JP2009164013A - Negative electrode, and battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery capable of improving capacity and charge and discharge characteristics. <P>SOLUTION: A wound electrode body 20 in which a positive electrode 21 and a negative electrode 22 are laminated and wound round via a separator 23 is equipped inside a battery can 11. A negative electrode active material layer is formed at the negative electrode 22, and this negative electrode active material layer contains first graphite particles and second graphite particles. As for the first graphite particles, the median diameter D<SB>50</SB>is 13 μm or more and 15 μm or less, the specific surface area by a BET mothod is 2 m<SP>2</SP>/g or more and 7 m<SP>2</SP>/g or less, and a breaking strength is 20 MPa or more and 40 MPa or less. As for the second graphite particles, the median diameter D<SB>50</SB>is 12 μm or more and 19 μm or less, the specific surface area by the BET method is 0.5 m<SP>2</SP>/g or more and 1.0 m<SP>2</SP>/g or less, and the breaking strength is 80 MPa or more and 100 MPa or less. Furthermore, a mass ratio of the first graphite particles against the mass of the second graphite particles is 1/9 or more and 3/7 or less. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a negative electrode including graphite particles and a battery including the same.

  In recent years, with the widespread use of portable devices such as video cameras, mobile phones, and notebook computers, there is an increasing demand for secondary batteries that are small, lightweight, and high capacity as power sources. As a response to such demand, there is a lithium ion secondary battery using a carbon material as a negative electrode active material and utilizing a lithium occlusion and release reaction.

  As the carbon material used as the negative electrode active material, graphite particles having high crystallinity are the mainstream. The reason for this is that graphite particles have high electron conductivity and excellent discharge performance at a large current, and are suitable for applications such as constant power discharge with little potential change due to discharge, and have a high true density (thus high bulk). (It is easy to obtain density) and is advantageous for high capacity. Furthermore, a material containing silicon, tin or the like having a higher capacity develops severe expansion and contraction with charge / discharge, but a carbon material has an advantage that such a volume change is extremely small.

  In order to cope with the recent increase in energy density of lithium secondary batteries, attempts have been made to improve the performance of graphite. However, the natural graphite particles have a reversible capacity very close to the theoretical capacity of graphite (372 mAh / g). For this reason, it has been studied to improve the capacity of the battery by filling the limited volume inside the battery with high density by adjusting the particle shape. In general, artificial graphite particles are inferior in reversible capacity to natural graphite particles because of their insufficient graphitization degree. Therefore, various studies have been made on artificial graphite particles, such as improving the purity of raw materials, optimizing graphitization conditions, and adding catalyst species that promote graphitization, in order to improve the reversible capacity.

Under such circumstances, attempts have been made to use a mixture of artificial graphite particles and spherical graphite particles as a negative electrode active material. (For example, refer to Patent Document 1).
JP 2004-127913 A

  In general, however, flaky artificial graphite particles have a higher discharge capacity than spherical graphite particles. However, when high volume density is applied to a negative electrode active material layer composed of a plurality of flaky artificial graphite particles, The acceptability deteriorates, and the battery characteristics such as charge / discharge efficiency tend to be lowered. The cause of the lithium ion acceptability deterioration is that when the negative electrode active material layer is formed by press treatment, the 002 plane orientation of the scaly artificial graphite particles becomes too strong by applying a large press pressure, and the lithium ion This is probably because the 002 plane approaches perpendicular to the insertion direction. On the other hand, spheroidal graphite particles are relatively excellent in charge / discharge efficiency (especially charge / discharge characteristics at high load), but the theoretical capacity per weight is small, the slipperiness is very poor, and the density cannot be increased. There is a problem. In addition, the spherical graphite particles themselves may collapse when pressed to increase the density. In the above-mentioned Patent Document 1, the physical properties of the artificial graphite particles and the spherical graphite particles to be mixed are controlled. However, the present applicant has verified that sufficient charge / discharge characteristics and discharge capacity are necessarily obtained. It's hard to say.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a negative electrode and a battery having higher capacity and excellent charge / discharge characteristics.

The negative electrode of the present invention has a negative electrode active material layer provided on a negative electrode current collector, and the negative electrode active material layer includes first graphite particles and second graphite particles as a negative electrode active material. The ratio of the mass of the first graphite particles to the mass of the second graphite particles is from 1/9 to 3/7. Here, the first graphite particles have a median diameter (D ₅₀ ) of 13 μm or more and 15 μm or less by a laser diffraction particle size distribution meter, a specific surface area of 2 m ² / g or more and 7 m ² / g or less by a BET method, and a fracture strength. 20 MPa or more and 40 MPa or less. On the other hand, the second graphite particles have a median diameter (D ₅₀ ) of 12 μm or more and 19 μm or less by a laser diffraction particle size distribution meter, a specific surface area of 0.5 m ² / g or more and 1.0 m ² / g or less by a BET method, The fracture strength is 80 MPa or more and 100 MPa or less.

  The battery of the present invention comprises an electrolyte together with the positive electrode and the negative electrode of the present invention described above.

  In the negative electrode and battery of the present invention, the negative electrode active material in the negative electrode active material layer includes the first graphite particles having a relatively small breaking strength and a relatively large specific surface area, a relatively large breaking strength, and a relatively high Since it is a mixture in which the second graphite particles having a small specific surface area are mixed at a predetermined mass ratio, the negative electrode active material layer is filled with a high density even with a smaller press pressure, and appropriate voids are present. Secured and excellent in acceptability of lithium ions.

According to the anode of the present invention, as the negative electrode active material, the first graphite particles having 15μm or less in median diameter above 13 .mu.m, 2m ² / g or more 7m ² / g or less in specific surface area, the 40MPa following breaking strength than 20MPa And a second graphite particle having a median diameter of 12 μm or more and 19 μm or less, a specific surface area of 0.5 m ² / g or more and 1.0 m ² / g or less, and a breaking strength of 80 MPa or more and 100 MPa or less at a predetermined mass ratio. Since it is made to contain, the volume density of a negative electrode active material layer can be improved comparatively easily, and discharge capacity can be improved. In addition, since the negative electrode active material layer can secure an appropriate gap, when this negative electrode is used together with an electrolyte in an electrochemical device such as a battery of the present invention, the electrolyte sufficiently penetrates into the negative electrode active material layer, Excellent charge / discharge characteristics will be exhibited.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(First battery)
FIG. 1 shows a cross-sectional structure of a secondary battery according to an embodiment of the present invention. This battery is, for example, a lithium ion secondary battery in which the capacity of the negative electrode is represented by a capacity based on insertion and extraction of lithium as an electrode reactant.

  This secondary battery is a so-called cylindrical type, and a wound electrode body 20 in which a belt-like positive electrode 21 and a negative electrode 22 are wound through a separator 23 inside a substantially hollow cylindrical battery can 11. have. The battery can 11 is made of, for example, iron (Fe) plated with nickel (Ni), and has one end closed and the other end open. Inside the battery can 11, a pair of insulating plates 12 and 13 are arranged perpendicular to the winding peripheral surface so as to sandwich the winding electrode body 20.

  At the open end of the battery can 11, a battery lid 14, a safety valve mechanism 15 provided inside the battery lid 14 and a heat sensitive resistance element (Positive Temperature Coefficient; PTC element) 16 are interposed via a gasket 17. It is attached by caulking, and the inside of the battery can 11 is sealed. The battery lid 14 is made of, for example, the same material as the battery can 11. The safety valve mechanism 15 is electrically connected to the battery lid 14 via the heat sensitive resistance element 16, and the disk plate 15A is reversed when the internal pressure of the battery exceeds a certain level due to an internal short circuit or external heating. Thus, the electrical connection between the battery lid 14 and the wound electrode body 20 is cut off. When the temperature rises, the heat sensitive resistance element 16 limits the current by increasing the resistance value and prevents abnormal heat generation due to a large current. The gasket 17 is made of, for example, an insulating material, and asphalt is applied to the surface.

  For example, a center pin 24 is inserted in the center of the wound electrode body 20. A positive electrode lead 25 made of aluminum (Al) or the like is connected to the positive electrode 21 of the spirally wound electrode body 20, and a negative electrode lead 26 made of nickel or the like is connected to the negative electrode 22. The positive electrode lead 25 is electrically connected to the battery lid 14 by being welded to the safety valve mechanism 15, and the negative electrode lead 26 is welded to and electrically connected to the battery can 11.

  FIG. 2 shows an enlarged part of the spirally wound electrode body 20 shown in FIG. The positive electrode 21 has, for example, a structure in which a positive electrode active material layer 21B is provided on both surfaces of a positive electrode current collector 21A. Although not shown, the positive electrode active material layer 21B may be provided only on one surface of the positive electrode current collector 21A. The positive electrode current collector 21A is made of, for example, a metal material such as aluminum, nickel, or stainless steel, and examples of the shape thereof include a foil shape, a net shape, and a lath shape.

  The positive electrode active material layer 21B includes, for example, one or more positive electrode materials capable of inserting and extracting lithium as an electrode reactant as a positive electrode active material.

As a positive electrode material capable of inserting and extracting lithium, for example, lithium-containing compounds such as lithium oxide, lithium sulfide, an intercalation compound containing lithium, or a phosphoric acid compound are suitable. You may mix and use. Among them, a composite oxide containing lithium and a transition metal element, or a phosphoric acid compound containing lithium and a transition metal element is preferable, and cobalt (Co), nickel, manganese (Mn), iron, aluminum is particularly preferable as the transition metal element. , One containing at least one of vanadium (V) and titanium (Ti) is preferable. The chemical formula is represented by, for example, Li _x MIO ₂ or Li _y MIIPO ₄ . In the formula, MI and MII contain one or more transition metal elements. The values of x and y vary depending on the charge / discharge state of the battery, and are generally 0.05 ≦ x ≦ 1.10 and 0.05 ≦ y ≦ 1.10.

Specific examples of the composite oxide containing lithium and a transition metal element include lithium cobalt composite oxide (Li _x CoO ₂ ), lithium nickel composite oxide (Li _x NiO ₂ ), and lithium nickel cobalt composite oxide (Li _x Ni _1-z Co _z O ₂ (z <1)), lithium nickel cobalt manganese composite oxide (Li _x Ni _(1-vw) Co _v Mn _w O ₂ (v + w <1)), or a spinel structure Examples thereof include lithium manganese composite oxide (LiMn ₂ O ₄ ). Specific examples of the phosphate compound containing lithium and a transition metal element include, for example, a lithium iron phosphate compound (LiFePO ₄ ) or a lithium iron manganese phosphate compound (LiFe _1-u Mn _u PO ₄ (u <1)). Can be mentioned.

  Examples of the positive electrode material capable of inserting and extracting lithium also include other metal compounds or polymer materials. Examples of other metal compounds include oxides such as titanium oxide, vanadium oxide, and manganese dioxide, or disulfides such as titanium sulfide and molybdenum sulfide. Examples of the polymer material include polyaniline and polythiophene.

  The positive electrode active material layer 21B may contain a conductive material or a binder as necessary. Examples of the conductive material include carbon materials such as graphite, carbon black, and ketjen black, and one kind or a mixture of two or more kinds is used. In addition to the carbon material, a metal material or a conductive polymer material may be used as long as it is a conductive material. Examples of the binder include synthetic rubbers such as styrene butadiene rubber, fluorine rubber or ethylene propylene diene rubber, or polymer materials such as polyvinylidene fluoride, and one kind or a mixture of two or more kinds is used. It is done.

  The negative electrode 22 has, for example, a configuration in which a negative electrode active material layer 22B is provided on both surfaces of a negative electrode current collector 22A. Although not shown, the negative electrode active material layer 22B may be provided only on one surface of the negative electrode current collector 22A. The anode current collector 22A is preferably made of a metal material having good electrochemical stability, electrical conductivity, and mechanical strength. Examples of the metal material include copper, nickel, and stainless steel, and copper having excellent electrical conductivity is more preferable. In addition, examples of the shape of the negative electrode current collector 22A include a foil shape, a net shape, and a lath shape.

  The negative electrode active material layer 22B includes, for example, a negative electrode material capable of occluding and releasing lithium as an electrode reactant as a negative electrode active material. For example, the negative electrode active material layer 21B is formed as necessary. The same conductive material and binder may be included. The binder may be included in a proportion of 3% by mass or more and 5% by mass or less in the entire negative electrode active material layer 22B.

The negative electrode material capable of inserting and extracting lithium contains a mixture of the following first and second graphite particles. The first graphite particle, and the median diameter _{D 50} by laser diffraction particle size distribution meter below 15μm above 13 .mu.m, specific surface area by the BET method is not more than 2m ² / g or more 7m ² / g, breaking strength 20 MPa or more and 40 MPa or less. On the other hand, the second graphite particles, and a median diameter _{D 50} by laser diffraction particle size distribution meter 12μm or 19μm or less and a specific surface area by BET method of 0.5 m ² / g or more 1.0 m ² / g or less The fracture strength is 80 MPa or more and 100 MPa or less. Here, the ratio of the mass of the first graphite particles to the mass of the second graphite particles is 1/9 or more and 3/7 or less (that is, mixing of the first graphite particles and the second graphite particles). The ratio is in the range of 70:30 to 90:10 by mass ratio). By including such two types of graphite particles at a predetermined ratio, the negative electrode active material layer 22B can be pressed with a smaller pressure, the volume density thereof can be increased, and the capacity can be increased. In addition, since an appropriate gap is secured in the negative electrode active material layer 22B and a lithium diffusion path is formed, the charge / discharge characteristics can be improved even if the volume density of the negative electrode active material layer 22B is increased. For example, the peak intensity ratio I ₀₀₂ / I ₁₁₀ of the X-ray diffraction of the negative electrode active material layer press-molded so as to have a volume density of 1.6 g / cm ³ or more using the above negative electrode material is about 40 to 150. It becomes. Here, I ₂₀₀ and I ₁₁₀ are peak intensities belonging to the (002) plane or the (110) plane in the X-ray diffraction pattern, respectively.

The fracture strength St (Sx) of the graphite particles is obtained by applying a load (load) to the graphite particles using a predetermined testing machine and measuring the relationship between the test force and the compression displacement. Specifically, first, the graphite particles is measurement sample, after measured by the median diameter (average particle diameter) D _50, for example, a laser diffraction particle size distribution measuring apparatus, the longest portion while observing with an optical microscope Graphite particles whose length falls within the median diameter D ₅₀ ± 10% are selected and extracted. Next, a test force P at which breakage occurs is measured by applying a load to the graphite particles extracted using, for example, a micro compression tester MCT-W500 manufactured by Shimadzu Corporation. In this way, using the value of the measured median diameter (average particle diameter) D ₅₀ and test force P, it is possible to determine the breaking strength St (Sx) from the following equation (1).
(Equation 1)
St (Sx) = 2.8P / (π × D ₅₀ × D ₅₀ )
St (Sx) is the breaking strength (unit: MPa) represents, P is the force at the time of the test (unit: N) _{represents, D 50} is the median diameter of the graphite particles (unit: mm) represents the.

The first graphite particle, for example, C-axis direction of the grating spacing d ₀₀₂ is less 0.3360nm calculated by X-ray diffractometry, which scale-like artificial graphite particles were spheroidized (pseudo spherical graphite particles) Can be used. This is because, if the first graphite particles have such a configuration, it is easier to realize a higher volume density of the negative electrode active material layer 22B and an improvement in charge / discharge characteristics as a secondary battery. The lattice spacing d ₀₀₂ is, for example, an X-ray diffraction method using CuKα rays as X-rays and high-purity silicon as a standard material (“Otani Sugirou, Carbon Fiber, p. 733-742 (1986), Modern Edit ").

Examples of the second graphite particles include isotropic artificial graphite particles in which a graphite structure (graphite crystal) is randomly oriented. Specifically, preferably spherulites graphite products of mesophase spheres, the lattice spacing d ₀₀₂ in the C-axis direction calculated by X-ray diffraction method may is below 0.3360 nm. This is because, if the second graphite particles have such a configuration, it is easier to realize a higher volume density of the negative electrode active material layer 22B and an improvement in charge / discharge characteristics as a secondary battery.

The volume density of the negative electrode active material layer 22B is preferably 1.6 g / cm ³ or more and 1.8 g / cm ³ or less. In the case where the thickness of the negative electrode active material layer 22B and the composition ratio of the material constituting the same are constant, by increasing the volume density of the negative electrode active material layer 22B, the filling amount of the negative electrode active material can be increased, and the battery capacity It is because it can be made high. Further, when the volume density of the negative electrode active material layer 22B is increased, the voids are reduced and the permeability of the electrolytic solution is lowered. However, since the first graphite particles and the second graphite particles described above are included. Thus, a lithium diffusion path can be secured, and deterioration of charge / discharge characteristics can be suppressed. In addition, by appropriately reducing the voids, the contact properties of the first and second graphite particles described above can be improved, the electron conductivity can be improved, and the load characteristics can be improved. However, even if the volume density of the negative electrode active material layer 22B is too high, the electrolyte permeability in the negative electrode 22 is too low and the battery characteristics are deteriorated. Therefore, the volume density of the negative electrode active material layer 22B is 1 0.8 g / cm ³ or less is preferable.

  The separator 23 separates the positive electrode 21 and the negative electrode 22 and allows lithium ions to pass through while preventing a short circuit of current due to contact between the two electrodes. The separator 23 is composed of, for example, a porous film made of a synthetic resin made of polytetrafluoroethylene, polypropylene, polyethylene, or the like, or a porous film made of an inorganic material such as a ceramic nonwoven fabric. The porous film may be laminated. Among these, a porous film made of polyolefin is preferable because it is excellent in the effect of preventing short circuit and can improve the safety of the battery due to the shutdown effect. In particular, polyethylene is preferable as a material constituting the separator 23 because a shutdown effect can be obtained within a range of 100 ° C. or higher and 160 ° C. or lower and the electrochemical stability is excellent. Polypropylene is also preferable, and other resins having chemical stability can be used by copolymerizing or blending with polyethylene or polypropylene.

  The separator 23 is impregnated with an electrolytic solution. The electrolytic solution includes, for example, a solvent and an electrolyte salt dissolved in the solvent.

  Examples of the solvent include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-fluoro-1,3-dioxolan-2-one, γ-butyrolactone, and γ-valerolactone. 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, methyl acetate, methyl propionate, ethyl propionate, acetonitrile, glutaronitrile, adiponitrile, Methoxyacetonitrile, 3-methoxypropionitrile, N, N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, nitromethane, nitroethane, sulfolane, dimethyl sulfoxide, trimethyl phosphate, lithium Room temperature molten salts such as triethyl acidate, ethylene sulfite, or bistrifluoromethylsulfonylimide trimethylhexylammonium. Among them, ethylene carbonate, propylene carbonate, vinylene carbonate, 4-fluoro-1,3-dioxolan-2-one, dimethyl carbonate, ethyl methyl carbonate or ethylene sulfite has excellent charge / discharge capacity characteristics and charge / discharge cycle characteristics. This is preferable. Any one of the solvents may be used alone, or a plurality of the solvents may be mixed and used.

Examples of the electrolyte salt include lithium hexafluorophosphate (LiPF ₆ ), bis (pentafluoroethanesulfonyl) imide lithium (Li (C ₂ F ₅ SO ₂ ) ₂ N), lithium perchlorate (LiClO ₄ ), Lithium hexafluoroarsenate (LiAsF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium trifluoromethanesulfonate (LiSO ₃ CF ₃ ), lithium bis (trifluoromethanesulfonyl) imide (Li (CF ₃ SO ₂ ) ₂ N), tris (trifluoromethanesulfonyl) methyllithium (LiC (SO ₂ CF ₃ ) ₃ ), lithium chloride (LiCl), lithium bromide (LiBr), LiB (C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , _{LiCF 3 SO 3, LiN (SO} 2 CF 3) 2, LiAlCl 4, LiSiF 6, difluoro [oxalato O, O '] lithium borate, or the like of lithium bis (oxalato) borate. Among these, LiPF ₆ is particularly preferable because it can obtain high ionic conductivity and improve cycle characteristics. As the electrolyte salt, any one of the above may be used alone, or a plurality of kinds may be mixed and used.

  For example, the secondary battery can be manufactured as follows.

  First, a positive electrode active material, a conductive material, and a binder are mixed to prepare a positive electrode mixture, and the positive electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a paste-like positive electrode mixture. A slurry is obtained. Subsequently, the positive electrode mixture slurry is applied to the positive electrode current collector 21A and the solvent is dried. Then, the positive electrode active material layer 21B is formed by compression molding using a roll press or the like, and the positive electrode 21 is manufactured. Further, the positive electrode active material layer 21B may be formed by attaching a positive electrode mixture to the positive electrode current collector 21A.

  Further, the above-mentioned graphite particles and a binder are mixed to prepare a negative electrode mixture, and this negative electrode mixture is dispersed in a solvent such as N-methyl-2-pyrrolidone to obtain a paste-like negative electrode mixture slurry. To do. Subsequently, the negative electrode mixture slurry is applied to the negative electrode current collector 22A, and the solvent is dried. Then, the negative electrode active material layer 22B is formed by compression molding using a roll press or the like, and the negative electrode 22 is manufactured.

  Next, the positive electrode lead 25 is attached to the positive electrode current collector 21A by welding or the like, and the negative electrode lead 26 is attached to the negative electrode current collector 22A by welding or the like. After that, the positive electrode 21 and the negative electrode 22 are wound through the separator 23, and the tip of the positive electrode lead 25 is welded to the safety valve mechanism 15, and the tip of the negative electrode lead 26 is welded to the battery can 11. The positive electrode 21 and the negative electrode 22 are sandwiched between a pair of insulating plates 12 and 13 and stored in the battery can 11. After the positive electrode 21 and the negative electrode 22 are accommodated in the battery can 11, the electrolytic solution is injected into the battery can 11 and impregnated in the separator 23. After that, the battery lid 14, the safety valve mechanism 15, and the heat sensitive resistance element 16 are fixed to the opening end of the battery can 11 by caulking through a gasket 17. Thereby, the secondary battery shown in FIG. 1 is completed.

  In the secondary battery, when charged, for example, lithium ions are released from the positive electrode active material layer 21B and inserted into the negative electrode active material layer 22B through the electrolytic solution. In addition, when discharging is performed, for example, lithium ions are released from the negative electrode active material layer 22B and inserted into the positive electrode active material layer 21B through the electrolytic solution.

In this embodiment, the anode active material in the anode active material layer 22B, a median diameter _{D 50} is at 15μm or less than 13 .mu.m, specific surface area of not more than 2m ² / g or more 7m ² / g, breaking strength 20MPa The first graphite particles that are 40 MPa or less, the median diameter D ₅₀ is 12 μm or more and 19 μm or less, the specific surface area is 0.5 m ² / g or more and 1.0 m ² / g or less, and the fracture strength is 80 MPa or more. What mixed with the 2nd graphite particle which is 100 Mpa or less by predetermined mass ratio was included as a negative electrode active material. Thereby, the volume density of the negative electrode active material layer 22B is increased by compression molding, and the total amount of the active material accommodated in the battery is increased, so that the battery capacity can be improved. At this time, since the volume density of the negative electrode active material layer 22B can be increased even at a lower press pressure, excessive stress is not applied to the negative electrode current collector 22A in the production stage of the negative electrode 22, and cracks are generated. There is no risk of breakage. Further, even when the volume density of the negative electrode active material layer 22B is increased by compression molding, an appropriate gap is formed in the negative electrode active material layer 22B, so that a sufficient lithium diffusion path can be secured inside the negative electrode active material layer 22B. Excellent charge / discharge characteristics can be obtained. The charge / discharge characteristics are also improved by improving the electronic conductivity by improving the contact property between the first and second graphite particles.

(Second battery)
FIG. 3 illustrates an exploded perspective configuration of the second battery. In this battery, a wound electrode body 30 to which a positive electrode lead 31 and a negative electrode lead 32 are attached is accommodated in a film-shaped exterior member 40. The battery structure using the film-shaped exterior member 40 is called a so-called laminate film type.

  For example, the positive electrode lead 31 and the negative electrode lead 32 are each led out in the same direction from the inside of the exterior member 40 toward the outside. The positive electrode lead 31 is made of, for example, a metal material such as aluminum. The negative electrode lead 32 is made of a metal material such as copper, nickel, or stainless steel, for example. Each metal material constituting the positive electrode lead 31 and the negative electrode lead 32 has a thin plate shape or a mesh shape.

  The exterior member 40 is made of, for example, a rectangular aluminum laminated film in which a nylon film, an aluminum foil, and a polyethylene film are bonded together in this order. In the exterior member 40, for example, a polyethylene film is opposed to the spirally wound electrode body 30, and each outer edge portion is in close contact with each other by fusion or an adhesive. An adhesive film 41 is inserted between the exterior member 40 and the positive electrode lead 31 and the negative electrode lead 32 to prevent intrusion of outside air. The adhesion film 41 is made of a material having adhesion to the positive electrode lead 31 and the negative electrode lead 32, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene.

  The exterior member 40 may be constituted by a laminate film having another structure instead of the above-described three-layer aluminum laminate film, or may be constituted by a polymer film such as polypropylene or a metal film. May be.

  FIG. 4 shows a cross-sectional configuration along line IV-IV of the spirally wound electrode body 30 shown in FIG. The electrode winding body 30 is obtained by winding a positive electrode 33 and a negative electrode 34 after being laminated via a separator 35 and an electrolyte 36, and an outermost peripheral portion thereof is protected by a protective tape 37. In FIG. 4, the electrode winding body 30 is shown in a simplified manner, but actually, the electrode winding body 30 has a flat (elliptical) cross section.

  FIG. 5 shows an enlarged part of the spirally wound electrode body 30 shown in FIG. The positive electrode 33 is obtained by providing a positive electrode active material layer 33B on both surfaces of a positive electrode current collector 33A. The negative electrode 34 has, for example, the same configuration as that of the negative electrode shown in FIG. 1, and is provided with a negative electrode active material layer 34B on both surfaces of a negative electrode current collector 34A. The configurations of the positive electrode current collector 33A, the positive electrode active material layer 33B, the negative electrode current collector 34A, the negative electrode active material layer 34B, and the separator 35 are respectively the positive electrode current collector 21A, the positive electrode active material layer 21B in the first battery described above. The configurations of the negative electrode current collector 22A, the negative electrode active material layer 22B, and the separator 23 are the same.

  The electrolyte 36 includes an electrolytic solution and a polymer compound that holds the electrolytic solution, and is in a so-called gel form. The gel electrolyte is preferable because it can obtain high ionic conductivity (for example, 1 mS / cm or more at room temperature) and can prevent battery leakage.

  Examples of the polymer compound include an ether polymer compound such as polyethylene oxide or a crosslinked product containing polyethylene oxide, an ester polymer compound such as polymethacrylate or an acrylate polymer compound, polyvinylidene fluoride, or vinylidene fluoride. And a vinylidene fluoride polymer such as a copolymer of styrene and hexafluoropropylene. These may be used alone, or a plurality of types may be mixed and used. In particular, from the viewpoint of redox stability, it is preferable to use a fluorine-based polymer compound such as a vinylidene fluoride polymer. The amount of the polymer compound added in the electrolytic solution varies depending on the compatibility between the two, but as an example, it is preferably in the range of 5% by mass to 50% by mass.

  The configuration of the electrolytic solution is the same as the configuration of the electrolytic solution in the first battery described above. However, the solvent in this case is not only a liquid solvent but also a broad concept including those having ion conductivity capable of dissociating the electrolyte salt. Accordingly, when a polymer compound having ion conductivity is used, the polymer compound is also included in the solvent.

  Instead of the electrolyte 36 in which the electrolytic solution is held by the polymer compound, the electrolytic solution may be used as it is. In this case, the separator 35 is impregnated with the electrolytic solution.

  This secondary battery can be manufactured by, for example, the following three types of manufacturing methods.

  In the first manufacturing method, first, the positive electrode 33 is formed by forming the positive electrode active material layers 33B on both surfaces of the positive electrode current collector 33A by the same procedure as in the first battery manufacturing method. Moreover, the negative electrode 34 is produced by forming the negative electrode active material layer 34B on both surfaces of the negative electrode current collector 34A by the same procedure as in the first battery manufacturing method.

  Subsequently, a gel solution 36 is formed by preparing a precursor solution containing an electrolytic solution, a polymer compound, and a solvent, applying the precursor solution to the positive electrode 33 and the negative electrode 34, and volatilizing the solvent. Subsequently, the positive electrode lead 31 and the negative electrode lead 32 are attached to the positive electrode current collector 33A and the negative electrode current collector 34A, respectively. Subsequently, after the positive electrode 33 and the negative electrode 34 provided with the electrolyte 36 are laminated via the separator 35, the positive electrode 33 and the negative electrode 34 are wound in the longitudinal direction, and a protective tape 37 is adhered to the outermost peripheral portion thereof. Form. Subsequently, for example, the wound electrode body 30 is sandwiched between two film-shaped exterior members 40, and then the outer edge portions of the exterior member 40 are bonded to each other by thermal fusion or the like. Enclose. At that time, the adhesion film 41 is inserted between the positive electrode lead 31 and the negative electrode lead 32 and the exterior member 40. Thereby, the secondary battery shown in FIGS. 3 to 5 is completed.

  In the second manufacturing method, first, the positive electrode lead 31 and the negative electrode lead 32 are attached to the positive electrode 33 and the negative electrode 34, respectively, and then the positive electrode 33 and the negative electrode 34 are stacked and wound via the separator 35, and at the outermost peripheral portion. By adhering the protective tape 37, a wound body that is a precursor of the wound electrode body 30 is formed. Subsequently, after sandwiching the wound body between the two film-shaped exterior members 40, the remaining outer peripheral edge portion excluding the outer peripheral edge portion on one side is bonded by thermal fusion or the like, thereby forming a bag-like exterior. It is housed inside the member 40. Subsequently, an electrolyte composition containing an electrolytic solution, a monomer that is a raw material of the polymer compound, a polymerization initiator, and other materials such as a polymerization inhibitor as necessary is prepared, and a bag-shaped exterior member After injecting into the inside of 40, the opening part of the exterior member 40 is sealed by heat sealing or the like. Finally, the gel electrolyte 36 is formed by thermally polymerizing the monomer to obtain a polymer compound. Thereby, the secondary battery shown in FIGS. 3 to 5 is completed.

  In the third manufacturing method, the wound body is formed to form the inside of the bag-shaped exterior member 40 in the same manner as in the first manufacturing method described above, except that the separator 35 coated with the polymer compound on both sides is used. Store in. Examples of the polymer compound applied to the separator 35 include a polymer containing vinylidene fluoride as a component, that is, a homopolymer, a copolymer, or a multi-component copolymer. Specifically, polyvinylidene fluoride, binary copolymers containing vinylidene fluoride and hexafluoropropylene as components, and ternary copolymers containing vinylidene fluoride, hexafluoropropylene and chlorotrifluoroethylene as components. Such as coalescence. In addition, the high molecular compound may contain the other 1 type, or 2 or more types of high molecular compound with the polymer which uses the above-mentioned vinylidene fluoride as a component. Subsequently, after the electrolytic solution is prepared and injected into the exterior member 40, the opening of the exterior member 40 is sealed by heat fusion or the like. Finally, the exterior member 40 is heated while applying a load, and the separator 35 is brought into close contact with the positive electrode 33 and the negative electrode 34 through the polymer compound. As a result, the electrolytic solution is impregnated into the polymer compound, and the polymer compound is gelled to form the electrolyte 36. Thus, the secondary battery shown in FIGS. 3 to 5 is completed. In the third manufacturing method, the swollenness characteristics are improved as compared with the first manufacturing method. Further, in the third manufacturing method, compared with the second manufacturing method, there are hardly any monomers or solvents that are raw materials for the polymer compound remaining in the electrolyte 36, and the formation process of the polymer compound is well controlled. Therefore, sufficient adhesion is obtained between the positive electrode 33, the negative electrode 34, the separator 35, and the electrolyte 36.

  In this secondary battery, lithium ions are occluded and released between the positive electrode 33 and the negative electrode 34 as in the first battery. That is, when charged, for example, lithium ions are extracted from the positive electrode 33 and inserted in the negative electrode 34 through the electrolyte 36. On the other hand, when discharging is performed, lithium ions are released from the negative electrode 34 and inserted into the positive electrode 33 through the electrolyte 36.

  The operations and effects of the secondary battery and the manufacturing method thereof are the same as those of the first battery described above.

(Third battery)
FIG. 6 illustrates an exploded perspective configuration of the third battery. In this battery, a positive electrode 51 is attached to an outer can 54, and a negative electrode 52 is accommodated in an outer cup 55, which are stacked via a separator 53 impregnated with an electrolyte and then caulked via a gasket 56. is there. The battery structure using the outer can 54 and the outer cup 55 is called a so-called coin type.

  The positive electrode 51 is obtained by providing a positive electrode active material layer 51B on one surface of a positive electrode current collector 51A. The negative electrode 52 is obtained by providing a negative electrode active material layer 52B and a coating 52C on one surface of a positive electrode current collector 52A. The configurations of the positive electrode current collector 51A, the positive electrode active material layer 51B, the negative electrode current collector 52A, the negative electrode active material layer 52B, and the separator 53 are respectively the positive electrode current collector 21A, the positive electrode active material layer 21B in the first battery described above. The configurations of the negative electrode current collector 22A, the negative electrode active material layer 22B, and the separator 23 are the same.

  In this secondary battery, lithium ions are occluded and released between the positive electrode 51 and the negative electrode 52 as in the first battery described above. That is, when charged, for example, lithium ions are extracted from the positive electrode 51 and inserted in the negative electrode 52 through the electrolytic solution. On the other hand, when discharging is performed, lithium ions are released from the negative electrode 52 and inserted into the positive electrode 51 through the electrolytic solution.

  The operations and effects of the coin-type secondary battery and the manufacturing method thereof are the same as those of the first battery described above.

  Specific examples of the present invention will be described in detail.

(Example 1-1)
First, as the first graphite particles, the median diameter (D ₅₀ ) by a laser diffraction particle size distribution meter is 14.6 μm, the specific surface area by BET method is 6.10 m ² / g, and the fracture strength is 35. is 5 MPa, the lattice spacing d ₀₀₂ in the C-axis direction calculated was prepared pseudo spherical graphite particles treated pseudo-spherical the scaly artificial graphite of 0.3370nm by X-ray diffraction method. As a second graphite particles, a median diameter determined by laser diffraction particle size distribution meter _{(D 50)} is 18.9Myuemu, BET specific surface area is 0.78 m ² / g, breaking strength 83. is 0 MPa, the lattice spacing d ₀₀₂ in the C-axis direction calculated was prepared spherulite graphite product of mesophase spherules is 0.3366nm by X-ray diffraction method. The breaking strength is a value measured by a micro compression tester MCT-W500 manufactured by Shimadzu Corporation.

Next, an electrode containing the first and second graphite particles as an active material was produced. Specifically, first, 95 parts by mass of powder as an active material in which the first and second graphite particles are mixed at a mass ratio of 30:70, and 5 parts by mass of polyvinylidene fluoride as a binder, Were mixed and dispersed in N-methyl-2-pyrrolidone as a solvent to obtain a mixture slurry. Next, the mixture slurry is uniformly applied to a current collector made of a copper foil having a thickness of 12 μm, dried, and compression-molded so as to have a volume density of 1.60 g / cm ³ to form an active material layer. An electrode was obtained.

Next, a coin-type test cell (diameter 20 mm, thickness 1.6 mm) having the structure shown in FIG. 7 was produced using this electrode. This test cell uses the above-mentioned electrode punched out into a pellet having a diameter of 16 mm as a test electrode 61, accommodates it in an outer can 62, attaches a counter electrode 63 to an outer cup 64, and electrolyzes them. The separator 65 impregnated with the liquid is laminated so as to sandwich it, and then caulked through a gasket 66. That is, the test electrode 61 is obtained by providing a current collector 61A made of a copper foil with an active material layer 61B containing first and second graphite particles, and the active material layer 61B sandwiches the separator 65 and the counter electrode 63. Are arranged to face each other. Here, lithium metal is used as the counter electrode 63, a polyethylene porous film is used as the separator 65, and ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) are used as the electrolyte solution 2: 2: A mixture containing a mixed solvent mixed at a volume ratio of ₆ and LiPF ₆ as an electrolyte salt was used. The concentration of LiPF ₆ in the electrolytic solution was 1 mol / dm ³ .

(Examples 1-2 to 1-19)
In forming the negative electrode active material, the types of the first and second graphite particles (median diameter D ₅₀ , specific surface area, fracture strength) and the mixing ratio of the first and second graphite particles are shown in Table 1 below. An electrode and a test cell (FIG. 7) were produced in the same manner as in Example 1-1 except that the changes were made as shown in Table 2.

(Examples 1-20 to 1-22)
In forming the negative electrode active material, the types of the first and second graphite particles (median diameter D ₅₀ , specific surface area, fracture strength) and the mixing ratio of the first and second graphite particles are shown in Table 1 below. Other than the change as shown in Table 2, except that the negative electrode active material layer was formed by compression molding so that the volume density was 1.80 g / cm ³ , the same as in Example 1-1 Thus, an electrode and a test cell (FIG. 7) were produced.

(Comparative Examples 1-1 to 1-32)
The physical properties (median diameter D ₅₀ , specific surface area, fracture strength) of the first and second graphite particles and the mixing ratio (abundance ratio) of the first and second graphite particles are shown in Tables 3 to 5 below. An electrode and a test cell as a comparative example (FIG. 7) were produced in the same manner as in Example 1-1 except that the change was made as described above. However, in Comparative Examples 1-7, 1-14 to 1-17, and 1-26 to 1-29, natural graphite was used as the first graphite particles. In Comparative Examples 1-1 to 1-3 and 1-7, only the first graphite particles were used as the negative electrode active material, and in Comparative Examples 1-4 to 1-6, only the second graphite particles were used. . Moreover, in Comparative Examples 1-8 to 1-13, the mixing ratio of the first graphite particles and the second graphite particles was 40:60 by mass ratio.

(Comparative Examples 1-33 to 1-35)
In forming the negative electrode active material, the types (median diameter D ₅₀ , specific surface area, fracture strength) of the first and second graphite particles were changed as shown in Table 5, and the negative electrode active material layer The electrode and the test cell (FIG. 7) were produced in the same manner as in Example 1-1 except that compression molding was performed so that the volume density was 1.80 g / cm ³ . However, in Comparative Example 1-34, natural graphite was used as the first graphite particles.

  About the test cell of each Example and comparative example produced as mentioned above, 5 C discharge capacity (mAh / g), discharge capacity maintenance factor (%), and charge capacity maintenance factor (%) were investigated as follows. The details will be described below.

  Regarding the 5C discharge capacity (mAh / g), first, each test cell was charged at a constant current of 0.2 C until the equilibrium potential reached 0 V with respect to lithium, and then the current value was reduced to 0.036 mA. Constant voltage charging was performed at a constant voltage of 0 V until the voltage decreased. After that, the battery was discharged at a constant current of 5 C until the equilibrium potential reached 1.5 V with respect to lithium, and the discharge capacity at that time was measured. Note that 0.2 C is a current value at which the theoretical capacity can be discharged in 5 hours, and 5 C is a current value at which the theoretical capacity can be discharged in 0.2 hours. Since the discharge capacity calculated in this way is based on the equilibrium potential, it reflects characteristics specific to the material constituting the active material layer of the test electrode 61.

  Further, the 0.2 C discharge capacity (mAh / g) was examined in the same manner except that the current value during constant current discharge was 0.2 C among the above conditions. Here, as a discharge capacity maintenance ratio, a ratio of 5C discharge capacity (mAh / g) to 0.2C discharge capacity (mAh / g), that is, discharge capacity maintenance ratio (%) = (5C discharge capacity / 0.2C discharge). Capacity) × 100 was determined.

  Further, the charge capacity maintenance rate was obtained as follows. First, each test cell was charged at a constant current of 0.2 C until the equilibrium potential reached 0 V with respect to lithium, and then charged at a constant voltage of 0 V until the current value decreased to 0.036 mA. Then, the charge capacity at that time (referred to as 0.2C charge capacity (mAh / g)) was measured. After that, the battery was discharged at a constant current of 0.2 C until the equilibrium potential reached 1.5 V with respect to lithium. On the other hand, the 2C charge capacity (mAh / g) was examined in the same manner except that the current value during constant current charging was set to 2C. Here, as a charge capacity maintenance rate, a ratio of 2C charge capacity (mAh / g) to 0.2C charge capacity (mAh / g), that is, charge capacity maintenance rate (%) = (2C charge capacity / 0.2C charge) Capacity) × 100 was determined.

Tables 1 to 5 collectively show the results of these 5C discharge capacity (mAh / g), discharge capacity retention rate (%), and charge capacity retention rate (%). However, 5C discharge capacity (mAh / g) is simply referred to as discharge capacity (mAh / g). Tables 1 to 5 also show the peak intensity ratio I ₀₀₂ / I ₁₁₀ obtained from the X-ray diffraction pattern of the negative electrode active material layer.

As shown in Tables 1 to 5, in Examples 1-1 to 1-22, in comparison with Comparative Examples 1-1 to 1-35, all items of discharge capacity, discharge capacity maintenance rate, and charge capacity maintenance rate Was found to be excellent. In Examples 1-1 to 1-22, the peak intensity ratio I ₀₀₂ / I _{110 of} the negative electrode active material layer was very small, and (002) plane orientation was suppressed, so that lithium ions were occluded and released. This is thought to be easily done. In Comparative Examples 1-4 to 1-6 in which the spherical graphite particles as the second graphite particles were used alone, the peak intensity ratio I ₀₀₂ / I ₁₁₀ was suppressed to be very small. It seems that the discharge capacity is lowered because the conductivity between the particles is insufficient.

  In Comparative Examples 1-1 to 1-13, the mixing ratio (abundance ratio) between the first graphite particles and the second graphite particles is inappropriate for Examples 1-1 to 1-22, and Comparative Example 1 In -14 to 1-35, the physical properties of at least one of the first graphite particles and the second graphite particles are inappropriate, so that sufficient battery characteristics (discharge capacity, discharge capacity maintenance rate and charge capacity maintenance rate) are obtained. It was not obtained.

(Example 2-1)

Next, a cylindrical secondary battery including the negative electrode 22 and the positive electrode 21 illustrated in FIG. 1 was produced. The negative electrode 22 was uniformly applied to both sides of a current collector made of a copper foil having a thickness of 12 μm and dried with the mixture slurry obtained in the same manner as that used in Example 1-1. The active material layer is formed by compression molding to 60 g / cm ^3, and the negative electrode lead 26 is attached to one end of the current collector. At this time, a lithium ion secondary battery in which the capacity of the negative electrode 22 was expressed by a capacity component based on insertion and extraction of lithium was made.

The positive electrode 21 was produced as follows. Specifically, 90 parts by mass of a lithium iron phosphate compound (LiFePO ₄ ) having a median diameter (D ₅₀ ) of 1 μm by a laser diffraction particle size distribution analyzer as an active material, and 5 parts by mass of carbon black as a conductive material, Then, 5 parts by mass of polyvinylidene fluoride as a binder was mixed to obtain a positive electrode mixture, and then dispersed in N-methyl-2-pyrrolidone to obtain a paste-like positive electrode mixture slurry. Subsequently, the positive electrode mixture slurry was applied to both surfaces of a positive electrode current collector 21A made of aluminum foil (15 μm thick), dried, and then compression molded by a roll press to form the positive electrode active material layer 21B. . Finally, an aluminum positive electrode lead 25 was attached to one end of the positive electrode current collector 21A.

Subsequently, the positive electrode 21 and the negative electrode 22 are laminated in the order of the negative electrode 22, the separator 23, the positive electrode 21, and the separator 23 through a separator 23 made of a microporous polypropylene stretched film having a thickness of 25 μm, and wound many times. A wound electrode body 20 was produced. Next, the wound electrode body 20 is sandwiched between the pair of insulating plates 12 and 13, and the negative electrode lead 26 is welded to the nickel-plated iron battery can 11, and the positive electrode lead 25 is welded to the safety valve mechanism 15. The body 20 was accommodated in the battery can 11. Further, by injecting an electrolyte into the battery can 11 and covering the battery lid 14 via a gasket 17, the cylindrical secondary battery (outer diameter 18 mm, height 65 mm) shown in FIG. Was completed. The electrolytic solution had a mixed solvent in which EC, EMC, and DMC were mixed at a volume ratio of 2: 2: 6, and LiPF ₆ as an electrolyte salt. The concentration of LiPF ₆ in the electrolytic solution was 1 mol / dm ³ .

(Examples 2-2 to 2-9)
In forming the negative electrode active material, the types of the first and second graphite particles (median diameter D ₅₀ , specific surface area, fracture strength) were changed except that they were changed as shown in Table 6 below. Produced the cylindrical secondary battery shown in FIG. 1 in the same manner as in Example 2-1.

(Examples 2-10 to 2-18)
In forming the negative electrode active material, except that the mixing ratio of the first and second graphite particles was changed as shown in Table 7 below, the others were as in Examples 2-1 to 2-9, respectively. Similarly, the cylindrical secondary battery shown in FIG. 1 was produced.

(Comparative Examples 2-1 to 2-18)
The physical properties (median diameter D ₅₀ , specific surface area, fracture strength) of the first and second graphite particles and the mixing ratio (abundance ratio) of the first and second graphite particles are shown in Tables 8 and 9 below. A cylindrical secondary battery as a comparative example was fabricated in the same manner as in Example 2-1, except that the change was made as described above. However, in Comparative Examples 2-7 and 2-15, natural graphite was used as the first graphite particles. In Comparative Examples 2-1 to 2-3, 2-7, and 2-8, only the first graphite particles are used, and in Comparative Examples 2-4 to 2-6, only the second graphite particles are used. . Moreover, in Comparative Examples 2-9 to 2-18, the mixing ratio of the first graphite particles and the second graphite particles was set to 40:60 by mass ratio.

  About the secondary battery of each Example and comparative example produced as mentioned above, 10 C discharge capacity (mAh / g) and discharge capacity maintenance factor (%) were investigated as follows. The details will be described below.

  For 10 C discharge capacity (mAh / g), first, each secondary battery was charged at a constant current of 0.2 C until the battery voltage reached 4.2 V, and then the current value was reduced to 0.036 mA. Constant voltage charging was performed at a constant voltage of 4.2 V until it decreased. Thereafter, the battery was discharged at a constant current of 10 C until the battery voltage reached 2.7 V, and the discharge capacity at that time was measured.

  Further, the 0.2 C discharge capacity (mAh / g) was examined in the same manner except that the current value during constant current discharge was 0.2 C among the above conditions. Here, as a discharge capacity maintenance ratio, a ratio of 10 C discharge capacity (mAh / g) to 0.2 C discharge capacity (mAh / g), that is, discharge capacity maintenance ratio (%) = (10 C discharge capacity / 0.2 C discharge) Capacity) × 100 was determined.

The results of the 10C discharge capacity (mAh / g) and the discharge capacity retention rate (%) are summarized in Tables 6 to 9. However, the 10C discharge capacity (mAh / g) is simply referred to as discharge capacity (mAh / g). Tables 6 to 9 also show the peak intensity ratio I ₀₀₂ / I ₁₁₀ obtained from the X-ray diffraction pattern of the negative electrode active material layer.

As shown in Tables 6 to 9, Examples 2-1 to 2-18 are superior to Comparative Examples 2-1 to 2-18 in both the discharge capacity and the discharge capacity retention rate. all right. In Examples 2-1 to 2-18, as in Examples 1-1 to 1-22, the peak intensity ratio I ₀₀₂ / I ₁₁₀ of the negative electrode active material layer was very small, and the (002) plane orientation was This is considered to be because lithium ions are easily occluded and released by being suppressed. In Comparative Examples 2-4 to 2-6 in which the spherical graphite particles as the second graphite particles were used alone, the peak intensity ratio I ₀₀₂ / I ₁₁₀ was suppressed to be very small. It seems that the discharge capacity is lowered because the conductivity between the particles is insufficient.

  Compared to Examples 2-1 to 2-18, in Comparative Examples 2-1 to 2-18, the mixing ratio (existence ratio) between the first graphite particles and the second graphite particles is inappropriate, and thus sufficient Battery characteristics (discharge capacity and discharge capacity retention rate) could not be obtained.

(Examples 3-1 and 3-2)
In forming the negative electrode active material, a test cell (FIG. 7) was produced in the same manner as in Example 1-1 except that polyvinylidene fluoride as a binder was changed to 4 parts by mass or 3 parts by mass. .

(Comparative Examples 3-1 and 3-2)
A test cell (FIG. 7) was prepared in the same manner as in Examples 3-1 and 3-2 except that only the first graphite particles were used as the negative electrode active material without using the second graphite particles. did.

  For each of the test cells of Examples 3-1 and 3-2 and Comparative Examples 3-1 and 3-2, 5C discharge capacity (mAh / g), discharge capacity maintenance ratio ( %) And charge capacity maintenance rate (%) were examined. The results are summarized in Table 10. However, 5C discharge capacity (mAh / g) is simply referred to as discharge capacity (mAh / g).

  As shown in Table 10, in Examples 3-1 and 3-2, although the amount of the binder added was reduced compared to Example 1-1, battery characteristics equivalent to or better than Example 1-1 were obtained. It was. On the other hand, in Comparative Examples 3-1 and 3-2, the battery characteristics deteriorated as the amount of the binder added was decreased. This is because, when only the pseudo-spherical graphite particles obtained by pseudo-spheroidizing the flaky artificial graphite are used as the negative electrode active material, the graphite particles take in a relatively large amount of the binder, so that the binder is reduced. This is considered to be because the adhesion between the negative electrode current collector is weakened and the resistance between the negative electrode active material layer and the negative electrode current collector is increased.

Thus, according to this embodiment, as the negative electrode active material in the negative electrode active material layer 22B, median diameter _{D 50} is at 15μm or less than 13 .mu.m, specific surface area be less 2m ² / g or more 7m ² / g The first graphite particles having a breaking strength of 20 MPa or more and 40 MPa or less, the median diameter D ₅₀ is 12 μm or more and 19 μm or less, and the specific surface area is 0.5 m ² / g or more and 1.0 m ² / g or less, Since the second graphite particles having a fracture strength of 80 MPa or more and 100 MPa or less are included at a predetermined mixing ratio, an appropriate void is formed even when the volume density of the negative electrode active material layer 22B is increased. It was found that a sufficient lithium diffusion path can be secured in the case of, and that excellent discharge capacity and charge / discharge characteristics can be obtained.

  Although the present invention has been described with reference to the embodiments and examples, the present invention is not limited to the embodiments and examples, and various modifications can be made. For example, in the above embodiments and examples, a battery using lithium as an electrode reactant has been described. However, other alkali metals such as sodium (Na) or potassium (K), or alkalis such as magnesium or calcium (Ca) are used. The present invention can also be applied to the case of using an earth metal or another light metal such as aluminum. At that time, the positive electrode active material capable of inserting and extracting the electrode reactant is selected according to the electrode reactant.

  In the above-described embodiments and examples, the secondary battery and the coin-type secondary battery including the battery element having the cylindrical and flat (elliptical) winding structures have been specifically described. The present invention provides a secondary battery having a battery element having a polygonal winding structure, a battery element having another structure such as a structure in which a positive electrode and a negative electrode are folded, or a structure in which a plurality of layers are stacked. The same applies to the secondary battery. In addition, the present invention can be similarly applied to secondary batteries having other exterior shapes such as a square shape.

  In the above embodiments and examples, the case where an electrolytic solution is used as the electrolyte and the case where a gel electrolyte in which the electrolytic solution is held in a polymer compound are used have been described. However, other electrolytes may be mixed and used. May be. Examples of other electrolytes include ion conductive inorganic compounds such as organic solid electrolytes, ion conductive ceramics, ion conductive glasses, or ionic crystals in which electrolyte salts are dissolved or dispersed in polymer compounds having ion conductivity. Inorganic solid electrolytes are included.

It is sectional drawing showing the structure of the 1st battery which concerns on embodiment of this invention. It is sectional drawing which expands and represents a part of winding electrode body in the 1st battery shown in FIG. It is a disassembled perspective view showing the structure of the 2nd battery which concerns on embodiment of this invention. It is sectional drawing showing the structure of the arrow direction along the IV-IV line of the wound electrode body shown in FIG. It is sectional drawing which expands and represents a part of winding electrode body shown in FIG. It is sectional drawing showing the structure of the 3rd battery which concerns on embodiment of this invention. It is sectional drawing showing the structure of the test cell used in the Example of this invention.

Explanation of symbols

  22A, 34A, 52A ... negative electrode current collector, 22B, 34B, 52B ... negative electrode active material layer, 11 ... battery can, 12, 13 ... insulating plate, 14 ... battery lid, 15 ... safety valve mechanism, 15A ... disk plate, 16 ... Heat-sensitive resistance element, 17, 56 ... Gasket, 20, 30 ... Wound electrode body, 21,33,51 ... Positive electrode, 21A, 33A, 51A ... Positive electrode current collector, 21B, 33B, 51B ... Positive electrode active material layer 22, 34, 52 ... negative electrode, 23, 35, 53 ... separator, 24 ... center pin, 25, 31 ... positive electrode lead, 26, 32 ... negative electrode lead, 36 ... electrolyte, 37 ... protective tape, 40 ... exterior member, 41 ... adhesion film, 54 ... exterior can, 55 ... exterior cup.

Claims (8)

A negative electrode active material layer provided on the negative electrode current collector;
The negative electrode active material layer has a median diameter (D ₅₀ ) of 13 μm or more and 15 μm or less by a laser diffraction particle size distribution analyzer, a specific surface area of 2 m ² / g or more and 7 m ² / g or less by a BET method, and a fracture strength. Having a median diameter (D ₅₀ ) of 12 μm or more and 19 μm or less by a laser diffraction particle size distribution meter, and a specific surface area by a BET method of 0.5 m ² / g or more and 1 0.02 m ² / g or less and a second graphite particle having a fracture strength of 80 MPa or more and 100 MPa or less as a negative electrode active material,
A ratio of the mass of the first graphite particles to the mass of the second graphite particles is from 1/9 to 3/7. 2. The negative electrode according to claim 1, wherein the negative electrode active material layer has a volume density of 1.6 g / cm ³ or more and 1.8 g / cm ³ or less.   The negative electrode according to claim 1, wherein the negative electrode active material layer contains a binder at a ratio of 3% by mass or more and 5% by mass or less.   The negative electrode according to claim 1, wherein the second graphite particles are spherical artificial graphite. A battery comprising an electrolyte together with a positive electrode and a negative electrode,
The negative electrode has a negative electrode active material layer provided on a negative electrode current collector,
The negative electrode active material layer has a median diameter (D ₅₀ ) of 13 μm or more and 15 μm or less by a laser diffraction particle size distribution analyzer, a specific surface area of 2 m ² / g or more and 7 m ² / g or less by a BET method, and a fracture strength. Having a median diameter (D ₅₀ ) of 12 μm or more and 19 μm or less by a laser diffraction particle size distribution meter, and a specific surface area by a BET method of 0.5 m ² / g or more and 1 0.02 m ² / g or less and a second graphite particle having a fracture strength of 80 MPa or more and 100 MPa or less as a negative electrode active material,
The ratio of the mass of the first graphite particles to the mass of the second graphite particles is 1/9 or more and 3/7 or less. The battery according to claim 5, wherein the negative electrode active material layer has a volume density of 1.6 g / cm ³ or more and 1.8 g / cm ³ or less.   The battery according to claim 5, wherein the negative electrode active material layer contains a binder at a ratio of 3% by mass or more and 5% by mass or less.   The battery according to claim 5, wherein the second graphite particles are spherical artificial graphite.

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