JP5125050B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous secondary electrolyte battery containing non-graphitizable carbon and graphitizable carbon in 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 particular, in an electric vehicle, it is an important development subject to increase the life and output of a non-aqueous secondary electrolyte battery. This is because the battery is required to have a life performance equivalent to the equipment life of the automobile, and the rapid discharge performance is necessary when the automobile starts.

  Examples of the positive electrode active material of the lithium ion secondary battery include lithium-containing layered cobalt oxide (hereinafter referred to as “Co-based compound”), lithium-containing layered nickel oxide (hereinafter referred to as “Ni-based compound”), or spinel type lithium manganese. A long-life nonaqueous electrolyte secondary battery using a composite oxide (hereinafter referred to as “Mn-based compound”) and using a carbon material capable of occluding and releasing lithium as a negative electrode active material has been put into practical use.

  As this carbon material, non-graphitizable carbon such as phenol formaldehyde resin charcoal, furfuryl alcohol resin charcoal, carbon black, vinylidene chloride charcoal, cellulose charcoal, pitch coke, mesocarbon micro beads, needle coke, bulk mesophase coke, In non-aqueous electrolyte secondary batteries using graphitizable carbon such as flue coke and gilsonite coke, the charge / discharge voltage changes gradually with the change in charge / discharge depth, and the charge / discharge state of the battery changes. It can be easily grasped.

  For this reason, non-aqueous electrolyte secondary batteries using non-graphitizable carbon or easily graphitizable carbon as a negative electrode active material are used as high-performance power sources for electric vehicles and hybrid electric vehicles, and further demand expansion is expected. ing.

  The non-graphitizable carbon does not have a hexagonal network structure, and the expansion and contraction of the active material particles accompanying charge / discharge is small. For this reason, a conductive path is hard to be cut | disconnected at the time of a charging / discharging cycle, and favorable charging / discharging cycling performance is shown. In addition, since the non-conductive film does not easily grow with reductive decomposition of the electrolyte, long-term storage performance is also good.

  However, since non-graphitizable carbon has many crystal structure distortions and voids, it has been difficult to produce a non-aqueous electrolyte secondary battery that has low electronic conductivity and good output performance.

  On the other hand, since graphitizable carbon has a relatively developed crystal structure, it is possible to produce a non-aqueous electrolyte secondary battery that has higher electronic conductivity than non-graphitizable carbon and exhibits good output performance. Is possible. Moreover, since graphitizable carbon has a higher true density than non-graphitizable carbon, it is easy to improve the electrode density, and it has an advantage that a high-capacity battery can be obtained.

  However, graphitizable carbon has a problem that it is difficult to obtain good charge / discharge cycle performance because the expansion and contraction in the C-axis direction accompanying charge / discharge is large, and the conductive path is easily cut. .

  As a method for solving such a problem, Patent Document 1 discloses that in a negative electrode containing non-graphitizable carbon and graphitizable carbon, the content of non-graphitizable carbon is 1 to 30% by weight or 0. A technique of 5 to 20% by weight is disclosed.

Patent Document 2 discloses a technique using a fired product of a mixture of non-graphitizable carbon and graphitizable carbon for the negative electrode. Further, Patent Document 3 discloses a technique for coating graphitizable carbon with non-graphitizable carbon, or a technique for coating non-graphitizable carbon with graphitizable carbon, and graphitized carbon and shell as cores. It is disclosed that the range of the weight ratio with graphitized carbon is 1: 1 to 1: 0.1.
Japanese Patent Laid-Open No. 06-333564 Japanese Patent Laid-Open No. 11-265718 Japanese Patent Laid-Open No. 08-069819

  In order to improve the charge / discharge cycle performance of the non-aqueous electrolyte secondary battery, as described in the above patent document, the negative electrode active material contains non-graphitizable carbon and graphitizable carbon in a predetermined amount. A method using a negative electrode has been proposed. However, the content of the non-graphitizable carbon and the graphitizable carbon described in Patent Document 1 cannot suppress expansion and contraction associated with charge / discharge of the graphitizable carbon, and charge / discharge cycle performance. It is not possible to obtain a sufficient effect in improving the quality. In addition, the methods described in Patent Documents 2 and 3 inevitably suffer from problems such as complicated manufacturing processes and excessive costs, and development of a simpler and more effective method is required.

  An object of the present invention is excellent in a battery including a positive electrode using a lithium composite oxide capable of occluding and releasing lithium as an active material, a negative electrode using a carbon material capable of occluding and releasing lithium as an active material, and a non-aqueous electrolyte. It is providing the nonaqueous electrolyte secondary battery which shows output performance and charging / discharging cycling performance.

The invention of claim 1 is a non-aqueous electrolyte secondary battery comprising a positive electrode using a transition metal composite oxide containing lithium as a positive electrode active material, a negative electrode using a carbon material as a negative electrode active material, and a non-aqueous electrolyte. , wherein the carbon material comprises particles of particle and graphitizable carbon of non-graphitizable carbon, the graphitizable carbon and the hardly graphitizable carbon particles occupied in the graphitizable carbon particles and wherein the ratio of particles is 4 to 40 wt%, average particle diameter of the easily graphitizable carbon particles is 0.3 to 1 times the average particle diameter of the flame-graphitizable carbon particles To do.

  According to the present invention, the ratio of the non-graphitizable carbon as the negative electrode active material and the graphitizable carbon in the graphitizable carbon is 4 to 40% by weight, and the average particle size of the graphitizable carbon is difficult. By setting the average particle size of graphitizable carbon to 0.3 to 1 times, better output performance than the average value calculated from the mixing ratio of the output performance of non-graphitizable carbon and graphitizable carbon can be obtained. It is possible to provide a nonaqueous electrolyte secondary battery that is obtained and has good charge / discharge cycle performance.

  That is, in the negative electrode containing non-graphitizable carbon and graphitizable carbon, in order to improve charge / discharge cycle performance and output performance, the ratio of the respective average particle diameters is a very important parameter. The expansion / contraction rate of graphitizable carbon accompanying charge / discharge is larger than the expansion / contraction rate of non-graphitizable carbon. Therefore, by selecting graphitizable carbon having an average particle size smaller than that of non-graphitizable carbon, the cutting of the conductive path due to expansion and contraction of graphitizable carbon is mitigated, and good electronic conductivity is ensured. Therefore, good charge / discharge cycle performance and output performance can be obtained.

  Hereinafter, the present invention will be described in detail, but it goes without saying that the present invention is not limited to the following embodiments.

  The non-aqueous electrolyte secondary battery of the present invention includes a positive electrode having a lithium composite oxide capable of occluding and releasing lithium as an active material, a non-graphitizable carbon and an easily graphitizable carbon capable of occluding and releasing lithium as an active material. In a non-aqueous electrolyte secondary battery in which a power generation element comprising a negative electrode, a non-aqueous electrolyte, and a separator is housed in a battery case, the graphitizable carbon occupies the non-graphitizable carbon and the graphitizable carbon. The ratio is 4 to 40% by weight, and the average particle size of graphitizable carbon is 0.3 to 1 times the average particle size of non-graphitizable carbon.

  In the present invention, the “ratio of graphitizable carbon and non-graphitizable carbon to non-graphitizable carbon” means the weight of graphitizable carbon relative to the total weight of graphitizable carbon and graphitizable carbon. It means the percentage (% by weight).

  In addition, the “average particle size” is a particle size measured by dry dispersion under the conditions of cascade use using a laser diffraction particle size distribution analyzer SALD-2000J (0.03 to 700 μ range) manufactured by Shimadzu Corporation. The particle diameter when the cumulative value is 50% is meant.

  In the present invention, “non-graphitizable carbon” means amorphous carbon that cannot be converted to graphite even when heated to an ultrahigh temperature of about 3300 K under normal pressure or reduced pressure.

  In addition, in non-graphitizable carbon, it is desirable that the change in the lattice volume accompanying charging / discharging is small, and the (002) plane spacing measured by the X-ray wide angle diffraction method is 3.70 angstroms or more. The size of the child is preferably 1.5 nm or less in the c-axis direction (Lc).

  In the present invention, “easily graphitizable carbon” means amorphous carbon that can be converted to graphite by high-temperature treatment at around 3300K.

  In addition, graphitizable carbon can be expected to increase the electronic conductivity by growing a certain degree of crystal structure, but if the crystal structure develops too much, the change in lattice volume accompanying charge / discharge becomes too large, Good charge / discharge cycle performance cannot be obtained. For this reason, it is preferable that the (002) plane spacing measured from the X-ray wide angle diffraction method of graphitizable carbon is 3.45 to 3.55 angstroms.

  When the ratio of graphitizable carbon to non-graphitizable carbon is less than 4% by weight, the electronic conductivity of the mixture of non-graphitizable carbon and graphitizable carbon is non-graphitizable. Since it is almost the same as carbon, good output performance cannot be obtained. On the other hand, when the ratio of the graphitizable carbon to the non-graphitizable carbon and the graphitizable carbon exceeds 40% by weight, the conductive path is cut off due to the expansion / contraction of the graphitizable carbon accompanying charge / discharge. Since it cannot suppress, charging / discharging cycle performance falls.

  Also, the smaller the average particle size of non-graphitizable carbon or graphitizable carbon is, the shorter the lithium ion diffusion path in the active material, the better the output performance can be obtained, but the average particle size is too small The growth of the non-conductive film accompanying the reaction between the electrolyte and the electrolyte is promoted, so that the average particle size of the non-graphitizable carbon is preferably 5 to 25 μm, and the average particle size of the graphitizable carbon is non-graphite It is necessary to make it 0.3 to 1 times that of carbon.

  In addition, when the average particle size of the graphitizable carbon is smaller than 0.3 times the average particle size of the non-graphitizable carbon, it is easy to graphitize the voids composed of the non-graphitizable carbon having a large average particle size. Since carbon is clogged too much, the diffusion path of lithium ions becomes narrow, resulting in a decrease in output performance. On the other hand, when the average particle size of the graphitizable carbon is larger than one time the average particle size of the non-graphitizable carbon, the above-described relaxation effect of expansion and contraction of the graphitizable carbon cannot be sufficiently obtained. Charge / discharge cycle performance decreases.

  In addition, as a negative electrode active material of the nonaqueous electrolyte secondary battery of the present invention, carbon such as graphite, carbon black, and vapor growth carbon fiber may be included in addition to non-graphitizable carbon and graphitizable carbon.

  The external appearance of the nonaqueous electrolyte secondary battery of the present invention is shown in FIG. 1, and the electrode group of the battery is shown in FIG. 1 and 2, 1 is a non-aqueous electrolyte secondary battery, 2 is an electrode group, 2a is a positive electrode, 2b is a negative electrode, 2c is a separator, 3 is a battery case, 3a is a case part of the battery case, and 3b is a battery case. , 4 is a positive terminal, 5 is a negative terminal, 6 is a safety valve, and 7 is an electrolyte injection port.

  In the nonaqueous electrolyte secondary battery of the present invention, an electrode group 2 in which a positive electrode 2a and a negative electrode 2b are wound in an oval shape via a separator 2c is housed in a case portion 3a of the battery case, The portion 3a and the battery case lid portion 3b are sealed by laser welding, a non-aqueous electrolyte (not shown) is injected from the injection port 7, and then the injection port 7 is sealed. .

  The positive electrode, separator, electrolyte, and the like used for the nonaqueous electrolyte secondary battery of the present invention are not particularly different from those conventionally used, and commonly used ones can be used. In FIG. 2, an ellipse is shown as the shape of the electrode group, but it may be a circle. Further, the shape of the electrode group is not limited to the winding type, and may be a shape in which flat plate plates are laminated.

Examples of the positive electrode active material used in the non-aqueous electrolyte secondary battery of the present invention include lithium manganate (LiMn ₂ O ₄ ), lithium cobaltate (LiCoO ₂ ), and lithium nickelate (LiNiO ₂ ) capable of inserting and extracting lithium. Lithium composite oxides capable of inserting and extracting lithium, lithium composite oxides in which the transition metal portion of each composite oxide is replaced with another transition metal or light metal, or a post-transition metal for performance improvement.

  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.

  The non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery of the present invention may be a non-aqueous electrolyte, a polymer electrolyte, a room temperature molten salt or ionic liquid, or a solid electrolyte.

  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 carbonates 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.

  The polymer electrolyte that can be used in the non-aqueous electrolyte secondary battery of the present invention is not particularly limited. For example, vinylidene fluoride / hexafluoropropylene copolymer (P (VDF / HFP)), polyvinylidene fluoride ( PVDF), polyvinyl chloride (PVC), polyacrylonitrile (PAN), polyethylene oxide, polypropylene oxide, polyvinylidene chloride, polymethyl methacrylate, polymethyl acrylate, poly 40 vinyl alcohol, polymethacrylonitrile, polyvinyl acetate, polyvinyl pyrrolidone, A lithium ion conductive polymer composed of polyethyleneimine, polybutadiene, polystyrene, polyisoprene, or derivatives thereof alone or in combination can be used.

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, LiPF 6, LiCF 3 SO 3, LiN (CF 3 SO 2) 2, LiN (C ₂ F ₅ SO ₂ ) ₂ , LiI, 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.

[Examples 1 to 4 and Comparative Examples 1 to 4]
[Example 1]
As the negative electrode active material, a 96: 4 weight ratio mixture of non-graphitizable carbon (hereinafter referred to as “HC”) and graphitizable carbon was used. As HC, the (002) plane spacing measured by X-ray wide angle diffraction method is 3.80 angstroms, the crystallite size is 1.1 nm in the c-axis direction (Lc), and the average grain size is 10 μm Was used. As graphitizable carbon, the (002) plane spacing measured by X-ray wide angle diffraction method is 3.48 Å, the crystallite size is 2.0 nm in the c-axis direction (Lc), and the average particle size Was 6 μm coke (hereinafter referred to as “Cs”). Therefore, the average particle size of Cs is 0.6 times the average particle size of HC.

  In the negative electrode, 94% by weight of the negative electrode active material and 6% by weight of polyvinylidene fluoride (hereinafter referred to as “PVdF”) as a binder are mixed, and this is mixed with N-methyl-2-pyrrolidone having a water content of 50 ppm or less ( (Hereinafter referred to as “NMP”) was added to a paste to form a paste, which was applied onto a copper foil and dried. The negative electrode was dried at 150 ° C. for 12 hours or more under a vacuum of 0.01 torr or less.

The positive electrode is a mixture of 87% by weight of LiMn ₂ O ₄ (hereinafter referred to as “Mn-based”) powder as a positive electrode active material, 5% by weight of acetylene black as a conductive additive and 8% by weight of PVdF as a binder. Then, NMP was added to the slurry to form a paste, which was applied onto an aluminum foil and dried. The drying conditions for the positive electrode were the same as those for the negative electrode.

  As shown in FIG. 2, the positive electrode and the negative electrode subjected to roll press are wound into an oval shape via a separator to form an electrode group, and then the electrode group is inserted into a long cylindrical bottomed aluminum container, Furthermore, after filling the core part of the electrode group with the filler, the electrolyte solution was injected, and the container and the lid were sealed and welded by laser welding to produce the nonaqueous electrolyte secondary battery A of Example 1. All processes from slurry preparation to electrode processing and battery assembly were performed in a dry room with a dew point of -50 ° C or lower. The design capacity of the manufactured battery was 550 mAh.

[Example 2]
A nonaqueous electrolyte secondary battery B of Example 2 was produced in the same manner as in Example 1 except that a mixture of HC and Cs at a weight ratio of 80:20 was used as the negative electrode active material.

[Example 3]
A nonaqueous electrolyte secondary battery C of Example 3 was produced in the same manner as in Example 1 except that a mixture of HC and Cs having a weight ratio of 70:30 was used as the negative electrode active material.

[Example 4]
A nonaqueous electrolyte secondary battery D of Example 4 was produced in the same manner as in Example 1 except that a mixture of HC and Cs having a weight ratio of 60:40 was used as the negative electrode active material.

[Comparative Example 1]
A nonaqueous electrolyte secondary battery E of Comparative Example 1 was produced in the same manner as Example 1 except that only HC was used as the negative electrode active material.

[Comparative Example 2]
A nonaqueous electrolyte secondary battery F of Comparative Example 2 was produced in the same manner as in Example 1 except that a mixture of HC and Cs having a weight ratio of 98: 2 was used as the negative electrode active material.

[Comparative Example 3]
A nonaqueous electrolyte secondary battery G of Comparative Example 3 was produced in the same manner as in Example 1, except that a mixture of HC and Cs having a weight ratio of 40:60 was used as the negative electrode active material.

[Comparative Example 4]
A nonaqueous electrolyte secondary battery H of Comparative Example 4 was produced in the same manner as in Example 1 except that only Cs was used as the negative electrode active material.

[Characteristic measurement]
For the nonaqueous electrolyte secondary batteries A to H of Examples 1 to 4 and Comparative Examples 1 to 4, initial discharge capacity measurement, output measurement, and charge / discharge cycle test were performed under the following conditions.
1. Initial discharge capacity measurement The test battery was charged to 4.2 V at a constant current of 550 mA in a 25 ° C. environment, and then charged at a constant voltage of 4.2 V so that the total charging time was 3 hours. . Thereafter, the battery was discharged to 2.5 V at a constant current of 550 mA. This charge / discharge was repeated three times, and the third discharge capacity was determined as the initial discharge capacity.
2. Output measurement Discharge at 55 mA, 110 mA, and 550 mA was performed for 10 seconds at a discharge depth (DOD) of 50% with respect to the initial discharge capacity. From the relationship between the voltage and current at 10 seconds when discharging at each current value, the current value when the lower limit voltage was 2.5 V was extrapolated, and the output was calculated from the obtained current value and lower limit voltage.
3. Charge / Discharge Cycle Test The test battery was charged and discharged 500 times under the same conditions as the initial discharge capacity measurement, and the discharge capacity at the 500th cycle was determined. The ratio of the discharge capacity at the 500th cycle to the initial discharge capacity was defined as “capacity holding ratio (%)”.

  In the nonaqueous electrolyte secondary batteries A to H of Examples 1 to 4 and Comparative Examples 1 to 4, the ratio of Cs to HC and Cs (Cs / (HC + Cs), weight%) and characteristic measurement results of the negative electrode active materials are shown. The results are summarized in Table 1. Further, the relationship between the ratio of Cs to HC and Cs in the negative electrode and the output is shown in FIG.

  From Table 1, the capacity retention decreased as the ratio of Cs increased, and the capacity retention decreased significantly in the battery G of Comparative Example 3 and the battery H of Comparative Example 4 in which the Cs ratio was 60% or more. Further, it was found from the relationship between the Cs ratio and the output shown in FIG. 3 that the output decreases as the Cs ratio decreases.

  In addition, from FIG. 3, when content of graphitizable carbon is 4 to 40 weight%, it is more than the average value calculated from the mixing ratio of the output performance of non-graphitizable carbon and graphitizable carbon. It was found that good output performance can be obtained.

  For example, when the mixing ratio of the output performance of non-graphitizable carbon and graphitizable carbon is 40:60, the average value calculated from the outputs of Comparative Example 1 and Comparative Example 4 is 37.6 W. It was found that the output of Example 3 was almost equal to the average value calculated from the mixing ratio of the non-graphitizable carbon and graphitizable carbon output performance.

  On the other hand, when the mixing ratio of the non-graphitizable carbon and the easily graphitizable carbon is set to 80:20, the average value calculated from the outputs of Comparative Example 1 and Comparative Example 4 is 33.2 W. It was found that the output of Example 2 was better than the average value calculated from the mixing ratio of the non-graphitizable carbon and graphitizable carbon output performance.

  In addition, in the batteries A to D of Examples 1 to 4, it was found that the capacity retention rate was 80% or more, the output was 33 W or more, and good charge / discharge cycle performance and high output characteristics were exhibited.

[Examples 5 to 7 and Comparative Examples 5 and 6]
[Example 5]
The nonaqueous electrolyte secondary of Example 5 was used in the same manner as in Example 1 except that a mixture of HC and Cs in a weight ratio of 75:25 was used as the negative electrode active material, and Cs having an average particle diameter of 3 μm was used. Battery I was produced. In battery I, the average particle size of Cs is 0.3 times the average particle size of HC.

[Example 6]
A nonaqueous electrolyte secondary battery J of Example 6 was produced in the same manner as Example 5 except that Cs having an average particle size of 7.5 μm was used. In the battery J, the average particle size of Cs is 0.75 times the average particle size of HC.

[Example 7]
A nonaqueous electrolyte secondary battery K of Example 7 was produced in the same manner as Example 5 except that Cs having an average particle diameter of 10 μm was used. In the battery K, the average particle size of Cs is 1.0 times the average particle size of HC.

[Comparative Example 5]
A nonaqueous electrolyte secondary battery L of Comparative Example 5 was produced in the same manner as Example 5 except that Cs having an average particle diameter of 1 μm was used. In the battery L, the average particle size of Cs is 0.1 times the average particle size of HC.

[Comparative Example 6]
A nonaqueous electrolyte secondary battery M of Comparative Example 6 was produced in the same manner as in Example 5 except that Cs having an average particle diameter of 15 μm was used. In the battery M, the average particle size of Cs is 1.5 times the average particle size of HC.

  For the nonaqueous electrolyte secondary batteries I to M of Examples 5 to 7 and Comparative Examples 5 and 6, initial discharge capacity measurement, output measurement, and charge / discharge cycle test were performed under the same conditions as in Example 1. The measurement results are summarized in Table 2.

  As shown in Table 2, it was found that good charge / discharge cycle performance and output performance can be obtained by setting the ratio of the average particle size of Cs to the average particle size of HC in the range of 0.4 to 1.

[Examples 8 to 10]
[Example 8]
As the negative electrode active material, a mixture of HC and Cs in a weight ratio of 75:25 was used. As HC, the (002) plane spacing measured by X-ray wide angle diffraction method was 3.80 angstroms, and the crystallite size was large. As the graphitizable carbon, the distance between the (002) planes measured by the X-ray wide angle diffraction method is 3. The nonaqueous electrolyte secondary of Example 8 was the same as Example 1 except that Cs having a thickness of 48 Å, a crystallite size of 2.0 nm in the c-axis direction (Lc), and an average particle size of 15 μm was used. Battery N was produced. In the battery N, the ratio of Cs to HC and Cs in the negative electrode is 25% by weight, and the average particle size of Cs is 0.75 times the average particle size of HC.

[Example 9]
As HC, (002) plane spacing measured by X-ray wide angle diffraction method is 3.70 angstroms, crystallite size is 1.5 nm in c-axis direction (Lc), and average grain size is 10 μm As the graphitizable carbon, the (002) plane spacing measured by X-ray wide angle diffraction method is 3.46 angstroms, and the crystallite size is 1.7 nm in the c-axis direction (Lc). A nonaqueous electrolyte secondary battery O of Example 9 was produced in the same manner as in Example 8, except that Cs having an average particle diameter of 7.5 μm was used.

[Example 10]
As HC, (002) plane spacing measured by X-ray wide angle diffraction method is 3.77 angstrom, crystallite size is 1.3 nm in c-axis direction (Lc), and average grain size is 15 μm As the graphitizable carbon, the (002) plane spacing measured by X-ray wide angle diffraction method is 3.44 angstroms, and the crystallite size is 2.1 nm in the c-axis direction (Lc). A nonaqueous electrolyte secondary battery P of Example 10 was produced in the same manner as in Example 8, except that Cs having an average particle diameter of 11.25 μm was used.

  For the non-aqueous electrolyte secondary batteries N to P of Examples 8 to 10, initial discharge capacity measurement, output measurement, and charge / discharge cycle test were performed under the same conditions as in Example 1. The measurement results are summarized in Table 3.

  As shown in Table 3, it was found that good charge / discharge cycle performance and output performance can be obtained even when the types of HC and Cs are changed.

[Examples 11 and 12 and Comparative Examples 7 to 10]
[Example 11]
A nonaqueous electrolyte battery Q of Example 11 was produced in the same manner as Example 6 except that LiNiO ₂ was used as the positive electrode active material. In the battery Q, the ratio of Cs to HC and Cs in the negative electrode is 25% by weight, and the average particle size of Cs is 0.75 times the average particle size of HC.

[Example 12]
A nonaqueous electrolyte battery R of Example 12 was produced in the same manner as in Example 6 except that LiCoO ₂ was used as the positive electrode active material. In the battery R, the ratio of Cs to HC and Cs in the negative electrode is 25% by weight, and the average particle size of Cs is 0.75 times the average particle size of HC.

[Comparative Example 7]
A nonaqueous electrolyte battery S of Comparative Example 7 was produced in the same manner as Comparative Example 1 except that LiNiO ₂ was used as the positive electrode active material. In the battery S, the negative electrode active material is only HC.

[Comparative Example 8]
A nonaqueous electrolyte battery T of Comparative Example 8 was produced in the same manner as Comparative Example 4 except that LiNiO ₂ was used as the positive electrode active material. In the battery T, the negative electrode active material is only Cs.

[Comparative Example 9]
A nonaqueous electrolyte battery U of Comparative Example 9 was produced in the same manner as Comparative Example 1 except that LiCoO ₂ was used as the positive electrode active material. In the battery U, the negative electrode active material is only HC.

[Comparative Example 10]
A nonaqueous electrolyte battery V of Comparative Example 10 was produced in the same manner as Comparative Example 4 except that LiCoO ₂ was used as the positive electrode active material. In the battery V, the negative electrode active material is only Cs.

  The contents of the nonaqueous electrolyte secondary batteries Q to V of Examples 11 and 12 and Comparative Examples 7 to 10 are summarized in Table 4. Table 4 also shows the results of Example 6, Comparative Example 1, and Comparative Example 4 for comparison.

  For the nonaqueous electrolyte secondary batteries Q to V of Examples 11 and 12 and Comparative Examples 7 to 10, initial discharge capacity measurement, output measurement, and charge / discharge cycle test were performed under the same conditions as in Example 1. The measurement results are summarized in Table 5. Table 5 also shows the results of Example 6, Comparative Example 1, and Comparative Example 4 for comparison.

  From the results shown in Table 5, even in a non-aqueous electrolyte secondary battery using various lithium composite oxides for the positive electrode, by controlling the ratio of Cs in the negative electrode and the ratio of the average particle size of HC and Cs, It was found that an output performance better than the average value calculated from the mixing ratio of the output performance of Cs and Cs can be obtained, and a nonaqueous electrolyte secondary battery having good charge / discharge cycle performance can be provided.

The figure which shows the external appearance of the nonaqueous electrolyte secondary battery of this invention. The figure which shows the electrode group of a battery. The figure which shows the relationship between the ratio of Cs with respect to HC and Cs in a negative electrode, and an output.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Nonaqueous electrolyte secondary battery 2 Electrode group 2a Positive electrode 2b Negative electrode 2c Separator 3 Battery case

Claims (1)

In a non-aqueous electrolyte secondary battery comprising a positive electrode having a transition metal composite oxide containing lithium as a positive electrode active material, a negative electrode having a carbon material as a negative electrode active material, and a non-aqueous electrolyte, the carbon material is hardly graphitized. and a sexual carbon in the particles and graphitizable carbon particles, the proportion of the easily graphitizable carbon particles and the flame-graphitizable carbon particles occupied in the graphitizable carbon particles 4 to 40 weight % a and a non-aqueous electrolyte secondary battery wherein an average particle diameter of the easily graphitizable carbon particles is 0.3 to 1 times the average particle diameter of the flame-graphitizable carbon particles.

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