JP5892200B2 - Electrode, battery, and electrode manufacturing method - Google Patents

Description

  The present disclosure relates to an electrode including an active material containing spherulitic graphitized mesophase spherules, a method for manufacturing the electrode, and a battery.

  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 ion 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. In addition, about the lithium ion secondary battery using a carbon material, it discloses by the following patent documents 1-8, for example.

  By the way, a negative electrode provided with a negative electrode active material layer containing a carbon material generally has a current collector such as a copper foil obtained by dissolving a paste slurry in which graphite particles, a binder, a thickener and the like are dissolved in water or an organic solvent. After being applied to the substrate and dried, it is produced by compression molding or cutting. Compression molding is an operation necessary to obtain a predetermined thickness and density in the negative electrode active material layer. In order to further increase the energy density of the battery, it is desired to further increase the volume density of the negative electrode active material layer. However, when the volume density of the negative electrode active material layer is increased, the negative electrode active material particles constituting the negative electrode active material layer may be crushed or dropped during compression molding.

  Therefore, a method has been proposed that avoids the problem of crushing or dropping off of the negative electrode active material particles accompanying press molding by using mesophase graphite spherules having higher compressive fracture strength (that is, higher hardness) (for example, (See Patent Document 9).

JP-A-57-208079 JP 58-93176 A JP 58-192266 A JP 62-90863 A JP-A-62-212666 JP-A-2-66856 JP 2004-95529 A JP-A-2005-44775 JP-A-7-272725

  However, when the mesophase graphite spherule having high hardness is used as in Patent Document 9, the negative electrode active material particles can be prevented from being crushed or dropped during compression molding, while the negative electrode active material layer is formed. This increases the load applied to the negative electrode current collector as the substrate. For this reason, the negative electrode current collector may crack or break, particularly in the vicinity of the end of the negative electrode active material layer, so the press pressure cannot be increased, and as a result, the volume density of the negative electrode active material layer is improved. The situation was impossible.

  On the other hand, when graphite particles having a low particle hardness, such as natural graphite, flaky graphite, or graphite obtained by pulverizing and granulating flaky graphite, are used as the negative electrode active material, high density packing is possible. It is advantageous for further increasing the energy density. However, when such a small particle hardness is filled at a high density, voids in the negative electrode active material layer (particularly near the surface) are reduced during compression molding, and the electrolyte cannot be sufficiently infiltrated or impregnated. There is a concern that the charge / discharge characteristics under high load and the charge characteristics at low temperature may deteriorate. Furthermore, scaly graphite and graphite obtained by pulverizing and granulating it have a larger specific surface area than mesophase graphite spherules, and decrease in peel strength between the negative electrode current collector and the negative electrode active material layer, It may cause a decrease in charge / discharge efficiency due to decomposition.

  The present disclosure has been made in view of such problems, and an object thereof is to provide a battery having a larger capacity and an excellent charge / discharge efficiency. Furthermore, the objective of this indication is to provide the electrode which has an active material suitable for such a battery, and its manufacturing method.

The electrode of the present disclosure has an active material layer provided on a current collector. This active material layer contains, as an active material, spherulitic graphitized mesophase spherules provided with pores. The mesophase spherulite spherulite graphitized material has a ratio of the outer surface area to the total surface area of 10% to 50%. The number of dents generated on the current collector due to the spherulitic graphitized mesophase spherules in a 5 mm × 5 mm square region on the surface of the electrode is 85 or less. However, the total surface area and the external surface area are determined by performing an αs plot analysis together with the nitrogen adsorption measurement, and the total surface area indicates the sum of the internal pore surface and the external surface area in the spherulitic graphitized mesophase spherules, The external surface area indicates a surface area obtained by excluding the surface area of the micropore from the total surface area. Further, the term “pore” as used herein refers to a cavity that is blocked from the outer surface and exists inside the spherulitic graphitized material, a cavity having one path connected to the outer surface (that is, a recess), and an outer surface of a certain region. It is a concept including all through holes (cavities having two or more paths connected to the outer surface) connected to the outer surface of other regions. The number of dents is an active material layer composed of 90 parts by mass of mesophase graphite spherules and 10 parts by mass of polyvinylidene fluoride on a current collector made of copper foil having a thickness of 12 μm, and its volume density is 1.80 g / cm ^3. In the area of 5 mm × 5 mm square on the surface of the active material layer when the ratio of the outer surface area to the total surface area is 4%. This is a relative value when the number of dents generated on the current collector is 100.

  The battery according to the present disclosure includes an electrolyte together with the positive electrode and the negative electrode according to the present disclosure.

  In the electrode and battery of the present disclosure, the number of dents generated on the current collector due to the mesophase graphite spherules in a 5 mm × 5 mm square region on the surface of the electrode is 85 or less. For this reason, when it is press-molded, the pores are crushed so as to exhibit a hardness that does not damage the negative electrode current collector, and a space in which the electrolytic solution can sufficiently permeate is secured. In addition, spherulitic graphitized mesophase spherulites have a smaller specific surface area than natural graphite, scaly graphite, or graphite obtained by pulverizing and granulating them, so that it is possible to improve peel strength and charge / discharge efficiency. It is advantageous.

An electrode manufacturing method according to the present disclosure includes: forming an active material layer containing spherulitic graphitized mesophase spherules provided with pores on a current collector; and pressing the active material layer. It is what was included. Here, as the spherulite graphitized material of mesophase spherules, the ratio of the outer surface area to the total surface area is 10% or more and 50% or less, and the volume density of the active material layer is 1.50 g / cm ³ or more by press molding. .80 g / cm ³ or less, and the number of dents generated on the current collector due to the spherulitic graphitized mesophase spherules in a 5 mm × 5 mm square region on its surface is 85 or less. To do. However, the total surface area and the external surface area are determined by performing an αs plot analysis together with the nitrogen adsorption measurement, and the total surface area indicates the sum of the internal pore surface and the external surface area in the spherulitic graphitized mesophase spherules, The external surface area indicates a surface area obtained by excluding the surface area of the micropore from the total surface area. The number of dents is an active material layer composed of 90 parts by mass of mesophase graphite spherules and 10 parts by mass of polyvinylidene fluoride on a current collector made of copper foil having a thickness of 12 μm, and its volume density is 1.80 g / cm ^3. In the area of 5 mm × 5 mm square on the surface of the active material layer when the ratio of the outer surface area to the total surface area is 4%. This is a relative value when the number of dents generated on the current collector is 100.

  According to the electrode of the present disclosure, it is possible to ensure a space in the active material layer that allows the electrolyte to sufficiently penetrate even when compression molding is performed at a high press pressure while suppressing an increase in hardness. .

  According to the battery of the present disclosure, since the electrode of the present disclosure is provided, the volume density of the active material layer can be improved relatively easily, and the discharge capacity can be improved. On the other hand, since the active material layer can secure an appropriate gap, when this electrode is used together with the electrolyte, the electrolyte sufficiently permeates the active material layer and exhibits excellent charge / discharge characteristics.

  According to the electrode manufacturing method of the present disclosure, an active material layer having a high volume density and a high discharge capacity can be easily formed without damaging the current collector.

3 is a cross-sectional view illustrating a configuration of a first battery according to an embodiment of the present disclosure. FIG. 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 indication. 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 indication. It is sectional drawing showing the structure of the test cell used in the Example of this indication.

  Hereinafter, embodiments of the present disclosure 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 disclosure. 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 may have a volume density of 1.50 g / cm ³ or more and 2.26 g / cm ³ or less. When the thickness of the negative electrode active material layer 22B and the composition ratio of the materials 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 capacity can be increased. This is because it can be increased. Further, by appropriately reducing the voids in the negative electrode active material layer 22B, the contact property between the spherulitic graphitized mesophase spherules (hereinafter referred to as mesophase graphite spherules) is improved, and the electron conductivity is increased. And the load characteristics can be improved. However, if the volume density of the negative electrode active material layer 22B is increased too much, voids are reduced and the electrolyte permeability is lowered. Therefore, in order to secure a lithium diffusion path and suppress a decrease in charge / discharge characteristics. It is desirable to be 2.26 g / cm ³ or less.

  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.

A negative electrode material capable of inserting and extracting lithium is a mesophase graphite spherule having pores therein. The mesophase graphite spherules have pores inside, so that the ratio of the outer surface area to the total surface area is, for example, 10% or more and 50% or less. Such mesophase graphite spherules have a smaller compressive fracture strength than conventional mesophase graphite spherules having no pores. That is, the mesophase graphite spheres have a preferable volume density (1.50 g / cm ³ or more and 2.26 g / cm ³ or less) with a smaller pressing pressure than conventional mesophase graphite spheres having no pores. It can be compression molded. In particular, mesophase graphite spherules having a ratio of the outer surface area to the total surface area of 15% or more and 27% or less can be compression-molded so as to have the above-mentioned preferable volume density with an even smaller press pressure. Therefore, since the negative electrode active material layer 22B includes the mesophase graphite spherules as the negative electrode active material, the negative electrode active material layer 22B has an appropriate gap serving as a lithium diffusion path and a high capacity.

The total surface area and outer surface area of the mesophase graphite spherules are determined by performing an αs plot analysis with nitrogen adsorption measurements. As is generally known, the nitrogen adsorption measurement is performed in the process of adsorbing and desorbing nitrogen on the sample to be measured at a temperature of 77 K. The adsorption isotherm and desorption isotherm reflecting the size and structure of the pores of the sample to be measured. To get a line. According to IUPAC (International Union of Pure and Applied Chemistry), the types of pores of the sample to be measured are micropores (diameters of 2 nm or less) and mesopores (diameters) depending on the size (diameter). Are classified into 2 nm or more and 50 nm or less) and macropores (50 nm or more).

  Using the αs plot analysis shown in Reference Document 1 and Reference Document 2 below, the adsorption isotherm obtained by nitrogen adsorption measurement is used to accurately determine the total surface area and outer surface area of the mesophase graphite microspheres that are the measurement target samples. can do.

(Reference 1) Carbon Society of Japan, “Latest Carbon Materials Experiment Technology (Physical Properties / Material Evaluation)”, Cypec, pp. 1-7 (2003).

(Reference 2) P.J.M.Carrott, R.A.Roberts, K.S.W.Sing, “Adsorption of nitrogen by porous and non-porous carbons”, Carbon, 25, (1987) 59-68.

  The total surface area determined by this αs plot analysis represents the sum of the internal pore surface and the external surface area in the mesophase graphite spherules. The external surface area determined by the αs plot analysis indicates a surface area obtained by excluding the surface area of the micropores from the total surface area. That is, the sum of the surface area of the mesopores, the surface area of the macropores, and the surface area of the flat surface in the mesophase graphite microspheres is shown. However, in the case of mesophase graphite microspheres, the surface area of the flat surface is extremely small compared to the surface area of mesopores and macropores and is negligible.

  By determining the ratio of the outer surface area to the total surface area, the ratio of the surface area of pores (mesopores and macropores) other than micropores to the total surface area in the mesophase graphite spherules can be expressed.

The mesophase graphite microspheres preferably have a specific surface area determined by the BET method based on nitrogen adsorption measurement of 0.1 m ² / g or more and 5 m ² / g or less, and 0.3 m ² / g or more and 2.0 m or less. ² / g or less is particularly desirable. If the specific surface area is 5.0 m ² / g or less, the mesophase graphite spherules are stably held on the negative electrode current collector 22A via the binder adhering to the surface even during charge and discharge, and the discharge capacity The battery characteristics such as Moreover, if the specific surface area is 0.1 m ² / g or more, good battery characteristics can be obtained without reducing the intercalation reactivity of lithium into the mesophase graphite spherules.

In addition, the mesophase graphite microspheres desirably have a median diameter (D ₅₀ ) of 5 μm or more and 50 μm or less by a laser diffraction particle size distribution meter in order to secure the specific surface area in the predetermined range. In particular, a median diameter (D ₅₀ ) of 10 μm or more and 35 μm or less is preferable because the specific surface area in the predetermined range described above can be obtained more easily.

Also, mesophase graphite globules are lattice spacing d ₀₀₂ in the C-axis direction calculated 0.3354nm than 0.3370nm or less by X-ray wide angle diffraction method (especially 0.3354nm or 0.3360nm or less), and The crystallite size Lc in the C-axis direction is desirably 80 nm or more (particularly 100 nm or more). The lattice spacing d ₀₀₂ and the crystallite size Lc in the C-axis direction are determined by filling a sample cell with, for example, a mixture of high-purity silicon powder of about 20% by mass with respect to mesophase graphite small spheres. Using an X-ray diffractometer (for example, RIN2000 X-ray diffractometer manufactured by Rigaku Corporation), a diffraction line is obtained by a reflection diffractometer method using a CuKα ray monochromatized with a graphite monochromator as a radiation source. Based on the Gakushin Law.

Further, in the mesophase graphite sphere, the Raman spectrum using argon ion laser light satisfies the following conditional expression (1). However, A is 1570cm ^-1 or more and 1620c.
Intensity of a peak appearing in a range of m ⁻¹ or less, and B is 1350 cm ⁻¹ or more and 1370 cm ⁻¹
It is the intensity of the peak that appears in the following range.
0.05 ≦ B / A ≦ 0.2 (1)

  This Raman spectrum is measured by a Raman spectroscope (for example, RENISHA Ramanscope) using an argon ion laser beam having a wavelength λ = 514.5 nm, on which a mesophase graphite sphere is placed on a glass cell.

  This is because if the mesophase graphite spherules are configured as described above, high volume density and good charge / discharge characteristics can be more easily realized.

  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 thickness of the separator 23 is preferably in the range of 10 μm to 50 μm. If the thickness is less than 10 μm, a short circuit may occur. If the thickness exceeds 50 μm, the ion permeability decreases and the volume efficiency of the battery decreases.

  The opening ratio of the separator 23 is preferably in the range of 30% to 70%. This is because when the aperture ratio is less than 30%, the ion permeability is lowered, and when it exceeds 70%, the strength is lowered, the insulating function is impaired, and a short circuit may occur.

  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), lithium tetraphenylborate (LiB (C ₆ H ₅ ) ₄ ), lithium methanesulfonate (LiCH ₃ SO _3), lithium trifluoromethanesulfonate LiCF ₃ SO _3), bis (trifluoromethanesulfonyl) imide lithium _{(LiN (SO 2 CF 3)} 2), four lithium chloride aluminate (LiAlCl _4), lithium hexafluoro silicate (LiSiF _6), lithium difluoro oxalate Examples thereof include borate (LiBF ₂ (O _x )) and lithium bisoxalate borate (LiBOB). Among these, LiPF6 is preferable because it can obtain high ion conductivity and can improve cycle characteristics. As the electrolyte salt, one of the above may be used alone, or a plurality of types may be mixed and used. The electrolyte salt, the above-mentioned 0.1 mol / dm ³ or more 3.0 mol / dm ³ or less in a solvent, preferably dissolved at a concentration 0.5 mol / dm ³ or more 1.5 mol / dm ^3.

  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, after applying this negative electrode mixture slurry to the negative electrode current collector 22A and drying the solvent, the volume density is 1.50 g / cm ³ or more and 2.26 g / cm ³ or less by a roll press machine or the like. The negative electrode active material layer 22B is formed by compression molding to produce the negative electrode 22.

  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 the present embodiment, the negative electrode active material in the negative electrode active material layer 22B includes mesophase graphite spherules having pores, and the compression fracture strength thereof is reduced. The capacity can be improved by increasing the total amount of the active material accommodated. At this time, since the volume density of the negative electrode active material layer 22B can be increased even at a lower press pressure, the mesophase is not imparted to the negative electrode current collector 22A in the production stage of the negative electrode 22 without excessive stress. There is no possibility of generating dents, cracks, openings or breaks with the graphite spheres as the starting point of stress generation. Here, when the ratio of the outer surface area to the total surface area in the mesophase graphite spheres is less than 10%, the fracture compressive strength is not sufficiently reduced, and the negative electrode current collector 22A may be caused to have a dent, crack, opening, or fracture. However, in the present embodiment, since the above ratio is 10% or more, there is no such fear.

  Further, in the present embodiment, even when the volume density 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. Here, when the ratio of the outer surface area to the total surface area in the mesophase graphite spheres exceeds 50%, the surface area derived from the mesopores and macropores becomes extremely large, and the mesophase graphite spheres themselves have excessive points of destruction and deformation. Therefore, the compressive fracture strength becomes extremely low. As a result, the press pressure applied to the negative electrode active material layer 22B tends to be non-uniform during press molding, and the vicinity of the surface layer is crushed, making it difficult to ensure a sufficient lithium diffusion path. However, in the present embodiment, since the above ratio is 50% or less, there is no such fear.

(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. In addition, such a polymer compound has, for example, a number average molecular weight in the range of 5.0 × 10 ^{5 to} 7.0 × 10 ⁵ or a weight average molecular weight of 2.1 × 10 ^{5 to} 3.1 ×. 10 ⁵ by weight, it is desirable that the intrinsic viscosity is in the range of ^{0.17 (dm 3 /g)~0.21(dm 3 / g} ).

  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 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 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 disclosure will be described in detail.

Example 1
First, the ratio of the outer surface area to the total surface area determined by αs plot analysis of the adsorption isotherm by nitrogen adsorption measurement is 16%, the median diameter (D ₅₀ ) by a laser diffraction particle size distribution analyzer is 30 μm, and nitrogen adsorption Mesophase graphite small spheres having a specific surface area determined by the BET method based on the measurement of 1.6 m ² / g were prepared. The nitrogen adsorption measurement was performed with a fully automatic gas adsorption device (OMNISORP 100CX manufactured by Beckman Coulter), and 77K
The adsorption isotherm of mesophase graphite spherules was obtained.

Next, an electrode containing the above mesophase graphite spheres as an active material was produced. Specifically, first, 90 parts by mass of the above mesophase graphite spherules and 10 parts by mass of polyvinylidene fluoride as a binder are mixed and dispersed in N-methyl-2-pyrrolidone (NMP) as a solvent. It was made into the mixture slurry. Next, the mixture slurry was uniformly applied to a current collector made of a copper foil having a thickness of 12 μm and dried, and compression molded so that the volume density was 1.80 g / cm ³ to form an active material layer. . After that, an electrode was obtained by punching a current collector provided with an active material layer into a pellet having a diameter of 16 mm. The area density of the active material layer relative to the area of the current collector was 12 mg / cm ² .

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 copper foil with an active material layer 61B containing the mesophase graphite spheres as an active material, and the active material layer 61B sandwiches the separator 65 therebetween. 63 is arranged so as to face 63. Here, lithium metal is used as the counter electrode 63, a polyethylene porous film is used as the separator 65, and a mixed solvent in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 1: 1 as an electrolytic solution. And LiPF ₆ as an electrolyte salt were used. The concentration of lithium hexafluorophosphate in the electrolyte was 1 mol / dm ³ .

(Examples 2 to 5)
Except that the ratio of the outer surface area to the total surface area in the mesophase graphite spherules, the median diameter D ₅₀ , and the specific surface area were each changed as shown in Table 1 below, the others were the same as in Example 1. A test cell (FIG. 7) was produced.

Furthermore, as Comparative Examples 1 to 5 with respect to Examples 1 to 5, the ratio of the outer surface area to the total surface area in the mesophase graphite spherules, the median diameter D ₅₀ , and the specific surface area were changed as shown in Table 1 below. A test cell (FIG. 7) was produced in the same manner as in Example 1 except for the above.

  About each test cell of Examples 1-5 and Comparative Examples 1-5 produced as mentioned above, relative press pressure, discharge capacity, discharge capacity maintenance factor, and the damage to the collector of an electrode were evaluated. The results are summarized in Table 1.

The relative press pressure was measured for the electrode of each Example and Comparative Example by measuring the press pressure required when the active material layer was compression molded so that the volume density was 1.80 g / cm ³ . Standardized based on press pressure.

  The discharge capacity was determined as follows. First, for each test cell, constant current charging was performed until the equilibrium potential reached 5 mV with respect to lithium at a constant current of 0.1 C, and then 5 mV until the total time after starting constant current charging reached 20 hours. A constant voltage charge was performed at a constant voltage. After that, the battery was discharged at a constant current of 0.1 C until the equilibrium potential reached 1.5 V with respect to lithium, and the discharge capacity (mAh / g) at that time was measured. Note that 0.1 C is a current value at which the theoretical capacity can be discharged in 10 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. Furthermore, the discharge capacity maintenance rate accompanying the progress of the charge / discharge cycle was determined in the following manner. Each test cell is repeatedly charged and discharged according to the above-described charging conditions and discharging conditions, and the discharge capacity at the first cycle and the discharge capacity at the 50th cycle are measured, and the discharge capacity retention rate (%) = (50 The discharge capacity at the cycle / the discharge capacity at the first cycle) × 100 was calculated.

  Evaluation of damage to the current collector of the electrode is performed by immersing and washing the electrode on which the active material layer is formed in an organic solvent to separate the active material layer from the current collector, and then drying the current collector. The body was observed 100 times with an optical microscope and visually observed. For visual observation, 5 mm × 5 mm square areas on the electrode surface were arbitrarily selected at three locations, and the number of dents caused by mesophase graphite spheres generated on the current collector by pressing during press molding was counted. This dent is a circular or elliptical dent generated on the surface of the current collector by pressing the surface of the current collector with a spherical mesophase graphite sphere, and the dimension of the smallest part is 3 to 70 μm. Those within the range of In addition, when two or more dents were observed at the same location, they were separated by visual observation, and the number of dents overlapping was determined and tabulated. In Table 1, the number of dents in Comparative Example 1 is set as a reference value 100, and the number of dents in other Examples and Comparative Examples is normalized and displayed.

As shown in Table 1, in Examples 1 to 5, the ratio of the outer surface area to the total surface area was 10% to 50%, the specific surface area was 0.1 m ² / g to 5 m ² / g, and the median diameter Since mesophase graphite spherules having (D ₅₀ ) of 5 μm or more and 50 μm or less were used as active materials, Comparative Examples 1 to 3 using mesophase graphite spherules having an outer surface area ratio of less than 10% as an active material. The relative press pressure (0.91 to 1) was lower (0.49 to 0.86), indicating that the press characteristics were improved. For this reason, in Examples 1-5, the number of dents of the current collector was significantly reduced as compared with Comparative Examples 1-3. Further, in Examples 1 to 5, the discharge capacity was 349 mAh / g or more and 356 mAh / g or less, and the discharge capacity maintenance rate was 92.4% or more and 92.9% or less. It was found that the capacity and discharge capacity maintenance rate were maintained.

  Furthermore, in Examples 1 to 5, the ratio of the outer surface area to the total surface area was higher than that of Comparative Examples 4 and 5 using mesophase graphite microspheres with an active material exceeding 50%, but the relative press pressure was higher. The discharge capacity and discharge capacity maintenance rate could be greatly increased.

  Although the present invention has been described with reference to the embodiments and examples, the present technology 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 battery and the coin-type battery including the battery element having the cylindrical and flat (elliptical) winding structure have been specifically described. The same applies to a battery including a battery element having a polygonal winding structure, or a battery element having 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. be able to. In addition, the present technology can be similarly applied to 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.

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 (15)

Having an active material layer provided on the current collector,
The active material layer includes, as an active material, spherulitic graphitized mesophase spherules provided with pores,
The mesophase spherulitic spherulite graphitized material has a ratio of an outer surface area to a total surface area of 10% to 50%,
The number of dents generated on the current collector due to the spherulitic graphitized mesophase spherules in a 5 mm × 5 mm square region on its surface is 85 or less.
(However, the total surface area and the external surface area are determined by performing an αs plot analysis together with the nitrogen adsorption measurement, and the total surface area indicates the sum of the internal pore surface and the external surface area in the spherulitic graphitized material of mesophase microspheres. The outer surface area is a surface area excluding the surface area of the micropores from the total surface area, and the number of dents is a current collector made of copper foil having a thickness of 12 μm, 90 parts by mass of mesophase graphite spherules and 10 polyvinylidene fluoride. The surface of the active material layer when the active material layer consisting of parts by mass is compression molded so that its volume density is 1.80 g / cm ^3, and the ratio of the outer surface area to the total surface area is 4% (This is a relative value when the number of dents generated on the current collector due to the spherulitic graphitized mesophase spherules in the upper 5 mm × 5 mm square region is defined as 100.) The electrode according to claim 1, wherein a ratio of the outer surface area to the total surface area is 15% or more and 27% or less. The spherulite graphitized material of the mesophase spherules has a specific surface area determined by a BET method based on a nitrogen adsorption measurement of 0.1 m ² / g or more and 5 m ² / g or less. Electrodes. The electrode according to any one of claims 1 to 3, wherein the mesophase spherulitic spherulite graphitized material has a median diameter (D ₅₀ ) measured by a laser diffraction particle size distribution meter of 5 µm or more and 50 µm or less. . The mesophase microsphere spherulitic graphitized material has a lattice plane distance d ₀₀₂ in the C-axis direction calculated by an X-ray wide-angle diffraction method of 0.3354 nm or more and 0.3370 nm or less, and a crystallite in the C-axis direction. The electrode according to any one of claims 1 to 4, wherein the electrode has a size of 80 nm or more. The electrode according to any one of claims 1 to 5, wherein the mesophase spherulitic spherulite graphitized material has a Raman spectrum satisfying the following conditional expression (1) using an argon ion laser beam.
0.05 ≦ B / A ≦ 0.2 (1)
However,
A: the intensity of the peak appearing in 1570 cm ^-1 or 1620 cm ^-1 or less in the range B: the intensity of the peak appearing at 1350 cm ^-1 or 1370 cm ^-1 or less in the range Electrode according to any one of the active material layer claims 1 to 6 volume density is less than 1.50 g / cm ³ or more 1.80 g / cm ³ of. A battery comprising an electrolyte together with a positive electrode and a negative electrode,
The positive electrode or the negative electrode has an active material layer provided on a current collector,
The active material layer includes, as an active material, spherulitic graphitized mesophase spherules provided with pores,
The mesophase spherulitic spherulite graphitized material has a ratio of an outer surface area to a total surface area of 10% to 50%,
A battery in which the number of dents generated on the current collector due to spherulitic graphitized mesophase spherules in a 5 mm × 5 mm square region on the surface of the positive electrode or the negative electrode is 85 or less.
(However, the total surface area and the external surface area are determined by performing an αs plot analysis together with the nitrogen adsorption measurement, and the total surface area indicates the sum of the internal pore surface and the external surface area in the spherulitic graphitized material of mesophase microspheres. The outer surface area is a surface area excluding the surface area of the micropores from the total surface area, and the number of dents is a current collector made of copper foil having a thickness of 12 μm, 90 parts by mass of mesophase graphite spherules and 10 polyvinylidene fluoride. The surface of the active material layer when the active material layer consisting of parts by mass is compression molded so that its volume density is 1.80 g / cm ^3, and the ratio of the outer surface area to the total surface area is 4% (This is a relative value when the number of dents generated on the current collector due to the spherulitic graphitized mesophase spherules in the upper 5 mm × 5 mm square region is defined as 100.) The battery according to claim 8, wherein a ratio of the outer surface area to the total surface area is 15% or more and 27% or less. The spherulitic graphitized material of the mesophase microsphere has a specific surface area determined by a BET method based on a nitrogen adsorption measurement of 0.1 m ² / g or more and 5 m ² / g or less. Battery. 11. The battery according to claim 8, wherein the mesophase small spherulitic graphitized material has a median diameter (D ₅₀ ) of 5 μm or more and 50 μm or less by a laser diffraction particle size distribution meter. . The mesophase microsphere spherulitic graphitized material has a lattice plane distance d ₀₀₂ in the C-axis direction calculated by an X-ray wide-angle diffraction method of 0.3354 nm or more and 0.3370 nm or less, and a crystallite in the C-axis direction. The battery according to any one of claims 8 to 11, which has a size of 80 nm or more. The battery according to any one of claims 8 to 12, wherein the mesophase spherulitic spherulitic graphitized material has a Raman spectrum using an argon ion laser beam that satisfies the following conditional expression (1).
0.05 ≦ B / A ≦ 0.2 (1)
However,
A: the intensity of the peak appearing in 1570 cm ^-1 or 1620 cm ^-1 or less in the range B: the intensity of the peak appearing at 1350 cm ^-1 or 1370 cm ^-1 or less in the range Cell according to any one of claims 13 claims 8 volume density of the active material layer is 1.50 g / cm ³ or more 1.80 g / cm ³ or less. Forming an active material layer containing spherulitic graphitized mesophase globules provided with pores on the current collector;
Pressing the active material layer,
As the spherulite graphitized product of the mesophase spherules, the ratio of the outer surface area to the total surface area is 10% to 50%,
Wherein the press molding, in 5mm × 5mm square regions on its surface with the volume density of the active material layer and 1.50 g / cm ³ or more 1.80 g / cm ³ or less, of the mesophase microspheres spherulite An electrode manufacturing method, wherein the number of dents generated on the current collector due to graphitized material is 85 or less.
(However, the total surface area and the external surface area are determined by performing an αs plot analysis together with the nitrogen adsorption measurement, and the total surface area indicates the sum of the internal pore surface and the external surface area in the spherulitic graphitized material of mesophase microspheres. The outer surface area is a surface area excluding the surface area of the micropores from the total surface area, and the number of dents is a current collector made of copper foil having a thickness of 12 μm, 90 parts by mass of mesophase graphite spherules and 10 polyvinylidene fluoride. The surface of the active material layer when the active material layer consisting of parts by mass is compression molded so that its volume density is 1.80 g / cm ^3, and the ratio of the outer surface area to the total surface area is 4% (This is a relative value when the number of dents generated on the current collector due to the spherulitic graphitized mesophase spherules in the upper 5 mm × 5 mm square region is defined as 100.)

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