JP2005243448A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery whose input density, power density and available capacity of the battery can be drawn out to the maximum extent by adjusting weight balance of a positive active material and a negative electrode active material in the nonaqueous electrolyte secondary battery and adjusting charge levels of a positive electrode and a negative electrode at the time of full charge. <P>SOLUTION: This nonaqueous electrolyte secondary battery uses a spinel type lithium-manganese compound oxide for the positive active material and hardly graphitizable carbon or easily graphitizable carbon capable of storing/releasing lithium for the negative electrode active material. When the composition of the hardly graphitizable carbon or the easily graphitizable carbon is expressed by Li<SB>x</SB>C<SB>6</SB>, x satisfies 0.46≤x≤0.85 when the open circuit voltage at 25°C is 4.25 V, and the applied weight of the positive active material is 5.34-14.33 g/cm<SP>2</SP>. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a non-aqueous electrolyte secondary battery using spinel-type lithium manganese composite oxide as a positive electrode active material and non-graphitizable carbon as a negative electrode active material.

  Non-aqueous electrolyte secondary batteries, including lithium ion secondary batteries, have excellent features such as high energy density and high output, so they are widely used as power sources for mobile devices such as mobile phones, video cameras, and personal computers. ing. In addition, in order to use a non-aqueous electrolyte secondary battery as a power source for an electric vehicle, a large-sized and large-capacity non-aqueous electrolyte secondary battery has been actively developed.

In these non-aqueous electrolyte secondary batteries, various lithium-containing composites such as lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), and spinel type lithium manganese composite oxide (LiMn ₂ O ₄ ) are used as the positive electrode active material. Oxides are used, and as the negative electrode active material, various carbon materials capable of occluding and releasing lithium, and host materials such as silicon, silicon oxide, and tin oxide are used. A typical positive electrode active material of a non-aqueous secondary battery currently on the market is lithium cobalt oxide (LiCoO ₂ ).

There are many patent documents that use a spinel type lithium manganese oxide as a positive electrode active material of a non-aqueous electrolyte secondary battery. For example, in Patent Document 1, spinel lithium manganate (LiMn ₂ O ₄ ) is rich in resources and low in price. However, there is a problem that capacity deterioration is likely to occur due to charge / discharge cycles, and that part of manganese elutes in the electrolyte at high temperatures, resulting in deterioration of cycle life characteristics and storage characteristics. It is described that there is.

  Patent Document 2 discloses a non-aqueous electrolyte secondary battery having excellent charge / discharge cycle characteristics by substituting a part of manganese of the spinel type lithium manganese composite oxide with one or more other elements. Patent Document 3 discloses that a high-capacity non-aqueous electrolyte secondary battery has excellent charge load characteristics even at high rate charging by using a spinel type lithium manganese composite oxide as a positive electrode active material. It is disclosed that it can be obtained.

  On the other hand, non-graphitizable carbon exceeds the theoretical capacity of graphite intercalation compounds, and when used as a negative electrode active material, a lithium secondary battery with a large capacity and good charge / discharge cycle characteristics can be obtained. Is disclosed in Patent Document 4. Further, Patent Document 5 discloses a technique of using graphitizable carbon as a negative electrode active material of a non-aqueous electrolyte secondary battery.

Furthermore, the non-aqueous electrolyte secondary battery using lithium manganate such as LiMn ₂ O ₄ as the positive electrode active material and non-graphitizable carbon as the negative electrode active material has charge acceptability (even when charged with a large current, Patent Document 6 discloses that lithium ions are quickly occluded in the crystal structure of carbon) and excellent high-rate discharge characteristics.

In addition, in a non-aqueous electrolyte secondary battery using a lithium-manganese composite oxide such as LiMn ₂ O ₄ as a positive electrode active material and graphite as a negative electrode active material, a voltage of 4.20 V or less is used to improve the life performance. Patent Document 7 discloses a technique for setting the charging depth x of graphite (Li _x C ₆ ) when fully charged to a range of 0.55 ≦ x ≦ 0.70.

  Further, in a non-aqueous electrolyte secondary battery using spinel type lithium manganese oxide as the positive electrode active material and non-graphitizable carbon as the negative electrode active material, the weight of the positive electrode active material is W1, and the weight of the negative electrode active material is W2. Patent Document 8 discloses a technique for setting the weight ratio to W1 / W2 ≦ 3.1.

JP 2000-156244 A JP-A-11-224693 JP 2000-251894 A Japanese Patent Laid-Open No. 6-188798 JP-A-6-093078 JP 2001-176499 A JP 2001-115326 A JP 2003-045497 A

Spinel-type lithium manganese composite oxide (LiMn ₂ O ₄ ) as a positive electrode active material exhibits excellent characteristics of high energy density and high output. In addition, non-graphitizable carbon and graphitizable carbon as a negative electrode active material have high capacity and high energy density, and also exhibit excellent characteristics such that the charge / discharge curve changes gently.

  Therefore, non-aqueous electrolyte secondary batteries using spinel-type lithium manganese composite oxide as the positive electrode active material and non-graphitizable carbon or graphitizable carbon as the negative electrode active material are expected to have high energy density, and the charge / discharge voltage is The charging / discharging state of the battery can be easily grasped by changing gently with the charging / discharging depth. Therefore, this non-aqueous electrolyte secondary battery is used as a high-performance power source for electric vehicles and hybrid electric vehicles, and further expansion of demand is expected.

  However, in the conventional non-aqueous electrolyte secondary battery using spinel-type lithium manganese composite oxide as the positive electrode active material and non-graphitizable carbon or graphitizable carbon as the negative electrode active material, the input density, output density, and battery of the battery There was a problem that the available capacity of was insufficient.

  Further, as disclosed in Patent Document 8, even if the weight ratio between the positive electrode active material and the negative electrode active material is within a certain range, the application weight of the active material and the electrode mixture layer thickness on the positive electrode plate and the negative electrode plate are optimal. Otherwise, if the electrode mixture layer is too thick, the battery characteristics are degraded due to peeling of the mixture layer, and high-rate discharge becomes impossible.

  Therefore, the object of the present invention is to solve this problem by adjusting the weight balance between the positive electrode active material and the negative electrode active material and matching the charge level of the positive electrode and the negative electrode at the time of full charge, and the input density and output density of the battery. It is another object of the present invention to provide a non-aqueous electrolyte secondary battery that can maximize the available capacity of the battery.

The invention of claim 1 is a non-aqueous electrolyte secondary battery using spinel-type lithium manganese composite oxide as a positive electrode active material and non-graphitizable carbon or graphitizable carbon capable of occluding and releasing lithium as a negative electrode active material. When the composition of the non-graphitizable carbon or graphitizable carbon is represented by Li _x C ₆ , the value of x when the open circuit voltage at 25 ° C. is 4.25 V is 0.46 ≦ x ≦ 0. 85, and the coating weight of the positive electrode active material is 5.34 to 14.33 mg / cm ² .

  In the non-aqueous electrolyte secondary battery of the present invention, since the battery input density is excellent, charging can be performed in a short time with a large current, and furthermore, since the output density is excellent, discharging with a large current is possible. It becomes. Moreover, since the available capacity of the battery can be maximized, a non-aqueous electrolyte secondary battery having a large capacity and high energy density can be obtained.

  As a result, the non-aqueous electrolyte secondary battery of the present invention can be widely used for, for example, a power source of an electric vehicle which requires a large size and a large capacity, and its industrial significance is great.

The non-aqueous electrolyte secondary battery of the present invention is a non-aqueous electrolyte using spinel-type lithium manganese composite oxide as a positive electrode active material and non-graphitizable carbon or graphitizable carbon capable of occluding and releasing lithium as a negative electrode active material. In the electrolyte secondary battery, when the composition of the non-graphitizable carbon or graphitizable carbon is represented by Li _x C ₆ , the value of x when the open circuit voltage at 25 ° C. is 4.25 V is 0.46 ≦ x ≦ 0.85 is satisfied, and the coating weight of the positive electrode active material is 5.34 to 14.33 mg / cm ² .

Here, x represents the charge depth of non-graphitizable carbon or graphitizable carbon. When x = 0, lithium is not occluded in the non-graphitizable carbon, and when x = 1, non-graphite. shows a state in which lithium of theory has been occluded (LiC ₆₎ in carbon.

  In addition, “when the open circuit voltage at 25 ° C. is 4.25 V” means that the non-aqueous electrolyte secondary battery of the present invention is charged, a certain amount of time elapses after the end of charging, and the open circuit voltage of the battery becomes a constant value. The constant value is 4.25 V at 25 ° C. Therefore, when the open circuit voltage of the battery is lower than 4.25 V at 25 ° C., it is necessary to continue charging.

  In addition, even if the battery whose open circuit voltage at 25 ° C. is 4.25 V is continued with constant voltage charging, the charging current hardly flows, and further charging is hardly possible. Further, when the constant current charging is continued forcibly and the voltage of the battery is set to a voltage far exceeding 4.25 V, the deterioration of the battery becomes severe. Therefore, the “battery whose open circuit voltage at 25 ° C. is 4.25 V” is considered to be a fully charged battery.

  As the charging method, any of a constant current method, a constant voltage method, a constant current-constant voltage method, and the like can be used, but a constant current-constant voltage method is preferable in order to prevent deterioration of the battery.

In the non-aqueous electrolyte secondary battery of the present invention, when the composition of the non-graphitizable carbon of the negative electrode active material is represented by Li _x C ₆ , the value of x when the open circuit voltage at 25 ° C. is 4.25 V is 0. The weight ratio of the spinel-type lithium manganese composite oxide, which is the positive electrode active material included in the battery, to the non-graphitizable carbon or graphitizable carbon, which is the negative electrode active material, is adjusted so that .46 ≦ x ≦ 0.85. There is a need to.

  The theoretical capacity of lithium that can be occluded and released from the spinel-type lithium manganese composite oxide is 148 mAh / g. However, when used in an actual nonaqueous electrolyte secondary battery, the utilization rate of the spinel-type lithium manganese composite oxide is about 73%, so that 108.0 mAh / g of lithium is occluded and released. In addition, although the capacity | capacitance of lithium occluded / released from a spinel type lithium manganese complex oxide changes with temperature and current density, when charging / discharging with current below 0.2C (5-hour rate) at 25 ° C. The maximum capacity of lithium is 108.0 mAh / g, but when charging / discharging at a current of 1 C (1 hour rate), the capacity of lithium is 95% of the maximum value (1 C charging / discharging coefficient = 0.0). 95) of 102.6 mAh / g.

  On the other hand, the theoretical capacity of lithium that can be occluded / released from non-graphitizable carbon or graphitizable carbon is 372 mAh / g. However, when used in an actual non-aqueous electrolyte secondary battery, the utilization rate of non-graphitizable carbon and graphitizable carbon is about 92%, so that 342.2 mAh / g of lithium is occluded / released. The The capacity of lithium that is actually occluded / released from the spinel-type lithium manganese composite oxide varies depending on the temperature and current density, but when discharged at 25 ° C. with a current of 1 C (one hour rate) or less. The 1C charge / discharge coefficient is 1, and the lithium capacity is a maximum value of 342.2 mAh / g.

  Adjustment of the weight ratio of the positive electrode active material and the negative electrode active material is performed as follows on the basis of 1C charge / discharge. The capacity of lithium that can be occluded and released from the spinel-type lithium manganese composite oxide is 102.6 mAh / g, the initial irreversible capacity of non-graphitizable carbon and graphitizable carbon is 80 mAh / g, non-graphitizable carbon and graphite Since the capacity of lithium of carbonized carbon is 342.2 mAh / g, when the value of x when the open circuit voltage at 25 ° C. is 4.25 V (fully charged state) is 0.5, it is difficult to graphitize. When 1 g of carbon or graphitizable carbon is used, the weight of the spinel type lithium manganese composite oxide is 2.45 g (= (342.2 × 0.5 + 80) /102.6).

  Here, “initially irreversible capacity of non-graphitizable carbon or graphitizable carbon” means non-graphitizable carbon when lithium is occluded in non-graphitizable carbon or graphitizable carbon during initial charging. Lithium that reacts with the electrolyte solution on the surface of graphitizable carbon and is consumed for film formation, and the capacity of lithium that is occluded in nongraphitizable carbon and graphitizable carbon but is not released during discharge That is, it means the capacity of lithium that is not used for charging and discharging.

The spinel-type lithium manganese composite oxide used for the positive electrode active material of the present invention includes, for example, a manganese compound such as Mn ₂ O ₃ , MnOOH, and γ-MnOOH, and a lithium compound such as lithium nitrate, lithium acetate, and lithium iodide. The target spinel type lithium manganese complex oxide composition can be produced by mixing with a slightly higher molar ratio of Li than the molar ratio of Mn and Li, and firing in air at 200 to 400 ° C. Whether or not the obtained lithium manganese composite oxide is a spinel type is determined from a chemical analysis and an X-ray diffraction pattern.

  In the spinel-type lithium manganese composite oxide used for the positive electrode active material of the present invention, a part of manganese may be substituted with other elements, and can be represented by the following general formula.

_{Li a Mn 2-b M c} O 4-δ ( where, M represents a metal element other than Li and Mn, 0 ≦ a ≦ 1.2,0 ≦ b ≦ 0.6,0 ≦ c ≦ 0.6 , 0 ≦ δ ≦ 0.1)
The non-graphitizable carbon used in the negative electrode active material of the present invention is obtained by firing an organic compound obtained by oxygen crosslinking, sulfonation, and nitration of heavy oil such as petroleum pitch and coal tar at a temperature of about 700 to 1500 ° C. And can be carbonized.

The structure of non-graphitizable carbon has a true specific gravity in the range of 1.5 to 1.7 g / cm ^2, a crystal plane distance d002 in X-ray diffraction of 0.37 to 0.39 nm, and a crystal thickness Lc of 0.1. The range of 5 to 1.5 nm is preferable, and the average particle size is preferably in the range of 0.1 to 200 μm.

  The graphitizable carbon used in the negative electrode active material of the present invention can be produced by firing at a high temperature of 2000 ° C. or higher using petroleum pitch or the like as a starting material. This graphitizable carbon has a developed graphite structure, has a (002) plane spacing of 3.40 angstroms or less by the X-ray wide angle diffraction method, and the crystallite size in the c-axis direction (Lc ) Is 200 to 1000 angstroms.

In the nonaqueous electrolyte secondary battery of the present invention, the input density and output density of the battery and the usable capacity of the battery are such that the charge depth of non-graphitizable carbon or graphitizable carbon (Li _x C ₆ ) as the negative electrode active material. Depends on x. In the present invention, the range of the charging depth (hereinafter referred to as “DOD”) x is widened for a predetermined input density and output density, that is, the capacity available for actual charge / discharge is maximized. .

  According to “storage battery terminology (SBA S 0405 (2001))”, “power density” is defined as “output that can be taken out per unit weight or unit volume of a battery”, and the unit is W / kg or W / l. .

  In the present invention, in accordance with the above “storage battery term”, “input density” is defined as “input per unit weight (W / Kg) when charging a battery”. Specifically, at 25 ° C., the prepared battery is first charged to 4.25 V at a constant current of 4 A, further 3 hours at a constant voltage of 4.25 V, and then to 2.5 V at a constant current of 4 A. Discharged. Furthermore, charging / discharging was performed under the same charging / discharging conditions, and the discharge capacity at the second cycle was defined as “battery capacity”. The charging power after 5 seconds at a certain depth of discharge (DOD) with respect to this “battery capacity” was calculated according to SAE standard J1798graft, and a value obtained by dividing this input by the battery weight was defined as “input density”.

  “Output density” is defined as “output per unit weight (W / Kg) when discharging a battery”. Specifically, after obtaining the input, the output after 15 seconds was calculated according to the same standard, and a value obtained by dividing the output by the battery weight was defined as “output density”.

  Furthermore, the “battery usable capacity” means a discharge capacity that can be actually charged / discharged when a complete battery is charged / discharged, and is a spinel type lithium manganese composite oxide that is a positive electrode active material and a negative electrode active material. The capacity is determined by the weight ratio of non-graphitizable carbon and graphitizable carbon.

  In the nonaqueous electrolyte secondary battery of the present invention, when the open circuit voltage at 25 ° C. is 4.25 V, the DOD (= x value) of the non-graphitizable carbon or graphitizable carbon that is the negative electrode active material is 0. If the value exceeds .65, the reactivity between the negative electrode and the electrolyte solution becomes extremely high, and when a safety test such as a nail penetration test is performed, the battery may run out of heat, so the range of x is 0.46. It is preferable that ≦ x <0.65.

In the nonaqueous electrolyte secondary battery of the present invention, the coating weight of the positive electrode active material is in the range of 5.34 to 14.33 g / cm ² . When the coating weight of the positive electrode active material is smaller than 5.34 g / cm ² , a battery having a high energy density cannot be obtained, while when the coating weight of the positive electrode active material is larger than 14.33 g / cm ² , The discharge capacity is reduced by the peeling of the layers, and as a result, a battery having a high energy density cannot be obtained.

  In addition, as the separator used in the nonaqueous electrolyte secondary battery of the present invention, a microporous membrane made of polyolefin resin such as polyethylene is used, and a plurality of microporous membranes having different materials, weight average molecular weights and porosity are laminated. Or those containing a suitable amount of various plasticizers, antioxidants, flame retardants and the like in these microporous membranes.

  There are no particular limitations on the organic solvent of the electrolytic solution used in the non-aqueous electrolyte secondary battery of the present invention. For example, low-viscosity chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate, ethylene carbonate, propylene High dielectric constant cyclic carbonate such as carbonate and butylene carbonate, γ-butyrolactone, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1-3 dioxolane, methyl acetate, methyl propionate, vinylene carbonate, dimethylformamide , Sulfolane, and mixed solvents thereof.

As the electrolyte salt used for the nonaqueous electrolyte secondary battery of the present invention is not particularly _{limited, LiClO 4, LiBF 4, LiAsF} 6, CF 3 SO 3 Li, LiPF 6, LiCF 3 SO 3, LiN (CF 3 _{SO 2) 2, LiN (C} 2 F 5 SO 2) 2, LiI, include LiAlCl _4, and the like and mixtures thereof. Preferably, a lithium salt obtained by mixing one or more of LiBF ₄ and LiPF ₆ is preferable.

  In the nonaqueous electrolyte secondary battery of the present invention, these organic solvents and an electrolyte are combined and used as an electrolytic solution. In these electrolytic solutions, it is preferable to use a mixture of ethylene carbonate, dimethyl carbonate, and methyl ethyl carbonate because the lithium ion conductivity is maximized.

  Other battery components include a current collector, a terminal, an insulating plate, a battery case, and the like. Conventionally, these components can be used as they are.

  Examples of the present invention will be described below together with comparative examples.

[Synthesis of spinel type lithium manganese oxide]
Lithium carbonate (Li ₂ CO ₃ ) and manganese carbonate (MnCO ₃ ) are mixed so that the molar ratio of lithium to manganese is 1: 2, and calcined at 800 ° C. for 12 hours to obtain LiMn ₂ O ₄ . It was. An X-ray diffraction pattern of this lithium manganese composite oxide is shown in FIG. From FIG. 1, it was found that the crystal structure of the obtained lithium manganese composite oxide was a spinel type.

[Synthesis of non-graphitizable carbon]
Non-graphitizable carbon was obtained by carbonizing a phenol resin by heat treatment at 2000 ° C. for 12 hours. An X-ray diffraction pattern of this hardly graphitizable carbon is shown in FIG. From FIG. 2, it was found that the obtained carbon spinel type non-graphitizable carbon. This non-graphitizable carbon has a (002) plane lattice spacing of 3.70 angstroms or more, a true density of less than 1.70 g / cm ³ , and a temperature of 700 ° C. or more by differential thermal analysis in an air stream. It is a carbonaceous material that does not have an exothermic peak.

[Synthesis of graphitizable carbon]
Graphitizable carbon was obtained by firing at a high temperature of 2300 ° C. using petroleum pitch as a starting material. This graphitizable carbon has a developed graphite structure, has a (002) plane spacing of 3.40 angstroms or less by the X-ray wide angle diffraction method, and the crystallite size in the c-axis direction (Lc ) Was 200 to 1000 angstroms.

[Examples 1 to 5 and Comparative Examples 1 and 2]
[Example 1]
A test battery was prepared using the spinel-type lithium manganese composite oxide obtained by the above synthesis method as a positive electrode active material and non-graphitizable carbon as a negative electrode active material. In the positive electrode plate, a spinel type lithium manganese oxide as an active material, acetylene black as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder are mixed in a weight ratio of 89: 4: 7. An appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to this mixture to obtain a positive electrode paste. The positive electrode paste is provided with a positive electrode mixture layer on both surfaces of the aluminum foil by applying the positive electrode paste uniformly on both surfaces of a 20 μm thick aluminum foil as a current collector with a doctor blade, drying, and roll pressing. I got a plate. The dimensions of the positive electrode plate were 3994 mm in length and 89 mm in width, and the thickness of the positive electrode mixture layer was 38 μm on one side. The weight of the spinel type lithium manganese composite oxide contained in the battery was 58 g.

  For the negative electrode plate, non-graphitizable carbon as a negative electrode active material and PVdF as a binder are mixed at a weight ratio of 94: 6, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) is mixed with this mixture. The negative electrode paste was added. This negative electrode paste was applied to a copper foil having a thickness of 10 μm as a current collector, dried, and roll-pressed to obtain a negative electrode plate having a negative electrode mixture layer on both surfaces of the copper foil. The dimensions of the negative electrode plate were 4150 mm in length and 91 mm in width, and the thickness of the negative electrode mixture layer was 40 μm on one side. The weight of the non-graphitizable carbon contained in the battery was 25 g.

The positive electrode plate and the negative electrode plate described above are laminated via a separator made of a microporous polypropylene film having a thickness of 20 μm and wound into an oval shape to produce a power generation element. It was stored in a bottomed aluminum container. Then, an electrolytic solution in which 1.2 mol / l lithium hexafluorophosphate (LiPF ₆ ) was dissolved in a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 3: 7 was poured. A long cylindrical non-aqueous electrolyte secondary battery having a battery capacity of 5 Ah and a weight of 300 g and having a safety valve was produced.

[Example 2]
A nonaqueous electrolyte secondary battery of Example 2 was produced in the same manner as in Example 1 except that the weight of the spinel-type lithium manganese composite oxide contained in the battery was 62 g and the weight of the non-graphitizable carbon was 24 g. This was designated as Battery B.

[Example 3]
A nonaqueous electrolyte secondary battery of Example 3 was produced in the same manner as in Example 1 except that the weight of the spinel-type lithium manganese composite oxide contained in the battery was 66 g and the weight of the non-graphitizable carbon was 22 g. This was designated as Battery C.

[Example 4]
A nonaqueous electrolyte secondary battery of Example 4 was produced in the same manner as in Example 1 except that the weight of the spinel type lithium manganese composite oxide contained in the battery was 69 g and the weight of the non-graphitizable carbon was 21 g. This was designated as Battery D.

[Example 5]
A nonaqueous electrolyte secondary battery of Comparative Example 2 was produced in the same manner as in Example 1 except that the weight of the spinel type lithium manganese composite oxide contained in the battery was 72 g and the weight of the non-graphitizable carbon was 20 g. This was designated as Battery E.

[Comparative Example 1]
A nonaqueous electrolyte secondary battery of Comparative Example 1 was produced in the same manner as in Example 1 except that the weight of the spinel type lithium manganese composite oxide contained in the battery was 53 g and the weight of the non-graphitizable carbon was 27 g. This was designated as Battery F.

[Comparative Example 2]
A nonaqueous electrolyte secondary battery of Comparative Example 3 was produced in the same manner as in Example 1, except that the weight of the spinel type lithium manganese composite oxide contained in the battery was 76 g and the weight of the non-graphitizable carbon was 18 g. This was designated as Battery G.

[Measurement of battery characteristics]
Regarding the batteries A to G of Examples 1 to 5 and Comparative Examples 1 and 2, the battery characteristics were measured as follows. At 25 ° C., the produced battery was charged to 4.25 V at a constant current of 3 A, further at a constant voltage of 4.25 V for a total of 3 hours, and then discharged to 2.5 V at a constant current of 3 A. Furthermore, charging / discharging was performed under the same charging / discharging conditions, and the discharge capacity at the second cycle was defined as “battery capacity”.

  The input when the current limit is 150A and the upper limit voltage after 5 seconds is 4.35V at the depth of discharge (DOD) for this "battery capacity" is calculated according to SAE standard J1798graft. The density was determined, the output when the lower limit voltage after 15 seconds was 2.5 V was calculated according to the same standard, and the output density was determined from this output.

  A method of obtaining the input and output will be described by taking the battery A of Example 1 as an example. In the battery A of Example 1, the weight of the spinel-type lithium manganese composite oxide included in the battery is 58 g, and the weight of the non-graphitizable carbon is 25 g. Since the capacity of the battery A is 5 Ah, the constant current of 5 A corresponds to 1 C (1 hour rate).

In the case of 1C charge / discharge at 25 ° C., the charge / discharge capacity per unit weight of spinel type lithium manganese composite oxide (LiMn ₂ O ₄ ) is 102.6 mAh / g, and the unit weight of non-graphitizable carbon (Li _x C ₆ ) The per charge / discharge capacity is 342.2 mAh / g. In the battery A, the lithium storage / release capacity of the positive electrode is 5951 mAh (= 102.6 × 58), the storage / release capacity of the negative electrode is 8555 mAh (= 342.2 × 25), and the irreversible capacity of the negative electrode is 2000 mAh. Accordingly, 2000 mAh is consumed as the irreversible capacity of the negative electrode out of 5951 mAh of the lithium storage / release capacity of the positive electrode. As a result, the chargeable / dischargeable capacity of the positive electrode is 3951 mAh (5951-2000). Therefore, the storage / release capacity of the negative electrode is 8555 mAh, but since the positive electrode can only charge and discharge 3951 mAh, this battery is charged until the open circuit voltage at 25 ° C. is 4.25 V, that is, in the fully charged state, The composition of the non-graphitizable carbon is Li _0.46 C ₆ (x = 0.46) (3951/8555 = 0.46). The maximum chargeable / dischargeable capacity at 1C of this battery is 3951 mAh.

  In addition, for the batteries A to G of Examples 1 to 5 and Comparative Examples 1 and 2, the active material amount of each battery is summarized in Table 2, and the battery characteristic measurement results are summarized in Table 3.

  Therefore, the battery capacity at a charging depth of 100% is 4.45 Ah, the battery after the end of the second cycle discharge is charged at a constant current of 4 A, and the charging depth of the battery is adjusted from 10% to 90% at 10% intervals. . At each charging depth, first, the voltage (Ec (V)) after 5 seconds when charging at 4 A is measured, the input (5 × Ec (W)) is obtained, and then 15 seconds when discharging at 4 A. The later voltage (Ed (V)) was measured to determine the output (5 × Ed (W)). By dividing this input by the battery weight, the “input density” can be obtained. The same applies to “output density”.

  FIG. 3 shows the relationship between the depth of discharge (DOD) and the output of the batteries A to G of Examples 1 to 5 and Comparative Examples 1 and 2, and FIG. 4 shows the relationship between the DOD and the input. 3 and 4, the symbol ◯ is for Example 1, Δ is for Example 2, □ is for Example 3, ◇ is for Example 4, ▽ is for Example 5, and ● is for Comparative Example 1. ▲ shows the relationship between DOD and charging power in Comparative Example 2.

  In the non-aqueous electrolyte secondary battery of the present invention, in order to shorten the discharge time as much as possible, the output density must be 1 kW / kg or more. Therefore, since the battery weight is 300 g, the output needs to be 300 W or more. is there. Therefore, the DOD value at the intersection of each curve in FIG. 3 and the output = 300 W straight line (broken line in FIG. 3) was read, and the value was defined as the “lower limit DOD (%) of output” for each battery.

  Further, for the same reason as in the case of discharging, in order to shorten the charging time as much as possible, the input needs to be 300 W or more. Therefore, the DOD value at the intersection of each curve in FIG. 4 and the input = 300 W straight line (broken line in FIG. 4) was read, and the value was taken as the “input lower limit DOD (%)” of each battery.

  Next, the DOD range that can be used for charging / discharging is determined from the difference between the lower limit DOD of the output of each battery and the lower limit DOD of the charging power, and the “available charge / discharge capacity” is calculated from the value and the maximum charge / discharge capacity. Asked. The results are summarized in Table 4.

FIG. 5 shows the relationship between the composition of the negative electrode in the fully charged state (the value of x in Li _x C ₆ ) and the available charge / discharge capacity. From FIG. 5, in the case of the batteries A to E of Examples 1 to 5 where the value x of Li _x C ₆ satisfies 0.46 ≦ x ≦ 0.85, the available charge / discharge capacity is larger than 2.5 Ah. However, in the case of the batteries F and G of Comparative Examples 1 and 2 in which the value of x was outside this range, it was found that the available charge / discharge capacity was 2.5 Ah or less.

  In addition, except having used easily graphitized carbon instead of non-graphitizable carbon, the battery similar to Examples 1-5 and Comparative Examples 1 and 2 was produced, and the same test was done. As a result, almost the same result as in the case of using non-graphitizable carbon was obtained.

[Examples 6 to 9]
[Example 6]
As an electrolytic solution, an electrolytic solution in which 1.2 mol / l lithium hexafluorophosphate (LiPF ₆ ) is dissolved in a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 5: 5. A nonaqueous electrolyte secondary battery of Example 6 was produced in the same manner as in Example 1 except that was used as Battery H.

[Example 7]
As an electrolytic solution, an electrolytic solution in which 1.0 mol / l lithium tetrafluoroborate (LiBF ₄ ) is dissolved in a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 3: 7 is used. A nonaqueous electrolyte secondary battery of Example 7 was produced in the same manner as Example 1 except that it was used, and this was designated as Battery I.

[Example 8]
Electrolysis in which 1.2 mol / l lithium hexafluorophosphate (LiPF ₆ ) is dissolved in a mixed solvent in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a volume ratio of 5: 5. A nonaqueous electrolyte secondary battery of Example 8 was produced in the same manner as Example 1 except that the liquid was used, and this was designated as Battery J.

[Example 9]
As an electrolytic solution, 1.2 mol / l lithium hexafluorophosphate (1.2 mol / l) was added to a mixed solvent in which ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 3: 4: 4. A nonaqueous electrolyte secondary battery of Example 9 was produced in the same manner as in Example 1 except that an electrolytic solution in which LiPF ₆ ) was dissolved was used, and this was designated as a battery K.

As a result of measuring the characteristics of the batteries H to K of Examples 6 to 9 under the same conditions as in Example 1, the fully charged state composition of the negative electrode (the value of x of Li _x C ₆ ) was x = 0.46. The charge / discharge capacity is about 2.75 Ah, which is the same result as in Example 1. The nonaqueous electrolyte secondary battery of the present invention has the same excellent result even when the type of the electrolyte is changed. Was found to be obtained.

[Examples 10 to 14 and Comparative Examples 3 and 4]
[Example 10]
Example 1 except that the weight of the spinel-type lithium manganese composite oxide contained in the battery was 51 g, the weight of the non-graphitizable carbon was 19 g, the length of the positive electrode plate was 5381 mm, and the length of the negative electrode plate was 5537 mm. In the same manner as described above, a non-aqueous electrolyte secondary battery of Example 10 was produced, and this was designated as a battery L.

[Example 11]
Example 1 except that the weight of the spinel-type lithium manganese composite oxide contained in the battery was 58 g, the weight of the non-graphitizable carbon was 22 g, the length of the positive electrode plate was 4561 mm, and the length of the negative electrode plate was 4717 mm. In the same manner as described above, a nonaqueous electrolyte secondary battery of Example 11 was produced, and this was designated as a battery M.

[Example 12]
Example 1 except that the weight of the spinel-type lithium manganese composite oxide contained in the battery was 66 g, the weight of the non-graphitizable carbon was 25 g, the length of the positive electrode plate was 3489 mm, and the length of the negative electrode plate was 3645 mm. In the same manner as described above, a nonaqueous electrolyte secondary battery of Example 12 was produced, and this was designated as a battery N.

[Example 13]
Example 1 except that the weight of the spinel-type lithium manganese composite oxide contained in the battery was 69 g, the weight of the non-graphitizable carbon was 26 g, the length of the positive electrode plate was 3110 mm, and the length of the negative electrode plate was 3267 mm. In the same manner as described above, a nonaqueous electrolyte secondary battery of Example 13 was produced, and this was designated as a battery O.

[Example 14]
Example 1 except that the weight of the spinel-type lithium manganese composite oxide contained in the battery was 72 g, the weight of the non-graphitizable carbon was 27 g, the length of the positive electrode plate was 2795 mm, and the length of the negative electrode plate was 2951 mm. In the same manner as described above, a nonaqueous electrolyte secondary battery of Example 14 was produced, and this was designated as a battery P.

[Comparative Example 3]
Example 1 except that the weight of the spinel-type lithium manganese composite oxide contained in the battery was 49 g, the weight of the non-graphitizable carbon was 19 g, the length of the positive electrode plate was 5634 mm, and the length of the negative electrode plate was 5790 mm. In the same manner as described above, a non-aqueous electrolyte secondary battery of Comparative Example 3 was produced and designated as Battery Q.

[Comparative Example 4]
Example 1 except that the weight of the spinel-type lithium manganese composite oxide contained in the battery was 73 g, the weight of the non-graphitizable carbon was 28 g, the length of the positive electrode plate was 2543 mm, and the length of the negative electrode plate was 2699 mm. In the same manner, a non-aqueous electrolyte secondary battery of Comparative Example 4 was produced, and this was designated as a battery R.

  For the batteries L to R of Examples 10 to 14 and Comparative Examples 3 and 4, the battery characteristics were measured under the same conditions as in Example 1. The amount of active material of each battery is summarized in Table 5, and the battery characteristic measurement results are summarized in Table 6. In Tables 5 and 6, the data of Example 2 are also shown for comparison.

  Next, input and output were obtained in the same manner as in Example 1, and “input density” and “output density” were obtained from these values. FIG. 6 shows the relationship between the depth of discharge (DOD) and the output for the batteries B and LR of Examples 2, 10 to 14 and Comparative Examples 3 and 4, and FIG. 7 shows the relationship between the DOD and the input. Show. 6 and FIG. 7, the symbol ◯ indicates Example 10, □ indicates Example 11, Δ indicates Example 2, ◇ indicates Example 12, ▽ indicates Example 13, and × indicates Comparative Example 14. ● indicates the relationship between DOD and charging power in Comparative Example 3, and ▲ indicates Comparative Example 4.

  In the non-aqueous electrolyte secondary battery of the present invention, in order to shorten the discharge time as much as possible, the output density must be 1 kW / kg or more. Therefore, since the battery weight is 300 g, the output needs to be 300 W or more. is there. Therefore, the DOD value at the intersection of each curve in FIG. 6 and the output = 300 W straight line (broken line in FIG. 6) was read, and the value was defined as the “lower limit DOD (%) of output” for each battery.

  Further, for the same reason as in the case of discharging, in order to shorten the charging time as much as possible, the input needs to be 300 W or more. Therefore, the DOD value at the intersection of each curve in FIG. 7 and the input = 300 W straight line (broken line in FIG. 7) was read, and the value was defined as the “input lower limit DOD (%)” of each battery.

  Next, the DOD range that can be used for charging / discharging is determined from the difference between the lower limit DOD of the output of each battery and the lower limit DOD of the charging power, and the “available charge / discharge capacity” is calculated from the value and the maximum charge / discharge capacity. Asked. The results are summarized in Table 7.

FIG. 8 shows the relationship between the positive electrode active material application weight and the available charge / discharge capacity. From FIG. 8, in the case of the batteries B and L to P of Examples ² and 10 to 14 in which the coating weight of the positive electrode active material satisfies 5.34 to 14.33 mg / cm ² , the available charge / discharge capacity is from 2.5 Ah. However, in the case of the batteries Q and R of Comparative Examples 3 and 4 in which the coating weight of the positive electrode active material was outside this range, it was found that the available charge / discharge capacity was 2.5 Ah or less.

The X-ray-diffraction figure of the synthesized spinel type lithium manganese complex oxide. X-ray diffraction pattern of synthesized non-graphitizable carbon. The figure which shows the relationship between the discharge depth (DOD) and output of batteries A-G. The figure which shows the relationship between the charging depth (DOD) and input of batteries A-G. Diagram showing the relationship between the available discharge capacity fully charged composition of the negative electrode (the value of x of Li _x C _6). The figure which shows the relationship between the discharge depth (DOD) of a battery B and LR, and an output. The figure which shows the relationship between the charging depth (DOD) and input of the batteries B and LR. The figure which shows the relationship between a positive electrode active material application | coating weight and available charge / discharge capacity.

Claims (1)

In a non-aqueous electrolyte secondary battery using a spinel-type lithium manganese composite oxide as a positive electrode active material and non-graphitizable carbon or graphitizable carbon capable of occluding and releasing lithium as a negative electrode active material, When the composition of carbon or graphitizable carbon is represented by Li _x C ₆ , the value of x when the open circuit voltage at 25 ° C. is 4.25 V satisfies 0.46 ≦ x ≦ 0.85, and the positive electrode active material The non-aqueous electrolyte secondary battery is characterized in that the coating weight of is 5.34 to 14.33 g / cm ² .

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