WO2014162529A1 - リチウムイオン二次電池用負極、リチウムイオン二次電池、およびそれらの製造方法 - Google Patents
リチウムイオン二次電池用負極、リチウムイオン二次電池、およびそれらの製造方法 Download PDFInfo
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- WO2014162529A1 WO2014162529A1 PCT/JP2013/060145 JP2013060145W WO2014162529A1 WO 2014162529 A1 WO2014162529 A1 WO 2014162529A1 JP 2013060145 W JP2013060145 W JP 2013060145W WO 2014162529 A1 WO2014162529 A1 WO 2014162529A1
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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
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/46—Separators, membranes or diaphragms characterised by their combination with electrodes
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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
- H01M4/04—Processes of manufacture in general
- H01M4/0402—Methods of deposition of the material
- H01M4/0404—Methods of deposition of the material by coating on electrode collectors
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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
- H01M4/362—Composites
- H01M4/366—Composites as layered products
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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
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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
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/403—Manufacturing processes of separators, membranes or diaphragms
- H01M50/406—Moulding; Embossing; Cutting
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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
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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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
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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- 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 negative electrode for a lithium ion secondary battery, a lithium ion secondary battery, and a method of manufacturing them.
- a film derived from boron is formed by subjecting a negative electrode active material to boric acid treatment, and a film having a B—O bond and a film containing lithium are formed on the negative electrode. It is described that the high temperature storage characteristics of the battery are improved by doing this.
- JP-A-2010-192430 Patent Document 2 describes that an additive containing boron is added to the electrolytic solution to improve the cycle characteristics of the battery.
- the electrode is treated with a boric acid solution to form a film containing a compound having a B—O bond, whereby the compound having a B—O bond remains on the negative electrode surface.
- the compound having a B—O bond dissolves in the electrolytic solution to lower physical properties of the positive electrode and the electrolytic solution itself, and there is a possibility that the battery characteristics such as an increase in internal resistance of the battery may be deteriorated.
- the present invention for solving the above problems is a lithium ion secondary battery comprising a negative electrode mainly composed of carbon as an active material, comprising a negative electrode active material and a covering material formed on the surface of the negative electrode active material.
- the coating material is made of a compound having boron and an alkyl group, and is adsorbed on the surface of the negative electrode active material.
- a boric acid ester compound such as the following compound (1) as a coating material.
- X is a hydrocarbon group.
- Y is hydrogen or a methyl group.
- the hydrocarbon group may be partially substituted with oxygen, sulfur, nitrogen and halogen, and X1, X2, X3, Y1, Y2 and Y3 may be different from each other.
- X preferably has 1 to 10 carbon atoms
- the present invention aims at providing the same coating as the SEI on the negative electrode in advance to achieve the same effect, I have conducted intensive research. As a result, by causing the boron compound to be physically adsorbed on the negative electrode surface, it is possible to obtain the same effect as that of the SEI film and prevent battery deterioration.
- the present invention uses a compound capable of physical adsorption on the surface of the negative electrode active material and provides a coating to exhibit an effect similar to that of SEI and improve the life of the battery.
- a boron-containing compound having an alkyl group particularly a boron compound having an alkyl group
- a carbon material such as graphite.
- the carbon material coated with the boron compound having an alkyl group makes it possible to prevent battery deterioration.
- the ability to reduce the amount of electrolyte additive is also an advantage.
- the lithium ion secondary battery according to one embodiment of the present invention can be manufactured, for example, by arranging the following negative electrode and positive electrode as opposed to each other with the separator interposed therebetween, and injecting an electrolyte.
- the structure of the lithium ion battery according to one embodiment of the present invention is not particularly limited, but usually, the positive electrode and the negative electrode and the separator separating them are wound to form a wound electrode group, or the positive electrode, the negative electrode and the separator It can be stacked to form a stacked electrode group.
- FIG. 1 is a view schematically showing an internal structure of a battery according to an embodiment of the present invention.
- a battery 1 according to an embodiment of the present invention shown in FIG. 1 includes a positive electrode 10, a separator 11, a negative electrode 12, a battery can 13, a positive current collecting tab 14, a negative current collecting tab 15, an inner lid 16, an internal pressure release valve 17, A gasket 18, a positive temperature coefficient (PTC) resistance element 19, a battery cover 20, and an axial center 21 are provided.
- the battery lid 20 is an integrated component including the inner lid 16, the internal pressure release valve 17, the gasket 18, and the resistance element 19. Further, the positive electrode 10, the separator 11 and the negative electrode 12 are wound around the axial center 21.
- the separator 11 is inserted between the positive electrode 10 and the negative electrode 12, and an electrode group wound around the axial center 21 is produced.
- the shaft 21 any known one can be used as long as it can support the positive electrode 10, the separator 11 and the negative electrode 12.
- the electrode group is a laminate of strip electrodes, or a positive electrode 10 and a negative electrode 12 wound into a flat or other arbitrary shape, or a separator 11 having a bag shape.
- the positive electrode 10 and the negative electrode 12 can be housed in this, and they can be sequentially stacked to form a multi-layered structure, etc. into various shapes.
- the shape of the battery can 13 may be a cylindrical shape, a flat oval shape, a flat oval shape, a square shape, or the like in accordance with the shape of the electrode group.
- the material of the battery can 13 is selected from materials having corrosion resistance to the non-aqueous electrolyte, such as aluminum, stainless steel, nickel plated steel, and the like. Moreover, when the battery can 13 is electrically connected to the positive electrode 10 or the negative electrode 12, the material of the battery can 13 does not deteriorate due to corrosion or alloying with lithium ions in a portion in contact with the non-aqueous electrolyte. Thus, the material of the battery can 13 is selected.
- Stainless steel is resistant to corrosion because a passive film is formed on the surface and is resistant to corrosion because it is a steel and can withstand internal pressure rise of the gas in which the electrolytic solution etc. in the battery can 13 is vaporized.
- Aluminum is characterized by high energy density per weight because it is lightweight.
- the electrode group is housed in the battery can 13, the negative electrode current collecting tab 15 is connected to the inner wall of the battery can 13, and the positive electrode current collecting tab 14 is connected to the bottom surface of the battery cover 20.
- the electrolyte is injected into the inside of the battery can 13 before sealing the battery.
- a method of injecting the electrolytic solution there is a method of adding directly to the electrode group in a state in which the battery cover 20 is released, or a method of adding from an injection port provided on the battery cover 20.
- a positive electrode current collecting tab 14 for current drawing and a negative electrode current collecting tab 15 are formed on each of the positive electrode 10 and the negative electrode 12 by spot welding or ultrasonic welding.
- the positive electrode current collecting tab 14 and the negative electrode current collecting tab 15 are made of metal foils of the same material as the rectangular positive electrode current collector and the negative electrode current collector plate, respectively, and for extracting current from the positive electrode 10 and the negative electrode 12 It is a member to be installed.
- the present invention can also be applied to lithium secondary batteries for mobile bodies such as automobiles, and since it is required that a large current flows, they are applied to lithium secondary batteries for mobile bodies such as automobiles. In some cases, a plurality of energizing tabs may be provided as needed.
- the negative electrode material according to one embodiment of the present invention is characterized in that the surface functional groups present on the surface of the negative electrode active material and the electrolysis are obtained by physically adsorbing the boric acid ester containing boron to carbon which is the negative electrode active material. It is possible to suppress the reaction with the liquid and to suppress the deterioration of the battery with time.
- the negative electrode active material is obtained by treating a graphitizable material obtained from natural graphite, petroleum coke, coal pitch coke or the like at a high temperature of 2500 ° C., mesophase carbon, amorphous carbon, or amorphous carbon on the surface of graphite Coated with carbon, carbon material whose surface crystallinity has been reduced by mechanical treatment on natural or artificial graphite surface, material having alkyl having silane group on the surface by silicon treatment, organic matter such as polymer coated on carbon surface Materials adsorbed, carbon fibers, lithium metal, silicon oxide, materials coated with carbon on the surface of silicon oxide, metals alloyed with lithium, and materials supported on the surface of carbon particles may be mentioned.
- a metal used for the negative electrode for example, a metal or an alloy selected from lithium, aluminum, tin, silicon, indium, gallium and magnesium is used.
- the above metal or metal oxide can also be used as the negative electrode active material. These compounds can be used alone or in mixtures of two or more as the negative electrode active material.
- Boric acid esters having a B—O bond are adsorbed on the surface of the negative electrode active material.
- the boric acid ester is represented by the following chemical formula (1).
- X is a hydrocarbon group having a carbon number of 1 or more, and may be partially substituted with oxygen, sulfur, nitrogen, or halogen.
- Y is hydrogen or a methyl group.
- X1, X2, X3, Y1, Y2 and Y3 may be different from each other. It is preferable that X is 1 or more and 10 or less carbon number.
- the boron located at the center of the borate ester represented by the chemical formula (1) is trivalent and has a non-covalent electron pair, so it is slightly negatively charged.
- it when adsorbed on the negative electrode surface, it electrostatically interacts with the anion part of the lithium salt used for the electrolyte, thereby contributing to the effective transport number improvement of lithium ions, thereby suppressing the increase in resistance. it is conceivable that.
- the lithium ion interacts with the oxygen atom adjacent to boron, and the effect of improving the lithium ion transport number can also be expected.
- the adsorption capacity to the carbon surface is increased, and the reaction with the electrolytic solution with time is suppressed. As a result, it is considered that the deterioration of the battery with time, that is, the increase in resistance is suppressed.
- the negative electrode can be manufactured by applying a negative electrode active material to a current collector as an electrode mixture in which the negative electrode active material is mixed with a binder or the like.
- the manufacturing method of the negative electrode 12 mixes an active material and boric acid ester with a binder, carries out application
- the thickness of the negative electrode mixture layer is preferably 50 to 200 ⁇ m. In the case of using the negative electrode current collector, it is desirable to use a copper foil having a thickness of 7 to 20 ⁇ m.
- Another method of manufacturing the negative electrode 12 is to mix the negative electrode active material and the boric acid ester in water or an organic solvent, remove the solvent to form a coating layer, and then mix with a binder, apply, press, etc. It is said that.
- the boric acid ester represented by the chemical formula (1) is dispersed in water, the state of the slurry is carefully observed, and when it becomes gelled, a surfactant is added, pH value adjustment of the solution, stirring speed, stirring Change the temperature etc. according to the material.
- the dispersing agent and the binder carboxymethyl cellulose, a styrene butadiene copolymer and the like can be used, and it is desirable that the proportion occupied in the negative electrode mixture layer is about 3 to 6% by mass.
- An increase in the binder component leads to an increase in the internal resistance value and a decrease in the battery capacity.
- the amount of the binder component is too small, the preparation of the electrode peeling may be difficult, or the storage of the battery and the reduction of the cycle life may be caused.
- the positive electrode 10 of the present embodiment is composed of a positive electrode active material, a conductive agent, a binder, and a positive electrode current collector.
- a carbon material is used as a negative electrode active material, a layered compound such as lithium cobaltate (LiCoO 2 ) or lithium nickelate (LiNiO 2 ) or these as a positive electrode active material capable of reversibly absorbing and releasing lithium serving as a counter electrode
- the manufacturing method of the positive electrode 10 mixes a positive electrode active material with a conductive material and a binder to form a slurry, and uses a mixer equipped with a stirring means such as a rotary blade so that powder particles of the positive electrode active material are uniformly dispersed. Knead enough.
- the sufficiently mixed slurry is coated on both sides by, for example, a roll transfer type coating machine on a positive electrode current collector made of an aluminum foil with a thickness of 15 to 25 ⁇ m. After applying on both sides, press dry.
- the thickness of the positive electrode mixture layer applied on the positive electrode current collector is desirably 50 to 250 ⁇ m.
- the conductive material may, for example, be a carbon material powder
- the binder may, for example, be polyvinylidene fluoride (PVDF).
- the mixing ratio of the conductive agent is preferably 5 to 20% by mass.
- non-aqueous solvent used in the electrolytic solution examples include ethylene carbonate, propylene carbonate, gamma-butyrolactone, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, etc., and those obtained by substituting these with a halide such as a fluorine-substituted compound or sulfur element These may be used alone or in combination of two or more.
- a mixed solvent system of a solvent having a large viscosity such as cyclic carbonate or cyclic lactone and a solvent having a small viscosity such as chain carbonate or chain ester.
- lithium salt LiPF 6 , LiBF 4 , LiClO 4 , LiAsF 6 , LiCF 3 SO 2 , Li (CF 3 SO 2 ) 2 N, Li (C 2 F 5 SO 2 ) N, lithium bis oxalate borate, lithium Lithium salts such as monooxalate difluoride can be used. These lithium salts may be used alone or in combination of two or more.
- the solvent blending ratio and the electrolyte type and concentration are determined based on the test results of the initial battery and storage and cycle life.
- electrolytes in which LiPF 6 and LiBF 4 are dissolved in a linear carbonate solvent such as ethylene carbonate, propylene carbonate, cyclic carbonates such as gamma butyrolactone, dimethyl carbonate, ethyl methyl carbonate, etc. It is desirable to use between 6 and 2.0 mol / L.
- compounds other than the main solvent and the electrolyte can be mixed alone or in combination as additives for improving various characteristics of the battery.
- a compound having a sulfur element such as vinylene carbonate, a compound having a carboxylic acid anhydride group, a compound having a sulfur element such as propanesultone, or a compound having a boron is mixed in an electrolytic solution as a third component other than a solvent and an electrolyte.
- the separator 11 is used for the purpose of preventing a short circuit due to direct contact between the positive electrode 10 and the negative electrode 12.
- a microporous polymer film such as polyethylene, polypropylene, or aramid resin, or a film in which a heat resistant substance such as alumina particles is coated on the surface of the polymer film can be used.
- Example 1 (Production of positive electrode)
- Li 1.02 Mn 1.98 Al 0.02 O 4 having an average particle diameter of 10 ⁇ m and a specific surface area of 1.5 m 2 / g was used.
- a mixture of 85% by weight of the positive electrode active material and 9: 2 of massive graphite and acetylene black is used as a conductive agent, and the conductive agent is dispersed in an NMP solution previously adjusted to 5% by weight PVDF as a binder to obtain a slurry. did.
- the mixing ratio of the positive electrode active material, the conductive agent, and the PVDF was 85: 10: 5 in weight ratio.
- This slurry was applied to a 20 ⁇ m thick aluminum foil (positive electrode current collector) as uniformly and uniformly as possible. After the application, it was dried at a temperature of 80 ° C. and applied and dried on both sides of the aluminum foil in the same procedure. Thereafter, compression molding was performed by a roll press machine, cutting was performed so as to have an application width of 5.4 cm and an application length of 50 cm, and aluminum foil lead pieces for taking out current were welded to produce a positive electrode 10.
- the negative electrode active material natural graphite having an interplanar spacing of 0.368 nm, an average particle diameter of 20 ⁇ m, and a specific surface area of 5 m 2 / g obtained by X-ray diffraction measurement was used.
- Trimethyl borate was dissolved in distilled water at a concentration of 10%. Next, after stirring the trimethyl borate aqueous solution and the natural graphite so that the concentration relative to the active material weight of trimethyl borate is 1 wt%, drying is performed in a thermostat at 80 ° C. to obtain a negative electrode active material having boron and an alkyl group. The When the obtained negative electrode material was measured by X-ray photoelectron spectroscopy, a peak attributed to boron could be confirmed at 192-193 eV, and it was confirmed that the material contained boron. In addition, the specific surface area of natural graphite produced in this way was reduced to 4 m 2 / g.
- the negative electrode material and the aqueous dispersion of carboxymethylcellulose were sufficiently mixed, and the aqueous dispersion of the styrene butadiene copolymer was dispersed to obtain a negative electrode slurry.
- the mixing ratio of the negative electrode material, carboxymethyl cellulose and styrene butadiene was 98: 1: 1 by weight.
- This slurry was applied substantially uniformly to a 10 ⁇ m thick rolled copper foil (negative electrode current collector). Coating and drying were performed on both sides of the rolled copper foil in the same procedure as for the positive electrode 10.
- the cylindrical battery 1 shown in FIG. 1 was produced using the produced positive electrode 10 and negative electrode 12.
- the positive electrode lead 7 and the negative electrode lead 5 of the tab portion for drawing current respectively are formed by ultrasonic welding.
- the positive electrode lead 7 and the negative electrode lead 5 of the tab portion are made of metal foil of the same material as that of the rectangular current collector, respectively, and are members installed for extracting current from the electrode.
- a separator 11 which is a single layer film of polyethylene is stacked and sandwiched between the tabbed positive electrode 1 and the negative electrode 2, and this is rolled into a cylindrical (helical) shape to form an electrode group as shown in FIG. It was accommodated in the battery can 13 of the cylindrical container. After the electrode group was housed in the battery can 13, an electrolytic solution was injected into the battery can 13 and sealed with a gasket.
- the concentration of LiPF 6 as an electrolyte is 1.0 mol / L in the electrolytic solution. It was dissolved in Furthermore, vinylene carbonate was mixed to 1 wt% with respect to the weight of the mixed solution.
- the battery lid 20 for sealing to which the positive electrode terminal is attached is injected into the battery can 13 through the gasket 18, and the electrolytic solution produced in this manner is sealed by caulking to form a cylindrical shape having a diameter of 18 mm and a length of 650 mm. Battery 1 was used.
- the battery was left for 60 days in a thermostat at 50 ° C. to confirm the storage characteristics of the battery. After 60 days, the battery was removed from the thermostat at 50 ° C., and placed in a thermostat at 25 ° C. for 1 day. After leaving it to stand and removing heat, it was discharged at 1500 mA to 3.0 V, discharged at 1500 mA to 3.0 V, and charged at a constant current and constant voltage for 5 hours with a charging current of 1500 mA and a voltage of 4.2 V. Next, the battery was discharged at 1500 mA, the voltage drop amount after the start of discharge was determined, and the value divided by 1500 mA of the current value was taken as the resistance value after storage for 60 days.
- the ratio between the initial resistance value and the resistance value after 60 days was determined, and this was taken as the resistance increase rate.
- Resistance increase rate (%) resistance value after 60 days ( ⁇ ) / initial resistance value ( ⁇ ) Examples 2 to 4 and Comparative Example 1
- An example in which natural graphite not subjected to boron treatment was used as the negative electrode active material was set as Comparative Example 1, and in the same manner as Example 1, a cylindrical battery was manufactured. Furthermore, the performance test was performed in the same manner as in Example 1.
- Example 1 The rate of increase in resistance was compared based on the case of using pure natural graphite not treated with boron (Comparative Example 1). In Example 1, the storage characteristics were increased by 17%, and it was confirmed that the battery had a long life. It is possible to suppress the increase in resistance after the storage test of the lithium ion secondary battery, and to improve the life characteristics of the battery.
- the film containing boron is formed on the surface of the negative electrode active material, it is considered that the performance deterioration due to the decomposition of the electrolyte solution at the interface of the negative electrode active material is suppressed, and the deterioration over time of the battery can be suppressed.
- the trivalent boron contained in the film containing boron has an unshared electron pair and electrostatically interacts with the anion portion of the lithium salt used for the electrolyte, the effective lithium ion It may have contributed to the improvement of the import number and suppressed the rise in resistance.
- the alkyl chain preferably has 1 to 10 carbon atoms.
- Example 5 A cylindrical battery was manufactured in the same manner as in Example 1 except that the method for manufacturing the boron-coated natural graphite material was changed.
- the negative electrode active material natural graphite having an interplanar spacing of 0.368 nm, an average particle diameter of 20 ⁇ m, and a specific surface area of 5 m 2 / g obtained by X-ray diffraction measurement was used. Natural graphite was thoroughly mixed with an aqueous dispersion of carboxymethylcellulose, and an aqueous solution of trimethyl borate was added and further mixed. Then, an aqueous dispersion of styrene butadiene copolymer was dispersed to prepare a negative electrode slurry. The mixing ratio of the negative electrode material, carboxymethyl cellulose and styrene butadiene was 98: 1: 1 by weight.
- This slurry was applied substantially uniformly to a 10 ⁇ m thick rolled copper foil (negative electrode current collector). Coating and drying were performed on both sides of the rolled copper foil in the same procedure as for the positive electrode 10. Then, it was compression-molded by a roll press machine and cut to have a coating width of 5.6 cm and a coating length of 54 cm, and a copper foil lead piece was welded to produce a negative electrode 12.
- the negative electrode material thus prepared was measured by X-ray photoelectron spectroscopy, it was possible to confirm a peak attributable to boron at 192 to 193 eV, and it was confirmed that the material contained boron. Subsequently, in the same manner as in Example 1, a cylindrical battery was produced, and the battery characteristics were measured.
- Example 6 using B (O-C2H5) 3 in place of trimethyl borate, Example 6 using B (O-C10H21) 3, and Example 7 using B (O-C18H37) 3 A cylindrical battery was produced in the same manner as in Example 5 as in Example 8. Furthermore, the performance test was performed in the same manner as in Example 1.
- Example 5 As described in Examples 5-6 7-8, even if the method of producing a negative electrode is different from the method described in Examples 1 2 3 4, the rate of increase in resistance is higher than in Comparative Example 1. It can be reduced. However, when the alkyl group is long, the negative electrode preparation method described in Example 5 is more effective in improving the storage characteristics. For example, when Example 3 and Example 7 are compared, Example 3 has a higher effect by 3%. The longer the alkyl, the more the surface-active effect is developed, which is thought to affect the carboxyl methyl cellulose used in the preparation of the negative electrode, the bi-solubility with the binder component, etc., and the covering effect became higher.
- the storage characteristics of the battery could be significantly improved.
- deterioration with time of the battery can be suppressed, and the life characteristics of the battery can be significantly improved.
Abstract
Description
<負極>
本発明の一実施形態に係る負極材は、負極活物質である炭素等にホウ素を含有するホウ酸エステル類を物理的に吸着させることで,負極活物質の表面に存在する表面官能基と電解液との反応を抑制し,電池の経時的な劣化を抑制することが可能になる。
本実施例の正極10は、正極活物質、導電剤、バインダ、及び正極集電体から構成される。炭素材を負極活物質として使用する場合は、対極となるリチウムを可逆的に吸蔵放出する正極活物質として、コバルト酸リチウム(LiCoO2)、ニッケル酸リチウム(LiNiO2)などの層状化合物、またはこれらの一種以上を遷移金属で置換したもの、あるいはマンガン酸リチウムLi1+xMn2-xO4(ただしx =0~0.33)、Li1+xMn2-x-yMyO4 (ただし、MはNi、Co、Fe、Cu、Al、Mgより選ばれた少なくとも一種の金属を含み、x=0~0.33、y=0~1.0、2-x-y>0)、LiMnO4、LiMn2O4、LiMnO2、LiMn2-xMxO4(ただし、MはNi、Co、Fe、Cu、Al、Mgより選ばれた少なくとも一種の金属を含み、x=0.01~0.1)、Li2Mn3MO8(ただし、MはNi、Co、Fe、Cu、Al、Mgより選ばれた少なくとも一種の金属を含む)、銅-Li酸化物(LiCuO2)、ジスルフィド化合物、Fe2(MoO4)3などを含む混合物、あるいはポロアニリン、ポリピロール、ポリチオフェンなどの一種または二種以上の混合物を用いることができる。
電解液に使用する非水溶媒としては、エチレンカーボネート、プロピレンカーボネート、ガンマブチロラクトン、ジメチルカーボネート、エチルメチルカーボネート、ジエチルカーボネート等、これらをフッ素置換体などのハロゲン化物や硫黄元素で置換したものが挙げられ、単独で用いても2種以上混合して用いてもよい。2種類以上の溶媒を用いる場合は、環状カーボネートや環状ラクトンのような粘度の大きい溶媒と、鎖状カーボネートや鎖状エステルのような粘度の小さい溶媒との混合溶媒系を用いるのが好ましい。
正極10および負極12の直接接触による短絡防止を目的にセパレータ11を用いる。セパレータ11には、ポリエチレン、ポリプロピレン、アラミド樹脂等の微多孔質の高分子フィルムやこの高分子フィルムにアルミナ粒子等の耐熱性物質を表面に被覆した膜等が使用できる。
<実施例1>
(正極の作製)
正極活物質には、平均粒径10μm、比表面積1.5m2/gのLi1.02Mn1.98Al0.02O4を用いた。正極活物質85重量%に、塊状黒鉛とアセチレンブラックを9:2に混合したものを導電剤とし、結着剤として予め5重量%PVDFに調整されたNMP溶液に導電剤を分散させてスラリーにした。正極活物質、導電剤、PVDFの混合比は、重量比で85:10:5にした。
(負極の作製)
負極活物質にはX線回折測定で得られた面間隔が0.368nm、平均粒径が20μm、比表面積が5m2/gの天然黒鉛を用いた。ホウ酸トリメチルを10%の濃度で蒸留水に溶解させた。次いで,ホウ酸トリメチルの活物質重量に対する濃度が1wt%になるように,ホウ酸トリメチル水溶液と天然黒鉛を撹拌後,80℃の恒温槽で乾燥させ,ホウ素とアルキル基を有する負極活物質を得た。得られた負極材をX線光電子分光法で測定すると,192-193 eVにホウ素に起因するピークを確認でき,ホウ素を含有していることを確認した。また,このようにして作製した天然黒鉛の比表面積は4m2/gに減少した。
(電池の作製)
作製した正極10と負極12を用いて図1に示す円筒型の電池1を作製した。それぞれ電流引き出し用のタブ部の正極リード7、負極リード5を超音波溶接により形成する。タブ部の正極リード7、負極リード5は、長方形の形状をした集電体とそれぞれ同じ材質の金属箔からできており、電極から電流を取り出すために設置する部材である。タブ付けされた正極1及び負極2の間にポリエチレンの単層膜であるセパレータ11を挟んで重ね、これを、図1に示すように、円筒状(螺旋状)に捲いて電極群とし、円筒状容器の電池缶13に収納した。電極群を電池缶13に収納した後、電池缶13内に電解液を注入し、ガスケットで密封させた。
(性能測定)
作製した円筒型の電池1について,充電電流1500mA、電圧4.2V、5時間の定電流定電圧充電をし、放電は放電電流1500mAで電池電圧3.0Vまで定電流放電した。この充電、放電プロセスを1サイクルとし、合計3サイクルした。3サイクル目の放電開始後10秒目の電圧降下量を求め,電流値の1500mAで除した値を初期抵抗値とした。この電池を再度,3.0Vまで1500mAで放電し,充電電流1500mA、電圧4.2V、5時間の定電流定電圧充電をした。これら一連の充放電試験は25℃の恒温槽内で試験した。25℃での試験終了後,電池の保存特性を確認するため,50℃の恒温槽内で60日間放置した。60日後,50℃の恒温槽から電池取り出し,25℃の恒温槽内に1日間した。放置し,除熱した後,3.0Vまで1500mAで放電し,3.0Vまで1500mAで放電し,充電電流1500mA、電圧4.2V、5時間の定電流定電圧充電をした。次いで,1500mAで放電して,放電開始後の電圧降下量を求め,電流値の1500mAで除した値を60日保存後の抵抗値とした。
<実施例2~4、比較例1>
ホウ酸トリメチルに代えてホウ酸トリエチルを用いた例を実施例2、B(O-C10H21)3を用いた例を実施例3、B(O-C18H37)3を用いた例を実施例4、ホウ素処理をしない天然黒鉛を負極活物質に用いた例を比較例1とし、実施例1と同様にして円筒型電池を作製した。さらに、実施例1と同様に性能試験を行った。
<実施例5>
ホウ素被覆天然黒鉛材の作製方法を変更し、実施例1と同様にして円筒型電池を作製した。
<実施例6~8>
ホウ酸トリメチルに代えてB(O-C2H5)3を用いた例を実施例6、B(O-C10H21)3を用いた例を実施例7、B(O-C18H37)3を用いた例を実施例8とし、実施例5と同様にして円筒型電池を作製した。さらに、実施例1と同様に性能試験を行った。
11 セパレータ
12 負極
13 電池缶
14 正極集電タブ
15 負極集電タブ
16 内蓋
17 内圧開放弁
18 ガスケット
19 PTC素子
20 電池蓋
21 軸芯
Claims (8)
- 負極活物質と、前記負極活物質の表面に形成された被覆材とを有するリチウムイオン二次電池用負極材であって,
前記被覆材は、アルキル基を有するホウ素化合物を含み、
前記ホウ素化合物は、前記負極活物質に吸着していることを特徴とするリチウムイオン二次電池用負極材。 - 請求項1に記載されたリチウムイオン二次電池用負極材であって、
前記ホウ素化合物はホウ酸エステル化合物であることを特徴とするリチウムイオン二次電池用負極材。 - 請求項1に記載されたリチウムイオン二次電池用負極材であって、
前記負極活物質は、非晶質炭素または黒鉛の少なくともいずれか一方を含むことを特徴とするリチウムイオン二次電池用負極材。 - 請求項1に記載されたリチウムイオン二次電池用負極材であって、
前記負極活物質は、天然黒鉛を含むことを特徴とするリチウムイオン二次電池用負極材。 - リチウムイオンを吸蔵放出する正極及び負極と、電解液とを備えるリチウムイオン二次電池であって、
前記負極は、請求項1ないし5のいずれかに記載の負極材を用いたことを特徴とするリチウムイオン二次電池。 - リチウムイオン二次電池用負極の製造方法であって、
炭素材の表面にホウ酸エステル化合物を付着させる工程と、
ホウ酸エステル化合物が付着した炭素材と、バインダとを混合し、負極合剤を作製する工程と、
負極合剤を集電体に塗布する工程とを備えることを特徴とするリチウムイオン二次電池用負極の製造方法。
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JP2015509781A JP6138922B2 (ja) | 2013-04-03 | 2013-04-03 | リチウムイオン二次電池用負極、リチウムイオン二次電池、およびそれらの製造方法 |
PCT/JP2013/060145 WO2014162529A1 (ja) | 2013-04-03 | 2013-04-03 | リチウムイオン二次電池用負極、リチウムイオン二次電池、およびそれらの製造方法 |
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US20190221851A1 (en) * | 2018-01-12 | 2019-07-18 | Toyota Motor Engineering & Manufacturing North America, Inc. | Interphase between lithium metal and solid electrolyte |
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JP2013004215A (ja) * | 2011-06-14 | 2013-01-07 | Hitachi Ltd | リチウムイオン二次電池 |
JP2013037772A (ja) * | 2011-08-03 | 2013-02-21 | Gs Yuasa Corp | 非水電解質二次電池および非水電解質二次電池の製造方法 |
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JP2013004215A (ja) * | 2011-06-14 | 2013-01-07 | Hitachi Ltd | リチウムイオン二次電池 |
JP2013037772A (ja) * | 2011-08-03 | 2013-02-21 | Gs Yuasa Corp | 非水電解質二次電池および非水電解質二次電池の製造方法 |
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