was added to 97% by weight of the mixed powder, wet mixed with water, dried, and calcined at 1100 ° C. for 10 hours under a nitrogen atmosphere flowing nitrogen at a flow rate of 5 L / min.

Thus, the negative electrode active material of Example 4 was manufactured.

X-ray diffraction measurement of the negative electrode active material of Example 4 confirmed the presence of a lithium vanadium composite oxide having a Li _1.1 V _0.9 O ₂ composition and ZrO ₂ (zirconium oxide). On the other hand, zirconium carbonate was not detected.

"Example 5"

In the same manner as in Example 1, a lithium vanadium composite oxide having a Li _1.1 V _0.9 O ₂ composition was prepared.

Next, 3% by weight of ZrO ₂ (zirconium oxide) was added to 97% by weight of the obtained lithium vanadium composite oxide, followed by dry mixing.

Thereafter, the mixture after dry mixing was treated with a microchemical method to prepare an anode active material of Example 5.

In addition, the process by the Mykenochemical method was performed for 5 minutes using Mechanofusion (AMS) (made by Hosokawa micron corporation).

X-ray diffraction measurement of the negative electrode active material of Example 5 confirmed the presence of a lithium vanadium composite oxide having a Li _1.1 V _0.9 O ₂ composition and ZrO ₂ (zirconium oxide).

`` Comparative Example 1 ''

In the same manner as in Example 1, a lithium vanadium composite oxide having a Li _1.1 V _0.9 O ₂ composition was prepared, which was used as a negative electrode active material of Comparative Example 1.

`` Comparative Example 2 ''

In the same manner as in Example 1, a lithium vanadium composite oxide having a Li _1.1 V _0.9 O ₂ composition was prepared.

Subsequently, 3% by weight of ZrO ₂ (zirconium oxide) was added to 97% by weight of the obtained lithium vanadium composite oxide, and dry mixing was performed for 2 hours using a ball mill to prepare a negative electrode active material of Comparative Example 2.

`` Comparative Example 3 ''

In the same manner as in Example 1, a lithium vanadium composite oxide having a Li _1.1 V _0.9 O ₂ composition was prepared.

Next, 3% by weight of Y ₂ O ₃ (yttrium oxide) was added to 97% by weight of the obtained lithium vanadium composite oxide, and dry mixing was performed for 2 hours using a ball mill to prepare a negative electrode active material of Comparative Example 3. It was.

"evaluation"

Of the prepared negative electrode active materials, the negative electrode active materials of Example 1 and Comparative Example 1 were observed using a scanning electron microscope to observe the surface form of the negative electrode active material. The SEM photograph of the negative electrode active material of Example 1 is shown in FIG. 1, and the SEM photograph of the negative electrode active material of Comparative Example 1 is shown in FIG.

Further, 80 parts by weight of the negative electrode active materials of Examples 1 to 5 and Comparative Examples 1 to 3, 10 parts by weight of carbon black (conductive aid), and 10 parts by weight of polyvinylidene fluoride were dissolved in N-methyl pyrrolidone to prepare a slurry. Was prepared, and this slurry was apply | coated to Cu foil, it dried, it cut | disconnected to the moderate magnitude | size, and the electrode for evaluation was produced.

In addition, a metal lithium thin film electrode (counter electrode) was prepared. A polypropylene separator was positioned between the obtained electrode and the counter electrode to form an electrode group, and the electrode group was housed in a coin-type battery container.

In addition, an electrolyte solution containing 1.3 M of LiPF ₆ dissolved in a mixed solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of EC: DMC = 3: 7 was poured, and then the battery container was sealed. By doing so, the batteries for evaluation of Examples 1 to 5 and Comparative Examples 1 to 3 were prepared.

The evaluation batteries of Examples 1 to 5 and Comparative Examples 1 to 3 were subjected to constant current charging until the end-of-charge voltage was 0V at a charging current of 0.2C, and then charged by constant voltage charging for 3 hours. Was carried out.

Thereafter, discharge was performed at a discharge current of 0.2C until the voltage became 2.0V. Table 1 shows the discharge capacity of each battery.

After charging was performed again at a charging current of 0.2C until the end voltage of charge was 0 V, the battery for evaluation was disassembled and the evaluation negative electrode was taken out. Differential scanning calorimetry (DSC) was performed under conditions of a start temperature of 40 ° C., a temperature increase rate of 10 ° C./min, and an end temperature of 300 ° C., and the exothermic peak temperature and the calorific value were measured. The results are shown in Table 1.

Compound attached to the surface Added amount (% by weight) Manufacturing method Exothermic peak temperature (℃) Calorific Value (mW / g) Discharge Capacity (Comparative Example 1 is 100%) Example 1 ZrO ₂ 3 deflation 132 20 100 Example 2 Y ₂ O ₃ 3 deflation 130 22 100 Example 3 Y ₂ O ₃ ZrO ₂ 3 3 deflation 130 20 100 Example 4 ZrO ₂ 3 Wet 130 20 100 Example 5 ZrO ₂ 3 Mykeno Chemical 130 20 100 Comparative Example 1 none 3 deflation 120 100 100 Comparative Example 2 none 3 deflation 120 100 100 Comparative Example 3 none 3 deflation 120 100 100

Since the amount added in Table 1 is attached to the surface of the lithium vanadium oxide, the added amount means the amount of adhesion.

As shown in Table 1, it can be seen that the negative electrode active material of Examples 1 to 5 showed a high exothermic peak temperature of about 10 ° C. and a small calorific value of about one fifth as compared with the negative electrode active materials of Comparative Examples 1 to 3. have. As described above, it can be seen that the negative electrode active materials of Examples 1 to 5 have a low calorific value, a high exothermic peak temperature, and excellent thermal stability even when heated in a charged state.

In the negative electrode active materials of Comparative Examples 2 and 3, despite the addition of zirconium oxide or yttrium oxide, the peak temperature and the calorific value appeared similarly to Comparative Example 1. This indicates that thermal stability is not obtained when zirconium oxide or yttrium oxide is simply mixed with Li _1.1 V _0.9 O ₂ .

SEM photographs of the negative electrode active materials of Example 1 and Comparative Example 1 are shown in FIGS. 1 and 2, respectively. Comparing FIG. 1 with FIG. 2, it is clear that in Example 1, ZrO ₂ is attached to the Li _1.1 V _0.9 O ₂ particle surface.

In this way, in order to improve the thermal stability of the negative electrode active material, it is not enough to simply mix zirconium oxide or yttrium oxide with Li _1.1 V _0.9 O ₂ , and it is understood that firing or processing such as a chemical chemical is required.

In addition, compared with the negative electrode active materials of Comparative Examples 1 to 3, the negative electrode active materials of Examples 1 to 5 had almost equal discharge capacities, and even when zirconium oxide or yttrium oxide were attached, the discharge capacities were in the ranges of addition ratios shown in Table 1, respectively. It turns out that there is no influence in particular.

"Examples 6 to 10"

In the same manner as in Example 1, a lithium vanadium composite oxide having a Li _1.1 V _0.9 O ₂ composition was prepared.

Next, zirconium carbonate was added to the obtained lithium vanadium composite oxide and dry mixed. At this time, the addition amount of lithium vanadium composite oxide 99.5: 0.5% by weight of zirconium carbonate (Example 6), 99: 1% by weight (Example 7), 97: 3% by weight (Example 8), 95: 5% by weight (implementation Example 9) and 90:10 wt% (Example 10).

In addition, what used 100 weight% of lithium vanadium complex oxides without adding a zirconium carbonate was made into the comparative example 4.

The obtained product was calcined at 1100 ° C. for 10 hours under a nitrogen atmosphere flowing nitrogen at a flow rate of 5 L / min. According to this process, the negative electrode active materials of Examples 6 to 10 and Comparative Example 4 were prepared.

X-ray diffraction was measured on the obtained negative electrode active materials of Examples 6 to 10, and the presence of ZrO ₂ (zirconium oxide) was confirmed. On the other hand, zirconium carbonate was not detected.

In addition, the negative electrode active materials of Examples 6 to 10 and Comparative Example 4 were carried out in the same manner as in Examples 1 to 5 and Comparative Examples 1 to 3, the discharge capacity was measured, and the calorific value was measured. The results are shown in FIG. The discharge capacity shown in FIG. 3 is a capacity ratio when the discharge capacity of the comparative example 4 whose addition amount of zirconium oxide is 0% is made into 100%.

As shown in Fig. 3, it can be seen that as the amount of addition of zirconium oxide increases, the amount of heat generated decreases, but the discharge capacity also tends to decrease. According to FIG. 3, the addition amount of zirconium oxide with respect to lithium vanadium complex oxide is 0.5 weight% or more and 10 weight% or less, Preferably it is 5 weight% or less, More preferably, 3 weight% or less is preferable.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited thereto, and various modifications and changes can be made within the scope of the claims and the detailed description of the invention and the accompanying drawings. Naturally, it belongs to the scope of the invention.

1 is a SEM photograph of the negative electrode active material of Example 1 of the present invention.

2 is a SEM photograph of the negative electrode active material of Comparative Example 1.

3 is a graph showing discharge capacity and calorific value results according to the amount of zirconium oxide added in Examples 6 to 10 and Comparative Example 4 of the present invention.

Claims (16)

Li _x M _y V _z O _{2 + d} (0.1 ≦ x ≦ 2.5, 0 ≦ y ≦ 0.5, 0.5 ≦ z ≦ 1.5, 0 ≦ d ≦ 0.5, and M is Al, Cr, Mo, Ti, W, Zr And a compound comprising an element selected from the group consisting of one of Group 2 to 15 elements and combinations thereof, on the surface of the lithium vanadium composite oxide represented by the above). Being Anode active material for lithium secondary battery. The method of claim 1, The compound is a negative electrode active material for a lithium secondary battery which is a compound containing an element selected from the group consisting of Zr, Mg, Al, Y and combinations thereof. The method of claim 1, The compound is selected from the group consisting of oxides, nitrides, halides, sulfides, hydroxides and combinations thereof including an element selected from the group consisting of Zr, Mg, Al, Y and combinations thereof. Active material. The method of claim 1, The compound is selected from the group consisting of yttrium oxide, zirconium oxide and combinations thereof. The method of claim 1, The adhesion amount of the compound is 0.5% by weight or more, 10% by weight or less negative electrode active material for a lithium secondary battery. The method of claim 5, The adhesion amount of the compound is 0.5% by weight or more, 5% by weight or less negative electrode active material for a lithium secondary battery. The method of claim 6, The adhesion amount of the compound is 0.5% by weight or more, 3% by weight or less for a negative electrode active material for a lithium secondary battery. The method of claim 1, The negative electrode active material is a lithium secondary battery negative electrode active material having a calorific value of 40mW / g to 0mW / g. A positive electrode including a positive electrode active material; Li _x M _y V _z O _{2 + d} (0.1 ≦ x ≦ 2.5, 0 ≦ y ≦ 0.5, 0.5 ≦ z ≦ 1.5, 0 ≦ d ≦ 0.5, and M is Al, Cr, Mo, Ti, W, Zr And a compound comprising an element selected from the group consisting of one of Group 2 to 15 elements and combinations thereof, on the surface of the lithium vanadium composite oxide represented by the above). A negative electrode including a negative electrode active material; And Nonaqueous electrolyte Lithium secondary battery comprising a. The method of claim 9, The compound is a lithium secondary battery is a compound containing an element selected from the group consisting of Zr, Mg, Al, Y and combinations thereof. The method of claim 10, The compound is a lithium secondary battery is selected from the group consisting of oxides, nitrides, halides, sulfides, hydroxides and combinations thereof comprising an element selected from the group consisting of Zr, Mg, Al, Y and combinations thereof. The method of claim 10, The compound is selected from the group consisting of yttrium oxide, zirconium oxide and combinations thereof. The method of claim 9, The adhesion amount of the compound is 0.5% by weight or more, 10% by weight or less lithium secondary battery. The method of claim 13, The adhesion amount of the compound is 0.5% by weight or more, 5% by weight or less lithium secondary battery. The method of claim 14, The adhesion amount of the compound is at least 0.5% by weight, 3% by weight or less lithium secondary battery. The method of claim 9, The negative active material is a lithium secondary battery having a calorific value of 40mW / g to 0mW / g.

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