JP2012227047A - Carbon material for secondary cell and manufacturing method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode structure capable of concurrently achieving high discharge capacity, high charge/discharge cycle characteristic and high charge/discharge efficiency as a secondary cell.SOLUTION: A carbon material for secondary cell includes a tabular particle with an average particle thickness of 2-500 nm and an average aspect ratio (average particle diameter/average particle thickness) of not less than 10.

Description

  The present invention generally relates to a carbon material for a secondary battery and a method for producing the same, and more specifically, a carbon material for a secondary battery, and a conductive agent, a negative electrode material, an electrode mixture, an electrode and a secondary battery including the same, and a secondary battery. The present invention relates to a method for producing a carbon material for a secondary battery and a negative electrode material for a secondary battery.

  As electronic devices become more portable and cordless, there is a demand for higher secondary battery capacity, higher cycle characteristics (longer life), and the like. In particular, as secondary batteries for small portable devices such as mobile phones and video cameras, in recent years, lithium ion secondary batteries have attracted attention, and lithium ion secondary batteries have become smaller and lighter and have higher energy density. It has been demanded.

  For example, Patent Document 1 discloses a negative electrode for a lithium secondary battery including a negative electrode active material capable of inserting and extracting lithium, a conductive carbon material, and a binder, and the negative electrode active material has a graphite structure (002) by powder X-ray diffraction. ) Is a graphite material using natural graphite or artificial graphite having a surface spacing d (002) of 0.335 to 0.337 nm, and the conductive carbon material has an average fiber diameter of 1 to 200 nm and a hollow structure inside. And has a structure in which graphene sheets are laminated in a direction perpendicular to the length direction of the fiber, and the plane spacing d (002) of the (002) plane of the graphite structure by powder X-ray diffraction is 0.336-0. Lithium secondary, which is a vapor grown carbon fiber in the range of 345 nm, and the vapor grown carbon fiber is contained in an amount of 0.1 to 10% by mass of the whole negative electrode without forming an aggregate having a size of 10 μm or more. Battery negative electrode It has been proposed, it is described that it is possible to provide an excellent lithium secondary battery long cycle life, the large current characteristics.

  Patent Document 2 includes a mixture of particles containing a compound containing a silicon atom and / or tin atom capable of inserting / extracting lithium ions, and vapor grown carbon fiber. Proposal of material, lithium ion secondary battery with large charge / discharge capacity, excellent charge / discharge cycle characteristics, small irreversible capacity, and low internal resistance, especially internal resistance at low temperature It is described that a secondary battery can be manufactured.

  However, in situations where electronic devices are becoming more portable, more cordless, and more compact, secondary batteries, especially lithium ion secondary batteries, are required to have higher capacity and higher cycle characteristics (longer life). This is the current situation.

JP 2007-42620 A JP 2004-178922 A

  Conventional graphite or hard carbon has a limit in charge / discharge capacity per unit mass (volume), so a metal containing silicon (Si) or tin (Sn) as a negative electrode active material for realizing further higher capacity System active materials are attracting attention. However, such a high-capacity metal active material is alloyed with lithium (Li) at the time of charging, so that the volume expands by up to 400% as compared with that before charging. Therefore, when the charge and discharge are repeated, the high capacity metal active material repeatedly expands / contracts with the absorption and release of Li, so that the negative electrode active material slides off from the electrode or the negative electrode active material breaks and is damaged. The structure of the negative electrode cannot be maintained. Such a deterioration phenomenon is called cycle deterioration, which leads to electrical isolation and capacity reduction of the negative electrode active material.

  In view of the above problems, an object of the present invention is to provide an ideal negative electrode structure that simultaneously achieves high discharge capacity, high charge / discharge cycle characteristics, and high charge / discharge efficiency as a secondary battery. Specifically, by reducing the volume expansion effect of the negative electrode active material, the sliding and damage of the active material is minimized, and the electric power supply to the active material is maintained, so that the capacity due to repeated charge and discharge is maintained. It aims at providing the novel negative electrode structure which prevents a fall.

  As a result of intensive studies to achieve the above object, the present inventors have surprisingly achieved by using a carbon material containing plate-like particles having a specific average particle thickness and a specific average aspect ratio. The present inventors have found that high capacity, high charge / discharge cycle characteristics and high charge / discharge efficiency of a secondary battery, particularly a lithium ion secondary battery, can be simultaneously achieved, and the present invention has been completed.

That is, the present invention provides the inventions described in the following items (1) to (14).
(1) A carbon material for a secondary battery comprising plate-like particles having an average particle thickness in the range of 2 nm to 500 nm and an average aspect ratio (average particle diameter / average particle thickness) of 10 or more. .
(2) The carbon material for a secondary battery according to (1), wherein the plate-like particles have an average particle diameter in the range of 0.5 μm to 500 μm.
(3) The carbon material for a secondary battery according to (1) or (2), wherein the plate-like particles are produced by carbonizing a thermosetting resin.
(4) A conductive agent for a secondary battery comprising the carbon material for a secondary battery according to any one of (1) to (3).
(5) The carbon material for a secondary battery according to any one of items (1) to (3), and carbon, metal, metalloid, or alloy thereof capable of occluding and releasing lithium ions, A negative electrode material for a secondary battery comprising oxide, nitride, or carbide-containing particles, wherein the particles are disposed between the plate-like particles.
(6) The negative electrode material for a secondary battery according to (5), wherein the metal or metalloid contains at least one element selected from the group consisting of silicon, tin, germanium, and aluminum.
(7) The carbon material for the secondary battery according to any one of the items (1) to (3) and / or the conductive agent for the secondary battery according to the item (4) and / or ( An electrode mixture for a secondary battery comprising the negative electrode material for a secondary battery according to item 5) or (6).
(8) A secondary battery electrode comprising the secondary battery electrode mixture according to item (7).
(9) A secondary battery comprising the secondary battery electrode according to item (8).
(10) The secondary battery according to item (9), which is a lithium ion secondary battery.
(11) A laminate in which a thermosetting resin layer is provided on at least one side of a support sheet made of a thermoplastic resin is carbonized until the support sheet substantially disappears, The manufacturing method of the carbon material for secondary batteries as described in (1) term.
(12) The method for producing a carbon material for a secondary battery according to (11), wherein the average particle thickness of the plate-like particles is controlled by adjusting the thickness of the thermosetting resin layer.
(13) One or more laminates in which a thermosetting resin layer is provided on at least one surface of a support sheet made of a thermoplastic resin, and carbon, metal, metalloid, or these capable of occluding and releasing lithium ions One or more layers containing particles containing an alloy, oxide, nitride or carbide are alternately arranged to obtain a composite laminate, and the composite laminate is carbonized until the support sheet substantially disappears. The manufacturing method of the negative electrode material for secondary batteries as described in the item (5).
(14) The method for producing a negative electrode material for a secondary battery according to (13), wherein the average particle thickness of the plate-like particles is controlled by adjusting the thickness of the thermosetting resin layer.

  According to the present invention, a specific carbon material for a secondary battery constitutes a conductive carbon network, thereby mitigating the influence of volume expansion of the negative electrode active material, and as a result, sliding and damage of the active material can be minimized. In addition, the electric supply to the active material is maintained, and the capacity reduction (cycle deterioration) due to repeated charge and discharge of the secondary battery is remarkably suppressed.

3 is a scanning electron microscope (SEM) photograph of the carbon material 3 obtained in Example 3. FIG. 4 is a SEM photograph of carbon material 4 obtained in Example 4. 6 is a SEM photograph of a cross section of an electrode obtained in Example 6.

  The carbon material for a secondary battery according to the present invention includes plate-like particles having an average particle thickness in the range of 2 nm to 500 nm and an average aspect ratio (average particle diameter / average particle thickness) of 10 or more. It consists of The carbon material for a secondary battery according to the present invention has an average particle thickness of 2 nm or more, so that the amount of Li chemically adsorbed on the surface is reduced, thereby suppressing an increase in irreversible capacity (charge capacity-discharge capacity). Can do. On the other hand, when the average particle thickness is 500 nm or less, the charge capacity per unit volume can be maintained sufficiently high. The average particle thickness of the carbon material for a secondary battery according to the present invention is preferably in the range of 20 nm to 250 nm, and more preferably in the range of 60 nm to 150 nm. Here, the average particle thickness according to the present invention is a simple average value obtained by randomly selecting 30 plate-like particles visible in an image obtained by SEM observation and measuring the thickness of each particle.

  Furthermore, the carbon material for a secondary battery according to the present invention is a plate-like particle having an average aspect ratio (average particle diameter / average particle thickness) of 10 or more. In addition, the conductive network formed of the carbon material is held without being cut, and thus the high-capacity active material is prevented from slipping, and the capacity reduction due to repeated charge and discharge is suppressed. Here, the conductive network means a connected carbon body having conductivity necessary for exchanging electricity between the high-capacity active material and the current collector. A high-capacity active material repeatedly expands and contracts due to charge and discharge, and when the conductive network is cut by the expansion and contraction, the high-capacity active material and the current collector are no longer able to exchange electricity. Does not charge / discharge, so the charge / discharge cycle characteristics of the secondary battery deteriorate. The average aspect ratio of the plate-like particles of the carbon material for a secondary battery according to the present invention is preferably 20 or more, and more preferably 100 or more.

  The carbon material for a secondary battery according to the present invention is generally defined by the average particle thickness and the average aspect ratio, and more specifically, the average particle diameter of the plate-like particles is 0.5 μm to 500 μm. It is preferable to be within the range. When the average particle diameter is within the above range, the conductive network formed by the carbon material becomes stronger, and the cycle characteristics due to repeated charge / discharge of the secondary battery are further improved. Here, the average particle diameter according to the present invention is a random selection of 30 plate-like particles visible in an image obtained by SEM observation, the major axis of each plate-like particle is measured, and this is used as the particle diameter. Average particle diameter.

  The carbon material for a secondary battery according to the present invention having the characteristic shape as described above is obtained by providing a laminate in which a thermosetting resin layer is provided on at least one surface of a support sheet made of a thermoplastic resin. Can be conveniently produced by a method of carbonization until substantially disappears. According to this method, the average particle thickness of the plate-like particles constituting the carbon material for a secondary battery can be easily controlled by adjusting the thickness of the thermosetting resin layer. The thermoplastic resin used for the support sheet is not particularly limited as long as it efficiently disappears during the carbonization treatment. Specific examples include polyethylene, polystyrene, polyacrylonitrile, acrylonitrile-styrene (AS) resin, acrylonitrile-butadiene. -Styrene (ABS) resin, polypropylene, vinyl chloride, methacrylic resin, polyethylene terephthalate, polyamide, polycarbonate, polyacetal, polyphenylene ether, polybutylene terephthalate, polyphenylene sulfide, polysulfone, polyethersulfone, polyetheretherketone, polyetherimide, Examples thereof include polyamideimide, polyimide, polyphthalamide, cycloolefin polymer having an alicyclic structure, and the like. Among these, a resin having a melting point higher than the temperature at which the thermosetting resin is cured is preferable, and polypropylene and cycloolefin polymer are preferable in terms of cost and handleability. In order to maintain Tg and shape retention in the thermoplastic resin, an alicyclic low molecular weight compound, a crystal nucleating agent, a nucleating agent, etc. are mixed, or an anti-blocking agent is used to prevent blocking of the support sheet. May be mixed. The thickness of the support sheet may be generally in the range of several μm to several hundred μm. The thickness of the support sheet may be appropriately set from the viewpoint of ease of handling as a laminate and easiness of disappearance during carbonization, but considering the handleability and the shape maintainability of the thermosetting resin, the thickness of the support sheet is 0. It is preferably 1 μm or more, more preferably 0.5 μm or more.

  The thermosetting resin provided on the support sheet is not particularly limited as long as it efficiently carbonizes during carbonization to generate plate-like particles. Specific examples include novolak type phenol resins and resol type phenols. Examples thereof include resins, melamine resins, furan resins, aniline resins, and modified products thereof. In preparing the laminate, a solution obtained by dissolving the thermosetting resin in an appropriate solvent may be applied to the support sheet by a coating method such as dipping, brushing, spraying, or the like. By adjusting the film thickness (thermosetting resin thickness) during coating of the thermosetting resin, the average particle thickness of the plate-like particles obtained after carbonization can be easily controlled. The coating thickness can be adjusted by appropriately changing the concentration of the thermosetting resin solution, the number of coatings, and the like.

  Conditions for the carbonization treatment are not particularly limited as long as the thermosetting resin is carbonized and the thermoplastic resin substantially disappears. Generally, carbonization can be performed by heat-treating the above laminate at a temperature of 800 ° C. to 2000 ° C. for 10 minutes to 24 hours in an atmosphere of an inert gas such as nitrogen or argon. Thereafter, the carbonized thermosetting resin is pulverized by a pulverization method such as a ball mill, and further subjected to a classification treatment as necessary, whereby plate-like particles having a desired average particle diameter can be obtained.

  The conductive agent for a secondary battery according to the present invention includes the carbon material for a secondary battery, and may further include a conductive auxiliary agent as necessary. As the conductive auxiliary agent, those generally known for secondary batteries such as graphite, acetylene black, ketjen black, conductive resin, conductive fiber, etc. can be used.

The negative electrode material for a secondary battery according to the present invention includes the carbon material for a secondary battery, the conductive auxiliary agent as necessary, and carbon, metal, metalloid, or an alloy thereof capable of occluding and releasing lithium ions, And particles containing an oxide, nitride or carbide, and the particles are arranged between the plate-like particles. The particles capable of occluding and releasing lithium ions, that is, the active material, preferably have an average primary particle size of 1 μm or less from the viewpoints of lithium diffusion reaction, relaxation of the effects of volume expansion, etc. Is more preferably 100 nm or less in nano size. Specific examples of the active material included in the negative electrode material for a secondary battery according to the present invention include silicon (Si), tin (Sn), germanium (Ge), aluminum (Al), silicon oxide (SiOx), and tin monoxide (SnO). ), Tin dioxide (SnO ₂ ), iron oxide (Fe ₂ O ₃ ), tin nitride (SnN), tin carbide (SnC), germanium monoxide (GeO), germanium nitride (Ge ₃ N ₄ ), germanium carbide (GeC) ), Aluminum oxide (Al ₂ O ₃ ), aluminum nitride (AlN), aluminum carbide (Al ₄ C ₃ ), aluminum lithium alloy (Al—Li system), and the like, but are not limited thereto. Among these, Si, SiO _x (X = 0.1 or more and less than 2), Fe ₂ O _{3 and the} like are preferable in that a higher capacity can be achieved. An active material may be used independently or may use 2 or more types together.

In the present specification, the carbon material for a secondary battery according to the present invention is mainly described as a material included in the negative electrode material, but it can also be used as a material included in the positive electrode material. In that case, as the active material contained in the positive electrode material, cobalt composite oxide such as LiCoO ₂ , manganese composite oxide such as LiMn ₂ O ₄ and Li ₂ MnO ₃ , nickel composite oxide such as LiNiO ₂ , LiFePO ₄ , LiFeVO ₄ , and other iron complex oxides, Li (Ni, Co) O ₂ , Li (Ni, Mn) O ₂ , Li (Co, Mg) O ₂ , Li (Ni, Co, Mn) O ₂ , Li A composite oxide such as (Ni, Co, Al) O ₂ , Li (Co, Mg, Al) O ₂ , or Li (Ni, Co, Mn, Al) O ₂ may be used.

  The negative electrode material for a secondary battery according to the present invention includes the carbon material for a secondary battery, the conductive auxiliary agent as necessary, and carbon, metal, metalloid, or an alloy thereof capable of occluding and releasing lithium ions, It can be produced by simply mixing particles containing oxide, nitride or carbide. The mixing method may be either a dry method or a wet method, and examples thereof include a rotating ball mill, a planetary ball mill, a disperser, and a homogenizer. By using the carbon material for a secondary battery according to the present invention, a negative electrode material for a secondary battery according to the present invention in which the particles are arranged between plate-like particles can be obtained by a general mixing method.

  The negative electrode material for a secondary battery according to the present invention includes one or more laminates in which a thermosetting resin layer is provided on at least one side of a support sheet made of a thermoplastic resin, and carbon capable of inserting and extracting lithium ions. Alternatively, a composite laminate is obtained by alternately arranging one or more layers containing particles containing metal, metalloid or alloys thereof, oxides, nitrides or carbides. It can manufacture conveniently by the method of carbonizing until it lose | disappears substantially. According to this method, the average particle thickness of the plate-like particles constituting the negative electrode material for a secondary battery can be easily controlled by adjusting the thickness of the thermosetting resin layer. The thermoplastic resin, the thickness of the support sheet, the thermosetting resin, the production of the laminate, the adjustment of the coating thickness, and the like are as described above for the method for producing the carbon material for a secondary battery according to the present invention. One or more layers containing particles capable of occluding / releasing lithium ions, that is, one or more layers containing an active material are coated with a dispersion (slurry) obtained by dispersing the active material in an appropriate dispersion medium, such as dipping or brushing. Similarly, it can be produced by obtaining an active material carrying sheet by applying it to a support sheet made of a thermoplastic resin. Subsequently, a laminated body including a required number of thermosetting resin layers and an active material carrying sheet can be alternately arranged to form a composite laminated body.

  As the conditions for the carbonization treatment of the composite laminate, as described above for the method for producing the carbon material for a secondary battery according to the present invention, the thermosetting resin is carbonized and the thermoplastic resin is substantially lost. If it is a thing, there will be no restriction | limiting in particular. Generally, carbonization can be performed by heat-treating the composite laminate at a temperature of 800 ° C. to 2000 ° C. for 10 minutes to 24 hours in an atmosphere of an inert gas such as nitrogen or argon. An active material is disposed between the carbonized thermosetting resins, and this is pulverized by a pulverizing method such as a ball mill, and further subjected to a classification treatment as necessary, thereby obtaining a plate shape having a desired average particle diameter. And particles containing carbon or metal or metalloid or alloys thereof, oxides, nitrides or carbides capable of occluding and releasing lithium ions, and the particles are interposed between the plate-like particles. The arranged negative electrode material can be obtained.

  The electrode mixture for a secondary battery according to the present invention comprises the above-mentioned negative electrode material for a secondary battery, and may further contain a binder, a viscosity modifier and the like as necessary. The secondary battery electrode mixture may be prepared by using a conventionally known method using a planetary mixer, three rolls, etc., and, if necessary, a binder, water, and the like. The slurry can be prepared by adding a solvent and drying, and further adjusting the viscosity by adding a viscosity modifier as necessary, and then preparing a slurry having a predetermined viscosity with an appropriate solvent or dispersion medium. When the secondary battery negative electrode material is prepared by simply mixing the secondary battery carbon material and the active material particles, the binder, water, solvent, viscosity modifier, etc. are added in any order. You may prepare an electrode mixture at once by adding. Examples of the binder include carboxymethylcellulose, polyvinylidene fluoride resin, polytetrafluoroethylene, styrene / butadiene copolymer, polyimide resin, polyamide resin, polyvinyl alcohol, polyvinyl butyral, polyacrylic acid or an alkali salt thereof, polyamic acid, etc. Is mentioned. These may be modified by surface modification or the like. The solvent or dispersion medium is not particularly limited as long as it is a material that can be uniformly mixed, and examples thereof include water, alcohols such as methanol and ethanol, N-methyl-2-pyrrolidone, and acetonitrile. These may be modified by surface modification or the like.

  The electrode for a secondary battery according to the present invention can be produced by a conventionally known method using the electrode mixture for a secondary battery. Specifically, in the secondary battery electrode according to the present invention, the secondary battery electrode mixture is coated on a current collector such as a copper foil or other metal foil, and the coating has a thickness of several μm to several hundred μm. And the coating is heat-treated at about 50 to 200 ° C. to remove the solvent or the dispersion medium.

  The secondary battery according to the present invention is not particularly limited as long as it is a chemical battery that can be used by repeated charging and discharging, and examples thereof include a lithium ion secondary battery, a lead storage battery, a nickel-cadmium battery, etc., among which a lithium ion secondary battery A battery is preferred. The secondary battery according to the present invention can be produced by a conventionally known method using the secondary battery electrode. In general, the battery includes a secondary battery electrode (for negative electrode and positive electrode) and an electrolyte, and further includes a separator that prevents the negative electrode and the positive electrode from being short-circuited. When the electrolyte is a solid electrolyte combined with a polymer and has the function of a separator, an independent separator is not necessary. In producing the secondary battery of the present invention, for example, the negative electrode and the positive electrode obtained above are prepared by cutting into a predetermined shape and size, and then the separator is interposed so that the positive electrode and the negative electrode are not in direct contact with each other. To make a single-layer cell. Next, an electrolyte is injected between the electrodes of the single-layer cell by a method such as injection. A secondary battery is obtained by inserting and sealing the thus obtained cell into an outer package made of a laminate film having a three-layer structure of polyester film / aluminum film / modified polyolefin film, for example. The obtained secondary battery may be used as a single cell or a module in which a plurality of cells are connected depending on the application.

When the secondary battery electrode according to the present invention is used as a negative electrode for a lithium ion secondary battery, the positive electrode used for preparing the lithium ion secondary battery according to the present invention can be manufactured by a conventionally known method. For example, a slurry having a predetermined viscosity is prepared with a suitable solvent or dispersion medium by adding a binder, a conductive agent, etc. to the positive electrode active material, and this is applied to a current collector such as a metal foil, What is necessary is just to remove a solvent or a dispersion medium by forming a coating of micrometer-several hundred micrometer, and heat-processing the coating at about 50-200 degreeC. The positive electrode active material may be a conventionally known material, for example, a cobalt composite oxide such as LiCoO ₂ , a manganese composite oxide such as LiMn ₂ O ₄ , a nickel composite oxide such as LiNiO ₂ , and a mixture of these oxides. , LiNiO ₂ in which a part of nickel is replaced with cobalt or manganese, iron composite oxides such as LiFeVO ₄ and LiFePO ₄ , and the like can be used.

  The conductive agent used for the positive electrode used in the production of the lithium ion secondary battery according to the present invention is preferably the conductive agent for the secondary battery according to the present invention. For the positive electrode and the negative electrode used for the production of the lithium ion secondary battery according to the present invention. By simultaneously using the conductive agent for a secondary battery according to the present invention, the lithium ion secondary battery according to the present invention has a higher capacity and more excellent charge / discharge cycle characteristics.

  As the electrolyte, a known electrolytic solution, a room temperature molten salt (ionic liquid), an organic or inorganic solid electrolyte, and the like can be used. Examples of the known electrolyte include cyclic carbonates such as ethylene carbonate and propylene carbonate, and chain carbonates such as ethyl methyl carbonate and diethyl carbonate. Examples of the room temperature molten salt (ionic liquid) include imidazolium salts, pyrrolidinium salts, pyridinium salts, ammonium salts, phosphonium salts, sulfonium salts, and the like. Examples of the solid electrolyte include polyether polymers, polyester polymers, polyimine polymers, polyvinyl acetal polymers, polyacrylonitrile polymers, polyfluorinated alkene polymers, polyvinyl chloride polymers, poly (vinyl chloride-fluoride). Vinylidene) -based polymers, poly (styrene-acrylonitrile) -based polymers, and organic polymer gels represented by linear polymers such as nitrile rubber; inorganic ceramics such as zirconia; silver iodide, silver iodide sulfur compounds, iodine And inorganic electrolytes such as silver rubidium compounds. Moreover, what melt | dissolved lithium salt in the said electrolyte can be used as an electrolyte for secondary batteries. A flame retardant electrolyte solubilizer can also be added to impart flame retardancy to the electrolyte. Similarly, a plasticizer can be added to reduce the viscosity of the electrolyte.

Examples of the lithium salt dissolved in the electrolyte include LiPF ₆ , LiClO ₄ , LiCF ₃ SO ₃ , LiBF ₄ , LiAsF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ and LiC ( CF ₃ SO ₂ ) _{3 and the} like. The lithium salts may be used alone or in combination of two or more. The lithium salt is generally used in a content of 0.1% by mass to 89.9% by mass, preferably 1.0% by mass to 79.0% by mass, based on the entire electrolyte. Components other than the lithium salt of the electrolyte can be added in an appropriate amount on condition that the content of the lithium salt is within the above range.

  The polymer used for the electrolyte is not particularly limited as long as it is electrochemically stable and has high ionic conductivity. For example, an acrylate polymer, polyvinylidene fluoride, or the like can be used. In addition, polymers synthesized from those containing a salt monomer composed of an onium cation having a polymerizable functional group and an organic anion having a polymerizable functional group have particularly high ionic conductivity, which further improves charge / discharge characteristics. It is more preferable at the point which can contribute. The polymer content in the electrolyte is preferably in the range of 0.1 mass% to 50 mass%, more preferably 1 mass% to 40 mass%.

  The flame retardant electrolyte solubilizer is not particularly limited as long as it is a compound that exhibits self-extinguishing properties and can dissolve the electrolyte salt in the presence of the electrolyte salt. For example, phosphate ester, halogen compound Phosphazene etc. can be used.

  Examples of the plasticizer include cyclic carbonates such as ethylene carbonate and propylene carbonate, and chain carbonates such as ethyl methyl carbonate and diethyl carbonate. The above plasticizers may be used alone or in combination of two or more.

  When a separator is used in the lithium ion secondary battery according to the present invention, a conventionally known material that can prevent a short circuit between the positive electrode and the negative electrode and is electrochemically stable may be used. Examples of the separator include a polyethylene separator, a polypropylene separator, a cellulose separator, a nonwoven fabric, an inorganic separator, a glass filter, and the like. When a polymer is included in the electrolyte, the electrolyte may also have a separator function, and in that case, an independent separator is unnecessary.

  Hereinafter, an example for explaining the present invention more concretely is provided. In addition, this invention is not limited to a following example in the range which does not deviate from the objective and the main point.

Example 1
1) Production of carbon material 1 (Preparation of thermosetting resin solution)
As a thermosetting resin, 2 g of a phenol resin (manufactured by Sumitomo Bakelite Co., Ltd., PR-217) was dissolved in methanol to prepare a 0.2 mass% phenol resin solution.
(Dip coating)
A polypropylene film (length 30 cm × width 20 cm) having a thickness of 100 μm was prepared as a support sheet made of a thermoplastic resin. After immersing this support sheet in the above phenolic resin solution at room temperature for 5 seconds, the support sheet is taken out and left to stand in an ambient atmosphere for 1 hour to dry, thereby covering the both sides of the support sheet with a thermosetting resin. Thus obtained thermosetting resin coated support sheet was obtained.
(Carbonization, grinding)
The obtained thermosetting resin-coated support sheet was placed in an alumina tube, and carbonized at 1100 ° C. for 4 hours in a nitrogen atmosphere. The obtained carbide was pulverized with a rotating ball mill (Irie Shokai 1-stage type-B) (pulverization conditions: 200 rpm, 5 minutes), and the obtained powdery carbon material was used as carbon material 1.
(Confirmation of structure)
As a result of observing the obtained powdery carbon material 1 with a scanning electron microscope (SEM) (JSM-7401F manufactured by JEOL Ltd.), it was confirmed that the average particle size was about 4 μm. The average particle size was measured by mixing the base of the produced carbon material powder well, sampling at about 0.03 g each at 5 locations, mixing again, and placing the sample on a plate with double-sided tape attached to the plate. SEM observation was performed with a spread of 05 g, and 30 particles visible in the SEM image were randomly observed to measure the respective particle diameters (major axis), and the average value thereof was taken as the average particle diameter. The average thickness obtained from SEM observation was 20 nm. For the average thickness, 0.05 g of the sample was spread on a plate with a double-sided tape attached, and SEM observation was performed. The thickness was determined by randomly observing 30 particles visible in the SEM image. Defined. Therefore, the average aspect ratio of the carbon material 1 was 200.

2) Production of electrode mixture for lithium ion secondary battery 1) Plate-like particles obtained in 1), commercially available nano-active material silicon powder (Si, average primary particle diameter: 50 nm, manufactured by Nanostructured & amorphous materials), commercially available Mixing carboxymethyl cellulose (CMC) (CMC Daicel 2200 manufactured by Daicel Finechem Co., Ltd.) as a binder and acetylene black (Denka Black manufactured by Denki Kagaku Kogyo Co., Ltd.) in a mass ratio of 30: 100: 4: 20 is necessary. Depending on the concentration, the viscosity was adjusted to obtain an electrode mixture for a lithium ion secondary battery. Specifically, first, CMC was dissolved in a predetermined amount of water to prepare a 2% by mass aqueous solution. Next, predetermined amounts of the plate-like particles, the active material, and the conductive auxiliary agent were added to the CMC aqueous solution so as to have the mass ratio described above, and the mixture was stirred and mixed with a rotation / revolution mixer. During the stirring and mixing, water was added little by little to the rotation / revolution mixer so that the final viscosity was 5000 mPa · sec.

3) Production of Lithium Ion Secondary Battery Electrode (Negative Electrode) The above lithium ion secondary battery electrode mixture was applied to a 20 μm thick copper foil, and then vacuum dried at 110 ° C. for 1 hour. After vacuum drying, it was pressure-formed by a roll press and punched out with a diameter of 13 mm to obtain an electrode for a lithium ion secondary battery. When the surface of the obtained electrode was observed with an SEM, it was confirmed that an active material was disposed between the plate-like particles.

4) Production of lithium ion secondary battery Electrode for lithium ion secondary battery (negative electrode) produced above, separator (polypropylene porous film: diameter φ16, thickness 25 μm), lithium metal (diameter φ12, thickness as working electrode) 1 mm) in the order of 20 mm type coin cell made by Hosen. Further, an electrolytic solution in which lithium perchlorate is dissolved at a concentration of 1 [mol / liter] in a mixed solution of ethylene carbonate and diethylene carbonate (volume ratio is 1: 1) is injected into a lithium ion secondary solution. A battery was produced.

5) Evaluation of initial charge / discharge characteristics As for the charge capacity, constant current charge was performed with a current density at the time of charge of 25 mA / g. The amount of electricity charged up to 25 mA / g was taken as the charge capacity. On the other hand, with respect to the discharge capacity, constant current discharge was performed with a current density at the time of discharge of 25 mA / g, and constant voltage discharge was performed at 2.5 V from the time when the potential reached 2.5 V, and the current density was 1.25 mA. The amount of electricity discharged up to / g was taken as the discharge capacity. In addition, evaluation of the charging / discharging characteristic was performed using the charging / discharging characteristic evaluation apparatus (Hokuto Denko Co., Ltd. product: HJR-1010mSM8).
The initial charge / discharge efficiency was defined by the following equation.
Initial charge / discharge efficiency (%) = initial discharge capacity (mAh / g) / initial charge capacity thermosetting resin-coated support sheet amount (mAh / g) × 100
As a result of evaluating the lithium ion secondary battery produced in 4) using the above evaluation method, the initial discharge capacity was 1523 mAh / g, and the initial charge / discharge efficiency (%) was 86%.

6) Cyclic evaluation The discharge capacity obtained after repeatedly measuring the initial charge / discharge characteristic evaluation conditions 50 times was taken as the discharge capacity of the 50th cycle. Moreover, the cycle property (50 cycle capacity maintenance rate) was defined by the following formula.
Cycle performance (%, 50 cycle capacity retention rate) = 50th cycle discharge capacity (mAh / g) / initial discharge capacity (mAh / g) × 100
As a result of evaluating the lithium ion secondary battery produced in 4) using the above evaluation method, it was confirmed that the cycle performance (%, 50 cycle capacity retention rate) was 90% or more.
Table 1 summarizes the structural parameters of the carbon material 1 and the electrode characteristics of Example 1.

Example 2
A carbon material 2 was prepared by repeating the procedure of Example 1 except that the concentration of the phenol resin solution was 1% by mass, and the electrode characteristics were measured. Table 1 shows the structural parameters of the carbon material 2 and the electrode characteristics of Example 2.

Example 3
The phenol resin was changed to 15 g of a resole resin (PR-51723, manufactured by Sumitomo Bakelite Co., Ltd.), methanol was changed to a methanol / acetone (mass ratio 1: 1) mixed solvent, and a 1.5% by mass resole resin solution was added. Charcoal was obtained by repeating the procedure of Example 1 except that the silicon oxide powder (SiOx, x = 1 to 1.2, average primary particle size: about 0.5 μm) was used as the nanoactive material. Material 3 was prepared and the electrode characteristics were measured. Table 1 shows the structural parameters of the carbon material 3 and the electrode characteristics of Example 3. Moreover, the SEM photograph of the carbon material 3 is shown in FIG.

Example 4
A carbon material 4 was prepared by repeating the procedure of Example 3 except that the concentration of the resole resin solution was 5% by mass, and the electrode characteristics were measured. Table 1 shows the structural parameters of the carbon material 4 and the electrode characteristics of Example 4. Moreover, the SEM photograph of the carbon material 4 is shown in FIG.

Example 5
1) Preparation of carbon material 5 (Preparation of thermosetting resin solution)
As a thermosetting resin, 25 g of a resole resin (manufactured by Sumitomo Bakelite Co., Ltd., PR-51723) was dissolved in a mixed solvent of methanol / acetone (mass ratio 1: 1) to prepare a 2.5% by mass resole resin solution.
(Dip coating 1)
A polypropylene film (length 30 cm × width 20 cm) having a thickness of 100 μm was prepared as a support sheet made of a thermoplastic resin. After immersing this support sheet in the above phenolic resin solution at room temperature for 5 seconds, the support sheet is taken out and left to stand in an ambient atmosphere for 1 hour to dry, thereby covering the both sides of the support sheet with a thermosetting resin. Thus obtained thermosetting resin coated support sheet was obtained.
(Preparation of SnO ₂ dispersion slurry)
After adding 20 g of tin dioxide powder (SnO ₂ ; average primary particle diameter of less than 100 nm; manufactured by Aldrich), which is a commercially available nano-active material, to methanol, the mixture was treated with an ultrasonic crusher for 60 minutes to disperse 2 mass% SnO _2. A slurry was obtained.
(Dip coating 2)
A polypropylene film (length 30 cm × width 20 cm) having a thickness of 100 μm was prepared as a support sheet made of a thermoplastic resin. After immersing this support sheet in the SnO ₂ dispersion slurry at room temperature for 5 seconds, the support sheet is taken out and left to stand in an ambient atmosphere for 1 hour to dry, thereby allowing the SnO ₂ dispersion on both sides of the support sheet. A coated SnO ₂ carrying support sheet was obtained.
(Composite laminate)
The above 10 thermosetting resin coated support sheets and 10 SnO ₂ carrying support sheets were alternately arranged to obtain a composite laminate comprising a total of 20 sheets.
(Carbonization, grinding)
The obtained composite laminate was put in an alumina tube, and carbonized at 1100 ° C. for 4 hours in a nitrogen atmosphere. The obtained carbide was pulverized with a rotating ball mill (Irie Shokai 1-stage type-B) (grinding conditions: 50 rpm, 20 seconds), and the obtained powdery carbon material was used as carbon material 5. As a result of observing the obtained carbon material powder in the same manner as in Example 1, it was confirmed that plate-like carbon core particles having a thickness of several tens to several hundreds of nanometers and a side of several μm were contained. The average thickness of the plate-like particles determined by SEM observation was 195 nm, and the average particle size was 430 μm. Therefore, the average aspect ratio of the carbon material 5 was 2205.
Using the carbon material 5, the procedure of Example 1 was repeated and the electrode characteristics were measured except that the nanoactive material was omitted. Table 1 summarizes the structural parameters of the obtained carbon material 5 and the electrode characteristics of Example 5.

Example 6
Except that the concentration of the resole resin solution was 1.5% by mass and that silicon oxide powder (SiOx, x = 1 to 1.2, average primary particle size: about 0.5 μm) was used as the nano-active material. The carbon material 6 was prepared by repeating the procedure of Example 5, and the electrode characteristics were measured. Table 1 shows the structural parameters of the carbon material 6 and the electrode characteristics of Example 6. Moreover, the electrode obtained in Example 6 was cut with scissors, and an SEM photograph of the cross section is shown in FIG.

Comparative Example 1
The phenol resin was changed to 80 g of a resole resin (manufactured by Sumitomo Bakelite Co., Ltd., PR-51723), and methanol was changed to a methanol / acetone (mass ratio 1: 1) mixed solvent to prepare an 8% by mass resole resin solution. The carbon material 7 was prepared by repeating the procedure of Example 1, and the electrode characteristics were measured. Table 1 shows the structural parameters of the carbon material 7 and the electrode characteristics of Comparative Example 1.

Comparative Example 2
That the concentration of the resole resin solution was changed to 1.5% by mass, and that silicon oxide powder (SiOx, x = 1 to 1.2, average primary particle size: about 0.5 μm) was used as the nano-active material. Except for the above, the carbon material 8 was prepared by repeating the procedure of Comparative Example 1, and the electrode characteristics were measured. Table 1 shows the structural parameters of the carbon material 8 and the electrode characteristics of Comparative Example 2.

Comparative Example 3
The electrode characteristics were measured by repeating the procedure of Example 3 except that the carbon material 3 was not used and the mass ratio of acetylene black as a conductive additive was 50. Table 1 shows the electrode characteristics of Comparative Example 3.

  The carbon material for a secondary battery according to the present invention can simultaneously achieve high discharge capacity, high charge / discharge cycle characteristics, and high charge / discharge efficiency as a secondary battery, and its industrial applicability is extremely large.

Claims (14)

  A carbon material for a secondary battery comprising plate-like particles having an average particle thickness in the range of 2 nm to 500 nm and an average aspect ratio (average particle diameter / average particle thickness) of 10 or more.   The carbon material for a secondary battery according to claim 1, wherein an average particle diameter of the plate-like particles is in a range of 0.5 µm to 500 µm.   The carbon material for a secondary battery according to claim 1 or 2, wherein the plate-like particles are generated by carbonizing a thermosetting resin.   The electrically conductive agent for secondary batteries containing the carbon material for secondary batteries of any one of Claims 1-3.   A carbon material for a secondary battery according to any one of claims 1 to 3, and carbon or metal or metalloid or alloy thereof, oxide, nitride or carbide capable of occluding and releasing lithium ions. And a negative electrode material for a secondary battery in which the particles are disposed between the plate-like particles.   The negative electrode material for a secondary battery according to claim 5, wherein the metal or metalloid includes at least one element selected from the group consisting of silicon, tin, germanium, and aluminum.   The carbon material for a secondary battery according to any one of claims 1 to 3 and / or the conductive agent for a secondary battery according to claim 4 and / or the negative electrode for a secondary battery according to claim 5 or 6. The electrode mixture for secondary batteries containing a material.   The electrode for secondary batteries containing the electrode mixture for secondary batteries of Claim 7.   A secondary battery comprising the secondary battery electrode according to claim 8.   The secondary battery according to claim 9, which is a lithium ion secondary battery.   The laminated body in which a layer of a thermosetting resin is provided on at least one surface of a support sheet made of a thermoplastic resin is carbonized until the support sheet substantially disappears. The manufacturing method of the carbon material for secondary batteries of description.   The manufacturing method of the carbon material for secondary batteries of Claim 11 which controls the average particle thickness of the said plate-shaped particle | grain by adjusting the thickness of the layer of the said thermosetting resin.   One or more laminates in which a thermosetting resin layer is provided on at least one surface of a support sheet made of thermoplastic resin, carbon, metal, metalloid, or an alloy thereof capable of occluding and releasing lithium ions, oxidation One or more layers containing particles containing oxides, nitrides or carbides are alternately arranged to obtain a composite laminate, and the composite laminate is carbonized until the support sheet substantially disappears. The manufacturing method of the negative electrode material for secondary batteries of Claim 5 characterized by the above-mentioned.   The manufacturing method of the negative electrode material for secondary batteries of Claim 13 which controls the average particle thickness of the said plate-shaped particle | grain by adjusting the thickness of the layer of the said thermosetting resin.