JP2012109280A - Negative electrode for lithium secondary battery and lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode desirable for a lithium secondary battery in which decrease in a rapid charge-discharge behavior and a cycle characteristic is reduced when the negative electrode density is increased, and provide a high capacity lithium secondary battery in which the energy density per the volume of a secondary battery is improved.SOLUTION: A negative electrode for a lithium secondary battery is formed by pressurizing and integrating the mixture of a graphite particle and an organic binder agent and a collector. In the negative electrode for a lithium secondary battery, a diffraction intensity ratio (002)/(110) measured by x-ray diffraction of the negative electrode is 500 or less. A lithium secondary battery includes the negative electrode for a lithium secondary battery, and a positive electrode including a lithium compound.

Description

  The present invention relates to a negative electrode for a lithium secondary battery and a lithium secondary battery. More specifically, the present invention relates to a lithium secondary battery having a high capacity and excellent in rapid charge / discharge characteristics and cycle characteristics suitable for use in portable equipment, electric vehicles, power storage, and the like, a negative electrode for obtaining the same, and a manufacturing method thereof. .

  The negative electrode of a conventional lithium secondary battery includes, for example, natural graphite particles, artificial graphite particles graphitized with coke, organic polymer materials, artificial graphite particles graphitized with pitch, graphite particles obtained by pulverizing these, and mesophase carbon. Examples include graphitized spheroidal graphite. These graphite particles are mixed with an organic binder and an organic solvent to form a graphite paste. This graphite paste is applied to the surface of a copper foil, and the solvent is dried to be used as a negative electrode for a lithium secondary battery. .

  For example, as disclosed in Patent Document 1, the use of graphite for the negative electrode eliminates the problem of content short circuit due to lithium dendrite and improves cycle characteristics.

Japanese Examined Patent Publication No. 62-23433

However, natural graphite, which has developed graphite crystals, has weaker bond strength between crystal layers in the C-axis direction than the bond in the crystal plane direction. It becomes what is called scale-like graphite particles. Since scaly graphite has a large aspect ratio, when graphite is kneaded with a binder and applied to a current collector to produce an electrode, the scaly graphite particles are oriented in the surface direction of the current collector, resulting in a charge / discharge capacity. In addition to the rapid deterioration of the rapid charge / discharge characteristics, there is a problem in that the internal characteristics of the electrode are broken due to expansion and contraction in the C-axis direction caused by repeated insertion and extraction of lithium into and from the graphite crystal, resulting in deterioration of cycle characteristics. In addition, when the negative electrode density is 1.45 g / cm ³ or more, lithium is difficult to be occluded / released in the negative electrode graphite, and there is a problem that rapid charge / discharge characteristics, discharge capacity per weight of the negative electrode, and cycle characteristics are deteriorated. .

  On the other hand, the lithium secondary battery can be expected to increase the energy density per volume by increasing the negative electrode density. Therefore, in order to improve the energy density per volume of the lithium secondary battery, there is a demand for a negative electrode in which rapid charge / discharge characteristics and cycle characteristics are less deteriorated when the negative electrode density is increased.

  In view of the above problems, the present invention provides a negative electrode suitable for a lithium secondary battery excellent in rapid charge / discharge characteristics and cycle characteristics, and further provides a negative electrode suitable for a high capacity lithium secondary battery.

  (1) The present invention relates to a diffraction intensity measured by X-ray diffraction of a negative electrode in a negative electrode for a lithium secondary battery in which a mixture of graphite particles and an organic binder and a current collector are pressed and integrated. The present invention relates to a negative electrode for a lithium secondary battery having a ratio (002) / (110) of 500 or less.

(2) Moreover, this invention relates to the negative electrode for lithium secondary batteries as described in said (1) whose density of the mixture of a graphite particle and an organic type binder is 1.45-1.95g / cm < ³ >.

  (3) Further, the present invention provides the lithium according to the above (1) or (2), wherein the graphite particles have an average particle size of 1 to 100 μm and the crystallite size Lc (002) in the C-axis direction of the crystal is 500 angstroms or more. The present invention relates to a negative electrode for a secondary battery.

  (4) Furthermore, this invention relates to the lithium secondary battery which has a positive electrode containing the negative electrode for lithium secondary batteries of this invention in any one of said (1)-(3), and a lithium compound.

  According to the present invention, a negative electrode for a lithium secondary battery excellent in cycle characteristics and rapid discharge characteristics can be obtained, which is suitable for use in a high capacity lithium secondary battery.

It is a partial cross section front schematic diagram which shows an example of the lithium secondary battery of this invention. In the Example of this invention, it is the schematic of the lithium secondary battery used for the measurement of charging / discharging capacity | capacitance and a discharge capacity maintenance factor.

  The negative electrode for a lithium secondary battery of the present invention is a negative electrode for a lithium secondary battery in which a mixture of graphite particles and an organic binder and a current collector are pressurized and integrated. The diffraction intensity ratio (002) / (110) measured by X-ray diffraction of the negative electrode is 500 or less. The diffraction intensity ratio (002) / (110) is preferably in the range of 10 to 500, more preferably 10 to 400, still more preferably 10 to 300, and particularly preferably 50 to 200. When the diffraction intensity ratio (002) / (110) exceeds 500, the rapid charge / discharge characteristics and cycle characteristics of the lithium secondary battery to be manufactured are deteriorated.

Here, the diffraction intensity ratio (002) / (110) of the negative electrode for a lithium secondary battery is detected in the vicinity of a diffraction angle 2θ = 26 to 27 degrees by X-ray diffraction using CuKα rays as an X-ray source (002). ) The surface diffraction peak and the intensity of the (110) plane diffraction peak detected near the diffraction angle 2θ = 70 to 80 degrees can be obtained by the following equation (1).
(002) plane diffraction peak intensity / (110) plane diffraction peak intensity (1) Formula

In the negative electrode for a lithium secondary battery of the present invention, it is preferable that the density of the mixture of the current collector, the pressurized, integrated graphite particles and the organic binder is 1.45 to 1.95 g / cm ^3. . The density is more preferably 1.5~1.9g / cm ^3, more preferably ^{1.6~1.85g / cm 3, 1.65~1.8g / cm} 3 is particularly preferred. By increasing the density of the mixture of the graphite particles and the binder in the negative electrode of the present invention, the energy density per volume of the lithium secondary battery obtained using this negative electrode can be increased. When the density of the mixture of the graphite particles and the organic binder is less than 1.45 g / cm ³ , the energy density per volume of the obtained lithium secondary battery becomes small. On the other hand, when the density of the mixture of the graphite particles and the organic binder exceeds 1.95 g / cm ³ , not only does the liquid injection property of the lithium secondary battery deteriorate, but it is also produced. The rapid charge / discharge characteristics and cycle characteristics of the lithium secondary battery are likely to deteriorate.

  The density of the mixture of the graphite particles and the binder after the integration can be appropriately adjusted depending on, for example, the pressure at the time of integral molding, the clearance of an apparatus such as a roll press, and the like.

  The crystallite size Lc (002) in the C-axis direction of the graphite particles used in the present invention is preferably 500 angstroms or more, more preferably 800 angstroms or more, and particularly preferably 1000 to 10,000 angstroms. When the crystallite size Lc (002) in the C-axis direction is less than 500 angstroms, the discharge capacity tends to be small.

  Further, the interlayer distance d (002) of the graphite particle crystals is preferably 3.38 angstroms or less, more preferably 3.37 angstroms or less, and even more preferably 3.36 angstroms or less. When the interlayer distance d (002) between crystals exceeds 3.38 angstroms, the discharge capacity tends to decrease. The Lc (002) and d (002) can be measured by X-ray wide angle diffraction.

  In addition, the graphite particles used in the negative electrode for a lithium secondary battery according to the present invention can set the diffraction intensity ratio (002) / (110) measured by X-ray diffraction of the negative electrode after pressing and integration to 500 or less. For example, scaly graphite, spheroidal graphite, graphite whose particle shape has been modified by mechanical treatment, or a mixture of a plurality of materials can be used, but a plurality of flat primary particles are oriented. It is preferable to use secondary graphite particles that are aggregated or bonded so that the surfaces are non-parallel. In the present invention, the flat particle means a shape having a major axis and a minor axis and is not completely spherical. For example, those having a shape such as a scale shape, a scale shape, or a part of a lump shape are included. In graphite particles, the orientation planes of a plurality of flat particles are non-parallel. The flat surfaces in the shape of each particle, in other words, the plane that is closest to the plane is the orientation plane, and the plurality of flat particles are A state in which the respective orientation surfaces are gathered without being aligned in a certain direction to form graphite particles.

  In this aggregated or bound flat particle, the term “bond” refers to a state in which the particles are chemically bound, for example, via carbonaceous carbonized binder such as pitch and tar. Means that the particles are not chemically bonded to each other, but are maintained in the shape of the negative electrode as well as the aggregate due to its shape and the like. From the viewpoint of mechanical strength, those bonded are preferable.

  The graphite particles used in the present invention preferably have an aspect ratio of 5 or less, more preferably 1.2 to 5, more preferably 1.2 to 3, and more preferably 1.3 to 2. 5 is particularly preferable. The graphite particles having an aspect ratio of 5 or less may be secondary particles in which a plurality of primary particles are aggregated or combined, and one particle is mechanically applied so that the aspect ratio is 5 or less. The shape may be changed, and further, a combination of these may be used.

  When this aspect ratio exceeds 5, the diffraction intensity ratio (002) / (110) measured by X-ray diffraction of the negative electrode after pressurization and integration tends to increase, and as a result, the obtained lithium secondary battery The rapid charge / discharge characteristics and cycle characteristics tend to deteriorate. When the aspect ratio is less than 1.2, the contact area between the particles decreases, and the conductivity of the negative electrode to be produced tends to decrease.

  In the present invention, when the graphite particles to be used are present as an aggregate or a combination of a plurality of particles, the primary particles of the graphite particles are recognized when observed with, for example, a scanning electron microscope (SEM). A particle unit. Further, the secondary particle refers to a mass in which the primary particles are aggregated or bonded.

  The aspect ratio is represented by A / B, where A is the length in the major axis direction of the particle and B is the length in the minor axis direction. The aspect ratio of the graphite particles in the present invention is such that the primary or secondary graphite particles are magnified with a microscope, and 10 particles having a major axis length of 10 to 50 μm are arbitrarily selected. Is measured and the arithmetic average value is taken.

  In one secondary graphite particle, the number of flat primary particles aggregated or bonded is preferably 3 or more, more preferably 5 or more. The size of each flat primary particle is preferably 1 to 100 μm, more preferably 5 to 80 μm, and even more preferably 5 to 50 μm, and these are aggregates or bonds. It is preferable that it is 2/3 or less of the average particle diameter of the obtained secondary graphite particles. Further, the aspect ratio of each flat primary particle is preferably 100 or less, more preferably 50 or less, and further preferably 20 or less. A preferable lower limit of the aspect ratio of the primary particles is 1.2, and it is preferably not spherical.

Furthermore, the graphite particles in the present invention preferably have a specific surface area of secondary particles of 8 m ² / g or less, more preferably 5 m ² / g or less. When the graphite particles are used for the negative electrode, the rapid charge / discharge characteristics and cycle characteristics of the obtained lithium secondary battery can be improved, and the irreversible capacity in the first cycle can be reduced. If the specific surface area exceeds 8 m ² / g, the irreversible capacity of the first cycle of the obtained lithium secondary battery tends to increase, the energy density is small, and a large number of binders are used when producing a negative electrode. It tends to be necessary. The specific surface area is more preferably 1.5 to ⁵ m ² / g, more preferably ^{2 to 5} m ² / g, from the viewpoint that the rapid charge / discharge characteristics, cycle characteristics, and the like of the obtained lithium secondary battery are further improved. Is particularly preferred. The specific surface area can be measured by a known method such as a BET method using nitrogen gas adsorption.

  The method for producing the negative electrode for a lithium secondary battery of the present invention is not particularly limited. For example, at least a graphitizable aggregate or graphite and a graphitizable binder are mixed and pulverized, and then the pulverized product and graphitized are mixed. 1 to 50% by weight of catalyst is mixed and calcined to obtain graphite particles, and then the organic particles and a solvent are added to and mixed with the graphite particles, and the mixture is applied to a current collector and dried. Then, after removing the solvent, it can be manufactured by pressurizing and integrating.

  Examples of the aggregate that can be graphitized include coke powder and resin carbide, but there is no particular limitation as long as it is a powder material that can be graphitized. Among these, coke powder that is easily graphitized such as needle coke is preferable. Moreover, as graphite, natural graphite powder, artificial graphite powder, etc. can be used, for example, but there is no restriction | limiting in particular if it is a powder form. The particle size of the graphitizable aggregate or graphite is preferably smaller than the particle size of the graphite particles to be produced, the average particle size is more preferably 1 to 80 μm, more preferably 1 to 50 μm, and more preferably 5 to 50 μm. It is particularly preferable if it is present. The aspect ratio of the graphitizable aggregate or graphite is preferably from 1.2 to 500, more preferably from 1.5 to 300, and even more preferably from 1.5 to 100. A range of ˜50 is particularly preferable. Here, the aspect ratio measurement is performed by the same method as described above. When the aspect ratio of graphitizable aggregate or graphite increases, the diffraction intensity ratio (002) / (110) measured by X-ray diffraction of the negative electrode after pressurization and integration tends to increase. If it is less than 2, the discharge capacity per graphite particle weight tends to be small.

  As the binder, for example, an organic material such as a thermosetting resin and a thermoplastic resin is preferable in addition to tar and pitch. The blending amount of the binder is preferably 5 to 80% by weight, more preferably 10 to 80% by weight, and further preferably 20 to 80% by weight based on the graphitizable aggregate or graphite. It is preferable to add 30 to 80% by weight. If the amount of the binder is too large or too small, the aspect ratio and specific surface area of the graphite particles to be produced tend to increase. The method of mixing the graphitizable aggregate or graphite and the binder is not particularly limited and can be performed using, for example, a kneader, but is preferably mixed at a temperature equal to or higher than the softening point of the binder. Specifically, when the binder is pitch, tar or the like, 50 to 300 ° C is preferable, and when the binder is a thermosetting resin, 20 to 180 ° C is preferable.

  Next, the mixture is pulverized, and the pulverized product and the graphitization catalyst are mixed. The particle size of the pulverized product is preferably 1 to 100 μm, more preferably 5 to 80 μm, further preferably 5 to 50 μm, and particularly preferably 10 to 30 μm.

  When the particle size of the pulverized product exceeds 100 μm, the specific surface area of the obtained graphite particles tends to increase, and when it is less than 1 μm, the (002) / (110) ratio of the obtained negative electrode tends to increase. The volatile matter of the pulverized product is preferably 0.5 to 50% by weight, more preferably 1 to 30% by weight, and even more preferably 5 to 20% by weight. The volatile matter is measured by weight reduction when the pulverized product is heated at 800 ° C. for 10 minutes. The graphitization catalyst to be mixed with the pulverized product is not particularly limited as long as it has a function as a graphitization catalyst. For example, metals such as iron, nickel, titanium, silicon and boron, carbides and oxides thereof Graphitization catalysts such as can be used. Of these, iron or silicon compounds are preferred. The chemical structure of the compound is preferably a carbide. The addition amount of these graphitization catalysts is preferably 1 to 50% by weight, more preferably 5 to 30% by weight, when the total amount of the pulverized product mixed with the graphitization catalyst and the graphitization catalyst is 100% by weight. 7 to 20% by weight is more preferable. When the amount of the graphitization catalyst is less than 1% by weight, not only the crystal development of the graphite particles to be produced deteriorates but also the specific surface area tends to increase. The catalyst becomes easier to remain. The graphitization catalyst used is preferably in the form of a powder, preferably in the form of a powder having an average particle size of 0.1 to 200 μm, more preferably 1 to 100 μm, and even more preferably 1 to 50 μm.

Next, the mixture is fired and graphitized, and before firing, the mixture of the pulverized product and the graphitized catalyst may be formed into a predetermined shape by a press or the like and then fired. The molding pressure in this case is preferably about 1 to 300 MPa. Firing is preferably performed under conditions where the mixture is not easily oxidized, and examples thereof include a method of firing in a nitrogen atmosphere, an argon atmosphere, a vacuum, and a self-volatile atmosphere. The graphitization temperature is preferably 2000 ° C or higher, more preferably 2500 ° C or higher, further preferably 2700 ° C or higher, and particularly preferably 2800 to 3200 ° C. When the graphitization temperature is low, the development of graphite crystals tends to be poor, the discharge capacity tends to be low, and the added graphitization catalyst tends to remain in the graphite particles produced. When a large amount of the graphitization catalyst remains in the graphite particles produced, the discharge capacity per graphite particle weight decreases. If the graphitization temperature is too high, the graphite may sublime. Firing, if performed in the molding prepared by molding into a predetermined shape by pressing or the like, the apparent density is preferably 1.65 g / cm ³ or less of the molded product after graphitization, more preferably if 1.55 g / cm ³ or less , more preferably if 1.50 g / cm ³ or less, particularly preferred if the 1.45 g / cm ³ or less. When the density of the molded product after graphitization is 1.65 g / cm ³ or more, the specific surface area of the produced graphite particles tends to increase. The apparent density of the molded product after graphitization can be appropriately adjusted by, for example, the particle size of the pulverized product mixed with the graphitization catalyst and the pressure when forming into a predetermined shape by a press or the like.

  Next, the powder is pulverized and the particle size is adjusted to obtain graphite particles that are the negative electrode carbon material. . The average particle diameter of the negative electrode carbon material after pulverization is preferably 1 to 100 μm, more preferably 5 to 50 μm, and particularly preferably 10 to 30 μm. If the average particle size becomes too large, the surface of the negative electrode to be produced is likely to be uneven, and as a result, the lithium secondary battery to be produced tends to be short-circuited and the cycle characteristics tend to deteriorate.

  In the present invention, the average particle diameter can be measured by a laser diffraction particle size distribution meter.

  The obtained graphite particles are kneaded with an organic binder and a solvent to form a paste, and are formed into a sheet shape, a pellet shape, or the like.

  As the organic binder, for example, polyethylene, polypropylene, ethylene propylene terpolymer, butadiene rubber, styrene butadiene rubber, butyl rubber, a high molecular compound having high ionic conductivity, and the like can be used.

  As the polymer compound having a high ion conductivity, polyvinylidene fluoride, polyethylene oxide, polyepichlorohydrin, polyphasphazene, polyacrylonitrile and the like can be used.

  The mixing ratio of the carbon material and the organic binder is preferably 0.5 to 20 parts by weight of the organic binder with respect to 100 parts by weight of the carbon material.

  There is no restriction | limiting in particular as a solvent, N-methyl- 2-pyrrolidone, a dimethylformamide, isopropanol, water etc. are mentioned. In the case of a binder using water as a solvent, it is preferable to use a thickener together.

  The amount of the solvent is not particularly limited, and the carbon material is kneaded with an organic binder and a solvent to prepare a mixture, the viscosity is appropriately adjusted, and then applied to the current collector. , Integrated into a negative electrode. As the current collector, for example, a metal current collector such as a foil or mesh of nickel, copper or the like can be used. The integration can be performed by a molding method such as a roll or a press, or a combination of them may be integrated. The pressure during the integration is preferably about 1 to 200 MPa.

  The negative electrode thus obtained is used for a lithium secondary battery. The lithium secondary battery of the present invention comprises a positive electrode containing a lithium compound and the negative electrode of the present invention. For example, the positive electrode and the negative electrode are arranged to face each other with a separator interposed therebetween and an electrolyte is injected. Compared to a lithium secondary battery using a conventional negative electrode, it has a high capacity and excellent cycle characteristics and rapid charge / discharge characteristics.

The positive electrode of the lithium secondary battery in the present invention contains a lithium compound, but the material thereof is not particularly limited. For example, LiNiO ₂ , LiCoO ₂ , LiMn ₂ O _{4 and the} like can be used alone or in combination.

  Lithium secondary batteries usually contain an electrolyte containing a lithium compound together with a positive electrode and a negative electrode.

As the electrolytic solution, lithium salts such as LiClO ₄ , LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSO ₃ CF ₃ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, for example, ethylene carbonate, diethyl carbonate, dimethyl carbonate, methyl A so-called organic electrolytic solution dissolved in a non-aqueous solvent such as ethyl carbonate, propylene carbonate, acetonitrile, propironitrile, dimethoxyethane, tetrahydrofuran, or γ-butyrolactone, or a so-called polymer electrolyte in a solid or gel form can be used.

  Moreover, it is preferable to add a small amount of an additive that exhibits a decomposition reaction when the lithium secondary battery is initially charged to the electrolytic solution. Examples of the additive include vinylene carbonate, biphenyl, propane sultone, and the addition amount is preferably 0.01 to 5% by weight.

  As the separator, for example, a nonwoven fabric mainly composed of polyolefin such as polyethylene or polypropylene, cloth, microporous film, or a combination thereof can be used. In addition, when it is set as the structure where the positive electrode and negative electrode of a lithium secondary battery to produce are not in direct contact, it is not necessary to use a separator.

  FIG. 1 shows a schematic diagram of a partial cross-sectional front view of an example of a cylindrical lithium secondary battery. The cylindrical lithium secondary battery shown in FIG. 1 is obtained by winding a positive electrode 1 processed into a thin plate shape and a negative electrode 2 processed in the same manner through a separator 3 such as a polyethylene microporous membrane, This is inserted into a battery can 7 made of metal or the like and sealed. The positive electrode 1 is bonded to the positive electrode lid 6 via the positive electrode tab 4, and the negative electrode 2 is bonded to the battery bottom via the negative electrode tab 5. The positive electrode lid 6 is fixed to a battery can (positive electrode can) 7 with a gasket 8.

  Examples of the present invention will be described below.

Example 1
50 parts by weight of coke powder having an average particle size of 10 μm and 30 parts by weight of coal tar pitch were mixed at 230 ° C. for 2 hours. Next, after pulverizing this mixture to an average particle size of 25 μm, 80 parts by weight of the pulverized product and 20 parts by weight of silicon carbide having an average particle size of 25 μm were mixed with a blender, and the mixture was put into a mold and press-molded at 100 MPa. And formed into a rectangular parallelepiped. This molded body was heat-treated at 1000 ° C. in a nitrogen atmosphere, and further heat-treated at 3000 ° C. in a nitrogen atmosphere to obtain a graphite molded body. Furthermore, this graphite molded body was pulverized to obtain graphite particles as a negative electrode carbon material. The following measurements were performed from the obtained negative electrode carbon material. (1) Average particle diameter by laser diffraction particle size distribution meter, (2) Specific surface area by BET method, (3) Aspect ratio (average value for 10 pieces), (4) Interlayer distance d of crystals by X-ray wide angle diffraction (002) and (5) Crystallite size Lc (002) in the C-axis direction of the crystal. These measured values are shown in Table 1.

  The average particle size was determined by using a laser diffraction particle size distribution analyzer (product name: SALD-3000, Shimadzu Corporation), and the particle size at 50% D was defined as the average particle size. The interlayer distance d (002) was measured using an X-ray diffractometer, using Cu-Kα rays as a single color with a Ni filter, and using high-purity silicon as a standard substance. The specific surface area was calculated according to the BET method by measuring the nitrogen adsorption at the liquid nitrogen temperature by a multipoint method using the product name ASAP 2010 of micromeritics.

Subsequently, 10% by weight of organic binder polyvinylidene fluoride (PVDF) dissolved in N-methyl-2-pyrrolidone was added to 90% by weight of the obtained negative electrode carbon material and kneaded to prepare a graphite paste. . This graphite paste was applied to a rolled copper foil having a thickness of 10 μm, further dried at 120 ° C. to remove N-methyl-2pyrrolidone, and compressed at 10 MPa with a vertical press to obtain a sample electrode. When the density of the mixed layer of (6) graphite particles and PVDF of this sample electrode was measured, it was 1.20 g / cm ³ and the thickness was 96 μm. The (002) and (110) diffraction peaks of the obtained test electrode were measured with an X-ray diffractometer, and the (7) (002) / (110) intensity ratio was measured from each peak top intensity. The results are also shown in Table 1. In the X-ray diffraction of (4), (5), and (6), the X-ray source was CuKα ray / 40 KV / 20 mA, and the step width was 0.02 °.

The produced sample electrode was punched out to a size of 2 cm ² and subjected to constant current charge / discharge by the three-terminal method, and the charge / discharge capacity and discharge capacity retention rate were measured as follows. FIG. 2 shows a schematic diagram of the lithium secondary battery used in this measurement. As shown in FIG. 2, the sample electrode was evaluated as follows: LiPF ₆ as an electrolytic solution 10 in a beaker type glass cell 9 with ethylene carbonate (EC) and methyl ethyl carbonate (MEC) (EC and MEC are in a volume ratio of 1: 2). A solution dissolved to a concentration of 1 mol / liter was added to the mixed solvent, the sample electrode 11, the separator 12 and the counter electrode 13 were stacked and arranged, and the reference electrode 14 was suspended from the top to prepare a model battery. The counter electrode 13 and the reference electrode 14 were made of metallic lithium, and the separator 4 was made of a polyethylene microporous film. Using the obtained model battery, the sample electrode 11 and the counter electrode 13 were charged to 0 V (V vs. Li / Li +) with a constant current of 0.2 mA / cm ^{2 with} respect to the area of the sample electrode. A test was conducted to discharge to 1 V (V vs. Li / Li +) at a constant current of ² mA / cm ² , and (8) discharge capacity per unit volume was measured.

  Further, 100 cycles of charge and discharge were repeated in the same manner, and (9) the discharge capacity retention rate when the discharge capacity in the first cycle was set to 100 was measured.

In addition, the battery was charged to 0 V (V vs. Li / Li +) at a constant current of 0.2 mA / cm ² and discharged to 1 V (V vs. Li / Li +) at a constant current of 6.0 mA / cm ^2. (10) The discharge capacity retention rate was measured when the discharge capacity when discharged at a constant current of 0.2 mA / cm ² was taken as 100.

  The measurement results are also shown in Table 1.

Example 2
A test electrode was prepared in the same manner as in Example 1 except that the density of the mixture layer of graphite particles and PVDF was changed to 1.45 g / cm ³ by changing the pressure of the vertical press to 23 MPa instead of 10 MPa. In the same manner as in Example 1, the (002) / (110) intensity ratio, discharge capacity per unit volume, discharge capacity maintenance rate after 100 cycles, and discharge capacity maintenance rate at a discharge current of 6.0 mA / cm ² were measured. did. The measurement results are also shown in Table 1.

Example 3
A test electrode was prepared in the same manner as in Example 1 except that the density of the mixture layer of graphite particles and PVDF was changed to 1.55 g / cm ³ by setting the pressure of the vertical press to 31 MPa. (002) / (110) intensity ratio, discharge capacity per unit volume, discharge capacity maintenance rate after 100 cycles, and discharge capacity maintenance rate at a discharge current of 6.0 mA / cm ² were measured. The measurement results are also shown in Table 1.

Example 4
A test electrode was prepared in the same manner as in Example 1 except that the density of the mixture layer of graphite particles and PVDF was changed to 1.65 g / cm ³ by setting the pressure of the vertical press to 50 MPa. (002) / (110) intensity ratio, discharge capacity per unit volume, discharge capacity maintenance rate after 100 cycles, and discharge capacity maintenance rate at a discharge current of 6.0 mA / cm ² were measured. The measurement results are also shown in Table 1.

Example 5
A test electrode was prepared in the same manner as in Example 1 except that the density of the mixture layer of graphite particles and PVDF was changed to 1.75 g / cm ³ by setting the pressure of the vertical press to 85 MPa. (002) / (110) intensity ratio, discharge capacity per unit volume, discharge capacity maintenance rate after 100 cycles, and discharge capacity maintenance rate at a discharge current of 6.0 mA / cm ² were measured. The measurement results are also shown in Table 1.

Example 6
A test electrode was prepared in the same manner as in Example 1 except that the density of the mixture layer of graphite particles and PVDF was changed to 1.85 g / cm ³ by setting the pressure of the vertical press to 143 MPa. (002) / (110) intensity ratio, discharge capacity per unit volume, discharge capacity maintenance rate after 100 cycles, and discharge capacity maintenance rate at a discharge current of 6.0 mA / cm ² were measured. The measurement results are also shown in Table 1.

Example 7
Chinese natural graphite was pulverized with a jet mill to produce scaly natural graphite particles. The average particle diameter, specific surface area, aspect ratio, d (002), and Lc (002) measurement results of the graphite particles are also shown in Table 1. A test electrode was prepared in the same manner as in Example 1 except that the density of the mixture layer of graphite particles and PVDF was changed to 1.00 g / cm ³ by using the graphite particles at a vertical press pressure of 2 MPa. . In the same manner as in Example 1, the (002) / (110) intensity ratio, the discharge capacity per unit volume, the discharge capacity maintenance rate after 100 cycles, and the discharge capacity maintenance rate at a discharge current of 6.0 mA / cm ² were obtained. It was measured. The measurement results are also shown in Table 1.

Comparative Example 1
A test electrode was prepared in the same manner as in Example 7 except that the density of the mixture layer of graphite particles and PVDF was changed to 1.50 g / cm ³ by setting the pressure of the vertical press to 27 MPa. (002) / (110) intensity ratio, discharge capacity per unit volume, discharge capacity maintenance rate after 100 cycles, and discharge capacity maintenance rate at a discharge current of 6.0 mA / cm ² were measured. The measurement results are also shown in Table 1.

Comparative Example 2
A test electrode was prepared in the same manner as in Example 7 except that the density of the mixture layer of graphite particles and PVDF was changed to 1.65 g / cm ³ by setting the pressure of the vertical press to 42 MPa. (002) / (110) intensity ratio, discharge capacity per unit volume, discharge capacity maintenance rate after 100 cycles, and discharge capacity maintenance rate at a discharge current of 6.0 mA / cm ² were measured. The measurement results are also shown in Table 1.

  As shown in Table 1, it was shown that the negative electrode for a lithium secondary battery of the present invention has a high capacity, excellent cycle characteristics and rapid discharge characteristics, and is suitable for use in a lithium secondary battery.

DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Positive electrode tab 5 Negative electrode tab 6 Positive electrode lid 7 Battery can 8 Gasket 9 Glass cell 10 Electrolytic solution 11 Sample electrode (negative electrode) 12 Separator 13 Counter electrode (positive electrode) 14 Reference electrode

Claims (4)

  In a negative electrode for a lithium secondary battery in which a mixture of graphite particles and an organic binder and a current collector are pressurized and integrated, a diffraction intensity ratio (002) / (measured by X-ray diffraction of the negative electrode) 110) The negative electrode for lithium secondary batteries whose 500 or less. 2. The negative electrode for a lithium secondary battery according to claim 1, wherein the density of the mixture of the graphite particles and the organic binder is 1.45 to 1.95 g / cm ³ .   3. The negative electrode for a lithium secondary battery according to claim 1, wherein the average particle diameter of the graphite particles is 1 to 100 μm and the crystallite size Lc (002) in the C-axis direction of the crystal is 500 angstroms or more.   The lithium secondary battery which has a positive electrode containing the negative electrode for lithium secondary batteries in any one of Claims 1-3, and a lithium compound.

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