JP2011077051A - Negative electrode active material, negative electrode, and battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a battery capable of obtaining high capacity and suppressing swelling. <P>SOLUTION: The battery is equipped with a wound electrode body 20 in which a positive electrode 21 and a negative electrode 22 are laminated and wound around via a separator 23 and an electrolyte 24 inside an exterior package member composed of an aluminum-laminated film. A negative electrode active material layer 22B contains a combined graphite material in which a plurality of primary particles composed of graphite having fine pores are combined so that oriented faces in at least a part of the primary particles become mutually in non-parallel to form secondary particles. In this combined graphite material, a volume of the fine pores having a pore diameter of 10 nm or more and 1×10<SP>5</SP>nm or less per unit mass, estimated by a mercury porosimetry, is 0.5 cm<SP>3</SP>/g or more and 1.5 cm<SP>3</SP>/g or less. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a negative electrode active material containing graphite, and a negative electrode and a battery using the same.

  In recent years, many portable electronic devices such as a camera-integrated VTR (videotape recorder), a mobile phone, or a portable computer have appeared, and their size and weight have been reduced. Accordingly, the development of batteries, particularly secondary batteries, has been actively promoted as portable power sources for electronic devices. Among these, lithium ion secondary batteries are attracting attention as being capable of realizing a high energy density.

  On the other hand, the lithium ion secondary battery has a high voltage, the positive electrode has a very noble oxidation potential, and the negative electrode has a very low reduction potential. There was a problem that the water solvent was decomposed and gas was generated. Therefore, conventionally, it has been studied to introduce a carbon material having a high specific surface area as a gas absorbing material into a battery regardless of whether it is a primary battery or a secondary battery (see, for example, Patent Documents 1 and 2). Moreover, although not as a gas absorption material, mixing and using a some carbon material is also examined (for example, refer patent documents 3-7).

Japanese Patent No. 30670080 JP-A-8-24637 Japanese Patent No. 3216661 JP-A-6-111818 JP 2001-196095 A JP 2002-8655 A Japanese Patent Laid-Open No. 2004-87437

  However, when activated carbon or the like having a high gas absorption capacity is added to the battery, there is a problem that side reactions occur in the battery and battery characteristics such as capacity are deteriorated.

  The present invention has been made in view of such problems, and an object thereof is to provide a negative electrode active material, a negative electrode, and a battery that can obtain a high capacity and can suppress swelling.

The negative electrode active material according to the present invention is a bonded graphite material in which a plurality of primary particles made of graphite having pores are combined to form secondary particles such that at least some of the alignment particles are non-parallel to each other. And mesocarbon microbeads or natural graphite, and the volume of pores having a pore diameter of 10 nm or more and 1 × 10 ⁵ nm or less estimated by the mercury intrusion method of this bonded graphite material is 0.5 cm ³ per unit mass. / G to 1.5 cm ³ / g, and the ratio of the combined graphite material to the total of the combined graphite material and mesocarbon microbeads or natural graphite is 3% by mass to 30% by mass. .

The negative electrode according to the present invention has a negative electrode active material layer on a negative electrode current collector, and the negative electrode active material layer has a plurality of primary particles made of graphite having pores as the negative electrode active material. It contains a bonded graphite material that is bonded so that the surfaces are not parallel to each other to form secondary particles, and mesocarbon microbeads or natural graphite, and this bonded graphite material is estimated by a mercury intrusion method. The volume of pores having a pore diameter of 10 nm or more and 1 × 10 ⁵ nm or less is 0.5 cm ³ / g or more and 1.5 cm ³ / g or less per unit mass, and the bonded graphite material and mesocarbon microbeads or natural graphite The ratio of the combined graphite material to the total is 3% by mass or more and 30% by mass or less.

The battery according to the present invention includes an electrolyte together with a positive electrode and a negative electrode, and the negative electrode has, as a negative electrode active material, a plurality of primary particles made of graphite having pores so that the orientation planes are non-parallel to each other at least partially. It contains a bonded graphite material that is bonded to form secondary particles, and mesocarbon microbeads or natural graphite. The pore diameter of this bonded graphite material is 10 nm or more and 1 × 10 ⁵ nm or less estimated by the mercury intrusion method. The volume of the pores is 0.5 cm ³ / g or more and 1.5 cm ³ / g or less per unit mass, and the ratio of the bound graphite material to the total of the bound graphite material and mesocarbon microbeads or natural graphite Is 3% by mass or more and 30% by mass or less.

According to the negative electrode active material, the negative electrode, and the battery of the present invention, primary particles are bonded to form secondary particles so that the orientation planes are non-parallel, and pores having a pore diameter of 10 nm or more and 1 × 10 ⁵ nm or less. Containing a bonded graphite material having a volume of 0.5 cm ³ / g or more and 1.5 cm ³ / g or less, and mesocarbon microbeads or natural graphite, and comprising the bonded graphite material and mesocarbon microbeads or natural graphite. Since the ratio of the bonded graphite material to the total is 3% by mass or more and 30% by mass or less, the capacity can be improved and the gas generated by the side reaction or the like can be absorbed to suppress the swelling. it can.

It is a disassembled perspective view showing the structure of the secondary battery which concerns on one embodiment of this invention. It is sectional drawing along the II-II line of the winding electrode body shown in FIG. It is an electron micrograph showing the cross-sectional structure of the negative electrode active material layer produced in the Example.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The order of explanation is as follows.

1. Configuration of secondary battery 2. Manufacturing method of secondary battery Action and effect of secondary battery

<1. Configuration of secondary battery>
FIG. 1 shows a configuration of a secondary battery according to an embodiment of the present invention. This secondary battery uses lithium as an electrode reactant, and includes a wound electrode body 20 to which a positive electrode terminal 11 and a negative electrode terminal 12 are attached inside a film-shaped exterior member 30.

  The positive electrode terminal 11 and the negative electrode terminal 12 are each led out from the inside of the exterior member 30 to the outside, for example, in the same direction. The positive electrode terminal 11 and the negative electrode terminal 12 are made of, for example, a metal material such as aluminum, copper (Cu), nickel (Ni), or stainless steel, and have a thin plate shape or a mesh shape, respectively.

  The exterior member 30 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. The exterior member 30 is disposed, for example, so that the polyethylene film side and the wound electrode body 20 face each other, and the outer edge portions are in close contact with each other by fusion or an adhesive. An adhesive film 31 for preventing the entry of outside air is inserted between the exterior member 30 and the positive electrode terminal 11 and the negative electrode terminal 12. The adhesion film 31 is made of a material having adhesion to the positive electrode terminal 11 and the negative electrode terminal 12, for example, a polyolefin resin such as polyethylene, polypropylene, modified polyethylene, or modified polypropylene.

  The exterior member 30 may be constituted by another aluminum laminate film in which an aluminum foil is sandwiched between other polymer films, a laminate film having another structure, a polymer film such as polypropylene, or a metal. You may make it comprise with a film.

  FIG. 2 shows a cross-sectional structure taken along line II-II of the spirally wound electrode body 20 shown in FIG. The wound electrode body 20 is obtained by laminating a positive electrode 21 and a negative electrode 22 via a separator 23 and an electrolyte 24 and winding them, and the outermost periphery is protected by a protective tape 25.

  The positive electrode 21 includes, for example, a positive electrode current collector 21A having a pair of opposed surfaces, and a positive electrode active material layer 21B provided on both surfaces of the positive electrode current collector 21A. The positive electrode current collector 21A has an exposed portion where the positive electrode active material layer 21B is not provided at one end in the longitudinal direction, and the positive electrode terminal 11 is attached to the exposed portion. The positive electrode current collector 21A is made of, for example, a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The positive electrode active material layer 21B includes, for example, any one or more of positive electrode materials capable of inserting and extracting lithium as a positive electrode active material, and a conductive material and a binder as necessary. May be included.

Examples of the positive electrode material capable of inserting and extracting lithium include lithium such as titanium sulfide (TiS ₂ ), molybdenum sulfide (MoS ₂ ), niobium selenide (NbSe ₂ ), or vanadium oxide (V ₂ O ₅ ). A chalcogenide containing no lithium, a lithium composite oxide containing lithium or a lithium-containing phosphate compound, or a polymer compound such as polyacetylene or polypyrrole.

Among them, a lithium composite oxide containing lithium and a transition metal element or a lithium-containing phosphoric acid compound containing lithium and a transition metal element is preferable because it can obtain a high voltage and a high energy density. A metal element containing at least one of cobalt (Co), nickel, manganese (Mn) and iron (Fe) 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 represent 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 include lithium cobalt composite oxide (Li _x CoO ₂ ), lithium nickel composite oxide (Li _x NiO ₂ ), lithium nickel cobalt composite oxide (Li _x Ni _1-z Co _z O ₂ (z <1). )), Lithium manganese composite oxide (LiMn ₂ O ₄ ) having a spinel structure, lithium iron phosphate compound (Li _y FePO ₄ ), or lithium iron manganese phosphate compound (Li _y Fe _1-v Mn _v PO ₄₎ (V <1)).

  Examples of the conductive material include carbon materials such as graphite, carbon black, and ketjen black, and one or more of them are used in combination. 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 or more of them are mixed. Used.

  The negative electrode 22 includes, for example, a negative electrode current collector 22A having a pair of opposed surfaces and a negative electrode active material layer 22B provided on both surfaces of the negative electrode current collector 22A. The negative electrode current collector 22A also has an exposed portion where the negative electrode active material layer 22B is not provided at one end in the longitudinal direction, and the negative electrode terminal 12 is attached to the exposed portion. The negative electrode current collector 22A is made of, for example, a metal foil such as a copper foil, a nickel foil, or a stainless steel foil.

  The negative electrode active material layer 22B includes, for example, any one or two or more negative electrode materials capable of inserting and extracting lithium as a negative electrode active material. A binder may be included. As the conductive material and the binder, the same materials as those described for the positive electrode 21 can be used.

  Examples of the anode material capable of inserting and extracting lithium include a carbon material, a material containing a metal element or a metalloid element capable of forming an alloy with lithium as a constituent element, a metal oxide, or a polymer compound. . Examples of the carbon material include graphitizable carbon, non-graphitizable carbon having a (002) plane spacing of 0.37 nm or more, or graphite having a (002) plane spacing of 0.340 nm or less. May be artificial graphite or natural graphite. Examples of a material containing a metal element or metalloid element capable of forming an alloy with lithium as a constituent element include, for example, a simple substance, an alloy, or a compound of a metal element capable of forming an alloy with lithium, or a metal element capable of forming an alloy with lithium. Examples include simple substances, alloys, or compounds of metal elements, or materials having at least a part of one or more of these phases, particularly those containing silicon (Si) or tin (Sn) as a constituent element. preferable. Examples of the metal oxide include iron oxide, ruthenium oxide, and molybdenum oxide. Examples of the polymer compound include polyacetylene and polypyrrole.

  Further, in the present embodiment, a combined graphite material in which a plurality of primary particles made of graphite having pores are combined to form secondary particles in such a manner that at least some of the alignment surfaces are non-parallel to each other. Contains. The graphite having pores is preferable because it can obtain a high capacity and can absorb the gas generated in the battery, and in particular, secondary particles bonded so that the orientation planes are not parallel to each other. This is because the lithium ion acceptability can be further improved.

  In this bonded graphite material, when the length in the major axis direction of the secondary particles is A and the length in the minor axis direction is B, the average aspect ratio represented by A / B is 1 or more and 4 or less in the discharge state. It is preferable that The aspect ratio value tends to increase when the orientation planes of the primary particles constituting the secondary particles are nearly parallel, and the aspect ratio value decreases when the orientation planes of the primary particles are more non-parallel. This is because if the average value is 4 or less, a higher effect can be obtained. The aspect ratio can be calculated based on the length A in the major axis direction and the length B in the minor axis direction of the secondary particles estimated by, for example, a scanning electron microscope (SEM). .

The specific surface area of the bonded graphite material is preferably 5 m ² / g or less. This is because if the specific surface area is too large, side reactions such as decomposition of the electrolytic solution increase, and the characteristics cannot be sufficiently improved. The specific surface area of the bonded graphite material is preferably 1 m ² / g or more. This is because if the specific surface area is too small, the gas absorption ability is lowered. The specific surface area of the bonded graphite material can be estimated by, for example, the BET (Brunauer Emmett Teller) one-point method.

Further, in this bonded graphite material, the volume of pores having a pore diameter of 10 nm or more and 1 × 10 ⁵ nm or less estimated by a mercury intrusion method is 0.5 cm ³ / g or more and 1.5 cm ³ / g or less per unit mass. More preferably, the volume of pores having a pore diameter of 10 nm or more and 2 × 10 ³ nm or less estimated by a mercury intrusion method is 0.1 cm ³ / g or more and 0.3 cm ³ / g or less per unit mass. preferable. This is because by having such a pore distribution, the lithium ion acceptability is further improved, and the capacity and cycle capacity maintenance rate can be further improved.

  This bonded graphite material can be obtained, for example, by mixing coke as a filler and pitch or the like as a molding agent or a sintering agent, followed by heat treatment and graphitization. According to this method, since filler (coke), binder pitch, and the like are used as raw materials, polycrystalline graphite is obtained, and sulfur or nitrogen contained in the raw materials is generated as a gas during heat treatment. A pore is formed in the path. In addition, this bonded graphite material can be obtained by granulating primary particles of graphite having pores. Any method may be used for the granulation. For example, a wet method in which a solvent or a liquid containing a granulation aid is used for stirring and rolling may be used, or a dry method in which no rolling is performed without addition. It may be used. Furthermore, it is more preferable to perform isotropic pressure treatment after the heat treatment or granulation treatment described above.

  The negative electrode active material layer 22B may use only this bonded graphite material as the negative electrode active material, but may also be used with one or more other negative electrode active materials. In that case, the ratio of the bonded graphite material in the negative electrode active material is more than 0% by mass, preferably in the range of 60% by mass or less, and more preferably in the range of 3% by mass to 30% by mass. This is because a higher cycle capacity maintenance rate can be obtained while suppressing swelling.

  The separator 23 has a high ion permeability and a predetermined mechanical strength, such as a porous film made of a polyolefin-based synthetic resin such as polypropylene or polyethylene, or a porous film made of an inorganic material such as a ceramic nonwoven fabric. It is comprised by the insulating thin film which has, and may be set as the structure which laminated | stacked these 2 or more types of porous films.

  The electrolyte 24 is constituted by a so-called gel electrolyte in which an electrolytic solution is held in a polymer compound. The electrolyte 24 may be impregnated in the separator 23, or may exist between the separator 23 and the positive electrode 21 and the negative electrode 22.

  The electrolytic solution includes, for example, a solvent and an electrolyte salt dissolved in the solvent. Examples of the solvent include lactone solvents such as γ-butyrolactone, γ-valerolactone, δ-valerolactone, and ε-caprolactone, ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate. Carbonate ester solvents such as 1,2-dimethoxyethane, 1-ethoxy-2-methoxyethane, 1,2-diethoxyethane, ether solvents such as tetrahydrofuran or 2-methyltetrahydrofuran, nitrile solvents such as acetonitrile, Nonaqueous solvents such as sulfolane-based solvents, phosphoric acids, phosphate ester solvents, or pyrrolidones are mentioned. Any one type of solvent may be used alone, or two or more types may be mixed and used.

Any electrolyte salt may be used as long as it dissolves in a solvent to generate ions, and one kind may be used alone, or two or more kinds may be used in combination. For example, for lithium salts, lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), lithium perchlorate (LiClO ₄ ), trifluoro Lithium methanesulfonate (LiCF ₃ SO ₃ ), bis (trifluoromethanesulfonyl) imidolithium (LiN (SO ₂ CF ₃ ) ₂ ), tris (trifluoromethanesulfonyl) methyllithium (LiC (SO ₂ CF ₃ ) ₃ ), four Examples thereof include lithium chloroaluminate (LiAlCl ₄ ) and lithium hexafluorosilicate (LiSiF ₆ ).

  Preferred examples of the polymer compound include a polymer of vinylidene fluoride such as polyvinylidene fluoride containing the structural unit shown in Chemical Formula 1 or a copolymer of vinylidene fluoride and hexafluoropropylene. This is because the redox stability is high.

  Examples of the polymer compound include those formed by polymerizing a polymerizable compound. Examples of the polymerizable compound include those containing a vinyl group or a group obtained by substituting a part of hydrogen with a substituent such as a methyl group. Specifically, monofunctional acrylates such as acrylic acid esters, monofunctional methacrylates such as methacrylic acid esters, polyfunctional acrylates such as diacrylic acid esters or triacrylic acid esters, and polyfunctional acrylates such as dimethacrylic acid esters or trimethacrylic acid esters. There are functional methacrylate, acrylonitrile, methacrylonitrile, and the like. Among them, an ester having an acrylate group or a methacrylate group is preferable. This is because the polymerization proceeds easily and the reaction rate of the polymerizable compound is high. Moreover, as a polymeric compound, what does not contain an ether group is preferable. This is because if an ether group is present, lithium ions are coordinated to the ether group, thereby reducing the ionic conductivity. Examples of such a polymer compound include polyacrylic acid ester, polymethacrylic acid ester, polyacrylonitrile, or polymethacrylonitrile containing the structural unit shown in Chemical Formula 2.

（式中、Ｒ１は、Ｃ_j Ｈ2_j-1 Ｏ_k を表す。ｊ，ｋは、１≦ｊ≦８，０≦ｋ≦４の範囲内の整数である。）

(In the formula, R1 represents C _j H2 _j-1 O _{k. J} and k are integers in the range of 1 ≦ j ≦ 8, 0 ≦ k ≦ 4.)

  Any one of the polymerizable compounds may be used alone, but it is desirable to mix a monofunctional compound and a polyfunctional compound, or to use a polyfunctional compound singly or in combination of two or more. . This is because such a configuration makes it easy to achieve both the mechanical strength of the polymer compound formed by polymerization and the electrolyte solution retention.

  Furthermore, the thing which has a structure which polymerized at least 1 sort (s) of the high molecular compound from the group which consists of polyvinyl acetal and its derivative (s) is mentioned preferably.

  The polyvinyl acetal includes a structural unit containing an acetal group shown in Chemical Formula 3 (1), a structural unit containing a hydroxyl group shown in Chemical Formula 3 (2), and a structural unit containing an acetyl group shown in Chemical Formula 3 (3) In a repeating unit. Specifically, for example, R2 is hydrogen polyvinyl formal shown in Chemical Formula 3 (1), or R2 is propyl group polyvinyl butyral.

（Ｒ２は水素原子もしくは炭素数１〜３のアルキル基を表す。）

(R2 represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms.)

  The ratio of the acetal group in the polyvinyl acetal is preferably in the range of 60 mol% to 80 mol%. This is because the solubility with the solvent can be improved within this range, and the stability of the electrolyte can be further increased. Moreover, it is preferable that the weight average molecular weight of polyvinyl acetal exists in the range of 10,000 or more and 500,000 or less. This is because if the molecular weight is too low, the polymerization reaction does not proceed easily, and if it is too high, the viscosity of the electrolytic solution increases.

  The polymer compound may be a polymer obtained by polymerizing only polyvinyl acetal or one of its derivatives, or a polymer obtained by polymerizing two or more of them, and a copolymer with monomers other than polyvinyl acetal and its derivatives. But you can. Moreover, what was polymerized with the crosslinking agent may be used.

  The electrolyte 24 may be used as it is as a liquid electrolyte without holding the electrolytic solution in the polymer compound. In this case, the electrolytic solution is impregnated in the separator 23.

<2. Manufacturing method of secondary battery>
For example, the secondary battery can be manufactured as follows.

  First, for example, the positive electrode active material layer 21B is formed on the positive electrode current collector 21A to produce the positive electrode 21. The positive electrode active material layer 21B is prepared, for example, by mixing a positive electrode active material powder, a conductive material, and a binder to prepare a positive electrode mixture, and then using the positive electrode mixture in a solvent such as N-methyl-2-pyrrolidone. The positive electrode mixture slurry is dispersed to form a positive electrode mixture slurry, and the positive electrode mixture slurry is applied to the positive electrode current collector 21A, dried, and compression molded. Further, for example, in the same manner as the positive electrode 21, the negative electrode active material layer 22 </ b> B is formed on the negative electrode current collector 22 </ b> A to produce the negative electrode 22.

  Next, the positive electrode terminal 11 is attached to the positive electrode current collector 21A, and the negative electrode terminal 12 is attached to the negative electrode current collector 22A. Subsequently, the positive electrode 21 and the negative electrode 22 are laminated via the separator 23, wound in the longitudinal direction, and a protective tape is adhered to the outermost peripheral portion, thereby producing a wound body that is a precursor of the wound electrode body 20. . After that, the wound body is sandwiched between the exterior members 30, and the outer peripheral edge of the exterior member 30 is heat-sealed except for one side, and an electrolyte composition containing an electrolyte and a monomer that is a raw material for the polymer compound is obtained. inject. Next, after the remaining one side of the exterior member 30 is heat-sealed and sealed, the monomer is polymerized to form the electrolyte 24. Thereby, the secondary battery shown in FIGS. 1 and 2 is obtained.

  Further, instead of injecting the electrolyte composition into the exterior member 30 and polymerizing the monomer to form the electrolyte 24, the positive electrode 21 and the negative electrode 22 are produced, and then the electrolytic solution and the polymer compound are formed thereon. The electrolyte 24 may be formed, wound around the separator 23, and sealed in the exterior member 30.

  Further, when an electrolytic solution is used as the electrolyte 24, the wound body is produced as described above and sandwiched between the exterior members 30, and then the electrolytic solution is injected to seal the exterior member 30.

<3. Action and Effect of Secondary Battery>
In the secondary battery, when charged, for example, lithium ions are extracted from the positive electrode 21 and inserted in the negative electrode 22 through the electrolyte 24. On the other hand, when discharging is performed, for example, lithium ions are extracted from the negative electrode 22 and inserted in the positive electrode 21 through the electrolyte 24. At that time, since the above-mentioned bonded graphite material is included in the negative electrode active material layer 22B, a high capacity is obtained, and the generated gas is absorbed and swelling is suppressed.

As described above, according to the present embodiment, the primary particles are bonded to form the secondary particles so that the orientation planes are not parallel, and the pores having a pore diameter of 10 nm or more and 1 × 10 ⁵ nm or less are formed. Since the bonded graphite material having a volume of 0.5 cm ³ / g or more and 1.5 cm ³ / g or less is contained, the capacity can be improved and the gas generated by the side reaction or the like can be absorbed and swollen. Can be suppressed.

  In particular, when the ratio of the bonded graphite material in the negative electrode active material is set to 60% by mass or less, the cycle capacity maintenance rate can be improved while suppressing swelling.

Further, if the volume of pores having a pore diameter of 10 nm or more and 2 × 10 ³ nm or less is set to 0.1 cm ³ / g or more and 0.3 cm ³ / g or less, or the aspect ratio A / B of the secondary particles If the average value is made 4 or less, or the specific surface area of the bonded graphite material is made 5 m ² / g or less, a higher effect can be obtained.

  Further, specific embodiments of the present invention will be described in detail.

(Experimental Examples 1-1 to 1-5)
A secondary battery using the film-shaped exterior member shown in FIGS.

First, 0.5 mol of lithium carbonate and 1 mol of cobalt carbonate were mixed, and this mixture was fired in air at 900 ° C. for 5 hours to synthesize a lithium cobalt composite oxide (LiCoO ₂ ) as a positive electrode active material. Subsequently, 85% by mass of this lithium cobalt composite oxide powder, 5% by mass of artificial graphite as a conductive material, and 10% by mass of polyvinylidene fluoride as a binder were prepared, and then a positive electrode mixture was prepared. A positive electrode mixture slurry was prepared by dispersing in N-methyl-2-pyrrolidone. Subsequently, this positive electrode mixture slurry was applied to both surfaces of a positive electrode current collector 21A made of an aluminum foil having a thickness of 20 μm and dried, and then compression molded to form the positive electrode active material layer 21B, whereby the positive electrode 21 was produced. After that, the positive electrode terminal 11 was attached to the positive electrode 21.

  Further, 50 parts by mass of coke powder having an average particle diameter of 10 μm, 15 parts by mass of pitch, 10 parts by mass of silicon carbide (volatilization temperature 2500 ° C. to 3000 ° C.) and 10 parts by mass of coal tar are mixed, and 1 at 200 ° C. Stir for hours. Next, the mixture was pulverized to an average particle size of 20 μm, put into a mold and press-molded, to obtain a rectangular graphite precursor compact having a size of 15 mm × 25 cm × 6 cm. This graphite precursor compact was heat-treated at 1000 ° C. or higher in a nitrogen atmosphere, and further heat-treated at about 3000 ° C. in a nitrogen atmosphere to produce a bonded graphite material. At that time, in Experiments 1-1 to 1-5, the pore distribution, specific surface area, and aspect ratio A / B of the bonded graphite material were changed by changing the heat treatment temperature and time. Table 1 shows the pore distribution, specific surface area, and aspect ratio A / B of the produced bonded graphite material. The pore distribution is measured by the mercury intrusion method, the specific surface area is measured by the BET one-point method using nitrogen and nitrogen helium mixed gas as a carrier and reference, and the aspect ratio A / B is taken out by arbitrary 10 by SEM. The average value was calculated.

  Moreover, when it analyzed by the X-ray-diffraction method about the obtained bonded graphite material of Experimental example 1-1 to 1-5, it was confirmed that all are graphite. Further, a cross-section of this bonded graphite material was taken out using a focused ion beam and observed with a transmission electron microscope. As a result, a plurality of primary particles were combined to form secondary particles. It was confirmed that at least a part of the orientation plane of the hexagonal mesh surface was non-parallel.

  The prepared bonded graphite material is used as a negative electrode active material, and 95% by mass of the negative electrode active material powder and 5% by mass of polyvinylidene fluoride as a binder are mixed to prepare a negative electrode mixture, and then N— which is a solvent. A negative electrode mixture slurry was prepared by dispersing in methyl-2-pyrrolidone. Next, this negative electrode mixture slurry was applied to both surfaces of a negative electrode current collector 22A made of a copper foil having a thickness of 15 μm and dried, and then compression molded to form a negative electrode active material layer 22B, whereby a negative electrode 22 was produced. FIG. 3 representatively shows a cross-sectional photograph of the negative electrode active material layer 22B produced in Experimental Example 1-3. As shown in FIG. 3, it can be seen that in the bonded graphite material, a plurality of primary particles are combined to form secondary particles such that the orientation planes are non-parallel.

  Subsequently, after attaching the negative electrode terminal 12 to the negative electrode 22, the prepared positive electrode 21 and negative electrode 22 are closely attached via a separator 23 made of a microporous polyethylene film having a thickness of 25 μm, and wound in the longitudinal direction. Was made. After that, the produced wound body was loaded between the exterior members 30, and the outer peripheral edge of the exterior member 30 was heat-sealed except for one side. The exterior member 30 was a moisture-proof aluminum laminate film in which a 25 μm thick nylon film, a 40 μm thick aluminum foil, and a 30 μm thick polypropylene film were laminated in order from the outermost layer.

  Next, an exterior member is prepared by dissolving an electrolytic solution in which lithium hexafluorophosphate is dissolved at a concentration of 1 mol / l in a solvent in which ethylene carbonate and diethyl carbonate are mixed at a mass ratio of ethylene carbonate: diethyl carbonate = 3: 7. The secondary battery was obtained by injecting into the interior of 30 and thermally fusing the remaining one side of the exterior member 30.

Further, as Comparative Example 1-1 with respect to Experimental Examples 1-1 to 1-5, Experimental Example 1 is used except that artificial graphite particles that are not granulated are used as the negative electrode active material instead of the bonded graphite material. Secondary batteries were fabricated in the same manner as -1 to 1-5. As Comparative Examples 1-2 and 1-3, bonded graphite materials in which the pore distribution, the specific surface area, and the aspect ratio A / B were changed by changing the heat treatment temperature, raw material composition ratio, and time during graphitization were used. A secondary battery was fabricated in the same manner as in Experimental Examples 1-1 to 1-5 except that they were used. For Comparative Examples 1-1 to 1-3, the pore distribution, specific surface area, and aspect ratio A / B were measured in the same manner as in Experimental Examples 1-1 to 1-5. The results are also shown in Table 1. In the artificial graphite used in Comparative Example 1-1, pores having a pore diameter of 10 nm to 1 × 10 ⁵ nm are not measured, and the specific surface area and aspect ratio A / B are those of primary particles.

  About the produced secondary battery of Experimental example 1-1 to 1-5 and Comparative example 1-1 to 1-3, it charged / discharged at 23 degreeC, and calculated | required the rated capacity and the discharge capacity maintenance factor of the 300th cycle. Charging was performed at a constant current and constant voltage of 100 mA for 15 hours up to an upper limit of 4.2 V, and discharging was performed at a constant current of 100 mA up to a final voltage of 2.5 V. The rated capacity was the discharge capacity at the first cycle, and the discharge capacity at the 300th cycle was determined by the ratio of the discharge capacity at the 300th cycle to the rated capacity, (discharge capacity at the 300th cycle / rated capacity) × 100.

  In addition, for each secondary battery that was charged and discharged for the first time under the above-described conditions separately, after measuring the thickness of the battery, it was charged again to 4.31 V for 3 hours and stored in a thermostatic bath at 60 ° C. for 1 month. The thickness of the battery after storage was measured. A value obtained by subtracting the battery thickness before storage from the battery thickness after storage was determined as the swelling after storage. The obtained results are shown in Table 1.

As shown in Table 1, according to Experimental Examples 1-1 to 1-5, compared with Comparative Examples 1-1 to 1-3, the rated capacity is equal to or higher, the discharge capacity retention rate is improved, and the swelling is increased. The amount has become smaller. That is, a high capacity can be obtained by using a bonded graphite material having a pore volume of not less than 10 nm and not more than 1 × 10 ⁵ nm having a volume of not less than 0.5 cm ³ / g and not more than 1.5 cm ³ / g. At the same time, it was found that cycle characteristics can be improved and swelling can be suppressed. It was also found that the average aspect ratio A / B of the secondary particles is preferably 4 or less, and the specific surface area of the bonded graphite material is preferably 5 m ² / g or less.

Furthermore, as can be seen by comparing Experimental Examples 1-1 to 1-5, the rated capacity and cycle characteristics are improved and then decreased as the volume of pores having a pore diameter of 10 nm or more and 2 × 10 ³ nm or less decreases. There was a tendency to increase, and the amount of swelling decreased and then increased. That is, it has been found that it is more preferable that the volume of pores having a pore diameter of 10 nm or more and 2 × 10 ³ nm or less is 0.1 cm ³ / g or more and 0.3 cm ³ / g or less.

(Experimental examples 2-1 to 2-18)
A secondary battery was fabricated in the same manner as in Experimental Example 1-3, except that mesocarbon microbeads, which are artificial graphite, or natural graphite was mixed and used in addition to the bonded graphite material. That is, the physical properties of the bonded graphite material used were as follows in Experimental Example 1-3: the pore volume with a pore diameter of 10 nm or more and 1 × 10 ⁵ nm or less was 1.0 cm ³ / g, and the pore diameter was 10 nm or more and 2 × 10 nm. The volume of the following pores is 0.2 cm ³ / g, the specific surface area is 3.5 m ² / g, and the aspect ratio A / B of the secondary particles is 2.1 on average. The mixing ratio of the bonded graphite material and the other negative electrode active material was changed as shown in Table 2 in Experimental Examples 2-1 to 2-18.

The specific surface area of the mesocarbon microbeads used in Experimental Examples 2-1 to 2-9 is 0.7 m ² / g, and the aspect ratio A / B is 1.1, which is used in Experimental Examples 2-10 to 2-18. The natural graphite had a specific surface area of 4 m ² / g and an aspect ratio A / B of 7. These are all primary particle values, and pores having a pore diameter of 10 nm or more and 1 × 10 ⁵ nm or less were not measured for natural graphite and mesocarbon microbeads.

  Further, as Comparative Example 2-1 with respect to Experimental Examples 2-1 to 2-18, except that natural graphite was used as the negative electrode active material instead of the bonded graphite material, the other was the same as Experimental Example 1-3. A secondary battery was produced. Natural graphite is the same as that used in Experimental Examples 2-10 to 2-18.

  For the fabricated secondary batteries of Experimental Examples 2-1 to 2-18 and Comparative Example 2-1, in the same manner as in Experimental Example 1-3, the rated capacity, the discharge capacity maintenance rate at the 300th cycle, The amount of swelling was examined. The obtained results are shown in Table 2 together with the results of Experimental Example 1-3 and Comparative Example 1-1.

  As shown in Table 2, also in Experimental Examples 2-1 to 2-12 in which other materials are mixed as the negative electrode active material, the rated capacity is equal to or higher than that of Experimental Example 1-3, and the discharge capacity maintenance rate The amount of swelling was able to be reduced. Moreover, the discharge capacity retention rate tended to decrease after increasing as the content of the bonded graphite material was increased. That is, it was found that the ratio of the bonded graphite material in the negative electrode active material is preferably in the range of more than 0% by mass and 60% by mass or less, and more preferably in the range of 3% by mass to 30% by mass.

(Experimental examples 3-1 to 3-6)
A secondary battery was fabricated in the same manner as in Experimental Example 2-2 except that instead of the electrolytic solution, a gel electrolyte 24 in which the electrolytic solution was held in a polymer compound was used. That is, the negative electrode active material was used by mixing 50% by mass of the bonded graphite material similar to Experimental Example 1-3 and 50% by mass of mesocarbon microbeads. In Experimental Example 3-1, the electrolyte 24 is prepared by dissolving a copolymer of vinylidene fluoride and hexafluoropropylene and an electrolytic solution in a mixed solvent and applying the solution to the positive electrode 21 and the negative electrode 22 to volatilize the mixed solvent. Was formed. As the electrolytic solution, a solution obtained by dissolving lithium hexafluorophosphate at a concentration of 1 mol / l in a solvent in which 60% by mass of ethylene carbonate and 40% by mass of propylene carbonate were mixed was used.

  In Experimental Example 3-2, a polymerizable compound having three structural parts a, b, and c shown in Chemical Formula 4 at a molar ratio of a: b: c = 2: 3: 5 was used, and an electrolytic solution was used. And the electrolyte 24 was formed by polymerizing the polymerizable compound. The composition of the electrolytic solution is the same as in Experimental Example 2-2. In a solvent in which ethylene carbonate and diethyl carbonate are mixed at a mass ratio of ethylene carbonate: diethyl carbonate = 3: 7, 1 mol / liter of lithium hexafluorophosphate is added. dissolved at a concentration of 1.

  In Experimental Example 3-3, trimethylolpropane triacrylate shown in Chemical Formula 5 and neopentylglycol diacrylate shown in Chemical Formula 6 were used at a mass ratio of 3: 7 as a polymerizable compound, and mixed with the electrolytic solution. And after inject | pouring in the inside of the exterior member 30, the electrolyte 24 was formed by polymerizing a polymeric compound. The composition of the electrolytic solution is the same as in Experimental Example 2-2.

  In Experimental Example 3-4, the compound shown in Chemical Formula 7 was used as the polymerizable compound, mixed with the electrolytic solution, injected into the exterior member 30, and then the polymerizable compound was polymerized to form the electrolyte 24. . The composition of the electrolytic solution is the same as in Experimental Example 2-2.

  In Experimental Example 3-5, polyvinylidene fluoride was applied to the surface of the separator 23, a wound body was prepared and housed in the exterior member 30, and then the electrolyte 24 was formed by injecting an electrolytic solution. The composition of the electrolytic solution is the same as in Experimental Example 2-2.

  In Experimental Example 3-6, after the polyvinyl formal and the electrolytic solution were mixed and injected into the exterior member 30, the electrolyte 24 was formed by polymerizing the polyvinyl formal. The composition of the electrolytic solution is the same as in Experimental Example 2-2.

  As Comparative Examples 3-1 to 3-6 with respect to Experimental Examples 3-1 to 3-6, except that the same artificial graphite as Comparative Example 1-1 was used as the negative electrode active material, the others were Experimental Examples 3-1 to A secondary battery was fabricated in the same manner as in 3-6.

  For Experimental Examples 3-1 to 3-6 and Comparative Examples 3-1 to 3-6, as in Experimental Example 2-2, the rated capacity, the discharge capacity retention rate at the 300th cycle, and the swelling amount after storage I investigated. The obtained results are shown in Table 3.

  As shown in Table 3, according to Experimental Examples 3-1 to 3-6, compared with Comparative Examples 3-1 to 3-6, the rated capacity and the discharge capacity retention rate are improved, and the amount of swelling is reduced. It was. That is, it was found that the same effect can be obtained also when the so-called gel electrolyte 24 is used.

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-described embodiments and examples, a plurality of primary particles made of graphite having pores are combined to form secondary particles at least partially so that the orientation planes are not parallel to each other. Using a bonded graphite material in which the volume of pores having a pore diameter of 10 nm or more and 1 × 10 ⁵ nm or less estimated by a mercury intrusion method is 0.5 cm ³ / g or more and 1.5 cm ³ / g or less per unit mass Although the battery which produced No. 22 was demonstrated, even if it does not produce a battery using this bonded graphite material, it should just contain this bonded graphite material at the time of manufacture or use.

  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 used. . 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 to be included, or a mixture of these with an electrolyte solution.

  Further, in the above-described embodiments and examples, the case where the wound electrode body in which the positive electrode 21 and the negative electrode 22 are wound is provided in the exterior member 30 is described. However, the positive electrode 21 and the negative electrode 22 are laminated in one or more layers. You may make it provide what was done.

  In addition, in the embodiments and examples described above, a battery using lithium as an electrode reactant has been described. However, other alkali metals such as sodium (Na) or potassium (K), or magnesium or calcium (Ca) The present invention can also be applied to the case of using an alkaline earth metal or another light metal such as aluminum. In addition, the present invention is not limited to the secondary battery, and can be similarly applied to other batteries such as a primary battery.

  DESCRIPTION OF SYMBOLS 11 ... Positive electrode terminal, 12 ... Negative electrode terminal, 20 ... Winding electrode body, 21 ... Positive electrode, 21A ... Positive electrode collector, 21B ... Positive electrode active material layer, 22 ... Negative electrode, 22A ... Negative electrode collector, 22B ... Negative electrode active Material layer, 23 ... separator, 24 ... electrolyte, 25 ... protective tape, 30 ... exterior member, 31 ... adhesion film.

Claims (17)

Bonded graphite material in which a plurality of primary particles made of graphite having pores are bonded so that orientation planes thereof are non-parallel to each other at least partially to form secondary particles, and mesocarbon microbeads or natural Containing graphite,
The volume of pores having a pore diameter of 10 nm or more and 1 × 10 ⁵ nm or less estimated by the mercury intrusion method of the bonded graphite material is 0.5 cm ³ / g or more and 1.5 cm ³ / g or less per unit mass,
The ratio of the combined graphite material to the total of the combined graphite material and the mesocarbon microbeads or natural graphite is 3% by mass or more and 30% by mass or less.
Negative electrode active material.   2. The negative electrode active according to claim 1, wherein the average value of the aspect ratio represented by A / B is 4 or less, where A is the length in the major axis direction of the secondary particles and B is the length in the minor axis direction. material. 3. The negative electrode active material according to claim 1, wherein the combined graphite material has a specific surface area of 5 m ² / g or less.   4. The negative electrode active material according to claim 1, wherein the combined graphite material is obtained by mixing at least coke and a binder pitch and heat-treating. 5.   4. The negative electrode active material according to claim 1, wherein the bonded graphite material is obtained by granulating the primary particles by a wet method or a dry method. 5.   The negative electrode active material according to claim 5, wherein the bonded graphite material is obtained by granulating the primary particles and then performing isotropic pressure treatment. A negative electrode active material layer on the negative electrode current collector,
The negative electrode active material layer has a plurality of primary particles made of graphite having pores as a negative electrode active material, so that at least part of the primary particles are bonded so that the orientation planes are not parallel to each other, thereby forming secondary particles. Containing bound graphite material and mesocarbon microbeads or natural graphite,
The volume of pores having a pore diameter of 10 nm or more and 1 × 10 ⁵ nm or less estimated by the mercury intrusion method of the bonded graphite material is 0.5 cm ³ / g or more and 1.5 cm ³ / g or less per unit mass,
The ratio of the combined graphite material to the total of the combined graphite material and the mesocarbon microbeads or natural graphite is 3% by mass or more and 30% by mass or less.
Negative electrode. An electrolyte is provided with a positive electrode and a negative electrode,
In the negative electrode, as the negative electrode active material, a plurality of primary particles made of graphite having pores are combined to form secondary particles in such a manner that at least some of the primary particles are bonded so that the orientation planes are not parallel to each other. Containing material and mesocarbon microbeads or natural graphite,
The volume of pores having a pore diameter of 10 nm or more and 1 × 10 ⁵ nm or less estimated by the mercury intrusion method of the bonded graphite material is 0.5 cm ³ / g or more and 1.5 cm ³ / g or less per unit mass,
The ratio of the combined graphite material to the total of the combined graphite material and the mesocarbon microbeads or natural graphite is 3% by mass or more and 30% by mass or less.
battery.   The bonded graphite material has an average aspect ratio represented by A / B of 4 or less, where A is the length in the major axis direction of the secondary particles and B is the length in the minor axis direction. Item 9. The battery according to Item 8. 10. The battery according to claim 8, wherein a specific surface area of the bonded graphite material is 5 m ² / g or less.   The battery according to any one of claims 8 to 10, wherein the bonded graphite material is obtained by mixing at least coke and a binder pitch and performing heat treatment.   The battery according to any one of claims 8 to 10, wherein the bonded graphite material is obtained by granulating the primary particles by a wet method or a dry method.   The battery according to claim 12, wherein the bonded graphite material is obtained by granulating the primary particles and then performing an isotropic pressure treatment.   The battery according to any one of claims 8 to 13, wherein the positive electrode, the negative electrode, and the electrolyte are housed inside a film-shaped exterior member.   The battery according to any one of claims 8 to 14, wherein the electrolyte includes an electrolytic solution and a polymer containing vinylidene fluoride as a component.   The battery according to any one of claims 8 to 14, wherein the electrolyte includes an electrolytic solution and a polymer having a structure obtained by polymerizing a polymerizable compound having an acrylate group or a methacrylate group.   The battery according to any one of claims 8 to 14, wherein the electrolyte includes an electrolytic solution and a polymer having a structure obtained by polymerizing at least one selected from the group consisting of polyvinyl acetal and derivatives thereof. .

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