WO2002089235A1 - Carbonaceous material for nonaqueous electrolytic secondary cell and nonaqueous electrolytic secondary cell comprising the same - Google Patents

Carbonaceous material for nonaqueous electrolytic secondary cell and nonaqueous electrolytic secondary cell comprising the same Download PDF

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Publication number
WO2002089235A1
WO2002089235A1 PCT/JP2002/003756 JP0203756W WO02089235A1 WO 2002089235 A1 WO2002089235 A1 WO 2002089235A1 JP 0203756 W JP0203756 W JP 0203756W WO 02089235 A1 WO02089235 A1 WO 02089235A1
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carbon material
weight
boron
surface layer
graphite
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PCT/JP2002/003756
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French (fr)
Japanese (ja)
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Minoru Teshima
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Japan Storage Battery Co., Ltd.
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Publication of WO2002089235A1 publication Critical patent/WO2002089235A1/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the present invention relates to a carbon material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the same.
  • a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, which can be repeatedly used by charging, including a positive electrode active material capable of reversibly electrochemically reacting with lithium ion
  • a non-aqueous electrolyte secondary battery comprising a negative electrode containing a negative electrode active material capable of reversibly occluding and releasing lithium ions, and a non-aqueous electrolyte containing a non-aqueous solvent, a solid polymer electrolyte, etc., has a high energy density. Therefore, it is widely used as a power source for portable devices such as portable wireless phones, portable computers, and portable video cameras.
  • As the negative electrode active material a highly crystalline carbon material, a so-called graphite-based carbon material, has been widely used in recent years because of its high ability to insert and extract lithium ions.
  • the graphite-based carbon material since the graphite-based carbon material has an active crystal edge, it reacts with the electrolytic solution at the time of initial charging, and a film is formed on the surface thereof.
  • the coating is electrochemically inert and does not elute during discharge. As a result, the amount of charge consumed for forming the coating film is not used for discharging. As a result, when the graphite-based carbon material is used as a negative electrode active material, a so-called irreversible capacity is generated. This has been a hindrance to the increase in capacity.
  • Japanese Patent Application Laid-Open No. H10-1444497 discloses a method of using a carbon material having an amorphous phase on the surface and a crystal phase inside as a negative electrode active material to reduce graphite crystal. Attempts have been made to prevent irreversible reaction with the electrolyte at the edge and to prevent the generation of irreversible capacity.
  • the charge-discharge cycle characteristics are improved for the following reasons.
  • the lithium metal cannot be completely eluted during discharge, the lithium metal cannot be involved in the battery reaction as the charge / discharge cycle progresses, and the lithium metal increases irreversibly. As a result, the discharge capacity decreases with charge and discharge, and the charge and discharge cycle characteristics deteriorate.
  • the diffusion rate of lithium 'ions between layers in the carbon material decreases as the temperature decreases. For this reason, when charged with a large current at a low temperature, more mossy metallic lithium is deposited unevenly on the graphite particle surface than at room temperature. As a result, the amount of lithium metal that cannot participate in the battery reaction increases, so that the high-rate charge / discharge characteristics at low temperatures deteriorate.
  • the present invention has been made in view of the above circumstances, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery having a high discharge capacity, excellent charge-discharge cycle characteristics, and excellent high-rate charge-discharge characteristics at low temperatures. To provide. Disclosure of the invention
  • the present invention provides a carbon material for a non-aqueous electrolyte secondary battery, in which all or a part of the surface of the core particles made of the carbon material is coated on a surface layer made of a carbon material having lower crystallinity than the core particles. And an open circuit potential of the core particle with respect to L i / L i + is more noble than that of the surface layer.
  • the reaction between the surface of the carbon material and the electrolytic solution is achieved by covering the whole or a part of the surface of the core material made of the carbon material with the surface layer made of the carbon material having lower crystallinity than the core particle. Since the generation of irreversible capacity is suppressed, a nonaqueous electrolyte secondary battery having a high discharge capacity can be obtained.
  • the surface of the core particle It is sufficient that the surface layer is present in part of the surface, and it is not necessary to cover the entire surface. This is because the reaction with the non-aqueous electrolyte solvent forms an electrochemically inactive film in the part where the core particles are exposed, which lowers the charge / discharge efficiency, but lithium ions pass through that part. Because it is quickly absorbed and released into the core particles, there is no problem from the viewpoint of preventing the precipitation of lithium metal.
  • the diffusion rate of lithium ions in the core particles can be improved.
  • An excellent non-aqueous electrolyte secondary battery can be obtained. This is considered for the following reasons. That is, the driving force when lithium ions are diffused in the negative electrode is the difference between the open circuit potential and the closed circuit potential of the negative electrode material with respect to L i ZL i + . By doing so, the diffusivity of lithium ions can be improved. As a result, the lithium ion concentration on the surface of the graphite particles is reduced, so that the deposition of mossy metallic lithium on the surface of the graphite particles is prevented. As a result, the increase in lithium metal that does not participate in the battery reaction is suppressed, and the charge / discharge cycle characteristics are improved.
  • the core particles contain boron
  • the boron atoms are substituted with carbon atoms to improve the crystallinity of the carbon material, and the open circuit potential becomes noble, so that the diffusion of lithium ions can be improved.
  • the amount of boron contained in the core particles is preferably 3% by weight or less. The reason for this is not necessarily clear, but can be considered as follows.
  • the boron that has not been substituted with carbon atoms forms impurities such as boron nitride on the surface of the core particle, thereby lowering the electronic conductivity of the carbonaceous materials.
  • the electron conductivity decreases, the internal resistance of the battery increases, causing ohmic loss, and the ohmic loss substantially reduces the discharge capacity by the reduction in discharge potential.
  • the internal resistance of the battery increases, and the discharge capacity gradually decreases. In this way, the charge / discharge cycle characteristics deteriorate It is thought that.
  • the carbon material in the surface layer is preferably a low-crystalline carbon material or an amorphous carbon material.
  • the proportion of the surface layer is less than 1% by weight, irreversible capacity is likely to occur.
  • the ratio of the surface layer portion exceeds 30% by weight, the discharge capacity per volume is reduced because the bulk density of the low-crystalline carbon material or the amorphous carbon material is lower than that of the crystalline carbon material.
  • the weight of the surface layer is preferably 1% by weight or more and 30% by weight or less based on the sum of the weight of the core particles and the weight of the surface layer. It is particularly preferable that the content be from 20% by weight to 20% by weight.
  • FIG. 1 is a longitudinal sectional view of a prismatic nonaqueous electrolyte secondary battery according to the present invention.
  • FIG. 2 shows the open circuit potentials of boron-containing graphite, MCMB, and amorphous carbon material.
  • FIG. 3 is a diagram showing charge / discharge cycle characteristics of the nonaqueous electrolyte secondary batteries in Examples 1, 2, 10 and Comparative Example 2.
  • FIG. 1 is a schematic sectional view of a prismatic nonaqueous electrolyte secondary battery 1 according to one embodiment of the present invention.
  • 1 is a prismatic nonaqueous electrolyte secondary battery
  • 2 is an electrode group
  • 3 is a negative electrode plate
  • 4 is a positive electrode plate
  • 5 is a separator
  • 6 is a battery case
  • 7 is a lid plate
  • 8 is a safety valve
  • 9 is a positive electrode.
  • Terminals, 10 is a negative electrode lead
  • 11 is a positive electrode lead.
  • the prismatic nonaqueous electrolyte secondary battery 1 has a positive electrode plate 4 formed by applying a positive electrode mixture to a current collector made of aluminum foil, and a negative electrode plate formed by applying a negative electrode mixture to a current collector formed of copper foil. 3 and a non-aqueous electrolyte are housed in a battery container 6.
  • a lid plate 7 provided with a safety valve 8 is attached to the battery container 6 by laser welding.
  • Positive electrode terminal 9 is connected to positive electrode plate 4 via positive electrode lead 11, and negative electrode plate 3 is electrically connected to battery case 6 via negative electrode lead 10.
  • the carbon material for the non-aqueous electrolyte secondary battery used in the present invention it is possible to use a carbon material capable of absorbing and releasing lithium ions, such as a graphite-based carbon material, a low-crystalline carbon material, and an amorphous carbon material.
  • a carbon material can be used.
  • graphite-based carbon material used in the present invention for example, natural graphite produced as an ore can be used, and its shape includes flaky, earth-like, and spherical shapes.
  • artificial graphite obtained by heat-treating graphitizable carbon such as pitch coater and petroleum coke in an inert atmosphere at 240 to 300 ° C. can also be used.
  • Specific examples include MCMB, graphitized mesophase pitch-based carbon fiber, black ⁇ 3, and whiskers.
  • the low-crystalline carbon material used in the present invention can be produced by heat-treating graphitizable carbon at 700 ° C. to 1200 ° C. in an inert atmosphere.
  • the amorphous carbon material used in the present invention is a non-graphitizable carbon material or an organic polymer compound that does not progress to graphitization even when heated to a high temperature (for example, phenol resin, furan resin, polystyrene, and the like). It can be obtained by subjecting vinylidene chloride resin, cellulose resin, furfuryl alcohol resin, etc.) to a heat treatment similar to that used to produce graphite materials.
  • the core particles are immersed in a petroleum-based pitch that has been heated and liquefied, and after drying and washing with a solvent.
  • a method of performing heat treatment in an inert atmosphere at 700 ° C. to 1200 ° C. can be used.
  • petroleum pitch may be dissolved in an organic solvent, core particles may be immersed in the pitch, dried and washed, and then heat-treated.
  • the core particles may be directly coated from the gas phase by chemical vapor deposition or the like.
  • a method for providing a surface layer made of an amorphous carbon material in the core particles a phenol resin, a furan resin, a polyvinylidene resin, a cellulose resin, a furfuryl alcohol resin, or the like is dissolved in an organic solvent.
  • the core particles are immersed therein, dried, washed with a solvent, and heat treated in an inert atmosphere at 700 ° C to 1200 ° C.
  • An example of the method is as follows.
  • the surface layer is formed on the core particles, it is preferable that processes such as pulverization and classification are not performed as much as possible. This is because the surface layer once formed may be peeled off or fall off by the above treatment.
  • the weight ratio of the surface layer portion to the sum of the weight of the core particles and the weight of the surface layer portion is calculated as follows.
  • the weight of the surface layer portion is calculated from the difference between the charged amount of the carbon material forming the surface layer portion in the process of forming the surface layer portion and the solvent-soluble matter in the cleaning step.
  • the weight of the core particles and the weight of the surface layer are calculated, The weight ratio of the surface layer is calculated.
  • the boron-containing graphite material used in the present invention is obtained by mixing a carbon material and a boron compound and heat-treating the mixture at a temperature of 200 ° C. to 280 ° C. in an inert atmosphere.
  • carbon materials include coal or petroleum heavy oils such as tar and pitch, pitch coaters, coal coaters, petroleum coaters, carbon black, pyrolytic carbon, organic resin materials, and the like.
  • Graphite can also be used.
  • As the boron compound boron, boric acid (H 3 B 0 3), boron oxide (B 2 0 3, B 4 0 5), or the like can be used boron carbide (B 4 C).
  • the boron content in the boron-containing graphite material is preferably 3% by weight or less. If it exceeds 3% by weight, boron not substituted with carbon atoms forms impurities such as boron nitride on the surface of the particles, which undesirably lowers the electron conductivity of the carbon material.
  • the boron content can be determined by ICP emission spectroscopy.
  • the carbon material used in the present invention can be prepared to have a predetermined particle size distribution by adjusting the particle size of the raw material in advance. Further, after heat treatment is performed to prepare a desired material, these materials may be pulverized and classified to prepare a material having a predetermined particle size distribution.
  • the particle size of the carbon material in the final form The fabric depends on the size of the core particles. Therefore, the average core particle size D 5 . Is preferably from 0.1 / m to 150 ⁇ um.
  • the particle size distribution of the carbon material used in the present invention can be measured by a laser diffraction / scattering method.
  • the BET specific surface area is generally in the range of 0.1 m 2 Zg to 10 m 2 / g. If it is less than 0.1 m 2 Zg, there is a problem that the current load per unit surface area of the particles will increase during charging, while if it exceeds 10 m 2 / g, the irreversible capacity will increase.
  • the BET specific surface area of the carbon material in the final form depends on the BET specific surface area of the core particles. Therefore, the core particles preferably have a BET specific surface area of 0.2 m 2 / g or more and 10 Om 2 Zg.
  • the BET specific surface area of the carbon material used in the present invention can be calculated by measuring by a low-temperature gas adsorption method using liquid nitrogen and analyzing by a BET method.
  • the open circuit potential of the carbon material used in the present invention with respect to LiZL i + can be measured using a triode cell using lithium metal for the counter electrode and the reference electrode.
  • the working electrode an electrode obtained by applying a negative electrode mixture containing a carbon material to be measured to a current collector can be used.
  • the electrolyte for example, a mixed solvent of ethylene carbonate and Jefferies chill carbonate (volume ratio 1: 1) can Rukoto used after dissolved 1 mo 1/1 of L i C 10 4 to.
  • the open circuit potential differs depending on the type of carbon material. When the graphite material is compared with the low crystalline carbon material or the amorphous carbon material, the open circuit potential of the graphite material is more noble.
  • the open circuit voltage of artificial graphite is more noble.
  • the open circuit voltage of the graphite material containing boron is more noble.
  • the open circuit potential becomes more precious.
  • various carbon materials can be selected and used so that the open-circuit potential of the core particles is more noble than the surface layer portion.
  • boron-containing graphite as the core particles, and it is preferable to use a low-crystalline carbon material or an amorphous carbon material as the surface layer.
  • the crystallinity of the carbon material used in the present invention is determined by an X-ray diffraction method using Cu K line, and the average spacing d of the (002) plane. 02 and the crystallite thickness Lc in the (002) plane direction.
  • d QQ2 is preferably 0.335 nm or more and 0.340 nm or less
  • L c is preferably 50 nm or more. d Q. If the value of 2 exceeds 0.340 nm, the crystallinity will be low and the discharge capacity will be small, which is not preferable.
  • the positive electrode active material for example, L i C o 0 2, L i N i 0 2, L i C o X N i ⁇ _ ⁇ 0 2, L iMn 2 0 4, Mn_ ⁇ 2, F e 0 2, V 2 0 5, V 6 ⁇ 13, T I_ ⁇ metal oxides tunnel structure or a layered structure, such as 2, metal hydroxides such as Okishi nickel hydroxide, a metal sulfide such as T i S, Poria diphosphate And the like, and a conductive polymer such as the above can be used.
  • composition formulas L i x MO 2 and L i y M 2 0 4 (where M represents one or more kinds of transition metal elements, 0 ⁇ ⁇ 1.2, 0 ⁇ y ⁇ 2)
  • M represents one or more kinds of transition metal elements, 0 ⁇ ⁇ 1.2, 0 ⁇ y ⁇ 2
  • the represented lithium transition metal composite oxide is particularly preferred as the positive electrode active material.
  • an electrolyte or a solid electrolyte such as an inorganic solid electrolyte and a polymer solid electrolyte can be used.
  • the solvent for the electrolytic solution may be ethylene carbonate, propylene carbonate, dimethinolecarbonate, getyl carbonate, ⁇ -butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, 1 Polar solvents such as 1,2-dimethoxetane, 1,2-dietoxetane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolan, and methinorea acetate, or mixtures thereof can be used.
  • Salts such as CF 2 CF 3 ) 2 , L i N (COCF 3 ) 2 and L i N (C ⁇ CF 2 CF 3 ) 2 or a mixture thereof can be used.
  • a woven fabric, a nonwoven fabric, a synthetic resin microporous membrane, or the like can be used as the separator.
  • a synthetic resin microporous membrane can be suitably used.
  • a polyolefin-based microporous membrane such as a polyethylene microporous membrane, a polypropylene microporous membrane, or a microporous membrane obtained by combining these is used. It is preferably used in terms of performance such as strength and film resistance.
  • a solid electrolyte such as a polymer solid electrolyte
  • a porous high molecular solid electrolyte membrane is used as the polymer solid electrolyte.
  • the solid polymer electrolyte may further contain an electrolytic solution.
  • the electrolysis solution constituting the gel may be the same as or different from the electrolyte solution contained in the pores or the like.
  • a synthetic resin microporous membrane and a solid polymer electrolyte may be used in combination.
  • Boron-containing graphite serving as core particles was prepared as follows. Boric acid (H 3 BO 3 ) is 0.026 wt%, 0.127 wt%, 0.626 wt%, 3.73 wt% of pitch coke in terms of boron atom weight. After the addition and mixing, the mixture was heated to 100 ° C. in an argon stream, kept for 10 hours, heated to 2400 ° C., and kept for 20 hours. Then, it was cooled to room temperature, pulverized and classified. By the above operation, four kinds of boron-containing graphites having different boron contents were obtained. For these,
  • the concentration of boron added was 0.0126% by weight, 0.127% by weight, 0.626% by weight, and 3.73% by weight.
  • the boron content of the samples was about 0.01% by weight, 0.1% by weight, 0.5% by weight, and 3% by weight, respectively.
  • MCMB meocarbon microphone mouth beads
  • the spherulite produced by heat treatment at a temperature of about 400 ° C under a pressure of 2G was separated and purified, It was obtained by graphitization at a temperature of about 280 ° C. in an active atmosphere.
  • the artificial graphite was obtained by heat-treating a semi-copper obtained by setting the pitch to a temperature of 500 ° C. or higher in an inert atmosphere at a temperature of 250 ° C. or higher.
  • a low-crystalline carbon material was prepared using the same raw materials and the same preparation conditions as the low-crystalline carbon material used as the surface layer. That is, a low-crystalline carbon material was obtained by subjecting the pitch coater to a heat treatment at about 1200 ° C. in an inert atmosphere. Since it is impossible to measure the open-circuit voltage and crystallinity described below only for the surface layer of the final form of the carbon material having the surface layer and the core particles according to the present invention, the surface layer is separately prepared. The open circuit voltage and crystallinity were measured for this.
  • An amorphous carbon material was prepared using the same raw materials and the same preparation conditions as the amorphous carbon material to be the surface layer. That is, the furfuryl alcohol resin was heat-treated in an inert atmosphere at about 1200 ° C. to obtain an amorphous carbon material. As in the case of the low-crystalline carbon material, it is impossible to measure the open-circuit voltage and crystallinity described below only for the surface layer portion of the final form of the carbon material having the surface layer portion and the core particles according to the present invention. The surface layer was separately prepared, and the open circuit voltage and crystal growth were measured for this.
  • the open circuit potential of the carbon material used in the present invention with respect to L i ZL i + was measured using a three-electrode cell using lithium metal as a counter electrode and a reference electrode.
  • a mixture of 90% by weight of the carbon material obtained as described above and 10% by weight of polyvinylidene fluoride (PVdF) as a binder was mixed with N —Methyl-2-pyrrolidone (NMP) is added as appropriate to prepare a paste, which is then applied to both sides of a 15-m-thick copper foil current collector, and dried at 100 ° C for 5 hours.
  • An electrode plate produced by compression molding so as to have a porosity of 30% was used.
  • a mixed solvent of ethylene carbonate and Jefferies chill carbonate (volume ratio 1: 1) was used to dissolve the L i C l O 4 of I mol Z l to. Made in this way
  • the open-circuit potential was measured as follows using the three-pole cell. First, one cycle of charge and discharge was performed at a current density of 5 OmA per g of carbon material at a temperature of 25 ° C and a potential range of 0 V to 1.5 V with respect to L ⁇ ⁇ +. Next, the battery was charged at a current density of 5 OmAZg for 0.25 h (15 minutes), followed by a pause of 2 hours. At this time, the potential measured immediately after the end of the pause after charging in the 20th cycle was measured as the open circuit potential.
  • Fig. 2 shows the open circuit potential (equilibrium potential for occlusion of lithium) of graphite containing 0.31% by weight of boron, MCMB, and an amorphous carbon material.
  • the potential with respect to Li ZLi + at the measurement point at the 20th cycle was defined as the open circuit potential.
  • the open circuit potential of the carbon material used in the present invention was measured by the method described above, and these values are summarized in Table 1.
  • the average spacing dQ 02 of the (002) plane and the crystallite thickness Lc in the (002) plane direction were measured by X-ray diffraction using Cu K rays. These values are summarized in Table 1.
  • N-methyl-2-pyrrolidone N-methyl-2-pyrrolidone
  • NMP polyvinylidene fluoride
  • the positive electrode plate 4 the lithium cobalt complex oxide as a positive electrode active material and (L i C O_ ⁇ 2) 90 wt%, and polyvinylidene fluoride (PVdF) 5 wt 0/0 as a binder, conductive agent N-methyl 2-pyrrolidone (NMP) is added to the positive electrode mixture prepared by mixing 5% by weight of acetylene black in the above to prepare a paste, which is then collected into a 20 ⁇ -thick aluminum foil current collector. It was prepared by applying it to both sides of the body, drying it, and compressing it to a porosity of 30%.
  • PVdF polyvinylidene fluoride
  • NMP conductive agent N-methyl 2-pyrrolidone
  • An electrode group 2 was produced by winding a positive electrode and a negative electrode into a long cylindrical shape with a separator interposed therebetween using a 25- ⁇ m-thick polyethylene microporous membrane as the separator 5. After this electrode group and the positive electrode lead 11 of the cover plate 7 are connected, the electrode group 2 is housed through the opening of the battery case 6 in which nickel is applied to iron, and the battery case 6 and the cover plate 7 are connected. It was sealed by laser welding. Then, after injecting the non-aqueous electrolyte from the liquid injection port on the side of the battery container 6, the non-aqueous electrolyte secondary battery 1 was hermetically sealed by welding the liquid injection port.
  • the electrolyte solution, ethylene carbonate: Jefferies chill carbonate 5: 5 using nonaqueous electrolytic solution of L i PF 6 was 1 mo 1 Z 1 dissolved in a mixed solvent (volume ratio).
  • a prismatic nonaqueous electrolyte secondary battery 1 having a width of 3 Omm, a height of 48 mm and a thickness of 4 mm and a rated capacity of 640 mAh was produced.
  • Example 1 a carbon material having a low crystalline carbon material coating amount of 1% by weight to 40% by weight was obtained by changing the cleaning temperature during the cleaning treatment with toluene from 20 ° C. to 120 ° C. .
  • Examples 5 to 9 were carried out in the same manner as in Example 1 except that the graphite material containing 0.1% by weight of boron was coated with a low-crystalline carbon material in place of the carbon material. Of the non-aqueous electrolyte secondary battery was manufactured. At this time, carbon material The proportions of the low-crystalline carbon material in them were 1% by weight, 10% by weight, 20% by weight, 30% by weight, and 40% by weight, respectively.
  • Example 2 The same as Example 1 except that the negative electrode plate 3 was prepared using a graphite containing 0.1% by weight of boron instead of a carbon material obtained by coating a low-crystalline carbon material on graphite containing 0.1% by weight of boron. As a result, a prismatic nonaqueous electrolyte secondary battery was fabricated.
  • a rectangular non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that the negative electrode plate 3 was manufactured using artificial graphite instead of the carbon material obtained by coating the low-crystalline carbon material on graphite containing 0.1% by weight of boron. A battery was manufactured.
  • composition of the core particles and the surface layer of the carbon material prepared as described above, together with the boron content of black containing boron and the material, and the content (% by weight) of the surface layer in the total carbon material, are shown in Table 2. Are shown together.
  • the batteries of Examples 1 to 12 and Comparative Examples 1 and 2 were charged for 3 hours under a constant current constant voltage charging condition of a charging current of 600 mA and a charging voltage of 4.20 V at a temperature of 25 ° C. Thereafter, discharge was performed under the conditions of a discharge current of 60 O mA and a final voltage of 2.75 V, and the initial discharge capacity was measured. .
  • Comparative Examples 1 and 2 made of a single carbon material was 78.1% or less. The reason is considered as follows. When charging at a high rate of charge current of 1 CmA, diffusion of lithium ions does not catch up to the inner part of the carbon material, the lithium ion concentration in the surface layer increases, and metallic lithium is deposited on the surface of the carbon material. Will precipitate out. The metallic lithium does not contribute to the battery reaction by dropping off from the electrode or by forming a film by reaction with the electrolytic solution. Such metal resources that do not contribute to the battery reaction It is thought that the discharge capacity will decrease because of the irreversible increase in the repetition of high-rate charging and discharging.
  • the capacity retention after 300 cycles was as good as 79.5% or more. This is because lithium ions quickly enter and occlude the inner core of noble core particles with an open circuit potential, thereby uniformly charging the entire carbon material and suppressing the precipitation of mossy metallic lithium. It is considered that it is.
  • a non-aqueous electrolyte secondary battery showing a high capacity retention of 79.5% or more even by repeating charge and discharge of 300 cycles can be obtained. It turned out to be obtained.
  • the discharge capacity test at a low temperature was performed on the batteries of Examples 1, 2, 10 and Comparative Example 2 as follows. After charging the battery for which initial capacity measurement has been completed in an atmosphere at a temperature of 20 ° C, charging at a constant current constant voltage of 600 mA and a charging voltage of 4.2 V for 3 hours, It was left at 20 ° C for 1 hour, and further discharged at 120 ° C under the conditions of a discharge current of 600 mA and a final voltage of 2.75 V. Calculate the discharge capacity ratio between the discharge capacity obtained at 120 ° C and the initial capacity measured at 25 ° C (discharge capacity at 120 ° C ⁇ discharge capacity at room temperature). did. The number of test batteries was three for each of the examples and comparative examples, and the average value thereof was used as an index for evaluating low-temperature discharge characteristics. Table 4 shows the results of the charge / discharge test at low temperatures.
  • the battery using the carbon material of Comparative Example 2 consisting of a single carbon material had a discharge capacity ratio of 82.2%, while the batteries of Examples 1, 2 and 10 all had a discharge capacity ratio of 90%. % Or better.
  • the amount of electricity that could not be discharged in the comparative example is considered to have been spent for the deposition of metallic lithium.
  • the negative electrode plates prepared in Examples 1, 2, 10 and Comparative Example 2 were used as working electrodes, and a lithium metal electrode was incorporated as a counter electrode and a reference electrode to form a three-electrode glass cell.
  • the three-pole glass cell fabricated in this manner was charged at a current of 0.2 CmA at a temperature of 25 ° C with a charge end voltage of 0.2 OV (V s L i / L i + ). After a pause of 5 minutes, the battery was discharged to 1.5 V (vs Li / Li + ).
  • the irreversible capacity was calculated by subtracting the amount of discharged electricity from the amount of charged electricity at this time.
  • the charge / discharge efficiency was calculated by dividing the amount of discharged electricity by the amount of charged electricity. Table 5 shows the irreversible capacity and charge / discharge efficiency thus obtained.
  • the charge / discharge efficiency of the battery using the carbon material of Comparative Example 2 consisting of a single carbon material was 88.9%, whereas the batteries using the carbon materials of Examples 1, 2, and 10 However, the charge and discharge efficiency was extremely high at 92% or more.
  • the irreversible capacity was 42 mAhZg in Comparative Example 2, whereas the irreversible capacity was 26 mAhZg or less in Examples 1, 2, and 10. This is because, in the carbon materials of Examples 1, 2, and 10, the core particles are coated with the low-crystalline carbon material, so that the reaction with the electrolytic solution is suppressed, and the generation of decomposition products is generated. It is considered that the amount of electricity consumed during the period decreased.
  • the carbon material for a non-aqueous electrolyte secondary battery according to the present invention and the non-aqueous electrolyte secondary battery using the same have a high discharge capacity, excellent charge-discharge cycle characteristics, and a high rate of charge at low temperatures. Excellent discharge characteristics.
  • the carbon material of the present invention can be mass-produced by a relatively simple manufacturing process. In particular, it can be said that the carbon material has an extremely high industrial value as a substitute for a graphite material that has been widely used.

Abstract

A carbonaceous material for nonaqueous electrolytic secondary cells characterized in that a part or whole of the surface of nucleus particles of a carbonaceous material is coated with a surface portion of a carbonaceous material having a lower crystallinity than that of the nucleus particles, and that the open-circuit potential of the nucleus particles to Li/Li+ is nobler than that of the surface portion. A nonaqueous electrolytic secondary cell comprising the carbonaceous material is also disclosed. The nonaqueous electrolytic secondary cell has a high discharge capacity because the irreversible capacity is not caused. The nonaqueous electrolytic secondary cell is excellent in charging/discharging cycle characteristics and high-rate charging/discharging characteristics because precipitation of lithium metal is prevented.

Description

明細 非水電解質二次電池用炭素材料及びそれを用いた非水電解質二次電池 技術分野  Description Carbon material for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery using the same
本発明は、 非水電解質二次電池用炭素材料とそれを用いた非水電解質二次電池に 関する。 背景技術  The present invention relates to a carbon material for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the same. Background art
正極と、 負極と、 非水電解質とからなり、 充電により繰り返し使用が可能な非水 電解質二次電池のうち、 リチウムィオンと可逆的に電気化学的反応をすることので きる正極活物質を含む正極と、 リチウムイオンを可逆的に吸蔵 ·放出できる負極活 物質を含む負極と、 非水溶媒や高分子固体電解質などを含む非水電解質とからなる 非水電解質二次電池は、 エネルギー密度が高いことから、 携帯用無線電話、 携帯用 ノ ソコン、 携帯用ビデオカメラなど携帯用機器の電源として広く用いられている。 前記負極活物質としては、 リチウムイオンの吸蔵 ·放出能力が高いことから高結 晶性の炭素材料、 いわゆる黒鉛系の炭素材料が近年広く用いられている。  A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, which can be repeatedly used by charging, including a positive electrode active material capable of reversibly electrochemically reacting with lithium ion A non-aqueous electrolyte secondary battery comprising a negative electrode containing a negative electrode active material capable of reversibly occluding and releasing lithium ions, and a non-aqueous electrolyte containing a non-aqueous solvent, a solid polymer electrolyte, etc., has a high energy density. Therefore, it is widely used as a power source for portable devices such as portable wireless phones, portable computers, and portable video cameras. As the negative electrode active material, a highly crystalline carbon material, a so-called graphite-based carbon material, has been widely used in recent years because of its high ability to insert and extract lithium ions.
しかし前記黒鉛系の炭素材料は結晶のエッジが活性なため、 初回充電時に電解液 と反応し、 その表面に被膜が形成される。 前記被膜は電気化学的に不活性なので放 電時に溶出することはない。 このため、 前記被膜の形成に費やされた充電電気量が 放電に使用されない結果、 前記黒鉛系の炭素材料を負極活物質として用いる場合に はいわゆる不可逆容量が発生し、 非水電解質二次電池における高容量化の妨げとな つている。  However, since the graphite-based carbon material has an active crystal edge, it reacts with the electrolytic solution at the time of initial charging, and a film is formed on the surface thereof. The coating is electrochemically inert and does not elute during discharge. As a result, the amount of charge consumed for forming the coating film is not used for discharging. As a result, when the graphite-based carbon material is used as a negative electrode active material, a so-called irreversible capacity is generated. This has been a hindrance to the increase in capacity.
上記の問題を解決するため、 特開平 1 0— 1 4 4 2 9 7号公報において、 表面に アモルファス相を有すると共に内部に結晶相を有する炭素材料を負極活物質として 用いることで、 黒鉛結晶のェッジにおける電解液との不可逆的な反応を防止し、 不 可逆容量の発生を防止する試みが提案されている。  In order to solve the above-mentioned problem, Japanese Patent Application Laid-Open No. H10-1444497 discloses a method of using a carbon material having an amorphous phase on the surface and a crystal phase inside as a negative electrode active material to reduce graphite crystal. Attempts have been made to prevent irreversible reaction with the electrolyte at the edge and to prevent the generation of irreversible capacity.
しかし上記方法によっても、 以下の理由により、 充放電サイクル特性を向上させ ることはできないという問題点があった。 すなわち、 前記黒鉛系の炭素材料はリチ ゥムイオンの拡散性が低いため、 大電流で充電する場合、 充電時にリチウムイオン が黒鉛粒子内奥部にまで十分に拡散することができない。 この結果、 黒鉛粒子表面 のリチウムイオン濃度が上昇し、 その表面に苔状の金属リチウムが不均一に析出す る。 不均一な金属リチウムは、 脆弱なために黒鉛粒子表面からの脱落により電気的 に孤立しやすく、 また、 電解液との反応により金属リチウム表面に電気化学的に不 活性な被膜を形成しゃすレ、。 これらの金属リチウムは放電時に完全に溶出できなく なるので、 充放電サイクルの進行に従つて電池反応に関与できなレ、金属リチウムが 不可逆的に増加することなる。 この結果、 充放電に伴って放電容量が減少し、 充放 電サイクル特性が低下するのである。 However, even with the above method, the charge-discharge cycle characteristics are improved for the following reasons. There was a problem that it was not possible. That is, since the graphite-based carbon material has low diffusivity of lithium ions, when charged with a large current, lithium ions cannot be sufficiently diffused into the interior of graphite particles during charging. As a result, the lithium ion concentration on the surface of the graphite particles increases, and moss-like metallic lithium is deposited unevenly on the surface. Non-uniform lithium metal is fragile and tends to be electrically isolated by falling off from the graphite particle surface, and also reacts with the electrolyte to form an electrochemically inactive coating on the lithium metal surface. . Since the lithium metal cannot be completely eluted during discharge, the lithium metal cannot be involved in the battery reaction as the charge / discharge cycle progresses, and the lithium metal increases irreversibly. As a result, the discharge capacity decreases with charge and discharge, and the charge and discharge cycle characteristics deteriorate.
また、 炭素材料中の層間におけるリチウム'イオンの拡散速度は温度が低くなるほ ど低下する。 このため低温下に大電流で充電を行うと、 室温の場合よりも多くの苔 状金属リチウムが黒鉛粒子表面上に不均一に析出することになる。 この結果、 電池 反応に関与できない金属リチウムが増加するので低温での高率充放電特性が低下す る。  Also, the diffusion rate of lithium 'ions between layers in the carbon material decreases as the temperature decreases. For this reason, when charged with a large current at a low temperature, more mossy metallic lithium is deposited unevenly on the graphite particle surface than at room temperature. As a result, the amount of lithium metal that cannot participate in the battery reaction increases, so that the high-rate charge / discharge characteristics at low temperatures deteriorate.
本発明は上記事情に鑑みてなされたものであって、 その目的は、 高い放電容量を 備え、 充放電サイクル特性に優れ、 低温での高率充放電特性に優れた非水電解質二 次電池を提供することにある。 発明の開示  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a non-aqueous electrolyte secondary battery having a high discharge capacity, excellent charge-discharge cycle characteristics, and excellent high-rate charge-discharge characteristics at low temperatures. To provide. Disclosure of the invention
本発明は、 非水電解質二次電池用炭素材料において、 炭素材料からなる中核粒子 の表面の全部又は一部が、 前記中核粒子よりも結晶性の低い炭素材料からなる表層 部に被覆されてなり、 かつ、 L i / L i +に対する前記中核粒子の開回路電位が前 記表層部よりも貴であることを特徴とする。  The present invention provides a carbon material for a non-aqueous electrolyte secondary battery, in which all or a part of the surface of the core particles made of the carbon material is coated on a surface layer made of a carbon material having lower crystallinity than the core particles. And an open circuit potential of the core particle with respect to L i / L i + is more noble than that of the surface layer.
まず、 炭素材料からなる中核粒子の表面の全部又は一部が、 前記中核粒子よりも 結晶性の低い炭素材料からなる表層部に被覆されてなることにより、 炭素材料表面 と電解液との反応が抑制されるので、 不可逆容量の発生が防止され、 高い放電容量 を備えた非水電解質二次電池を得ることができる。 このとき、 前記中核粒子の表面 の一部に表層部が存在すればよく、 表面の全部を被覆する必要はない。 なぜなら、 確かに中核粒子が露出している部分では非水電解液溶媒との反応により電気化学的 に不活性な被膜が形成されるために充放電効率は低下するが、 その部分を通してリ チウムイオンが中核粒子内部に速やかに吸蔵 ·放出されるので、 リチウム金属の析 出を防止する観点からは何ら問題を生じないからである。 First, the reaction between the surface of the carbon material and the electrolytic solution is achieved by covering the whole or a part of the surface of the core material made of the carbon material with the surface layer made of the carbon material having lower crystallinity than the core particle. Since the generation of irreversible capacity is suppressed, a nonaqueous electrolyte secondary battery having a high discharge capacity can be obtained. At this time, the surface of the core particle It is sufficient that the surface layer is present in part of the surface, and it is not necessary to cover the entire surface. This is because the reaction with the non-aqueous electrolyte solvent forms an electrochemically inactive film in the part where the core particles are exposed, which lowers the charge / discharge efficiency, but lithium ions pass through that part. Because it is quickly absorbed and released into the core particles, there is no problem from the viewpoint of preventing the precipitation of lithium metal.
つぎに、 L i Z L i +に対する前記中核粒子の開回路電位が前記表層部よりも貴 であることにより、 前記中核粒子におけるリチウムイオンの拡散速度を向上させる ことができるので、 充放電サイクル特性に優れた非水電解質二次電池を得ることが できる。 これは以下の理由によると考えられる。 すなわち、 負極中においてリチウ ムイオンが拡散する際の駆動力となるのは負極材料の L i Z L i +に対する開回路 電位と閉回路電位との差であるので、 前記開回路電位を貴なものとすることにより リチウムイオンの拡散性を向上させることができる。 この結果、 黒鉛粒子表面のリ チウムィオン濃度が低下するので、 前記黒鉛粒子表面上への苔状の金属リチウムの 析出が防止される。 この結果、 電池反応に関与しない金属リチウムの増加が抑制さ れるので、 充放電サイクル特性が向上するのである。 Next, since the open circuit potential of the core particles with respect to L i ZL i + is more noble than that of the surface layer portion, the diffusion rate of lithium ions in the core particles can be improved. An excellent non-aqueous electrolyte secondary battery can be obtained. This is considered for the following reasons. That is, the driving force when lithium ions are diffused in the negative electrode is the difference between the open circuit potential and the closed circuit potential of the negative electrode material with respect to L i ZL i + . By doing so, the diffusivity of lithium ions can be improved. As a result, the lithium ion concentration on the surface of the graphite particles is reduced, so that the deposition of mossy metallic lithium on the surface of the graphite particles is prevented. As a result, the increase in lithium metal that does not participate in the battery reaction is suppressed, and the charge / discharge cycle characteristics are improved.
また、 リチウムイオンの拡散性が向上した結果、 低温下における高率充放電特性 も向上する。  In addition, as a result of the improved diffusion of lithium ions, the high-rate charge / discharge characteristics at low temperatures are also improved.
前記中核粒子がホウ素を含むことによって、 ホウ素原子が炭素原子と置換されて 炭素材料の結晶性が向上し、 また、 開回路電位が貴となるので、 リチウムイオンの 拡散性を向上させることができる。 この結果、 充放電サイクル特性に優れ、 低温で の高率充放電特性に優れた非水電解質二次電池を得ることができる。 中核粒子に含 まれるホウ素の量は、 3重量％以下であることが好ましい。 この理由は必ずしも明 らかではないが、 以下のように考えることができる。 ホウ素の量が 3重量％を超え ると、 炭素原子と置換されなかったホウ素が中核粒子表面に窒化ホウ素等の不純物 を形成するため、 炭素材科の電子伝導性を低下させる。 電子伝導性が低下すると電 池の内部抵抗が増大するため、 オーム損が生じ、 このオーム損により放電電位が低 下した分だけ放電容量が実質的に低下する。 充放電を繰り返すうちに電池の内部抵 抗が増加し、 放電容量が漸次低下する。 このようにして充放電サイクル特性が低下 すると考えられるのである。 When the core particles contain boron, the boron atoms are substituted with carbon atoms to improve the crystallinity of the carbon material, and the open circuit potential becomes noble, so that the diffusion of lithium ions can be improved. . As a result, a non-aqueous electrolyte secondary battery having excellent charge / discharge cycle characteristics and excellent high-rate charge / discharge characteristics at low temperatures can be obtained. The amount of boron contained in the core particles is preferably 3% by weight or less. The reason for this is not necessarily clear, but can be considered as follows. When the amount of boron exceeds 3% by weight, the boron that has not been substituted with carbon atoms forms impurities such as boron nitride on the surface of the core particle, thereby lowering the electronic conductivity of the carbonaceous materials. As the electron conductivity decreases, the internal resistance of the battery increases, causing ohmic loss, and the ohmic loss substantially reduces the discharge capacity by the reduction in discharge potential. As charge and discharge are repeated, the internal resistance of the battery increases, and the discharge capacity gradually decreases. In this way, the charge / discharge cycle characteristics deteriorate It is thought that.
そして、 表層部の炭素材料は低結晶性炭素材料又は非晶質炭素材料であることが 好ましい。 このことによつて非水電解質液と前記中核粒子との反応を抑制すること ができる。 この結果、 不可逆容量の発生を抑制できるので高い放電容量を備えた非 水電解質二次電池を得ることができる。  The carbon material in the surface layer is preferably a low-crystalline carbon material or an amorphous carbon material. Thereby, the reaction between the non-aqueous electrolyte solution and the core particles can be suppressed. As a result, generation of irreversible capacity can be suppressed, and a nonaqueous electrolyte secondary battery having a high discharge capacity can be obtained.
表層部の割合が 1重量％未満であると、 不可逆容量が発生しやすい。 一方、 表層 部の割合が 3 0重量％を超えると、 低結晶性炭素材料または非晶質炭素材料の嵩密 度は結晶性炭素材料に比べて低いため、 体積当たりの放電容量が減少する。 以上よ り、 前記表層部の重量は、 前記中核粒子の重量と前記表層部の重量とを合計したも のに対して、 1重量％以上 3 0重量％以下であることが好ましく、 さらに、 5重 量％以上 2 0重量％以下が特に好ましい。 図面の簡単な説明  If the proportion of the surface layer is less than 1% by weight, irreversible capacity is likely to occur. On the other hand, when the ratio of the surface layer portion exceeds 30% by weight, the discharge capacity per volume is reduced because the bulk density of the low-crystalline carbon material or the amorphous carbon material is lower than that of the crystalline carbon material. As described above, the weight of the surface layer is preferably 1% by weight or more and 30% by weight or less based on the sum of the weight of the core particles and the weight of the surface layer. It is particularly preferable that the content be from 20% by weight to 20% by weight. BRIEF DESCRIPTION OF THE FIGURES
第 1図は、 この発明に係る角形非水電解質二次電池の縦断面図である。  FIG. 1 is a longitudinal sectional view of a prismatic nonaqueous electrolyte secondary battery according to the present invention.
第 2図は、 ホウ素含有黒鉛、 MCM B、 及び非晶質炭素材料の開回路電位を示す。 第 3図は、 実施例 1、 2、 1 0、 及ぴ比較例 2における、 非水電解質二次電池の 充放電サイクル特性を示す図である。 発明を実施するための最良の形態  FIG. 2 shows the open circuit potentials of boron-containing graphite, MCMB, and amorphous carbon material. FIG. 3 is a diagram showing charge / discharge cycle characteristics of the nonaqueous electrolyte secondary batteries in Examples 1, 2, 10 and Comparative Example 2. BEST MODE FOR CARRYING OUT THE INVENTION
以下に、 本発明の一実施形態について図面を参照しつつ説明する。  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
図 1は、 本発明の一実施形態にかかる角形非水電解質二次電池 1の概略断面図で ある。 図 1において、 1は角形非水電解質二次電池、 2は電極群、 3は負極板、 4 は正極板、 5はセパレータ、 6は電池容器、 7は蓋板、 8は安全弁、 9は正極端子、 1 0は負極リード、 1 1は正極リードである。  FIG. 1 is a schematic sectional view of a prismatic nonaqueous electrolyte secondary battery 1 according to one embodiment of the present invention. In Fig. 1, 1 is a prismatic nonaqueous electrolyte secondary battery, 2 is an electrode group, 3 is a negative electrode plate, 4 is a positive electrode plate, 5 is a separator, 6 is a battery case, 7 is a lid plate, 8 is a safety valve, and 9 is a positive electrode. Terminals, 10 is a negative electrode lead, and 11 is a positive electrode lead.
この角形非水電解質二次電池 1は、 アルミニゥム箔からなる集電体に正極合剤を 塗布してなる正極板 4と、 銅箔かちなる集電体に負極合剤を塗布してなる負極板 3 と、 非水電解液とを電池容器 6に収納してなるものである。  The prismatic nonaqueous electrolyte secondary battery 1 has a positive electrode plate 4 formed by applying a positive electrode mixture to a current collector made of aluminum foil, and a negative electrode plate formed by applying a negative electrode mixture to a current collector formed of copper foil. 3 and a non-aqueous electrolyte are housed in a battery container 6.
電池容器 6には、 安全弁 8を設けた蓋板 7がレーザー溶接によって取り付けられ、 正極端子 9は正極リード 1 1を介して正極板 4と接続され、 負極板 3は負極リード 1 0を介して電池容器 6と電気的に接続されている。 A lid plate 7 provided with a safety valve 8 is attached to the battery container 6 by laser welding. Positive electrode terminal 9 is connected to positive electrode plate 4 via positive electrode lead 11, and negative electrode plate 3 is electrically connected to battery case 6 via negative electrode lead 10.
本発明で用いられる非水電解質二次電池用炭素材料としては、 リチウムイオンを 吸蔵 '放出できる炭素材料を用いることが可能であり、 例えば、 黒鉛系炭素材料、 低結晶性炭素材料、 非晶質炭素材料などを挙げることができる。  As the carbon material for the non-aqueous electrolyte secondary battery used in the present invention, it is possible to use a carbon material capable of absorbing and releasing lithium ions, such as a graphite-based carbon material, a low-crystalline carbon material, and an amorphous carbon material. A carbon material can be used.
本発明で用いられる黒鉛系炭素材料としては、 例えば鉱石として産出される天然 黒鉛を用いることが可能であり、 その形状としては燐片状ゃ土状そして球状のもの などがある。 また、 ピッチコータス、 石油系コークスなどの易黒鉛化性炭素を不活 性雰囲気中 2 4 0 0〜 3 0 0 0 °Cで熱処理することによって得られる人造黒鉛も用 いることができる。 具体的には、 M C M B、 黒鉛化メソフェーズピッチ系炭素繊維、 黒 ^3、ゥイスカーなどである。  As the graphite-based carbon material used in the present invention, for example, natural graphite produced as an ore can be used, and its shape includes flaky, earth-like, and spherical shapes. In addition, artificial graphite obtained by heat-treating graphitizable carbon such as pitch coater and petroleum coke in an inert atmosphere at 240 to 300 ° C. can also be used. Specific examples include MCMB, graphitized mesophase pitch-based carbon fiber, black ^ 3, and whiskers.
本発明で用いられる低結晶性炭素材料は、 易黒鉛化性炭素を不活性雰囲気中 7 0 0 °C〜 1 2 0 0 °Cで熱処理することにより製造することができる。  The low-crystalline carbon material used in the present invention can be produced by heat-treating graphitizable carbon at 700 ° C. to 1200 ° C. in an inert atmosphere.
本発明で用いられる非晶性炭素材料は、 高温度に加熱されても黒鉛化の進行しな い難黒鉛化性の炭素材料や有機高分子化合物 （例えば、 フエノール樹脂、 フラン樹 月旨、 ポリ塩化ビニリデン樹脂、 セルロース樹脂、 フルフリルアルコール樹脂等） に 対して、 黒鉛材料を製造するのと同様の熱処理を行うことによって得ることができ る。  The amorphous carbon material used in the present invention is a non-graphitizable carbon material or an organic polymer compound that does not progress to graphitization even when heated to a high temperature (for example, phenol resin, furan resin, polystyrene, and the like). It can be obtained by subjecting vinylidene chloride resin, cellulose resin, furfuryl alcohol resin, etc.) to a heat treatment similar to that used to produce graphite materials.
本発明において、 中核粒子に低結晶性炭素材料からなる表層部を設ける方法とし ては、 加熱して液状とした石油系ピッチに中核粒子を浸漬し、 これを乾燥後、 溶媒 で洗浄した後、 7 0 0 °C〜 1 2 0 0 °Cの不活性雰囲気中で熱処理する方法が挙げら れる。 また、 有機溶媒に石油ピッチを溶かし、 その中に中核粒子を浸漬し、 これを 乾燥、 洗浄した後、 熱処理してもよい。 また、 化学蒸着などにより気相から中核粒 子に直接被覆してもよい。  In the present invention, as a method of providing a surface layer portion made of a low-crystalline carbon material on the core particles, the core particles are immersed in a petroleum-based pitch that has been heated and liquefied, and after drying and washing with a solvent, A method of performing heat treatment in an inert atmosphere at 700 ° C. to 1200 ° C. can be used. Alternatively, petroleum pitch may be dissolved in an organic solvent, core particles may be immersed in the pitch, dried and washed, and then heat-treated. Alternatively, the core particles may be directly coated from the gas phase by chemical vapor deposition or the like.
本発明において、 中核粒子に非晶質炭素材料からなる表層部を設ける方法として は、 有機溶媒にフエノール樹脂、 フラン樹脂、 ポリ塩ィヒビ二リデン樹脂、 セルロー ス樹脂、 フルフリルアルコール樹脂等を溶解させ、 その中に中核粒子を浸漬し、 こ れを乾燥後、 溶媒で洗浄した後、 7 0 0 °C〜 1 2 0 0 °Cの不活性雰囲気中で熱処理 する方法が例示できる。 In the present invention, as a method for providing a surface layer made of an amorphous carbon material in the core particles, a phenol resin, a furan resin, a polyvinylidene resin, a cellulose resin, a furfuryl alcohol resin, or the like is dissolved in an organic solvent. The core particles are immersed therein, dried, washed with a solvent, and heat treated in an inert atmosphere at 700 ° C to 1200 ° C. An example of the method is as follows.
なお、 中核粒子に表層部を形成させた後は、 粉碎、 分級等の処理はできるだけ行 わないのが好ましい。 なぜなら、 上記処理により、 一旦形成された表層部が剥離、 脱落する虞があるからである。  After the surface layer is formed on the core particles, it is preferable that processes such as pulverization and classification are not performed as much as possible. This is because the surface layer once formed may be peeled off or fall off by the above treatment.
本発明において、 中核粒子の重量と表層部の重量とを合計したものに対する、 表 層部の重量比は、 以下のようにして計算される。 前記表層部の重量は、 前記表層部 形成過程において表層部を形成する炭素材料の仕込み量と、 洗浄工程における洗浄 溶媒可溶分との差から計算される。 このようにして算出された前記表層部の重量を、 中核粒子の仕込み重量と前記表層部の重量との和で除することにより、 中核粒子の 重量と表層部の重量とを合計したものに対する、 表層部の重量比が計算される。  In the present invention, the weight ratio of the surface layer portion to the sum of the weight of the core particles and the weight of the surface layer portion is calculated as follows. The weight of the surface layer portion is calculated from the difference between the charged amount of the carbon material forming the surface layer portion in the process of forming the surface layer portion and the solvent-soluble matter in the cleaning step. By dividing the weight of the surface layer thus calculated by the sum of the charged weight of the core particles and the weight of the surface layer, the weight of the core particles and the weight of the surface layer are calculated, The weight ratio of the surface layer is calculated.
本発明で用いられるホウ素含有黒鉛材料は、 炭素材料と、 ホウ素化合物とを混合 し、 これを不活性雰囲気中 2 0 0 0 °C〜 2 8 0 0 °Cの温度で熱処理することによつ て得ることができる。 炭素材料としては、 タール、 ピッチなどの石炭系又は石油系 重質油、 ピッチコータス、 石炭コータス、 石油コータス、 カーボンブラック、 熱分 解炭素、 有機樹脂材料などを挙げることができ、 天然黒鉛や人造黒鉛も使用できる。 また、 ホウ素化合物としては、 ホウ素、 ホウ酸 （H 3 B 0 3)、 酸化ホウ素 （B 2 0 3、 B 4 0 5 )、 炭化ホウ素 （B 4 C ) などを用いることができる。 ホウ素含有黒鉛材料 中におけるホウ素含有量は 3重量％以下が好ましい。 3重量％を超えると、 炭素原 子と置換されなかったホウ素が粒子表面に窒化ホウ素などの不純物を形成する結果、 炭素材料の電子伝導性を低下させるので好ましくない。 ホウ素の含有量は、 I C P 発光分光分析により定量できる。 The boron-containing graphite material used in the present invention is obtained by mixing a carbon material and a boron compound and heat-treating the mixture at a temperature of 200 ° C. to 280 ° C. in an inert atmosphere. Can be obtained. Examples of carbon materials include coal or petroleum heavy oils such as tar and pitch, pitch coaters, coal coaters, petroleum coaters, carbon black, pyrolytic carbon, organic resin materials, and the like. Graphite can also be used. As the boron compound, boron, boric acid (H 3 B 0 3), boron oxide (B 2 0 3, B 4 0 5), or the like can be used boron carbide (B 4 C). The boron content in the boron-containing graphite material is preferably 3% by weight or less. If it exceeds 3% by weight, boron not substituted with carbon atoms forms impurities such as boron nitride on the surface of the particles, which undesirably lowers the electron conductivity of the carbon material. The boron content can be determined by ICP emission spectroscopy.
本発明に用いられる炭素材料は、 原料を予め粒度調整することにより所定の粒度 分布をもつものに調製できる。 また、 熱処理を行って所望の材料を調製した後にこ れらを粉碎、 分級して所定の粒度分布をもつものに調製することもできる。 本発明 に係る、 中核粒子が表層部を備えてなる最終形態の炭素材料の平均粒径 D 5。は、The carbon material used in the present invention can be prepared to have a predetermined particle size distribution by adjusting the particle size of the raw material in advance. Further, after heat treatment is performed to prepare a desired material, these materials may be pulverized and classified to prepare a material having a predetermined particle size distribution. The average particle diameter D 5 of the final form of the carbon material according to the present invention in which the core particles have a surface layer portion. Is
1 μ πι以上 1 0 0 μ πι以下が好ましい。 1 μ m未満であると比表面積が大きくなり、 不可逆容量が大きくなるので好ましくない。 他方、 1 0 0 を超えるとペースト したときの塗工性が悪くなるので好ましくない。 当該最終形態の炭素材料の粒径分 布は、 前記中核粒子の粒径に依存する。 したがって、 中核粒子の平均粒径 D5。は 0. 1 / m以上 150 ^um以下であることが好ましい。 本発明に用いられる炭素材 料の粒径分布については、 レーザー回折 ·散乱法により測定できる。 It is preferably 1 μπι or more and 100 μππ or less. If it is less than 1 μm, the specific surface area increases and the irreversible capacity increases, which is not preferable. On the other hand, if it exceeds 100, the coatability at the time of pasting deteriorates, which is not preferable. The particle size of the carbon material in the final form The fabric depends on the size of the core particles. Therefore, the average core particle size D 5 . Is preferably from 0.1 / m to 150 ^ um. The particle size distribution of the carbon material used in the present invention can be measured by a laser diffraction / scattering method.
本発明に用いられる炭素材料の平均粒径 D5。が上記の範囲にある場合には、 B ET比表面積は概ね 0. 1 m2Zg以上 10m2/g以下の範囲になる。 0. 1 m2 Zg未満であると、 充電時に粒子単位表面積当たりの電流負荷が大きくなつてしま うという問題があり、 他方、 1 0m2/gを超えると不可逆容量が大きくなる。 当 該最終形態の炭素材料の B E T比表面積は、 前記中核粒子の B E T比表面積に依存 する。 したがって、 中核粒子の BET比表面積は 0. 2m2/g以上 1 0. Om2 Zgであることが好ましい。 本発明で用いられる炭素材料の BET比表面積につい ては、 液体窒素を用いた低温ガス吸着法によって測定し、 BET法で解析すること により算出できる。 Average particle diameter D 5 of the carbon material used in the present invention. Is in the above range, the BET specific surface area is generally in the range of 0.1 m 2 Zg to 10 m 2 / g. If it is less than 0.1 m 2 Zg, there is a problem that the current load per unit surface area of the particles will increase during charging, while if it exceeds 10 m 2 / g, the irreversible capacity will increase. The BET specific surface area of the carbon material in the final form depends on the BET specific surface area of the core particles. Therefore, the core particles preferably have a BET specific surface area of 0.2 m 2 / g or more and 10 Om 2 Zg. The BET specific surface area of the carbon material used in the present invention can be calculated by measuring by a low-temperature gas adsorption method using liquid nitrogen and analyzing by a BET method.
本発明に用いられる炭素材料の L iZL i +に対する開回路電位は、 対極及び参 照電極に金属リチウムを用いた三極式セルを用いて測定できる。 作用電極には、 測 定対象の炭素材料を含む負極合剤を集電体に塗布してなるものを用いることができ る。 電解質としては、 例えば、 エチレンカーボネートとジェチルカーボネートとの 混合溶媒 （体積比 1 ： 1) に 1 mo 1 / 1の L i C 104を溶解させたものを用い ることができる。 一般に、 炭素材料の種類によって開回路電位は異なる。 黒鉛材料 と、 低結晶性炭素材料または非晶質炭素材料とを比較した場合、 黒鉛材料の開回路 電位の方が貴である。 また、 黒鉛材料の中で比較すると、 例えば人造黒鉛と MCM Bとを比較すると、 人造黒鉛の開回路電圧の方が貴である。 そして、 ホウ素を含ん だ黒鉛材料と、 ホウ素を含まない黒鉛材料とを比較すると、 ホウ素を含んだ黒鉛材 料の開回路電圧の方が貴である。 更に、 ホウ素含有量が増加するに従って、 開回路 電位も貴になる。 このように、 炭素材料の種類により開回路電位は異なるので、 中 核粒子の開回路電位が表層部よりも貴となるように各種炭素材料を選択して用いる ことができる。 このとき、 開回路電位の観点からは、 中核粒子としてホウ素含有黒 鉛を用いるのが好ましく、 表層部として低結晶性炭素材料または非晶質炭素材料を 用いるのが好ましい。 本発明に用いられる炭素材料の結晶性は、 C u Kひ線を用いた X線回折法により、 (002) 面の平均面間隔 d。02、及び （002) 面方向の結晶子厚み L cにより 評価できる。 本発明に係る炭素材料の中核粒子において、 dQQ2は 0. 33 5 nm 以上 0. 340 nm以下が好ましく、 L cは 50 n m以上であることが好ましい。 dQ。2が 0. 340 nmを超えると、 結晶性が低くなるため、 放電容量が小さくな るので好ましくない。 The open circuit potential of the carbon material used in the present invention with respect to LiZL i + can be measured using a triode cell using lithium metal for the counter electrode and the reference electrode. As the working electrode, an electrode obtained by applying a negative electrode mixture containing a carbon material to be measured to a current collector can be used. As the electrolyte, for example, a mixed solvent of ethylene carbonate and Jefferies chill carbonate (volume ratio 1: 1) can Rukoto used after dissolved 1 mo 1/1 of L i C 10 4 to. Generally, the open circuit potential differs depending on the type of carbon material. When the graphite material is compared with the low crystalline carbon material or the amorphous carbon material, the open circuit potential of the graphite material is more noble. Also, when comparing among graphite materials, for example, when comparing artificial graphite and MCMB, the open circuit voltage of artificial graphite is more noble. When comparing graphite materials containing boron and graphite materials containing no boron, the open circuit voltage of the graphite material containing boron is more noble. In addition, as the boron content increases, the open circuit potential becomes more precious. As described above, since the open-circuit potential varies depending on the type of carbon material, various carbon materials can be selected and used so that the open-circuit potential of the core particles is more noble than the surface layer portion. At this time, from the viewpoint of the open circuit potential, it is preferable to use boron-containing graphite as the core particles, and it is preferable to use a low-crystalline carbon material or an amorphous carbon material as the surface layer. The crystallinity of the carbon material used in the present invention is determined by an X-ray diffraction method using Cu K line, and the average spacing d of the (002) plane. 02 and the crystallite thickness Lc in the (002) plane direction. In the core particles of the carbon material according to the present invention, d QQ2 is preferably 0.335 nm or more and 0.340 nm or less, and L c is preferably 50 nm or more. d Q. If the value of 2 exceeds 0.340 nm, the crystallinity will be low and the discharge capacity will be small, which is not preferable.
正極活物質としては、 例えば、 L i C o 02、 L i N i 02、 L i C o XN i χ_χ 02、 L iMn 204、 Mn〇2、 F e 02、 V205、 V6〇13、 T i〇2等のトンネ ル構造または層状構造の金属酸化物、 ォキシ水酸化ニッケル等の金属水酸化物、 T i S等の金属硫化物、 ポリア二リン等の導電性ポリマーなどを用いることができ、 さらに、 これらを混合して用いることもできる。 これらの中で、 組成式 L i xMO 2、 L i yM204 (ただし、 Mは一種類以上の遷移金属元素を示す、 0≤χ^ 1. 2、 0≤y≤ 2) で表されるリチウム遷移金属複合酸化物が正極活物質として特に 好ましい。 As the positive electrode active material, for example, L i C o 0 2, L i N i 0 2, L i C o X N i χ _ χ 0 2, L iMn 2 0 4, Mn_〇 2, F e 0 2, V 2 0 5, V 6 〇 13, T I_〇 metal oxides tunnel structure or a layered structure, such as 2, metal hydroxides such as Okishi nickel hydroxide, a metal sulfide such as T i S, Poria diphosphate And the like, and a conductive polymer such as the above can be used. Among them, the composition formulas L i x MO 2 and L i y M 2 0 4 (where M represents one or more kinds of transition metal elements, 0≤χ ^ 1.2, 0≤y≤2) The represented lithium transition metal composite oxide is particularly preferred as the positive electrode active material.
非水電解質としては、 電解液または無機固体電解質、 ポリマー固体電解質等の固 体電解質を使用することができる。  As the non-aqueous electrolyte, an electrolyte or a solid electrolyte such as an inorganic solid electrolyte and a polymer solid electrolyte can be used.
電解液を用いる場合、 電解液溶媒としては、 エチレンカーボネート、 プロピレン カーボネート、 ジメチノレカーボネート、 ジェチルカーボネート、 γ—ブチロラクト ン、 スルホラン、 ジメチルスルホキシド、 ァセトニトリル、 ジメチルホルムアミ ド、 ジメチルァセトアミ ド、 1, 2—ジメ トキシェタン、 1, 2—ジエトキシェタン、 テトラヒ ドロフラン、 2—メチルテトラヒ ドロフラン、 ジォキソラン、 メチノレアセ テート等の極性溶媒、 もしくはこれらの混合物を使用することができる。  When an electrolytic solution is used, the solvent for the electrolytic solution may be ethylene carbonate, propylene carbonate, dimethinolecarbonate, getyl carbonate, γ-butyrolactone, sulfolane, dimethyl sulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, 1 Polar solvents such as 1,2-dimethoxetane, 1,2-dietoxetane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolan, and methinorea acetate, or mixtures thereof can be used.
また、 上記の電解液溶媒に溶解させるリチウム塩としては、 L i P F 6、 L i CFurther, as the lithium salt dissolved in the above-mentioned electrolyte solvent, L i PF 6 , L i C
104、 L i BF4、 L i A s F6、 L i CF3C〇2、 L i C F 3 (C F 3) 3、 L i C F 3 (C2F5) 3、 L i CF3S03、 L i N (S 02C F 3) 2、 L i N (S〇2 10 4 , L i BF 4 , L i As F 6 , L i CF 3 C〇 2 , L i CF 3 (CF 3 ) 3 , L i CF 3 (C 2 F 5 ) 3 , L i CF 3 S0 3 , L i N (S 0 2 CF 3 ) 2 , L i N (S〇 2
CF2CF3) 2、 L i N (COCF3) 2および L i N (C〇CF2CF3) 2などの 塩、 もしくはこれらの混合物を用いることができる。 Salts such as CF 2 CF 3 ) 2 , L i N (COCF 3 ) 2 and L i N (C〇CF 2 CF 3 ) 2 or a mixture thereof can be used.
セパレータとしては、 織布、 不織布、 合成樹脂微多孔膜等を用いることができる。 特に、 合成樹脂微多孔膜を好適に用いることができ、 中でもポリエチレン製微多孔 膜、 ポリプロピレン製微多孔膜、 あるいはこれらを複合した微多孔膜等のポリオレ フィン系微多孔膜が、 厚さ、 膜強度、 膜抵抗等の性能面から好適に用いられる。 As the separator, a woven fabric, a nonwoven fabric, a synthetic resin microporous membrane, or the like can be used. In particular, a synthetic resin microporous membrane can be suitably used. Among them, a polyolefin-based microporous membrane such as a polyethylene microporous membrane, a polypropylene microporous membrane, or a microporous membrane obtained by combining these is used. It is preferably used in terms of performance such as strength and film resistance.
また、 電解質として高分子固体電解質等の固体電解質を用いることで、 セパレー タを兼ねさせることも可能であり、 この場合、 高分子固体電解質として有孔性の高 分子固体電解質膜を使用して、 この高分子固体電解質にさらに電解液を含有させて も良い。 また、 ゲル状の高分子固体電解質を用いる場合には、 ゲルを構成する電角军 液と、 細孔中等に含有されている電解液とは同じでも良いし、 異なっていてもよい。 また、 合成樹脂微多孔膜と高分子固体電解質等を組み合わせて用いてもよい。  Also, by using a solid electrolyte such as a polymer solid electrolyte as the electrolyte, it is also possible to double as a separator.In this case, a porous high molecular solid electrolyte membrane is used as the polymer solid electrolyte. The solid polymer electrolyte may further contain an electrolytic solution. When a gel polymer solid electrolyte is used, the electrolysis solution constituting the gel may be the same as or different from the electrolyte solution contained in the pores or the like. Further, a synthetic resin microporous membrane and a solid polymer electrolyte may be used in combination.
以下、 本願発明の実施形態をいくつかの実施例に基づいてさらに具体的に説明す る。 なお、 本発明は、 以下の実施例により何ら限定されるものではなく、 その主旨 を変更しない範囲において適宜変更して実施することが可能である。  Hereinafter, embodiments of the present invention will be described more specifically based on some examples. It should be noted that the present invention is not limited in any way by the following examples, and can be implemented by appropriately changing the scope without changing the gist of the invention.
(炭素材料）  (Carbon material)
(ホウ素含有黒鉛）  (Boron-containing graphite)
中核粒子となるホウ素含有黒鉛は次のようにして調製した。 ホウ酸 （H3B O 3) をピッチコークスに対して、 ホウ素原子の重量換算で 0. 0 1 2 6重量％、 0. 1 2 7重量％、 0. 6 26重量％、 3. 7 3重量％添加混合した後、 アルゴン気流 中 1 0 00 °Cまで加熱し、 1 0時間保持した後、 さらに 2400 °Cまで加熱し、 2 0時間保持した。 その後、 室温まで冷却し、 粉碎、 分級した。 上記の操作により、 ホウ素含有量の異なった、 4種類のホウ素含有黒鉛を得た。 これらについて、 Boron-containing graphite serving as core particles was prepared as follows. Boric acid (H 3 BO 3 ) is 0.026 wt%, 0.127 wt%, 0.626 wt%, 3.73 wt% of pitch coke in terms of boron atom weight. After the addition and mixing, the mixture was heated to 100 ° C. in an argon stream, kept for 10 hours, heated to 2400 ° C., and kept for 20 hours. Then, it was cooled to room temperature, pulverized and classified. By the above operation, four kinds of boron-containing graphites having different boron contents were obtained. For these,
1 CP発光分光分析法によりホウ素含有量を測定したところ、 添加ホウ素濃度で 0. 0 1 2 6重量％、 0. 1 2 7重量％、 0. 6 26重量％、 3. 7 3重量％の試料の ホウ素含有量はそれぞれ、 約 0. 0 1重量％、 0. 1重量％、 0. 5重量％、 3重 量％であった。  1 When the boron content was measured by CP emission spectroscopy, the concentration of boron added was 0.0126% by weight, 0.127% by weight, 0.626% by weight, and 3.73% by weight. The boron content of the samples was about 0.01% by weight, 0.1% by weight, 0.5% by weight, and 3% by weight, respectively.
(MCMB)  (MCMB)
中核粒子となる MCMB (メソカーボンマイク口ビーズ) は、 コールタール、 コ 一ルタールビッチなどを出発原料として用い、 これらを常圧から 2 0 k g/c m MCMB (mesocarbon microphone mouth beads), which are core particles, use coal tar, coal tar bitch, etc. as starting materials, and use them at normal pressure to 20 kg / cm
2 · Gの加圧下、 約 4 0 0°Cの温度で熱処理して生成した球晶を分離 ·精製し、 不 活性雰囲気中、 約 2 8 0 0 °Cの温度で黒鉛化することにより得た。 The spherulite produced by heat treatment at a temperature of about 400 ° C under a pressure of 2G was separated and purified, It was obtained by graphitization at a temperature of about 280 ° C. in an active atmosphere.
(人造黒鉛）  (Artificial graphite)
人造黒鉛はピッチを 5 0 0 °C以上の温度にすることにより得られるセミコ一タス を 2 5 0 0 °C以上で不活性雰囲気下、 熱処理することにより得た。  The artificial graphite was obtained by heat-treating a semi-copper obtained by setting the pitch to a temperature of 500 ° C. or higher in an inert atmosphere at a temperature of 250 ° C. or higher.
(低結晶性炭素材料）  (Low crystalline carbon material)
表層部となる低結晶性炭素材料と同じ原料、 同じ調製条件で低結晶性炭素材料を 調製した。 すなわち、 ピッチコータスを不活性雰囲気中約 1 2 0 0 °Cで熱処理する ことにより低結晶性炭素材料を得た。 本発明に係る、 表層部と中核粒子を備えた最 終形態の炭素材料の表層部のみについて、 後述の開回路電圧、 結晶性を測定するこ とは不可能なので、 表層部を別途調製し、 これについて開回路電圧、 結晶性を測定 した。  A low-crystalline carbon material was prepared using the same raw materials and the same preparation conditions as the low-crystalline carbon material used as the surface layer. That is, a low-crystalline carbon material was obtained by subjecting the pitch coater to a heat treatment at about 1200 ° C. in an inert atmosphere. Since it is impossible to measure the open-circuit voltage and crystallinity described below only for the surface layer of the final form of the carbon material having the surface layer and the core particles according to the present invention, the surface layer is separately prepared. The open circuit voltage and crystallinity were measured for this.
(非晶質炭素材料）  (Amorphous carbon material)
表層部となる非晶質炭素材料と同じ原料、 同じ調製条件で、 非晶質炭素材料を調 製した。 すなわち、 フルフリルアルコール樹脂を、 約 1 2 0 0 °C不活性雰囲気中で 熱処理することにより非晶質炭素材料を得た。 低結晶性炭素材料の場合と同様、 本 発明に係る、 表層部と中核粒子を備えた最終形態の炭素材料の表層部のみについて、 後述の開回路電圧、 結晶性を測定することは不可能なので、 表層部を別途調製し、 これについて開回路電圧、 結晶 1·生を測定した。  An amorphous carbon material was prepared using the same raw materials and the same preparation conditions as the amorphous carbon material to be the surface layer. That is, the furfuryl alcohol resin was heat-treated in an inert atmosphere at about 1200 ° C. to obtain an amorphous carbon material. As in the case of the low-crystalline carbon material, it is impossible to measure the open-circuit voltage and crystallinity described below only for the surface layer portion of the final form of the carbon material having the surface layer portion and the core particles according to the present invention. The surface layer was separately prepared, and the open circuit voltage and crystal growth were measured for this.
(炭素材料の開回路電位）  (Open circuit potential of carbon material)
本発明に用いられる炭素材料の L i Z L i +に対する開回路電位は、 対極及び参 照電極に金属リチウムを用いた三極式セルを用いて測定した。 作用電極には、 前記 のようにして得られた炭素材料 9 0重量％と、 結着剤としてのポリフッ化ビニリデ ン （P V d F ) 1 0重量％とを混合してなる合剤に、 N—メチルー 2—ピロリ ドン (NM P ) を適宜加えてペースト状に調製した後、 これを厚さ 1 5 mの銅箔集電 体両面に塗布し、 さらに 1 0 0 °Cで 5時間乾燥し、 多孔度 3 0 %となるように圧縮 成形することによって作製した電極板を切り出したものを使用した。 電解質として は、 エチレンカーボネートとジェチルカーボネートとの混合溶媒 （体積比 1 ： 1 ) に l m o l Z lの L i C l O 4を溶解させたものを用いた。 このようにして作製し た三極式セルを用いて、 以下のようにして開回路電位を測定した。 まず、 温度 2 5°Cの下で、 炭素材料 1 g当たり 5 OmAの電流密度で、 L丄 丄 +に対して 0V〜1. 5 Vの電位範囲で 1サイクルの充電及び放電を行った。 つぎに、 同じく 電流密度 5 OmAZgで 0. 25 h (15分間） 充電した後、 2時間休止するのを 1サイクルとして、 これを 35サイクル行った。 このとき、 20サイクル目の充電 後、 休止時間終了直前に測定された電位を開回路電位として測定した。 20サイク ル目の充電電気量は、 5 OmA/g X 0. 25 h X 20サイクル = 25 OmAhZ gとして計算した。 一測定例として、 ホウ素 0. 31重量％含有黒鉛、 MCMB、 及び非晶質炭素材料の開回路電位 （リチウムを吸蔵する平衡電位） を図 2に示す。 図中、 20サイクル目の測定点における L i Z L i +に対する電位を開回路電位と した。 本発明に使用した炭素材料について、 上述の方法により開回路電位を測定し、 これらの値を表 1にまとめた。 The open circuit potential of the carbon material used in the present invention with respect to L i ZL i + was measured using a three-electrode cell using lithium metal as a counter electrode and a reference electrode. For the working electrode, a mixture of 90% by weight of the carbon material obtained as described above and 10% by weight of polyvinylidene fluoride (PVdF) as a binder was mixed with N —Methyl-2-pyrrolidone (NMP) is added as appropriate to prepare a paste, which is then applied to both sides of a 15-m-thick copper foil current collector, and dried at 100 ° C for 5 hours. An electrode plate produced by compression molding so as to have a porosity of 30% was used. As the electrolyte, a mixed solvent of ethylene carbonate and Jefferies chill carbonate (volume ratio 1: 1) was used to dissolve the L i C l O 4 of I mol Z l to. Made in this way The open-circuit potential was measured as follows using the three-pole cell. First, one cycle of charge and discharge was performed at a current density of 5 OmA per g of carbon material at a temperature of 25 ° C and a potential range of 0 V to 1.5 V with respect to L 丄 丄 +. Next, the battery was charged at a current density of 5 OmAZg for 0.25 h (15 minutes), followed by a pause of 2 hours. At this time, the potential measured immediately after the end of the pause after charging in the 20th cycle was measured as the open circuit potential. The amount of charge in the 20th cycle was calculated as 5 OmA / g × 0.25 h × 20 cycles = 25 OmAhZ g. As an example of measurement, Fig. 2 shows the open circuit potential (equilibrium potential for occlusion of lithium) of graphite containing 0.31% by weight of boron, MCMB, and an amorphous carbon material. In the figure, the potential with respect to Li ZLi + at the measurement point at the 20th cycle was defined as the open circuit potential. The open circuit potential of the carbon material used in the present invention was measured by the method described above, and these values are summarized in Table 1.
(炭素材料の結晶性）  (Crystallinity of carbon material)
本発明に用いられる炭素材料について、 C u K 線を用いた X線回折法により、 (002) 面の平均面間隔 d Q02、及び （002) 面方向の結晶子厚み L cを測定 した。 これらの値を、 表 1に併せてまとめた。 With respect to the carbon material used in the present invention, the average spacing dQ 02 of the (002) plane and the crystallite thickness Lc in the (002) plane direction were measured by X-ray diffraction using Cu K rays. These values are summarized in Table 1.
<表 1〉 <Table 1>
ホウ素含有量 開回路電位 02 し c Boron content Open circuit potential 02 c
炭素材料  Carbon material
(重量％) (V) knm) 、nm)  (% By weight) (V) knm), nm)
ホウ素含有  Boron-containing
0.01 0. 1085 0.3359 >100  0.01 0.108 5359> 100
黒鉛  Graphite
ホウ素含有  Boron-containing
0. 1 0.1124 0.3356 >100  0.1 0.1124 0.3356> 100
黒鉛  Graphite
ホウ素含有  Boron-containing
0.5 0. 1189 0.3354 >100  0.5 0. 1189 0.3354> 100
黒鉛  Graphite
ホウ素含有  Boron-containing
3 0. 1331 0.3354 >100  3 0.1331 0.3354> 100
黒鉛  Graphite
MCMB 0 0.0865 0.3363 >100 人造黒鉛 0 0.0900 0.3361 >100  MCMB 0 0.0865 0.3363> 100 Artificial graphite 0 0.0900 0.3361> 100
低結晶性  Low crystallinity
0 0.0340 0.3710 3.0  0 0.0340 0.3710 3.0
炭素材料  Carbon material
5?曰曰  5?
0 0.0230 0.3801 1.1  0 0.0230 0.3801 1.1
ォ不 4 上記の炭素材料を用いて、 実施例及び比較例の非水電解質二次電池を作製した。 (実施例 1 )  Using the above carbon materials, non-aqueous electrolyte secondary batteries of Examples and Comparative Examples were produced. (Example 1)
ホウ素 0. 0 1重量％含有黒鉛 500 gと、 コールタールピッチ 500 gとを 2 00 °C、 常圧で 2時間混合し、 黒鉛をピッチにより被覆した。 このようにして得ら れた、 ピッチにより被覆された黒鉛に、 トルエンを 1 ： 1で加え、 撹拌下にて 6 0°Cから 80°C、 1時間の洗浄処理を行った。 次いで、 これをアルゴン気流中 40 0 °Cまで加熱し、 3時間保持した後、 さらに 1000 °Cまで加熱し、 5時間保持し た。 その後、 室温まで冷却し、 さらに軽く粉碎、 分級することにより、 ホウ素含有 黒鉛の表面に低結晶性炭素材料を備えてなる炭素材料を得た。 炭素材料中における 低結晶性炭素材料の割合は、 5重量％であった。  500 g of graphite containing 0.01% by weight of boron and 500 g of coal tar pitch were mixed at 200 ° C. and normal pressure for 2 hours, and the graphite was coated with the pitch. Toluene was added to the pitch-coated graphite thus obtained at a ratio of 1: 1 and washed with stirring at 60 ° C. to 80 ° C. for 1 hour. Next, this was heated to 400 ° C. in an argon stream and maintained for 3 hours, and then further heated to 1000 ° C. and maintained for 5 hours. Thereafter, the mixture was cooled to room temperature, further lightly pulverized and classified to obtain a carbon material having a low-crystalline carbon material on the surface of boron-containing graphite. The proportion of the low-crystalline carbon material in the carbon material was 5% by weight.
前記のようにして得られた炭素材料 90重量％と、 結着剤としてのポリフッ化ビ 二リデン （PVdF) 10重量％とを混合してなる負極合剤に、 N—メチルー 2— ピロリ ドン （NMP) を適宜加えてペース ト状に調製した後、 これを厚さ 1 5 μηι の銅箔集電体両面に塗布し、 さらに 100 °Cで 5時間乾燥し、 多孔度 30 %となる ように圧縮成形することによつて負極板 3を作製した。 N-methyl-2-pyrrolidone (N-methyl-2-pyrrolidone) was added to a negative electrode mixture obtained by mixing 90% by weight of the carbon material obtained as described above and 10% by weight of polyvinylidene fluoride (PVdF) as a binder. NMP) to make a paste. The negative electrode plate 3 was produced by applying the solution to both surfaces of the copper foil current collector, drying at 100 ° C. for 5 hours, and compression-molding to have a porosity of 30%.
正極板 4は、 正極活物質としてのリチウムコバルト複合酸化物 （L i C o〇2) 90重量％と、 結着剤としてのポリフッ化ビニリデン （PVdF) 5重量0 /0と、 導 電剤としてのアセチレンブラック 5重量％とを混合してなる正極合剤に、 N—メチ ルー 2—ピロリ ドン （NMP) を適宜加えてペースト状に調製した後、 これを厚さ 20 μπιのアルミニウム箔集電体の両面に塗布、 乾燥し、 多孔度 30%となるよう に圧縮成形することによつて作製した。 The positive electrode plate 4, the lithium cobalt complex oxide as a positive electrode active material and (L i C O_〇 2) 90 wt%, and polyvinylidene fluoride (PVdF) 5 wt 0/0 as a binder, conductive agent N-methyl 2-pyrrolidone (NMP) is added to the positive electrode mixture prepared by mixing 5% by weight of acetylene black in the above to prepare a paste, which is then collected into a 20 μπι-thick aluminum foil current collector. It was prepared by applying it to both sides of the body, drying it, and compressing it to a porosity of 30%.
セパレータ 5として厚さ 25 t mのポリエチレン微多孔膜を用い、 上記の正極と 負極とを、 セパレータを介して長円筒状に卷回することで電極群 2を作製した。 こ の電極群と蓋板 7の正極リード 1 1とを接続した後、 電極群 2を鉄に二ッケルメッ キを施した電池容器 6の開口部から収納し、 電池容器 6と蓋板 7とをレーザー溶接 により封口した。 そして、 電池容器 6側面の注液口から非水電解液を注入した後、 この注液口を溶接することで、 非水電解質二次電池 1を気密封口した。  An electrode group 2 was produced by winding a positive electrode and a negative electrode into a long cylindrical shape with a separator interposed therebetween using a 25-μm-thick polyethylene microporous membrane as the separator 5. After this electrode group and the positive electrode lead 11 of the cover plate 7 are connected, the electrode group 2 is housed through the opening of the battery case 6 in which nickel is applied to iron, and the battery case 6 and the cover plate 7 are connected. It was sealed by laser welding. Then, after injecting the non-aqueous electrolyte from the liquid injection port on the side of the battery container 6, the non-aqueous electrolyte secondary battery 1 was hermetically sealed by welding the liquid injection port.
電解液には、 エチレンカーボネート ：ジェチルカーボネート =5 ： 5 (体積比） の混合溶媒に L i P F 6を 1 m o 1 Z 1溶解させた非水電解液を用いた。 The electrolyte solution, ethylene carbonate: Jefferies chill carbonate = 5: 5 using nonaqueous electrolytic solution of L i PF 6 was 1 mo 1 Z 1 dissolved in a mixed solvent (volume ratio).
このようにして、 幅 3 OmmX高さ 48mmX厚さ 4mmの外形寸法を有し、 定 格容量 640 m A hの角形非水電解質二次電池 1を作製した。  In this way, a prismatic nonaqueous electrolyte secondary battery 1 having a width of 3 Omm, a height of 48 mm and a thickness of 4 mm and a rated capacity of 640 mAh was produced.
(実施例 2ないし 4、 及ぴ、 10ないし 12)  (Examples 2 to 4, and 10 to 12)
ホウ素 0. 01重量％含有黒鉛に代えて、 表 2に示す炭素材料を用いた以外は、 実施例 1と同様にして、 実施例 2ないし 4、 及び 10ないし 12の角形非水電解質 二次電池を作製した。  The prismatic nonaqueous electrolyte secondary batteries of Examples 2 to 4, and 10 to 12 in the same manner as in Example 1 except that the carbon material shown in Table 2 was used instead of the graphite containing 0.01% by weight of boron. Was prepared.
(実施例 5ないし 9)  (Examples 5 to 9)
実施例 1において、 トルエンによる洗浄処理時の洗浄温度を 20°Cから 120°C とすることにより、 低結晶性炭素材料の被覆量が 1重量％から 40重量％である炭 素材料を得た。 ホウ素 0. 1重量％含有黒鉛に低結晶性炭素材料を被覆した炭素材 料に代えて、 当該黒鉛材料を負極活物質として用いた以外は、 実施例 1と同様にし て、 実施例 5ないし 9の角形非水電解質二次電池を作製した。 このとき、 炭素材料 中における低結晶性炭素材料の割合は、 それぞれ、 1重量％、 1 0重量％、 2 0重 量％、 3 0重量％、 4 0重量％であった。 In Example 1, a carbon material having a low crystalline carbon material coating amount of 1% by weight to 40% by weight was obtained by changing the cleaning temperature during the cleaning treatment with toluene from 20 ° C. to 120 ° C. . Examples 5 to 9 were carried out in the same manner as in Example 1 except that the graphite material containing 0.1% by weight of boron was coated with a low-crystalline carbon material in place of the carbon material. Of the non-aqueous electrolyte secondary battery was manufactured. At this time, carbon material The proportions of the low-crystalline carbon material in them were 1% by weight, 10% by weight, 20% by weight, 30% by weight, and 40% by weight, respectively.
(比較例 1 )  (Comparative Example 1)
ホウ素 0 . 1重量％含有黒鉛に低結晶性炭素材料を被覆した炭素材料に代えて、 ホ ゥ素 0 . 1重量％含有黒鉛を用いて負極板 3を作製した以外は、 実施例 1と同様に して角形非水電解質二次電池を作製した。 The same as Example 1 except that the negative electrode plate 3 was prepared using a graphite containing 0.1% by weight of boron instead of a carbon material obtained by coating a low-crystalline carbon material on graphite containing 0.1% by weight of boron. As a result, a prismatic nonaqueous electrolyte secondary battery was fabricated.
(比較例 2 )  (Comparative Example 2)
ホウ素 0 . 1重量％含有黒鉛に低結晶性炭素材料を被覆した炭素材料に代えて人 造黒鉛を用いて負極板 3を作製した以外は、 実施例 1と同様にして角形非水電解質 二次電池を作製した。  A rectangular non-aqueous electrolyte secondary battery was prepared in the same manner as in Example 1 except that the negative electrode plate 3 was manufactured using artificial graphite instead of the carbon material obtained by coating the low-crystalline carbon material on graphite containing 0.1% by weight of boron. A battery was manufactured.
上述のように調製した炭素材料の中核粒子ならびに表層部の構成を、 ホウ素を含 む黒 &材料のホウ素含有量、 全体の炭素材料に占める表層部の含有量 （重量％) と ともに、 表 2にまとめて示す。  The composition of the core particles and the surface layer of the carbon material prepared as described above, together with the boron content of black containing boron and the material, and the content (% by weight) of the surface layer in the total carbon material, are shown in Table 2. Are shown together.
<表 2 > <Table 2>
中核粒子 層部 電池 ホウ素含有量 表層部含有量 Core particles Layer part Battery Boron content Surface layer content
灰 ォ科 炭素材料  Ash family Carbon material
(重量％) (重量％) ホウ素含有黒 低結晶性  (Wt%) (wt%) Boron-containing black Low crystallinity
実施例 1 0. 01 5  Example 10 0.015
鉛 炭素材料  Lead carbon material
ホウ素含有黒 低結晶性  Boron-containing black Low crystallinity
実施例 2 0. 1 5  Example 2 0.15
鉛 炭素材料  Lead carbon material
ホウ素含有黒 低結晶性  Boron-containing black Low crystallinity
実施例 3 0. 5 5  Example 3 0.5 5
鉛 炭素材料  Lead carbon material
ホウ素含有黒 低結晶性  Boron-containing black Low crystallinity
実施例 4 3 5  Example 4 3 5
鉛 炭素材料  Lead carbon material
ホウ素含有黒 低結晶性  Boron-containing black Low crystallinity
実施例 5 0. 1 1  Example 5 0.1 1 1
鉛 炭素材料  Lead carbon material
ホウ素含有黒 低結晶性  Boron-containing black Low crystallinity
実施例 6 0. 1 1 0  Example 6 0.10.10
鉛 JiAi^^M料  Lead JiAi ^^ M fee
ホウ素含有黒 低結晶性  Boron-containing black Low crystallinity
実施例 7 0. 1 20  Example 7 0.120
鉛 灰素亇才料  Lead Ash
ホウ素含有黒 低結晶性  Boron-containing black Low crystallinity
実施例 8 0. 1 30  Example 8 0.1 30
鉛 炭素材料  Lead carbon material
ホウ素含有黒 低結晶性  Boron-containing black Low crystallinity
実施例 9 0. 1 40  Example 9 0.1 40
鉛 灰素材料  Lead ash material
ホウ素含有黒 曰曰  Boron-containing black
夹施例 1 0 0. 1 5  夹 Example 1 0 0.1 5
鉛 灰 3^材料  Lead ash 3 ^ material
黒鉛化 低結晶性  Graphitized Low crystallinity
実施例 1 1 0 5  Example 1 1 0 5
MCMB 灰 ォ料  MCMB gray fee
低結晶性  Low crystallinity
実施例 1 2 人造黒鉛 0 5  Example 1 2 Artificial graphite 0 5
炭素材料  Carbon material
ホウ素含有黒  Boron-containing black
比較例 1 0. 1 0  Comparative Example 1 0.10
鉛  Lead
比較例 2 人造黒鉛 0 0  Comparative Example 2 Artificial graphite 0 0
(初期放電容量測定） (Initial discharge capacity measurement)
実施例 1ないし 1 2、 および比較例 1 、 2の電池について、 温度 2 5 °Cにおいて、 充電電流 6 0 0 mA、 充電電圧 4 . 2 0 Vの定電流一定電圧充電条件で 3時間充電 した後、 放電電流 6 0 O mA、 終止電圧 2 . 7 5 Vの条件で放電を行い、 初期の放 電容量を測定した。 .  The batteries of Examples 1 to 12 and Comparative Examples 1 and 2 were charged for 3 hours under a constant current constant voltage charging condition of a charging current of 600 mA and a charging voltage of 4.20 V at a temperature of 25 ° C. Thereafter, discharge was performed under the conditions of a discharge current of 60 O mA and a final voltage of 2.75 V, and the initial discharge capacity was measured. .
(充放電サイクル試験） 初期容量の測定を終えた電池を温度 2 5 °Cにおいて、 充電電流 6 0 0 mA、 充電 電圧 4 . 2 0 Vの定電流一定電圧充電条件で 2 . 5時間充電した後、 放電電流 6 0 O mA、 終止電圧 2 . 7 5 Vの条件で放電させた。 これを 1サイクルとして、 3 0 0サイクルの充放電を繰り返した。 そして、 3 0 0サイクル目の放電容量を初期容 量で除して、 容量保持率を算出した。 なお、 試験電池数は、 それぞれの実施例、 比 較例に対して 3個とし、 それらの平均値を以つて充放電サイクル寿命特性評価の指 標とした。 充放電サイクル試験の結果を表 3に示す。 また、 実施例 1、 2、 1 0、 及ぴ比較例 2の電池について、 充放電サイクル試験における容量推移を図 3に示す。 (Charge / discharge cycle test) The battery whose initial capacity was measured was charged at a constant current constant voltage of 600 mA and a charging voltage of 4.2 V at a temperature of 25 ° C for 2.5 hours, and then a discharging current of 60 The battery was discharged under the conditions of O mA and a cut-off voltage of 2.75 V. With this as one cycle, charging and discharging of 300 cycles were repeated. Then, the capacity at the 300th cycle was divided by the initial capacity to calculate the capacity retention. The number of test batteries was three for each of the examples and comparative examples, and the average value of the three was used as an index for evaluating the charge / discharge cycle life characteristics. Table 3 shows the results of the charge / discharge cycle test. FIG. 3 shows a change in capacity of the batteries of Examples 1, 2, 10 and Comparative Example 2 in a charge / discharge cycle test.
<表 3〉  <Table 3>
Figure imgf000018_0001
単一の炭素材料から成る比較例 1、 2の容量保持率は 7 8 . 1 %以下であった。 この理由は以下のように考えられる。 充電電流が 1 C mAという高率充電時におい ては、 炭素材料の内奥部にまでリチウムイオンの拡散が追いつかず、 表層部におけ るリチウムイオン濃度が高くなり、 炭素材料の表面に金属リチウムが析出してしま う。 当該金属リチウムは電極からの脱落により、 または電解液との反応による被膜 形成により、 電池反応に寄与しなくなる。 電池反応に寄与しないこのような金属リ チウムは、 高率充電と放電を繰り返すことにより不可逆的に増加するため、 放電容 量が低下すると考えられるのである。
Figure imgf000018_0001
The capacity retention of Comparative Examples 1 and 2 made of a single carbon material was 78.1% or less. The reason is considered as follows. When charging at a high rate of charge current of 1 CmA, diffusion of lithium ions does not catch up to the inner part of the carbon material, the lithium ion concentration in the surface layer increases, and metallic lithium is deposited on the surface of the carbon material. Will precipitate out. The metallic lithium does not contribute to the battery reaction by dropping off from the electrode or by forming a film by reaction with the electrolytic solution. Such metal resources that do not contribute to the battery reaction It is thought that the discharge capacity will decrease because of the irreversible increase in the repetition of high-rate charging and discharging.
これに対して、 中核粒子と表層部からなる炭素材料において、 前記中核粒子の結 晶性が前記表層部よりも高く、 かつ前記中核粒子の開回路電圧が前記表層部よりも 貴である実施例 1ないし 1 1の電池においては、 3 0 0サイクル後の容量保持率が 7 9 . 5 %以上と良好であった。 これは、 開回路電位の貴な中核粒子の内奥部にま でリチウムイオンが速やかに揷入、 吸蔵されることにより、 炭素材料全体が均一に 充電され、 苔状金属リチウムの析出を抑制できたためであると考えられる。  On the other hand, in the carbon material composed of the core particle and the surface layer, an example in which the crystallinity of the core particle is higher than that of the surface layer and the open circuit voltage of the core particle is more noble than that of the surface layer In the batteries 1 to 11, the capacity retention after 300 cycles was as good as 79.5% or more. This is because lithium ions quickly enter and occlude the inner core of noble core particles with an open circuit potential, thereby uniformly charging the entire carbon material and suppressing the precipitation of mossy metallic lithium. It is considered that it is.
中核粒子がホウ素を含有してなる実施例 1ないし 4では、 容量保持率が 8 9 . 2 %以上であつたのに対し、 ホウ素を含まない実施例 1 2では、 容量保持率は 8 0 . 7 %であった。 これは、 ホウ素を含有することにより、 黒鉛材料の結晶性が高くな り、 また、 開回路電圧が貴になったことにより、 リチウムイオンの拡散性が向上し たためと考えられる。  In Examples 1 to 4 in which the core particle contains boron, the capacity retention was 89.2% or more, whereas in Example 12 without boron, the capacity retention was 80. 7%. This is presumably because the inclusion of boron increased the crystallinity of the graphite material and increased the open circuit voltage, which improved the diffusion of lithium ions.
実施例 1ないし 4においては、 ホウ素含有量が増加するにつれて、 0 . 1重量％ までは容量保持率は増加した。 これは、 ホウ素の含有量が増加するに従い、 中核粒 子の結晶性が高くなり、 かつ、 開回路電位が貴になることによりリチウムイオンの 拡散性が向上したためと考えられる。 他方で、 ホウ素含有量が 0 . 1重量％を超え ると容量保持率は減少に転じた。 この理由は必ずしも明らかではないが、 以下のよ うに考えられる。 ホウ素添加量の増加に従い、 炭素原子と置換されなかったホウ素 が窒化ホウ素等の不純物を形成し、 これが炭素材料の電子伝導性を低下させてしま う。 充放電を繰り返すことにより電子伝導性が低下していくため、 放電容量が低下 すると考えられるのである。  In Examples 1 to 4, as the boron content increased, the capacity retention increased to 0.1% by weight. This is considered to be due to the fact that as the boron content increases, the crystallinity of the core particles becomes higher, and the open circuit potential becomes more noble, thereby improving the diffusion of lithium ions. On the other hand, when the boron content exceeded 0.1% by weight, the capacity retention started to decrease. The reason for this is not necessarily clear, but is considered as follows. As the amount of boron added increases, boron that is not replaced by carbon atoms forms impurities such as boron nitride, which reduces the electronic conductivity of the carbon material. It is thought that the discharge capacity is reduced because the electron conductivity is reduced by repeated charge and discharge.
実施例 2、 6ないし 9、 及び比較例 1を比較することにより、 表層部の含有量と 容量保持率との関係を検討する。 表層部の含有量が 1 0重量％までは容量保持率は 増加した。 これは、 表層部の含有率が増加するに従い、 中核粒子の表面が十分に被 覆されることによると考えられる。 しかし表層部の含有量が 1 0重量％を超えると、 容量保持率は逆に減少した。 これは、 そもそも低結晶性炭素材料は黒鉛材料に比べ て充放電サイクル寿命特性が劣るためと考えられる。 以上より、 ホウ素を 0 . 0 1〜3重量％含有する黒鉛材料を中核粒子とし、 表層 部に低結晶性あるいは非晶質炭素材料を用い、 前記表層部の含有量が全体の重量に 対して 1〜3 0重量％である炭素材料を負極活物質として用いることにより、 3 0 0サイクルの充放電の繰返しによっても 7 9 . 5 %以上の高い容量保持率を示す非 水電解質二次電池を得られることがわかった。 By comparing Examples 2, 6 to 9 and Comparative Example 1, the relationship between the content of the surface layer portion and the capacity retention is examined. Up to the surface layer content of 10% by weight, the capacity retention increased. This is considered to be due to the fact that the surface of the core particles was sufficiently covered as the content of the surface layer increased. However, when the content of the surface layer portion exceeded 10% by weight, the capacity retention decreased on the contrary. This is presumably because low-crystalline carbon materials have inferior charge-discharge cycle life characteristics compared to graphite materials. As described above, a graphite material containing 0.01 to 3% by weight of boron is used as the core particles, a low crystalline or amorphous carbon material is used for the surface layer, and the content of the surface layer is based on the total weight. By using a carbon material of 1 to 30% by weight as a negative electrode active material, a non-aqueous electrolyte secondary battery showing a high capacity retention of 79.5% or more even by repeating charge and discharge of 300 cycles can be obtained. It turned out to be obtained.
(低温での充放電試験）  (Low temperature charge / discharge test)
低温での放電容量試験は、 実施例 1、 2、 1 0、 及び比較例 2の電池に対して、 以下のようにして行った。 初期容量測定を終えた電池を温度一 2 0 °Cの雰囲気下に おいて、 充電電流 6 0 0 mA、 充電電圧 4 . 2 0 Vの定電流一定電圧充電条件で 3 時間充電した後、 一 2 0 °Cにて 1時間放置し、 さらに、 一 2 0 °Cにおいて放電電流 6 0 0 mA、 終止電圧 2 . 7 5 Vの条件で放電を行った。 このようにして得られた 一 2 0 °Cでの放電容量と 2 5 °Cにおいて測定した初期容量との放電容量比 （一2 0 °Cでの放電容量 ÷室温での放電容量） を算出した。 なお、 試験電池数は、 それぞ れの実施例、 比較例に対して 3個とし、 それらの平均値を以つて低温放電特性評価 の指標とした。 低温での充放電試験の結果を表 4に示す。  The discharge capacity test at a low temperature was performed on the batteries of Examples 1, 2, 10 and Comparative Example 2 as follows. After charging the battery for which initial capacity measurement has been completed in an atmosphere at a temperature of 20 ° C, charging at a constant current constant voltage of 600 mA and a charging voltage of 4.2 V for 3 hours, It was left at 20 ° C for 1 hour, and further discharged at 120 ° C under the conditions of a discharge current of 600 mA and a final voltage of 2.75 V. Calculate the discharge capacity ratio between the discharge capacity obtained at 120 ° C and the initial capacity measured at 25 ° C (discharge capacity at 120 ° C ÷ discharge capacity at room temperature). did. The number of test batteries was three for each of the examples and comparative examples, and the average value thereof was used as an index for evaluating low-temperature discharge characteristics. Table 4 shows the results of the charge / discharge test at low temperatures.
く表 4 >  Table 4>
Figure imgf000020_0001
Figure imgf000020_0001
単一の炭素材料からなる比較例 2の炭素材料を用いた電池では放電容量比が 8 2 . 2 %であったのに対して、 実施例 1、 2および 1 0の電池ではいずれも 9 0 %以上 と非常に良好であった。 これは、 実施例の炭素材料では、 開回路電位の貴な中核粒 子の内奥部にまでリチウムイオンが速やかに揷入、 吸蔵されることにより、 炭素材 料全体が均一に充電された結果、 苔状金属リチウムの析出が抑制されたことによる と考えられる。 なお、 比較例において放電できなかった電気量は、 金属リチウムの 析出に費やされたものと考えられる。  The battery using the carbon material of Comparative Example 2 consisting of a single carbon material had a discharge capacity ratio of 82.2%, while the batteries of Examples 1, 2 and 10 all had a discharge capacity ratio of 90%. % Or better. This is because, in the carbon material of the example, lithium ions quickly enter and occlude deep inside the core particle having a noble open circuit potential, and as a result, the entire carbon material is uniformly charged. This is probably because the precipitation of mossy metallic lithium was suppressed. The amount of electricity that could not be discharged in the comparative example is considered to have been spent for the deposition of metallic lithium.
(不可逆容量の測定） 実施例 1、 2、 10、 及び比較例 2において作製した負極板を作用電極とし、 金 属リチウム電極を対極および参照電極として組み込んで 3極式ガラスセルを構成し た。 非水電解液には、 エチレンカーボネートとジェチルカーポネートの体積比 1 ： 1混合溶媒に 1 mo 1/1の L i C 104を溶解させたものを使用した。 (Measurement of irreversible capacity) The negative electrode plates prepared in Examples 1, 2, 10 and Comparative Example 2 were used as working electrodes, and a lithium metal electrode was incorporated as a counter electrode and a reference electrode to form a three-electrode glass cell. The non-aqueous electrolyte, a volume ratio of ethylene carbonate and oxygenate chill Capo sulfonate 1: was used to dissolve the L i C 10 4 of 1 mo 1/1 to 1 mixed solvent.
このようにして作製した 3極式ガラスセルについて、 温度 25°Cの下で、 充電終 止電圧を 0. OV (V s L i /L i +) として電流 0. 2 CmAで充電し、 1 5 分間休止した後、 1. 5V (v s L i /L i +) まで放電を行った。 このときの 充電電気量から放電電気量を減ずることにより不可逆容量を算出した。 また、 放電 電気量を充電電気量で除することにより充放電効率を算出した。 このようにして得 られた不可逆容量と充放電効率とを表 5に示す。 The three-pole glass cell fabricated in this manner was charged at a current of 0.2 CmA at a temperature of 25 ° C with a charge end voltage of 0.2 OV (V s L i / L i + ). After a pause of 5 minutes, the battery was discharged to 1.5 V (vs Li / Li + ). The irreversible capacity was calculated by subtracting the amount of discharged electricity from the amount of charged electricity at this time. The charge / discharge efficiency was calculated by dividing the amount of discharged electricity by the amount of charged electricity. Table 5 shows the irreversible capacity and charge / discharge efficiency thus obtained.
<表 5 >  <Table 5>
Figure imgf000021_0001
Figure imgf000021_0001
単一の炭素材料からなる比較例 2の炭素材料を用いた電池の充放電効率は 88. 9%であったのに対して、 実施例 1、 2、 および 10の炭素材料を用いた電池では、 いずれも充放電効率が 92%以上と非常に高かった。 また、 不可逆容量についても、 比較例 2では 42mAhZgであったのに対し、 実施例 1、 2、 及ぴ 1 0では、 2 6mAhZg以下と非常に小さかった。 これは、 実施例 1、 2、 及ぴ 1 0の炭素材 料では、 中核粒子の表面が低結晶性炭素材料により被覆されているため、 電解液と の反応が抑制され、 分解反応物の生成に消費される電気量が減少したためと考えら れる。 産業上の利用可能性  The charge / discharge efficiency of the battery using the carbon material of Comparative Example 2 consisting of a single carbon material was 88.9%, whereas the batteries using the carbon materials of Examples 1, 2, and 10 However, the charge and discharge efficiency was extremely high at 92% or more. In addition, the irreversible capacity was 42 mAhZg in Comparative Example 2, whereas the irreversible capacity was 26 mAhZg or less in Examples 1, 2, and 10. This is because, in the carbon materials of Examples 1, 2, and 10, the core particles are coated with the low-crystalline carbon material, so that the reaction with the electrolytic solution is suppressed, and the generation of decomposition products is generated. It is considered that the amount of electricity consumed during the period decreased. Industrial applicability
以上のように、 本発明に係る非水電解質二次電池用炭素材料及びそれを用いた非 水電解質二次電池は、 高い放電容量を備え、 充放電サイクル特性に優れ、 低温での 高率充放電特性に優れる。 本発明の炭素材料は、 比較的簡単な製造工程で量産可能であり、 特に従来から多 く使用されている黒鉛材料に代わるものとして、 その工業的価値はきわめて高いも のと言える。 As described above, the carbon material for a non-aqueous electrolyte secondary battery according to the present invention and the non-aqueous electrolyte secondary battery using the same have a high discharge capacity, excellent charge-discharge cycle characteristics, and a high rate of charge at low temperatures. Excellent discharge characteristics. The carbon material of the present invention can be mass-produced by a relatively simple manufacturing process. In particular, it can be said that the carbon material has an extremely high industrial value as a substitute for a graphite material that has been widely used.

Claims

請求の範囲 The scope of the claims
1 . 炭素材料からなる中核粒子の表面の全部又は一部が、 前記中核粒子よりも結晶 性の低い炭素材料からなる表層部に被覆されてなり、 かつ、 L i / L i +に対する 前記中核粒子の開回路電位が前記表層部よりも賁であることを特徴とする非水電解 質二次電池用炭素材料。 1. The whole or a part of the surface of the core particle made of a carbon material is covered with a surface layer made of a carbon material having lower crystallinity than the core particle, and the core particle with respect to L i / L i + A carbon material for a non-aqueous electrolyte secondary battery, wherein the open circuit potential of the carbon material is higher than that of the surface layer.
2 . 前記中核粒子がホゥ素を含む黒鉛材料からなることを特徴とする請求の範囲第 1項に記載の非水電解質二次電池用炭素材料。  2. The carbon material for a non-aqueous electrolyte secondary battery according to claim 1, wherein the core particles are made of a graphite material containing boron.
3 . 前記表層部が低結晶性炭素材料又は非晶質炭素材料からなることを特徴とする 請求の範囲第 1項または第 2項に記載の非水電解質二次電池用炭素材料。  3. The carbon material for a non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the surface layer portion is made of a low-crystalline carbon material or an amorphous carbon material.
4 . 前記表層部の重量が、 前記中核粒子の重量と前記表層部の重量とを合計したも のに対して、 1重量％以上 3 0重量％以下であることを特徴とする請求の範囲第 1 項ないし第 3項のいずれかに記載の非水電解質二次電池用炭素材料。  4. The weight of the surface layer is 1% by weight or more and 30% by weight or less based on the sum of the weight of the core particles and the weight of the surface layer. 4. The carbon material for a non-aqueous electrolyte secondary battery according to any one of items 1 to 3.
5 . 正極と、 負極と、 非水電解質とからなる非水電解質二次電池において、 前記負 極が請求の範囲第 1項ないし第 4項のいずれかに記載の炭素材料を含むことを特徴 とする非水電解質二次電池。  5. A nonaqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a nonaqueous electrolyte, wherein the negative electrode includes the carbon material according to any one of claims 1 to 4. Non-aqueous electrolyte secondary battery.
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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8877384B2 (en) 2009-05-15 2014-11-04 Nippon Steel Chemical Co., Ltd. Negative electrode active material of lithium secondary battery, negative electrode of lithium secondary battery, lithium secondary battery for vehicle installation using the negative electrode active material and negative electrode, and method for manufacturing the negative electrode active material
EP3404744A1 (en) * 2017-05-16 2018-11-21 Panasonic Intellectual Property Management Co., Ltd. Negative electrode active material and nonaqueous secondary battery
CN108878801A (en) * 2017-05-16 2018-11-23 松下知识产权经营株式会社 Non-aqueous secondary batteries negative electrode active material and non-aqueous secondary batteries

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP5603590B2 (en) * 2009-05-29 2014-10-08 新日鉄住金化学株式会社 Negative electrode active material for lithium secondary battery and in-vehicle lithium secondary battery using the same
WO2012090728A1 (en) * 2010-12-29 2012-07-05 三洋電機株式会社 Non-aqueous electrolyte secondary cell
JP5637199B2 (en) * 2012-10-12 2014-12-10 日産自動車株式会社 Electrode for lithium ion secondary battery
JP6941782B2 (en) * 2017-03-28 2021-09-29 パナソニックＩｐマネジメント株式会社 Negative electrode active material and battery
JP7054871B2 (en) * 2017-05-16 2022-04-15 パナソニックＩｐマネジメント株式会社 Negative electrode active material for non-water secondary batteries and non-water secondary batteries

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000156230A (en) * 1998-11-18 2000-06-06 Samsung Sdi Co Ltd Carbonic active material for lithium ion secondary battery
JP2001039705A (en) * 1999-05-25 2001-02-13 Sanyo Electric Co Ltd Carbon material, electrode and nonaqueous electrolyte secondary battery
JP2001345122A (en) * 2000-06-01 2001-12-14 Asahi Glass Co Ltd Secondary power source and method of manufacturing secondary power source

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP2000156230A (en) * 1998-11-18 2000-06-06 Samsung Sdi Co Ltd Carbonic active material for lithium ion secondary battery
JP2001039705A (en) * 1999-05-25 2001-02-13 Sanyo Electric Co Ltd Carbon material, electrode and nonaqueous electrolyte secondary battery
JP2001345122A (en) * 2000-06-01 2001-12-14 Asahi Glass Co Ltd Secondary power source and method of manufacturing secondary power source

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US8877384B2 (en) 2009-05-15 2014-11-04 Nippon Steel Chemical Co., Ltd. Negative electrode active material of lithium secondary battery, negative electrode of lithium secondary battery, lithium secondary battery for vehicle installation using the negative electrode active material and negative electrode, and method for manufacturing the negative electrode active material
EP3404744A1 (en) * 2017-05-16 2018-11-21 Panasonic Intellectual Property Management Co., Ltd. Negative electrode active material and nonaqueous secondary battery
CN108878801A (en) * 2017-05-16 2018-11-23 松下知识产权经营株式会社 Non-aqueous secondary batteries negative electrode active material and non-aqueous secondary batteries
CN108878881A (en) * 2017-05-16 2018-11-23 松下知识产权经营株式会社 Non-aqueous secondary batteries negative electrode active material and non-aqueous secondary batteries

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