WO2013146766A1 - リチウムイオン二次電池 - Google Patents
リチウムイオン二次電池 Download PDFInfo
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- WO2013146766A1 WO2013146766A1 PCT/JP2013/058745 JP2013058745W WO2013146766A1 WO 2013146766 A1 WO2013146766 A1 WO 2013146766A1 JP 2013058745 W JP2013058745 W JP 2013058745W WO 2013146766 A1 WO2013146766 A1 WO 2013146766A1
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- secondary battery
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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
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
- H01M4/502—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese for non-aqueous cells
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- 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
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/058—Construction or manufacture
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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
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/139—Processes of manufacture
- H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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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
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
- H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
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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
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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
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/621—Binders
- H01M4/622—Binders being polymers
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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
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/621—Binders
- H01M4/622—Binders being polymers
- H01M4/623—Binders being polymers fluorinated polymers
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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
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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
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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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
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T29/00—Metal working
- Y10T29/49—Method of mechanical manufacture
- Y10T29/49002—Electrical device making
- Y10T29/49108—Electric battery cell making
- Y10T29/4911—Electric battery cell making including sealing
Definitions
- the present invention relates to a lithium ion secondary battery.
- lithium ion secondary batteries Since lithium ion secondary batteries have a small volume, a large mass capacity density, and a high voltage can be taken out, they are widely used as power sources for small devices. For example, it is used as a power source for mobile devices such as mobile phones and notebook computers. Also, in recent years, in addition to small mobile device applications, large secondary devices that require a long life with a large capacity, such as electric vehicles (EV) and power storage fields, are being considered due to consideration for environmental issues and increased awareness of energy conservation. Application to batteries is expected.
- EV electric vehicles
- the positive electrode of the lithium ion secondary battery includes a positive electrode active material such as a lithium composite oxide, a conductive agent such as carbon, and a positive electrode mixture including a binder such as polyvinylidene fluoride (PVDF) and a current collector bonded thereto.
- a positive electrode active material such as a lithium composite oxide
- a conductive agent such as carbon
- a positive electrode mixture including a binder such as polyvinylidene fluoride (PVDF) and a current collector bonded thereto.
- PVDF polyvinylidene fluoride
- lithium composite oxide used for the positive electrode active material examples include LiCoO 2 , LiNiO 2 , LiMnO 2 , LiNi 1/3 Co 1/3 Mn 1/3 O 2 having a layered structure, and LiMn 2 O 4 having a spinel structure. Etc. Among these, LiMn 2 O 4 is considered to be particularly suitable as a positive electrode material for large batteries because it is safe and inexpensive. However, when LiMn 2 O 4 is exposed to a high-temperature environment, Mn is eluted and battery capacity may be easily deteriorated under charge / discharge cycles or storage at high temperatures. Attempts have been made to suppress elution of Mn by adding various elements to the positive electrode active material to stabilize the crystal structure, but it has not been fully solved, and LiMn 2 O 4 is It remained as an issue when using it.
- Patent Document 1 discloses a method in which polymer particles of a resin containing sulfur are added to an electrode.
- Patent Document 2 discloses a method in which polysulfone, polyethersulfone, or the like is added to an electrode as an overcharge inhibitor for a lithium nickel manganese positive electrode having a layered structure. Is disclosed.
- Patent Documents 3 and 4 disclose a method of using a sulfur-containing resin as a negative electrode binder.
- lithium manganate is likely to elute Mn into the electrolyte, especially at a high temperature of 40 ° C. or higher, and the eluted Mn may be deposited on the negative electrode to cause an increase in internal resistance or a decrease in battery capacity.
- the elution of Mn from the positive electrode active material has been attempted with a substitution element, it has not yet been completely solved.
- the method of suppressing the influence of deposited Mn is also considered by adding the additive which forms a SEI film
- the present invention provides a positive electrode for a secondary battery that improves the high-temperature cycle characteristics of a lithium ion secondary battery using spinel-type lithium manganate and can provide a secondary battery with a high capacity retention rate in a high-temperature charge / discharge cycle.
- the purpose is to provide.
- the positive electrode for a secondary battery according to the present invention includes a positive electrode active material and a positive electrode binder, the positive electrode active material includes lithium manganate having a spinel structure, and the positive electrode binder includes at least polyvinylidene fluoride (PVDF) and a sulfone bond. And a resin having
- FIG. 3 is a graph showing measured values of alternating current impedance (real part value at 0.1 Hz) with respect to PES concentration after initial charging of batteries manufactured in the same manner as in Comparative Examples 1 and 2 and Examples 1 to 4. .
- the positive electrode for a secondary battery according to the present embodiment includes spinel lithium manganate as an active material, and further includes a resin having PVDF and a sulfone bond as a binder.
- the positive electrode active material preferably contains lithium manganate having a spinel structure.
- the lithium manganate having a spinel structure has the following formula (1): LiMn 2-x M x O 4 (1) (Wherein M is at least one element selected from the group consisting of Mg, Al, Co, Ni, Fe and B, and 0 ⁇ x ⁇ 2). Stoichiometric composition may also be used. Of the compounds represented by the formula (1), only one kind may be used, or two or more kinds may be used in combination.
- lithium manganate has a lower capacity than lithium cobaltate and lithium nickelate, the production cost of Mn is low compared to Ni and Co, so the material cost is low, and the thermal stability is high because of the spinel structure. For this reason, it is preferable as a positive electrode active material for large-sized secondary batteries such as electric vehicles and power storage. In this embodiment, it is preferable that 50 mass% or more of lithium manganate which has a spinel structure is contained in a positive electrode active material.
- the positive electrode active material may further include a positive electrode active material having a layered structure such as lithium cobaltate (LiCoO 2 ) or lithium nickelate (LiNiO 2 ).
- the average particle diameter (D50) of the lithium manganate having a spinel structure used in the present embodiment is preferably 1 ⁇ m or more and 30 ⁇ m or less, and more preferably 5 ⁇ m or more and 20 ⁇ m or less.
- the specific surface area is preferably 0.1 to 1 m 2 / g, and more preferably 0.2 to 0.5 m 2 / g.
- the average particle diameter (D50) is a value measured by a laser diffraction / scattering method.
- the specific surface area is a value measured and calculated by the BET method.
- Binder for positive electrode In the present embodiment, at least PVDF and a resin having a sulfone bond are used in combination as the positive electrode binder.
- the present inventors pay attention to the fact that the binder covers the surface of the active material, and by coating the surface of the lithium manganate having a spinel structure with a polymer that exhibits the same function as the SEI film, We intensively investigated whether the reaction with the liquid and Mn elution could be directly suppressed. As a result, it was found that the combined use of PVDF and a resin having a sulfone bond such as polyethersulfone (PES) is very effective in improving the high-temperature cycle characteristics.
- PES polyethersulfone
- Patent Documents 1 to 4 there is no description or suggestion that using PVDF and a resin having a sulfone bond in combination as a positive electrode binder in a positive electrode using lithium manganate exhibits a particularly excellent effect. Absent.
- the present inventors have also found preferable electrode formulations and terminal structures of PES. The details will be described below.
- the resin having a sulfone bond may contain a benzene ring and / or an ether bond in addition to the sulfone bond, and preferably has at least the following structure, for example.
- repeating unit constituting the resin having a sulfone bond are given below.
- the abbreviations mean the following.
- Ph phenyl group or phenylene group
- —SO 2 — sulfonyl group
- —O— oxy group
- —S— thio group
- —CO— carbonyl group
- CH 3 — methyl group.
- n An integer of 100 to 10,000.
- polysulfone, polyethersulfone (PES) or polyphenylsulfone is preferably used as the resin containing a sulfone bond. These may be used alone or in combination of two or more. Among these, in the present embodiment, it is preferable to use PES having the repeating unit represented by f.
- PES is preferable as a positive electrode binder when lithium manganate is included in the positive electrode active material.
- PVDF has no functional group that interacts with the active material or lithium ions, it does not directly affect the battery reaction.
- PES contains a sulfone bond (—S ( ⁇ O) 2 —) as a functional group.
- the sulfone bond is characteristically contained in a sulfone compound such as propane sultone known as an additive for forming an SEI film on the negative electrode. Therefore, it is presumed that the PES coats the surface of the positive electrode active material to exhibit an action similar to that of the SEI film, the decomposition reaction with the electrolytic solution and Mn elution are suppressed, and the high-temperature cycle characteristics are improved. Therefore, if it is a resin having a sulfone bond, it is expected to exhibit the same effect as PES.
- PES contains an ether bond (—O—) and a benzene ring in addition to a sulfone bond.
- the ether group is also contained in a vinyl compound such as vinylene carbonate (VC), which is known as an additive for forming an SEI film on the negative electrode.
- VC vinylene carbonate
- the terminal of PES has a substituent which can raise affinity with a positive electrode active material, It is more preferable to have a hydroxyl group, a carboxy group, etc. preferable.
- PES has a terminal hydroxyl group
- adhesion between the positive electrode current collector and PES can be improved.
- PES has a hydroxyl group at the terminal
- the affinity with the positive electrode active material is further increased, so that a uniform and dense coating layer can be formed on the surface of the positive electrode active material.
- the content of the terminal hydroxyl group in PES is 0.6 or more per 100 polymerization repeating units, it is preferable that the above effects can be sufficiently obtained.
- the upper limit depends on the molecular weight of the polymer and is not particularly limited, but is preferably 2 or less, for example, from the viewpoint of ease of production and production cost.
- PES is preferably used together with PVDF.
- the PES concentration in the binder (PES / (PVDF + PES) ⁇ 100 mass%) is not particularly limited, but is preferably 10 mass% to 60 mass%. If the concentration of PES is too high, PES is inferior in oxidation resistance compared to a fluorine-based resin such as PVDF, so that there is a possibility that electrode deterioration due to decomposition of PES may occur.
- PES forms a coating layer similar to the SEI film on the surface of the active material. However, the coating layer becomes too thick with PES alone, and the interface resistance of the positive electrode, that is, the internal resistance of the battery increases. It will have an adverse effect. Furthermore, the adhesive strength of the electrode may be low with PES alone. On the other hand, if the PES concentration is too low, the above-mentioned effect due to the addition of PES is reduced.
- positive electrode binders may be included as long as the object of the present invention is not impaired.
- examples of other positive electrode binders include P (VDF-TFE) copolymer, polyvinyl chloride and polyvinylidene chloride copolymer, acrylic resin, polyvinyl butyral, and polyvinyl acetal.
- the positive electrode according to the present embodiment is a positive electrode obtained by dispersing and kneading a positive electrode active material containing lithium manganate, a positive electrode binder containing PVDF and PES, and a conductive aid, if necessary, in a solvent such as NMP.
- a slurry can be prepared, and this positive electrode slurry can be applied to a positive electrode current collector and dried.
- the content of each of these compounds contained in the positive electrode slurry is not particularly limited.
- the positive electrode active material is 85 to 96% by mass and the binder is 2 to 8% with respect to the total mass of the solid content in the positive electrode slurry. It is preferable to contain 2% by mass to 8% by mass and a conductive assistant.
- PES and PVDF are uniformly dissolved in the positive electrode slurry because PES can uniformly cover the surface of the positive electrode active material.
- Patent Document 1 it is considered that PES is dispersed in the form of particles in the electrode, but it is difficult to obtain the effect of the present invention.
- preparing the positive electrode slurry it is preferable to prepare a binder solution in which PVDF and PES are previously dissolved in a solvent, and then mix the positive electrode active material, the conductive additive, and the binder solution.
- Examples of the conductive aid used for the positive electrode include highly crystalline carbon, carbon black, and carbon fiber. These may use only 1 type and may use 2 or more types together.
- the positive electrode current collector aluminum, stainless steel, nickel, titanium, or an alloy thereof can be used.
- the obtained positive electrode can adjust the electrode density by compressing the positive electrode active material layer by a method such as a roll press.
- FIG. 1 shows a laminated secondary battery as an example of the secondary battery according to this embodiment.
- the secondary battery shown in FIG. 1 includes a positive electrode composed of a positive electrode active material and a positive electrode active material layer 1 including a positive electrode binder and a positive electrode current collector 3 according to this embodiment, and a negative electrode active material capable of occluding and releasing lithium.
- a separator 5 is sandwiched between the negative electrode composed of the negative electrode active material layer 2 and the negative electrode current collector 4.
- the positive electrode current collector 3 is connected to the positive electrode tab 8, and the negative electrode current collector 4 is connected to the negative electrode tab 7.
- a laminated outer package 6 is used as the outer package, and the inside of the secondary battery is filled with a non-aqueous electrolyte.
- the negative electrode of the secondary battery according to this embodiment is not particularly limited, for example, a negative electrode active material layer is formed on at least one surface of a negative electrode current collector such as a copper foil.
- the negative electrode active material layer includes at least a negative electrode active material, a negative electrode binder, and, if necessary, a conductive additive.
- the negative electrode active material contained in the negative electrode of the secondary battery according to the present embodiment is not particularly limited, and carbon materials such as graphite and amorphous carbon can be used. From the viewpoint of energy density, graphite is used. preferable. Further, as a negative electrode active material, materials such as Si, Sn, and Al that form an alloy with Li, Si oxide, Si composite oxide containing Si and other metal elements other than Si, Sn oxide, Sn and Sn Sn composite oxides containing other metal elements other than the above, Li 4 Ti 5 O 12 , composite materials obtained by coating these materials with carbon, and the like can also be used. A negative electrode active material can be used individually by 1 type, and can also be used in combination of 2 or more type.
- the average particle diameter (D50) of the negative electrode active material is preferably 5 to 50 ⁇ m, more preferably 10 to 30 ⁇ m.
- the specific surface area is preferably 0.5 ⁇ 5m 2 / g, more preferably 0.5 ⁇ 2m 2 / g.
- a fluorine compound such as polyvinylidene fluoride (PVDF) or a rubber compound such as styrene butadiene rubber (SBR) can be used.
- PVDF polyvinylidene fluoride
- SBR styrene butadiene rubber
- a thickener such as carboxymethyl cellulose (CMC) or a sodium salt thereof can be used in combination.
- CMC carboxymethyl cellulose
- the amount of the negative electrode binder relative to the total weight of the negative electrode active material, the negative electrode binder, and the conductive additive is not particularly limited, but is preferably 0.5% by weight to 15% by weight, and preferably 1% by weight to 8% by weight. More preferred.
- Examples of the conductive aid used for the negative electrode include highly crystalline carbon, carbon black, carbon fiber, and the like. These may use only 1 type and may use 2 or more types together.
- the production method of the negative electrode is not particularly limited. For example, first, a negative electrode active material, a negative electrode binder, and, if necessary, a conductive additive are dispersed and kneaded in a predetermined blending amount in a solvent to prepare a negative electrode slurry.
- a solvent such as NMP
- an organic solvent such as NMP is used as the solvent for the negative electrode slurry when a fluorine compound is used as the negative electrode binder, and water is used when a rubber compound is used.
- the negative electrode can be produced by coating this negative electrode slurry on a negative electrode current collector and drying it.
- the obtained negative electrode can adjust an electrode density by compressing a negative electrode active material layer by methods, such as a roll press.
- Non-aqueous electrolyte Although it does not specifically limit as a non-aqueous electrolyte, for example, the solution which melt
- lithium salt examples include LiPF 6 , lithium imide salt, LiAsF 6 , LiAlCl 4 , LiClO 4 , LiBF 4 , LiSbF 6, and the like.
- At least one solvent selected from the group consisting of cyclic carbonates, chain carbonates, aliphatic carboxylic acid esters, ⁇ -lactones, cyclic ethers and chain ethers can be used.
- the cyclic carbonate include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and derivatives thereof (including fluorinated products).
- the chain carbonate include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dipropyl carbonate (DPC), and derivatives thereof (including fluorinated products).
- Examples of the aliphatic carboxylic acid ester include methyl formate, methyl acetate, ethyl propionate, and derivatives thereof (including fluorinated products).
- Examples of ⁇ -lactone include ⁇ -butyrolactone and its derivatives (including fluorinated products).
- Examples of the cyclic ether include tetrahydrofuran, 2-methyltetrahydrofuran and derivatives thereof (including fluorinated products).
- Examples of the chain ether include 1,2-diethoxyethane (DEE), ethoxymethoxyethane (EME), ethyl ether, diethyl ether, and derivatives thereof (including fluorinated compounds).
- non-aqueous solvents include dimethyl sulfoxide, 1,3-dioxolane, formamide, acetamide, dimethylformamide, dioxolane, acetonitrile, propionitrile, nitromethane, ethyl monoglyme, phosphate triester, trimethoxymethane, Dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, 3-methyl-2-oxazolidinone, 1,3-propane sultone, anisole, N-methylpyrrolidone, and derivatives thereof (fluorinated compounds) Can also be used. These may use only 1 type and may use 2 or more types together.
- the concentration of the lithium salt in the nonaqueous electrolytic solution is preferably 0.7 mol / L or more and 1.5 mol / L or less.
- concentration of the lithium salt By setting the concentration of the lithium salt to 0.7 mol / L or more, sufficient ionic conductivity can be obtained.
- concentration of lithium salt 1.5 mol / L or less a viscosity can be made low and the movement of lithium ion is not prevented.
- the non-aqueous electrolyte may contain an additive in order to form a good quality SEI film on the negative electrode surface.
- the SEI film functions to suppress the reactivity with the electrolytic solution or to smooth the desolvation reaction accompanying the insertion and desorption of lithium ions to prevent structural deterioration of the negative electrode active material.
- examples of such additives include propane sultone, vinylene carbonate, and cyclic disulfonic acid esters. These may use only 1 type and may use 2 or more types together.
- the concentration of the additive in the non-aqueous electrolyte is preferably 0.2% by mass or more and 5% by mass or less.
- concentration of the additive is 0.2% by mass or more, a sufficient SEI film is formed.
- resistance can be made low because the density
- Positive electrode tab negative electrode tab
- at least 1 type selected from the group which consists of Al, Cu, phosphor bronze, Ni, Ti, Fe, brass, stainless steel can be used as a material.
- Separator Although it does not specifically limit as a separator, The porous film which consists of polyolefin, such as a polypropylene and polyethylene, a fluorine resin, etc. can be used. In addition, inorganic separators such as cellulose and glass separators can also be used.
- Exterior body Although it does not specifically limit as an exterior body, Cans, such as a coin shape, a square shape, and a cylindrical shape, and a laminate exterior body can be used. Among these, a laminate outer package which is a flexible film made of a laminate of a synthetic resin and a metal foil is preferable from the viewpoint of being able to reduce the weight and improving the energy density of the secondary battery.
- a laminate-type secondary battery including a laminate outer package is excellent in heat dissipation, and thus is suitable as a vehicle-mounted battery such as an electric vehicle.
- a positive electrode tab and a negative electrode tab are connected to the positive electrode for a secondary battery and the negative electrode according to this embodiment via a positive electrode current collector and a negative electrode current collector, respectively.
- the positive electrode and the negative electrode are arranged opposite to each other with the separator interposed therebetween, and an electrode laminate is produced in which the positive electrode and the negative electrode are laminated.
- the electrode laminate is accommodated in an exterior body and immersed in an electrolytic solution.
- a secondary battery is manufactured by sealing the exterior body so that a part of the positive electrode tab and the negative electrode tab protrudes to the outside.
- Example 1 (Preparation of negative electrode) Graphite powder (average particle size (D50): 22 ⁇ m, specific surface area: 1.0 m 2 / g) as negative electrode active material, styrene butadiene rubber (SBR) latex (average particle size 100 nm, solid content 50% by mass) as binder, increase Carboxymethylcellulose sodium salt (CMC) was prepared as a sticking agent. A 2% by mass CMC aqueous solution was prepared, mixed so that the mass ratio of the graphite powder and the solid content of CMC was 98.0: 1.0, and water was added appropriately while adjusting the viscosity of the slurry. Dispersion kneading.
- SBR styrene butadiene rubber
- CMC Carboxymethylcellulose sodium salt
- LiMn 2 O 4 powder (average particle size (D50): 15 ⁇ m, specific surface area: 0.5 m 2 / g) as a positive electrode active material, PVDF as a binder, and terminal hydroxyl groups from 0.6 to 1.
- 4 Sumika Excel 5003PS (trade name, manufactured by Sumitomo Chemical Co., Ltd.) as a PES containing 4 and carbon black as a conductive auxiliary agent were prepared.
- a PVDF solution in which 8% by mass of PVDF was dissolved in NMP and a PES solution in which 20% by mass of the PES was dissolved in NMP were prepared.
- the positive electrode active material, the PVDF solution, the PES solution, and the conductive additive are dispersed and kneaded so that the mass ratio of the solid content is 93: 3.6: 0.4: 3, and NMP is added as appropriate.
- a positive electrode slurry was prepared while adjusting the viscosity. The ratio of PES in the binder at this time (PES / (PVDF + PES) ⁇ 100 (mass%)) is 10 mass%.
- the positive electrode slurry was applied on a 20 ⁇ m thick aluminum foil as a positive electrode current collector. Thereafter, the positive electrode active material layer was formed by drying at 125 ° C. for 10 minutes to evaporate NMP. A positive electrode was produced by pressing the positive electrode active material layer. In addition, the mass of the positive electrode active material layer per unit area after drying was set to 0.024 g / cm 2 .
- the produced positive electrode and negative electrode were each cut into 5 cm ⁇ 6 cm. Of these, a side of 5 cm ⁇ 1 cm was a portion where the electrode active material layer was not formed (uncoated portion) in order to connect the tab, and a portion where the electrode active material layer was formed was 5 cm ⁇ 5 cm.
- a positive electrode tab made of aluminum having a width of 5 mm, a length of 3 cm, and a thickness of 0.1 mm was ultrasonically welded to the uncoated portion of the positive electrode with a length of 1 cm. Also, a nickel negative electrode tab having the same size as the positive electrode tab was ultrasonically welded to the uncoated portion of the negative electrode.
- the negative electrode and the positive electrode were arranged on both sides of a 6 cm ⁇ 6 cm polyethylene / polypropylene separator so that the electrode active material layers overlapped with the separator interposed therebetween to obtain an electrode laminate.
- Three sides of the two 7 cm ⁇ 10 cm aluminum laminate films except one of the long sides were bonded to each other with a width of 5 mm by thermal fusion to produce a bag-shaped laminate outer package.
- the electrode laminate was inserted into the bag-shaped laminate outer package so that the distance from the short side of the laminate outer package was 1 cm. Further, 0.2 g of the non-aqueous electrolyte was injected and vacuum impregnated, and then the opening was sealed with a width of 5 mm by thermal fusion under reduced pressure. Thus, a laminate type secondary battery was produced.
- Example 1 In the preparation of the positive electrode slurry, a secondary battery was prepared and evaluated in the same manner as in Example 1 except that only PVDF was used (PES concentration 0 mass%).
- Table 1 shows the evaluation results of Examples 1 to 5 and Comparative Examples 1 and 2 according to the order of the PES concentration in the binder.
- Examples 1 to 5 in which the PES concentration was 10 to 60% by mass, the charge / discharge efficiency and the rate characteristics were almost the same as those in Comparative Example 1 using only PVDF, and the capacity retention rate was improved.
- Comparative Example 2 using only PES the capacity retention rate significantly decreased with the decrease in the initial characteristics. From this result, it was found that by using PVDF and PES in combination as a binder, the high-temperature cycle characteristics of a secondary battery using lithium manganate can be improved.
- Example 6 A secondary battery was produced and evaluated in the same manner as in Example 4 except that Sumika Excel 4100P (trade name, manufactured by Sumitomo Chemical Co., Ltd.) was used as the PES not containing a hydroxyl group at the terminal. Table 1 shows the results. A higher capacity retention rate was obtained than in Comparative Examples 1 and 2. However, since Example 4 using PES having a hydroxyl group at the terminal showed a higher capacity retention rate, it was found that PES having a hydroxyl group at the terminal is more preferable.
- the PES having a terminal hydroxyl group used in Examples 1 to 5 contains 0.6 to 1.4 hydroxyl groups per 100 polymerization repeating units. Therefore, the effect is considered to be obtained if the hydroxyl group content is at least 0.6 per 100 polymerization repeating units.
- Table 2 shows the results of Comparative Example 3 and Comparative Example 4.
- Comparative Example 4 in which PVDF and PES were used in combination with the negative electrode binder (PES concentration 50%) had a significantly lower capacity retention rate. The reason for this is not clear, but when the PES is reduced and decomposed at the negative electrode or the negative electrode active material is coated with PES, the migration of lithium ions is greatly reduced or the formation of the SEI film on the negative electrode is inhibited. It is possible that this has happened. From this result, it was found that the effect of PES in this embodiment is effective only for the positive electrode.
- Comparative Example 5 A secondary battery was produced in the same manner as in Comparative Example 1 except that LiCoO 2 having a layered structure (average particle diameter (D50): 11 ⁇ m, specific surface area: 0.5 m 2 / g) was used as the positive electrode active material. evaluated. However, the mass of the positive electrode active material layer per unit area was 0.018 g / cm 2 .
- Example 6 A secondary battery was produced in the same manner as in Example 4 except that LiCoO 2 having a layered structure (average particle diameter (D50): 11 ⁇ m, specific surface area: 0.5 m 2 / g) was used as the positive electrode active material. evaluated. However, the mass of the positive electrode active material layer per unit area was 0.018 g / cm 2 .
- Comparative Examples 5 and 6 are shown in Table 2.
- the positive electrode active material was LiCoO 2
- the effect using PES was not recognized. From this, it was found that this embodiment is particularly effective when the positive electrode active material contains lithium manganate having a spinel structure. This is because, in lithium manganate (LiMn 2 O 4 ), elution of Mn into the electrolyte is a major cause of high-temperature deterioration, whereas in LiCoO 2 , Co elution and its influence are small, so the coating effect of PES is small. It is estimated that it was not obtained.
- Example 7 A secondary battery was produced and evaluated using a negative electrode (PVDF) produced by the same method as in Comparative Example 3 and a positive electrode produced by the same method as in Example 4. Table 2 shows the results. Also in this case, the capacity retention rate of Example 7 using PVDF and PES was higher than that of Comparative Example 3 using only PVDF as the positive electrode binder. In Comparative Example 3 and Example 7 in which the negative electrode binder is PVDF, the difference in capacity retention is 6 pt, whereas in Comparative Example 1 and Example 4 in which the negative electrode binder is SBR, the difference in capacity retention is 9. It was found that the effect of PES was larger when SBR was used as the negative electrode binder.
- FIG. 2 shows the measured value of the real part of the impedance at 0.1 Hz with respect to the PES concentration. It was found that the impedance increased in proportion to the PES concentration in the binder. This is presumably because the PES coating layer formed on the active material surface becomes thicker as the PES concentration increases, and lithium ions do not move easily.
- the PES concentration in the positive electrode binder in the present embodiment is 1.6 times or less of the battery resistance when only PVDF is used.
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Abstract
Description
本実施形態に係る二次電池用正極は、活物質としてスピネル構造のマンガン酸リチウムを含み、さらに、バインダーとしてPVDFおよびスルホン結合を有する樹脂を含む。
本実施形態において、正極活物質は、スピネル構造を有するマンガン酸リチウムを含むことが好ましい。スピネル構造を有するマンガン酸リチウムは、下記式(1):
LiMn2-xMxO4 (1)
(式中、MはMg、Al、Co、Ni、FeおよびBからなる群から選択される少なくとも一種の元素であり、0≦x<2である。)で表され、例えばLi過剰組成など非化学量論組成であってもよい。式(1)で表される化合物のうち、一種のみを用いてもよく、二種以上を併用することもできる。マンガン酸リチウムは、コバルト酸リチウムやニッケル酸リチウムより容量は低いものの、NiやCoと比較してMnの産出量が多いため材料コストが低く、スピネル構造を有するため熱的安定性が高い。このため、電気自動車や電力貯蔵用などの大型二次電池向けの正極活物質材料として好ましい。本実施形態において、スピネル構造を有するマンガン酸リチウムは、正極活物質中50質量%以上含まれることが好ましい。
本実施形態においては、正極用バインダーとして、少なくとも、PVDFとスルホン結合を有する樹脂とを併用する。
a:(-Ph-SO2-)n、
b:(-Ph-SO2-Ph-)n、
c:(-Ph-SO2-Ph-Ph-SO2-Ph-)n、
d:(-Ph-SO2-Ph-Ph-Ph-SO2-Ph-)n、
e:(-Ph-SO2-Ph-Ph-Ph-SO2-)n、
f:(-Ph-SO2-Ph-O-)n、
g:(-Ph-SO2-Ph-SO2-Ph-O-)n、
h:(-Ph-SO2-Ph-SO2-Ph-O-Ph-O-)n、
i:(-Ph-SO2-Ph-Ph-SO2-Ph-O-)n、
j:(-Ph-SO2-Ph-Ph-SO2-Ph-O-Ph-O-)n、
k:(-Ph-SO2-Ph-Ph-SO2-Ph-O-Ph-Ph-O-)n、
l:(-Ph-SO2-Ph-Ph-O-Ph-O-)n、
m:(-Ph-SO2-Ph-O-Ph-O-Ph-O-)n、
n:(-Ph-SO2-Ph-O-Ph-Ph-O-)n、
o:(-Ph-SO2-Ph-CH2-Ph-SO2-Ph-O-)n、
p:〔-Ph-SO2-Ph-Ph-O-Ph-C(CH3)(CH3)-Ph-O-〕n、
q:〔-Ph-SO2-Ph-O-Ph-C(Ph)(Ph)-Ph-O-〕n、
r:(-Ph-SO2-Ph-S-)n、
s:(-Ph-SO2-Ph-O-Ph─CO-Ph-O-)n、
t:(-Ph-SO2-Ph-O-Ph-O-)n、
u:〔-Ph-SO2-Ph-O-Ph-C(CH3)(CH3)-Ph-O-〕n、
v:(-Ph-Ph-SO2-Ph-Ph-SO2-Ph-O-)n、
w:〔-(CH3)(CH3)-Ph-SO2-Ph(CH3)(CH3)-O-Ph-CO-Ph-O-〕n。
本実施形態に係る正極は、マンガン酸リチウムを含む正極活物質と、PVDFとPESを含む正極バインダーと、必要により導電助剤等とを、NMPなどの溶剤中に分散混練して得られた正極スラリーを調製し、この正極スラリーを正極集電体に塗工、乾燥することで製造することができる。正極スラリー中に含有されるこれら各化合物の含有量は、特に限定はされないが、例えば、正極スラリー中の固形分の全質量に対し、正極活物質は85~96質量%、バインダーは2~8質量%、導電助剤を2~8質量%の範囲で含むことが好ましい。
本実施形態における二次電池は、本実施形態に係る正極を備えていれば特に限定されない。図1に本実施形態に係る二次電池の一例として、ラミネート型二次電池を示す。図1に示す二次電池は、本実施形態に係る正極活物質と正極バインダーを含む正極活物質層1と正極集電体3とからなる正極と、リチウムを吸蔵放出し得る負極活物質を含む負極活物質層2と負極集電体4とからなる負極との間に、セパレータ5が挟まれている。正極集電体3は正極タブ8と接続され、負極集電体4は負極タブ7と接続されている。外装体にはラミネート外装体6が用いられ、二次電池内部は非水電解液で満たされている。
本実施形態に係る二次電池の負極は特に限定されないが、例えば、銅箔等の負極集電体の少なくとも一方の面に負極活物質層が形成されてなる。負極活物質層は、少なくとも負極活物質と、負極バインダーと、必要に応じて導電助剤とを含む。
本実施形態に係る二次電池の負極に含まれる負極活物質は特に限定されず、黒鉛、非晶質炭素等の炭素材料を用いることができるが、エネルギー密度の観点から、黒鉛を用いることが好ましい。また、負極活物質として、Si、Sn、Al等のLiと合金を形成する材料、Si酸化物、SiとSi以外の他の金属元素とを含むSi複合酸化物、Sn酸化物、SnとSn以外の他の金属元素とを含むSn複合酸化物、Li4Ti5O12、これらの材料にカーボンを被覆した複合材料等を用いることもできる。負極活物質は、1種を単独で用いることができ、2種以上を組み合わせて用いることもできる。負極活物質の平均粒径(D50)は5~50μmが好ましく、10~30μmがより好ましい。比表面積は、0.5~5m2/gが好ましく、0.5~2m2/gがより好ましい。
非水電解液としては特に限定されないが、例えばリチウム塩を非水溶媒に溶解した溶液を用いることができる。
正極タブ、負極タブとしては、特に限定されないが、例えばAl、Cu、燐青銅、Ni、Ti、Fe、真鍮、ステンレスからなる群から選択される少なくとも一種を材料として用いることができる。
セパレータとしては、特に限定されないが、ポリプロピレン、ポリエチレン等のポリオレフィンや、フッ素系樹脂等からなる多孔性フィルムを用いることができる。また、セルロースやガラスセパレータなどの無機系セパレータを用いることもできる。
外装体としては、特に限定されないが、コイン型、角型、円筒型等の缶や、ラミネート外装体を用いることができる。この中でも、軽量化が可能であり、二次電池のエネルギー密度の向上を図る観点から、合成樹脂と金属箔との積層体からなる可撓性フィルムであるラミネート外装体が好ましい。ラミネート外装体を備えるラミネート型の二次電池は、放熱性にも優れているため、電気自動車などの車載用電池として好適である。
本実施形態に係る二次電池の製造方法は特に限定されないが、例えば、以下に示す方法が挙げられる。本実施形態に係る二次電池用正極および前記負極にそれぞれ正極集電体及び負極集電体を介して正極タブ、負極タブを接続する。前記正極と前記負極とを前記セパレータを挟んで対向配置させ、積層させた電極積層体を作製する。該電極積層体を外装体内に収容し、電解液に浸す。正極タブ、負極タブの一部を外部に突出するようにして外装体を封止することで、二次電池を作製する。
(負極の作製)
負極活物質として黒鉛粉末(平均粒径(D50):22μm、比表面積:1.0m2/g)、バインダーとしてスチレンブタジエンゴム(SBR)ラテックス(平均粒径100nm、固形分50質量%)、増粘剤としてカルボキシメチルセルロースナトリウム塩(CMC)を用意した。2質量%のCMC水溶液を作製し、黒鉛粉末とCMCの固形分の質量比が98.0:1.0となるように混ぜ合わせ、適宜、水を加えてスラリーの粘度調整をしながら十分に分散混練した。次に、黒鉛粉末とSBRとCMCの固形分の質量比が98.0:1.0:1.0となるようにSBRを加えて、よく混ぜ合わせ負極スラリーを調製した。該負極スラリーを負極集電体である厚み15μmの銅箔上に塗布した。その後、50℃にて10分間乾燥後再度120℃で10分乾燥させることにより、負極活物質層を形成した。該負極活物質層をプレスすることにより、負極を作製した。なお、乾燥後の単位面積当たりの負極活物質層の質量は0.008g/cm2とした。
正極活物質としてLiMn2O4粉末(平均粒径(D50):15μm、比表面積:0.5m2/g)と、バインダーとしてPVDFと、末端水酸基を100重合繰り返し単位当り0.6~1.4含むPESとしてスミカエクセル5003PS(商品名、住友化学(株)製)と、導電助剤としてカーボンブラックとを用意した。PVDFをNMPに8質量%溶解させたPVDF溶液と、該PESをNMPに20質量%溶解させたPES溶液を作製した。該正極活物質と、PVDF溶液と、PES溶液と、導電助剤とを、固形分の質量比が93:3.6:0.4:3となるように分散混練して、適宜NMPを加えて粘度を調整しながら正極スラリーを作製した。このときのバインダー中のPESの割合(PES/(PVDF+PES)×100(質量%))は10質量%である。該正極スラリーを正極集電体である厚み20μmのアルミニウム箔上に塗布した。その後、125℃にて10分間乾燥させてNMPを蒸発させることにより正極活物質層を形成した。該正極活物質層をプレスすることにより正極を作製した。なお、乾燥後の単位面積当たりの正極活物質層の質量は0.024g/cm2とした。
EC:DEC=30:70(体積%)の比率で混合した非水溶媒に、電解質としてLiPF6を1mol/Lとなるように溶解させた非水電解液を用意した。この非水電解液に、添加剤としてビニレンカーボネートを1.5質量%添加した。
作製した正極および負極を各々5cm×6cmに切り出した。このうち、一辺5cm×1cmはタブを接続するために電極活物質層を形成していない部分(未塗布部)とし、電極活物質層が形成された部分は5cm×5cmとした。幅5mm×長さ3cm×厚み0.1mmのアルミニウム製の正極タブを、正極の未塗布部に長さ1cmで超音波溶接した。また、正極タブと同サイズのニッケル製の負極タブを、負極の未塗布部に超音波溶接した。6cm×6cmのポリエチレンおよびポリプロピレンからなるセパレータの両面に前記負極と前記正極とを電極活物質層同士がセパレータを隔てて重なるように配置して、電極積層体を得た。2枚の7cm×10cmのアルミニウムラミネートフィルムの長辺の一方を除いて三辺を熱融着により幅5mmで接着して、袋状のラミネート外装体を作製した。該袋状のラミネート外装体に、ラミネート外装体の一方の短辺より1cmの距離となるように前記電極積層体を挿入した。さらに前記非水電解液を0.2g注液して真空含浸させた後、減圧下にて開口部を熱融着により幅5mmで封止した。これにより、ラミネート型の二次電池を作製した。
作製した二次電池に対して、初回充放電を行った。まず、20℃にて5時間率(0.2C)相当の10mAの定電流で4.2Vまで充電した後、合計で8時間4.2V定電圧充電を行った。その後、10mAで3.0Vまで定電流放電した。初回充電容量に対する初回放電容量の比率((初回放電容量/初回充電容量)×100%)を充放電効率(%)として算出した。
初回充放電後の二次電池に対して1C(50mA)で4.2Vまで充電した後、合計で2.5時間4.2V定電圧充電を行った。次に、1Cで3.0Vまで定電流放電した後、5分間放置して、0.2C(10mA)で3.0Vまで再度放電した。1C放電時の容量をD1(mAh)、0.2C放電時の容量をD2(mAh)としたときに、D1/(D1+D2)×100(%)をレート特性の指標として算出した。
レート特性評価後の二次電池を、1C(50mA)で4.2Vまで充電した後、合計で2.5時間4.2V定電圧充電を行った。その後、1Cで3.0Vまで定電流放電を行った。この充放電サイクルを55℃で300回繰り返した。サイクル1回目の放電容量(C1)に対する300サイクル後の放電容量(C300)の比率(C300/C1×100%)を容量維持率(%)として算出した。
正極スラリーの調製において、PVDFとPESの質量比をPVDF:PES=8:2(PES濃度20質量%)とした以外は実施例1と同様の方法で二次電池を作製し、評価した。
正極スラリーの調製において、PVDFとPESの質量比をPVDF:PES=2:1(PES濃度33質量%)とした以外は実施例1と同様の方法で二次電池を作製し、評価した。
正極スラリーの調製において、PVDFとPESの質量比をPVDF:PES=1:1(PES濃度50質量%)とした以外は実施例1と同様の方法で二次電池を作製し、評価した。
正極スラリーの調製において、PVDFとPESの質量比をPVDF:PES=2:3(PES濃度60質量%)とした以外は実施例1と同様の方法で二次電池を作製し、評価した。
正極スラリーの調製において、PVDFのみを用いた(PES濃度0質量%)以外は実施例1と同様の方法で二次電池を作製し、評価した。
正極スラリーの調製において、PESのみを用いた(PES濃度100質量%)以外は実施例1と同様の方法で二次電池を作製し、評価した。
正極スラリーの調製において、PESのみを用いた(PES濃度100質量%)以外は実施例1と同様の方法で二次電池を作製し、評価した。
末端に水酸基を含まないPESとしてスミカエクセル4100P(商品名、住友化学(株)製)を用いた以外は実施例4と同様の方法で二次電池を作製し、評価した。表1に結果を示す。比較例1~2に比べて高い容量維持率が得られた。ただし、末端に水酸基を有するPESを用いた実施例4の方がより高い容量維持率を示していることから、末端に水酸基を有するPESの方がより好ましいことがわかった。実施例1~5で用いた末端水酸基を有するPESは100重合繰り返し単位当り0.6~1.4の水酸基を含むものである。したがって、水酸基含有量は少なくとも100重合繰り返し単位当り0.6以上あれば、その効果が得られるものと考えられる。
比較例1と同じ黒鉛粉末とPVDFとを用意した。PVDFをNMPに8質量%溶解させたPVDF溶液を作製した。黒鉛粉末とPVDF溶液とを固形分の質量比が95.0:5.0となるように分散混練させて、適宜NMPを加えて粘度を調整しながら負極スラリーを作製した。該負極スラリーを負極集電体である厚み15μmの銅箔上に塗布した。その後、125℃にて10分間乾燥させてNMPを蒸発させることにより、負極活物質層を形成した。該負極活物質層をプレスすることにより、負極を作製した。なお、乾燥後の単位面積当たりの負極活物質層の質量は0.0083g/cm2とした。それ以外は比較例1と同様の方法で二次電池を作製し、評価した。
比較例3と同じ黒鉛粉末とPVDF溶液と、PESとしてスミカエクセル5003PS(商品名、住友化学(株)製)をNMPに20質量%溶解させたPES溶液とを用意した。黒鉛粉末とPVDF溶液とPES溶液とを固形分の質量比を95:2.5:2.5となるように配合して負極スラリーを作製した以外は比較例3と同様の方法で二次電池を作製し、評価した。
正極活物質として層状構造を有するLiCoO2(平均粒径(D50):11μm、比表面積:0.5m2/g)を用いた以外は比較例1と同様の方法で二次電池を作製し、評価した。ただし、単位面積当たりの正極活物質層の質量は0.018g/cm2とした。
正極活物質として層状構造を有するLiCoO2(平均粒径(D50):11μm、比表面積:0.5m2/g)を用いた以外は実施例4と同様の方法で二次電池を作製し、評価した。ただし、単位面積当たりの正極活物質層の質量は0.018g/cm2とした。
比較例3と同様な方法で作製した負極(PVDF)と、実施例4と同様な方法で作製した正極とを用いて二次電池を作製し、評価した。表2に結果を示す。この場合も、正極バインダーにPVDFのみを用いた比較例3よりもPVDFとPESを用いた実施例7の方が高い容量維持率が得られた。負極バインダーがPVDFである比較例3と実施例7では容量維持率の差が6ptであるのに対して、負極バインダーがSBRである比較例1と実施例4では容量維持率の差は9.3ptであり、負極バインダーにSBRを用いた方がPESの効果が大きいことがわかった。この理由は明らかではないが、負極活物質がSBR及びCMCに被覆された場合と、PVDFが被覆された場合とでは溶出したMnの析出状態が変わり、負極劣化に影響を及ぼしていることが考えられる。この結果から、負極活物質として黒鉛を含む場合は、負極バインダーとしてSBRおよび増粘剤としてCMC又はその誘導体を含むことがより好ましい。
Claims (9)
- 正極活物質と正極バインダーを含むリチウムイオン二次電池用正極であって、
前記正極活物質が、スピネル構造を有するマンガン酸リチウムを含み、
前記正極バインダーが、少なくともポリフッ化ビニリデン(PVDF)とスルホン結合を有する樹脂とを含む、リチウムイオン二次電池用正極。 - 前記正極バインダー中、前記スルホン結合を有する樹脂の割合が10質量%以上60質量%以下である、請求項1に記載のリチウムイオン二次電池用正極。
- 前記スルホン結合を有する樹脂は、ポリエーテルスルホン(PES)であることを特徴とする請求項1または2に記載のリチウムイオン二次電池用正極。
- 前記PESは、その末端に水酸基を有することを特徴とする請求項3に記載のリチウムイオン二次電池用正極。
- 前記PESは100重合繰り返し単位当り0.6以上の末端水酸基を含むことを特徴とする請求項4に記載のリチウムイオン二次電池用正極。
- スピネル構造を有するマンガン酸リチウムを含む正極活物質と、導電剤と、PVDFおよびPESを含むバインダーとを含む正極スラリーを集電体上に塗工・乾燥する工程を含む、リチウムイオン二次電池用正極の製造方法。
- 請求項1~5のいずれか1項に記載のリチウムイオン二次電池用正極を備えたリチウムイオン二次電池。
- さらに、黒鉛を含む負極活物質と、スチレンブタジエンゴム(SBR)を含む負極バインダーと、カルボキシメチルセルロース(CMC)又はその誘導体を含む増粘剤とを含む負極を備えた請求項7に記載のリチウムイオン二次電池。
- 請求項1~5のいずれか1項に記載のリチウムイオン二次電池用正極と、負極とを対向配置して電極素子を作製する工程と、
前記電極素子と電解液と、を外装体の中に封入する工程と、
を含むことを特徴とする、リチウムイオン二次電池の製造方法。
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CN112864396A (zh) * | 2021-03-10 | 2021-05-28 | 昆山宝创新能源科技有限公司 | 一种正极片以及包括该正极片的锂离子电池和电子装置 |
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