WO2017195330A1 - 非水電解質二次電池用正極及び非水電解質二次電池 - Google Patents
非水電解質二次電池用正極及び非水電解質二次電池 Download PDFInfo
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- H01M10/0561—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of inorganic materials only
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- H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
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- 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
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- 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
- H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
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- 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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- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
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- H01M2004/021—Physical characteristics, e.g. porosity, surface area
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- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/028—Positive electrodes
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- H01M2300/00—Electrolytes
- H01M2300/0017—Non-aqueous electrolytes
- H01M2300/002—Inorganic electrolyte
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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 positive electrode for a nonaqueous electrolyte secondary battery and a nonaqueous electrolyte secondary battery.
- non-aqueous electrolyte lithium ion secondary batteries have come into practical use as compact, lightweight, high capacity, and chargeable / dischargeable batteries.
- a lithium ion secondary battery uses a nonaqueous electrolytic solution in which a lithium salt is dissolved in a nonaqueous solvent as the electrolytic solution. Since these non-aqueous electrolytes are flammable materials, conventional batteries are provided with safety mechanisms such as safety valves and separators. When an abnormal state such as the battery generating heat due to overcharge or the like, the safety valve is opened to prevent the battery from bursting, and the increased internal pressure of the battery is released.
- a positive electrode active material provided with a carbonaceous film covering the surface of olivine-based inorganic particles is known (see, for example, Patent Document 1).
- the positive electrode active material layer is generally formed by mixing a positive electrode active material, a conductive additive such as acetylene black, and a binder. Therefore, the positive electrode active material layer includes a carbon material as a carbonaceous film or a conductive additive.
- Carbon materials can generally be classified into those having a certain crystal structure such as graphite and fullerene, and amorphous carbon (microcrystalline carbon).
- Amorphous carbon can be generally classified into graphitizable carbon (soft carbon) and non-graphitizable carbon (hard carbon).
- Graphitizable carbon is a carbon material that tends to become graphite by high-temperature treatment.
- Graphitizable carbon is generally amorphous carbon in which a plurality of basic structural units (BSU) are assembled, and has an oriented structure in which a plurality of basic structural units are oriented.
- the basic structural unit is a structural unit in which a plurality of carbon hexagonal mesh surfaces are laminated, and has a graphite-like structure microscopically.
- carbon materials obtained by heat-treating pitches, graphitizable cokes, and the like are classified as graphitizable carbon (for example, see Patent Document 2).
- Non-graphitizable carbon is a carbon material whose graphitization progresses slowly during high temperature treatment.
- non-graphitizable carbon is generally amorphous carbon in which a plurality of basic structural units are assembled, and has a non-oriented structure in which the plurality of basic structural units are not oriented.
- carbon materials obtained by heat-treating thermosetting resins, carbon black, non-graphitizable coke, carbon materials obtained by heat-treating plant-based materials, and the like are classified as non-graphitizable carbon (for example, see Patent Document 2). ).
- JP2015-65134A Japanese Patent Laid-Open No. 2015-070032
- the built-in electrolyte solution boils and the battery safety valve opens due to the influence of heat generated during overcharging. If the safety valve is opened, the electrolyte in the battery will blow out, which may adversely affect surrounding equipment.
- the method of blocking the conductive ion passage of the separator with heat limits the type of separator material, and if the heat generation proceeds excessively, the entire separator contracts. As a result, the function of preventing the short circuit between the positive and negative electrodes may be impaired, and the function of stopping the abnormal state may not work.
- This invention is made
- the present invention includes a positive electrode active material layer including a plurality of positive electrode active material particles, the positive electrode active material layer includes a carbonaceous film provided on a surface of the positive electrode active material particles, and a plurality of positive electrode active materials
- a nonaqueous electrolyte characterized in that it contains 0 wt% or more and 20 wt% or less of a conductive assistant disposed between particles, and at least one of the carbonaceous film and the conductive assistant is graphitizable carbon.
- a positive electrode for a secondary battery is provided.
- the positive electrode for a non-aqueous electrolyte secondary battery of the present invention includes a positive electrode active material layer including a plurality of positive electrode active material particles, an electrode reaction (for example, conversion of ions to the positive electrode active material) occurs in the positive electrode active material particles along with charge and discharge. Intercalation and deintercalation of ions from the positive electrode active material) can proceed, and the non-aqueous electrolyte secondary battery can be charged and discharged.
- the positive electrode active material layer includes a carbonaceous film provided on the surface of the positive electrode active material particles, and includes a conductive auxiliary agent disposed between the particles of the plurality of positive electrode active material particles in an amount of 0 wt% to 20 wt%.
- the carbonaceous film or the conductive assistant can be used as an electron conduction path, and electrons can be exchanged promptly with the electrode reaction. For this reason, battery characteristics can be improved.
- a material having a relatively low conductivity can be used for the positive electrode active material particles.
- At least one of the carbonaceous film and the conductive additive is graphitizable carbon (soft carbon).
- graphitizable carbon soft carbon
- the carbonaceous film and the conductive auxiliary agent which are electron conduction paths, can be increased in resistance, and the charging current flowing in the battery in the overcharged state can be reduced. It can be reduced quickly.
- heat generation due to the electrochemical reaction of the electrolytic solution and heat generation due to current flowing through the carbonaceous film or the conductive additive can be suppressed, and the battery can be prevented from reaching a high temperature. Boiling can be suppressed. As a result, an increase in the internal pressure of the battery due to overcharging can be suppressed, and the battery can be prevented from bursting.
- the positive electrode of the present invention when used, a battery in which the positive electrode active material layer has a safety improvement mechanism can be manufactured.
- a battery can be manufactured using a separator that does not have a shutdown mechanism, the heat resistance of the battery can be improved.
- the protection circuit can be simplified. Furthermore, the safety of a large battery can be improved.
- (A) is a schematic plan view of a positive electrode for a nonaqueous electrolyte secondary battery according to an embodiment of the present invention
- (b) and (c) are schematic cross-sectional views of the positive electrode taken along broken line AA in (a).
- It is an expanded sectional view of the positive electrode active material layer contained in the positive electrode for nonaqueous electrolyte secondary batteries of one Embodiment of this invention.
- It is an expanded sectional view of the positive electrode active material layer contained in the positive electrode for nonaqueous electrolyte secondary batteries of one Embodiment of this invention.
- (A) is a schematic plan view of the negative electrode contained in the nonaqueous electrolyte secondary battery of one embodiment of the present invention
- (b) is a schematic cross-sectional view of the negative electrode taken along broken line BB in (a). It is a schematic structure figure of the electric power generation element contained in the nonaqueous electrolyte secondary battery of one embodiment of the present invention.
- (A) is explanatory drawing of the microstructure of graphitizable carbon
- (b) is explanatory drawing of the microstructure of non-graphitizable carbon.
- (A)-(c) is a graph which shows the result of an overcharge test (1).
- (A)-(c) is a graph which shows the result of an overcharge test (1).
- (A) and (b) are TEM photographs of the positive electrode active material (1).
- (A) and (b) are TEM photographs of the positive electrode active material (3). It is a schematic sectional drawing of a beaker cell. It is a graph which shows the result of a voltage application experiment. It is a graph which shows the result of an overcharge test (2).
- the positive electrode for a non-aqueous electrolyte secondary battery of the present invention includes a positive electrode active material layer including a plurality of positive electrode active material particles, and the positive electrode active material layer includes a carbonaceous film provided on a surface of the positive electrode active material particles. And a conductive additive disposed between the particles of the plurality of positive electrode active material particles in an amount of 0 wt% or more and 20 wt% or less, and at least one of the carbonaceous film and the conductive additive is graphitizable carbon. It is characterized by being.
- the carbonaceous film and the conductive additive contained in the positive electrode of the present invention are amorphous carbon in which a plurality of basic structural units having a structure in which a plurality of carbon hexagonal network surfaces are stacked, and an orientation in which a plurality of basic structural units are oriented. It is preferable to have a tissue. As a result, when the nonaqueous electrolyte secondary battery is overcharged, the resistance of the carbonaceous film and the conductive additive can be increased, and heat generation of the positive electrode active material layer can be suppressed.
- the carbonaceous film and the conductive additive contained in the positive electrode of the present invention are preferably those obtained by firing a pitch-based material (pitch-based carbon material). Thereby, when the nonaqueous electrolyte secondary battery is overcharged, the resistance of the carbonaceous film and the conductive additive can be increased.
- Carbonaceous coating and conductive auxiliaries contained in the positive electrode of the present invention preferably has a 1.8 g / cm 3 or more 2.1 g / cm 3 or less of the material density. Thereby, when the nonaqueous electrolyte secondary battery is overcharged, the resistance of the carbonaceous film and the conductive additive can be increased.
- the positive electrode active material particles contained in the positive electrode active material layer of the positive electrode of the present invention are preferably olivine type compound particles or NASICON type compound particles.
- the positive electrode of the present invention preferably further includes a positive electrode current collector sheet, and the positive electrode active material layer is preferably provided on the positive electrode current collector sheet. As a result, the conductive distance between the positive electrode current collector sheet and the positive electrode active material can be shortened, and the exchange of electrons associated with the electrode reaction can be performed promptly.
- the positive electrode active material layer included in the positive electrode of the present invention preferably does not substantially contain non-graphitizable carbon (hard carbon) and graphite.
- the positive electrode active material layer can be increased in resistance, and heat generation of the overcharged battery can be suppressed.
- the present invention includes a positive electrode of the present invention, a negative electrode having a negative electrode active material, a separator sandwiched between the positive electrode and the negative electrode, a nonaqueous electrolyte, the positive electrode, the negative electrode, the separator, and the nonaqueous electrolyte.
- a non-aqueous electrolyte secondary battery including a battery case that houses the battery is also provided. According to the nonaqueous electrolyte secondary battery of the present invention, it is possible to increase the resistance of the positive electrode active material layer when the nonaqueous electrolyte secondary battery is overcharged, and to suppress the battery from becoming high temperature. be able to.
- the negative electrode active material is preferably a carbon material
- the non-aqueous electrolyte is preferably an electrolytic solution in which a lithium salt is dissolved in a non-aqueous solvent
- the carbonaceous film and the conductive auxiliary agent are In the overcharged state, graphitizable carbon that is electrochemically decomposed or reacted to increase resistance is preferable.
- FIG. 1A is a schematic plan view of a positive electrode for a nonaqueous electrolyte secondary battery according to the present embodiment
- FIGS. 1B and 1C are schematic cross-sectional views of the positive electrode taken along a broken line AA in FIG.
- FIG. 2 and 3 are enlarged sectional views of the positive electrode active material layer included in the positive electrode of the present embodiment.
- FIG. 4 is a schematic cross-sectional view of the nonaqueous electrolyte secondary battery of the present embodiment.
- FIG. 5A is a schematic plan view of a negative electrode included in the nonaqueous electrolyte secondary battery of the present embodiment
- FIG. 5B is a schematic cross-sectional view of the negative electrode taken along a broken line BB in FIG. is there.
- FIG. 6 is a schematic structural diagram of a power generation element included in the nonaqueous electrolyte secondary battery of the present embodiment.
- the positive electrode 5 for a non-aqueous electrolyte secondary battery includes a positive electrode active material layer 1 including a plurality of positive electrode active material particles 6, and the positive electrode active material layer 1 is provided on the surface of the positive electrode active material particles 6.
- the conductive auxiliary agent 7 including the carbonaceous film 8 and disposed between the plurality of positive electrode active material particles 6 is included in an amount of 0 wt% or more and 20 wt% or less, and at least one of the carbonaceous film 8 and the conductive auxiliary agent 7 is It is characterized by being easily graphitizable carbon.
- the nonaqueous electrolyte secondary battery 30 of the present embodiment includes a positive electrode 5 of the present embodiment, a negative electrode 32 having a negative electrode active material, a separator 34 sandwiched between the positive electrode 5 and the negative electrode 32, a nonaqueous electrolyte 15, A battery case 11 that accommodates the positive electrode 5, the negative electrode 32, the separator 34, and the nonaqueous electrolyte 15 is provided.
- the positive electrode 5 for a nonaqueous electrolyte secondary battery and the nonaqueous electrolyte secondary battery 30 of this embodiment will be described.
- the positive electrode 5 for a nonaqueous electrolyte secondary battery is a positive electrode constituting the nonaqueous electrolyte secondary battery 30 or a positive electrode used for manufacturing the nonaqueous electrolyte secondary battery 30.
- a positive electrode 5 for a nonaqueous electrolyte secondary battery includes a positive electrode active material layer 1 including a plurality of positive electrode active material particles 6.
- the positive electrode 5 can include the positive electrode current collector sheet 3, and the positive electrode active material layer 1 can be provided on the positive electrode current collector sheet 3.
- the positive electrode 5 can have a structure as shown in FIGS. 1A and 1B, for example.
- the positive electrode current collector sheet 3 can be a metal foil such as an aluminum foil, for example.
- the positive electrode 5 may include a base layer 2 between the positive electrode current collector sheet 3 and the positive electrode active material layer 1.
- the underlayer 2 can be provided, for example, as shown in FIG.
- the positive electrode active material layer 1 may be a porous layer containing positive electrode active material particles 6 and a binder.
- the positive electrode active material layer 1 includes at least one of a carbonaceous film 8 provided on the surface of the positive electrode active material particles 6 and a conductive additive 7 disposed between the plurality of positive electrode active material particles 6.
- the carbonaceous film 8 and the conductive support agent 7 are graphitizable carbon (soft carbon).
- the positive electrode active material layer 1 can have both a carbonaceous film 8 provided on the surface of the positive electrode active material particles 6 and a conductive additive 7 disposed between the plurality of positive electrode active material particles 6. . In this case, both the carbonaceous film 8 and the conductive additive 7 are graphitizable carbon.
- the positive electrode active material layer 1 can have a fine structure as shown in FIG.
- Such a positive electrode active material layer 1 is prepared, for example, by mixing a positive electrode active material powder on which a carbonaceous film 8 is formed, a conductive additive 7, and a binder to prepare a paste. It can form by apply
- the solvent used for preparing the paste include dimethylformamide, N-methylpyrrolidone, isopropanol, toluene and the like.
- the positive electrode active material layer 1 can include a conductive auxiliary of 0 wt% or more and 20 wt% or less. The conductive aid can be expected to improve the output, but if it is too much, the capacity per volume of the electrode is reduced.
- the carbonaceous coating 8 can be formed by forming a coating layer of an organic compound on the surface of the positive electrode active material particles 6 and heat-treating and carbonizing the coating layer in a non-oxidizing atmosphere.
- the organic compound may be petroleum pitch or coal pitch.
- the carbonaceous film 8 can be made into a pitch-based carbon material which is graphitizable carbon.
- the said heat processing can be performed at 500 degreeC or more and 1000 degrees C or less, for example.
- the conductive auxiliary agent 7 for example, coke-based soft carbon which is graphitizable carbon can be used.
- the positive electrode active material layer 1 has a carbonaceous film 8 provided on the surface of the positive electrode active material particles 6, and may not substantially contain the conductive additive 7.
- the carbonaceous film 8 is graphitizable carbon.
- the positive electrode active material layer 1 can have a fine structure as shown in FIG.
- Such a positive electrode active material layer 1 is prepared by, for example, preparing a paste by mixing a positive electrode active material powder on which a carbonaceous film 8 is formed and a binder, and applying this paste onto the positive electrode current collector sheet 3. Can be formed.
- the positive electrode active material layer 1 since the positive electrode active material layer 1 has the above-described configuration, the positive electrode active material layer 1 can have high resistance when the nonaqueous electrolyte secondary battery 30 is overcharged.
- the charging current flowing through the battery 30 in the charged state can be quickly reduced.
- heat generation due to the electrochemical reaction of the electrolytic solution 15 and heat generation due to current flowing through the carbonaceous film 8 or the conductive additive 7 can be suppressed, and the battery 30 can be prevented from reaching a high temperature. It is possible to suppress boiling of the electrolytic solution 15. As a result, an increase in the internal pressure of the battery 30 due to overcharging can be suppressed, and the battery 30 can be prevented from bursting.
- graphitizable carbon is a carbon material that tends to become graphite by high-temperature treatment.
- graphitizable carbon is amorphous carbon in which a plurality of basic structural units 10 (BSU) are aggregated as in the microstructure shown in FIG. 7A, for example. It has an oriented texture.
- the basic structural unit 10 is a structural unit in which a plurality of carbon hexagonal mesh surfaces 4 are laminated, and has a graphite-like structure microscopically.
- the basic structural unit 10 may be a crystallite.
- the carbonaceous film 8 and the conductive additive 7 contained in the positive electrode active material layer 1 are graphitizable carbon is confirmed by observation with a transmission electron microscope, X-ray diffraction measurement, or Raman spectrum measurement. can do.
- 90% or more of the total amount of the carbonaceous film 8 and the conductive additive 7 contained in the positive electrode active material layer 1 may be graphitizable carbon. This is confirmed by confirming that 90% or more of the total amount of the carbonaceous film 8 and the conductive additive 7 included in the transmission electron micrograph of the positive electrode active material layer 1 is graphitizable carbon. be able to. It can also be confirmed by X-ray diffraction measurement.
- carbon materials obtained by heat treatment of pitches such as petroleum pitch and coal pitch, graphitizable cokes, and the like are classified as graphitizable carbon. Therefore, it can be confirmed whether or not it is graphitizable carbon also by examining the raw materials and heat treatment temperature of the carbonaceous film 8 and the conductive additive 7 contained in the positive electrode active material layer 1.
- the carbonaceous film 8 and the conductive additive 7 may be graphitizable carbon having a material density of 1.8 g / cm 3 or more and 2.1 g / cm 3 or less.
- graphitizable carbon has a material density larger than that of non-graphitizable carbon, and therefore, by examining this, whether or not it is graphitizable carbon can be confirmed.
- the underlayer 2 When the underlayer 2 is provided between the positive electrode current collector sheet 3 and the positive electrode active material layer 1, the underlayer 2 can be a carbon layer containing graphitizable carbon. Accordingly, the carbon layer can have high conductivity, and an electrode reaction at the positive electrode active material particles 6 (for example, intercalation of ions into the positive electrode active material, deintercalation of ions from the positive electrode active material) ) Can be exchanged promptly. Further, when the nonaqueous electrolyte secondary battery 30 is overcharged, the resistance of the underlayer 2 can be increased, and a large current flows between the positive electrode current collector sheet 3 and the positive electrode active material layer 1. This can be suppressed.
- the underlayer 2 may be a porous layer containing particles of graphitizable carbon and a binder.
- the underlayer 2 can be formed by preparing a paste by mixing graphitizable carbon powder and a binder, and applying the paste onto the positive electrode current collector sheet 3. Further, the positive electrode active material layer 1 can be formed on the base layer 2.
- non-graphitizable carbon is a carbon material whose graphitization proceeds slowly during high-temperature treatment.
- non-graphitizable carbon is amorphous carbon having a microstructure as shown in FIG. 7B, for example, in which a plurality of basic structural units 10 are assembled, and the plurality of basic structural units 10 are oriented. It has a non-oriented structure.
- carbon materials obtained by heat-treating thermosetting resins, carbon black, non-graphitizable coke, carbon materials obtained by heat-treating plant-based materials, and the like are classified as non-graphitizable carbon.
- the positive electrode active material particles 6 may be particles of a substance having an olivine type crystal structure (olivine type compound).
- olivine type compound for example, LiFePO 4, Li x M y PO 4 ( proviso that 0.05 ⁇ x ⁇ 1.2,0 ⁇ y ⁇ 1, M is Fe, Mn, Cr, Co, Cu, And at least one of Ni, V, Mo, Ti, Zn, Al, Ga, Mg, B, and Nb).
- the positive electrode active material particles 6 may be NASICON type compound particles that can be represented by Y x M 2 (PO 4 ) 3 .
- NASICON type compounds have rhombohedral crystals, for example, Li 3 + x Fe 2 (PO 4 ) 3 , Li 2 + x FeTi (PO 4 ) 3 , Li x TiNb (PO 4 ) 3 and Li 1 + x. FeNb (PO 4 ) 3 and the like can be mentioned.
- the positive electrode active material particles 6 may be particles of a lithium transition metal composite oxide (layered system, spinel, etc.) capable of reversibly occluding and releasing lithium ions.
- the positive electrode active material layer 1 may contain the above-mentioned positive electrode active material particle 6 individually by 1 type, and may contain multiple types.
- the positive electrode active material particles 6 are, for example, Na b M 2 c Si 12 O 30 such as Na 6 Fe 2 Si 12 O 30 and Na 2 Fe 5 Si 12 O 30 as sodium transition metal composite oxide particles.
- Oxide particles represented (M 2 is one or more transition metal elements, 2 ⁇ b ⁇ 6, 2 ⁇ c ⁇ 5); Na 2 Fe 2 Si 6 O 18 and Na 2 MnFeSi 6 O 18 and other Na d M 3 e Si 6 O particles of oxide represented by 18 (M 3 is one or more transition metal elements, 3 ⁇ d ⁇ 6,1 ⁇ e ⁇ 2); Na 2 FeSiO of 6 such as Na f M Oxide particles represented by 4 g Si 2 O 6 (M 4 is one or more elements selected from the group consisting of transition metal elements, Mg and Al, 1 ⁇ f ⁇ 2, 1 ⁇ g ⁇ 2); NaFePO 4, Na 3 Fe 2 ( PO 4) phosphate particles such as 3; NaFeBO 4, Na 3 Fe 2 (BO 4) 3 or the
- the positive electrode active material layer 1 may contain the above-mentioned positive electrode active material particle 6 individually by 1 type, and may contain multiple types.
- binder contained in the positive electrode active material layer 1 examples include polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), styrene-butadiene copolymer (SBR), acrylonitrile rubber, and acrylonitrile rubber-PTFE mixture. Can be mentioned.
- Nonaqueous electrolyte secondary battery 30 includes the positive electrode 5, the negative electrode 32, the separator 34 sandwiched between the positive electrode 5 and the negative electrode 32, the nonaqueous electrolyte 15, the positive electrode 5, and the negative electrode 32. And a battery case 11 that houses the separator 34 and the non-aqueous electrolyte 15.
- the nonaqueous electrolyte secondary battery 30 is, for example, a lithium ion secondary battery or a sodium ion secondary battery.
- the nonaqueous electrolyte secondary battery 30 includes a positive electrode 5 for a nonaqueous electrolyte secondary battery. Since description about the positive electrode 5 for nonaqueous electrolyte secondary batteries was mentioned above, it abbreviate
- the positive electrode 5 can constitute the power generation element 22 as shown in FIG. 6 together with the negative electrode 32 and the separator 34.
- the negative electrode 32 has a porous negative electrode active material layer 36 containing a negative electrode active material.
- the negative electrode 32 can have a negative electrode current collector sheet 38.
- the negative electrode active material layer 36 can include a negative electrode active material, a conductive agent, a binder, and the like. Examples of the negative electrode active material include graphite (graphite), partially graphitized carbon, hard carbon, soft carbon, LiTiO 4 , Sn, and Si.
- the negative electrode active material layer 36 may contain the above-mentioned negative electrode active material individually by 1 type, and may contain multiple types.
- the negative electrode active material layer 36 can be provided on the negative electrode current collector sheet 38.
- the negative electrode active material layer 36 can be provided on both main surfaces of the negative electrode current collector sheet 38, for example, as in the negative electrode 32 shown in FIGS.
- the separator 34 has a sheet shape and is disposed between the positive electrode 5 and the negative electrode 32. Further, the separator 34 can constitute the power generation element 22 as shown in FIG. 6 together with the positive electrode 5 and the negative electrode 32. By providing the separator 34, it is possible to prevent a short-circuit current from flowing between the positive electrode 5 and the negative electrode 32.
- the separator 34 is not particularly limited as long as it can prevent a short-circuit current from flowing and can transmit ions conducted between the positive electrode and the negative electrode.
- a polyolefin microporous film, a cellulose sheet, or an aramid sheet may be used. Can do.
- the battery case 11 is a container that accommodates the positive electrode 5, the negative electrode 32, the separator 34, and the nonaqueous electrolyte 15. Further, the battery case 11 may have an opening closed by the lid member 12. As a result, the power generation element 22 can be accommodated in the battery case 11.
- the nonaqueous electrolyte 15 is accommodated in the battery case 11 and becomes an ion conductive medium between the positive electrode and the negative electrode.
- the nonaqueous electrolyte 15 includes a nonaqueous solvent and an electrolyte salt dissolved in the nonaqueous solvent.
- the non-aqueous solvent contained in the non-aqueous electrolyte 15 carbonate compounds (cyclic carbonate compounds, chain carbonate compounds, etc.), lactones, ethers, esters, etc. can be used, and two or more of these solvents can be mixed. It can also be used. Among these, it is particularly preferable to use a mixture of a cyclic carbonate compound and a chain carbonate compound.
- Examples of the electrolyte salt contained in the nonaqueous electrolyte 15 include LiCF 3 SO 3 , LiAsF 6 , LiClO 4 , LiBF 4 , LiPF 6 , LiBOB, LiN (CF 3 SO 2 ) 2 , LiN (C 2 F 5 SO 2 ) And the like. Moreover, you may mix
- Positive electrode active material powder preparation experiment A carbonaceous film (conductive film) was formed on the surface of lithium iron phosphate (LiFePO 4 ) powder using different carbon precursors, and positive electrode active material powders (1) to (4) were formed. Prepared. Specifically, it was prepared as follows.
- Carbon precursor adhesion treatment to positive electrode active material 480 g of the positive electrode active material after pretreatment was added to 100 g of the above carbon precursor solution, and the dew point was controlled for kneading treatment at 20 rpm for 1 hour in a planetary mixer. Performed in a dry box. Then, it heated at 40 degreeC in the oven which can remove a solvent, acetone which is a dilution solvent was removed, and the mixture with a carbon content of 4 weight% was prepared.
- Carbonization treatment The above mixture was subjected to a carbonization treatment at 700 ° C. for 2 hours in an electric furnace in a nitrogen atmosphere to prepare a positive electrode active material powder (1).
- Positive Electrode Active Material Powder (2) Modified ethylene tar pitch (carbon precursor) not containing quinoline insolubles was diluted with acetone to prepare a carbon precursor solution containing 20 wt% modified ethylene tar pitch. Using this carbon precursor solution, a positive electrode active material powder (2) was prepared in the same manner as the positive electrode active material powder (1).
- positive electrode active material powder (3) Pyrene (carbon precursor) was diluted with acetone to prepare a carbon precursor solution containing 20% by weight of pyrene. Using this carbon precursor solution, a positive electrode active material powder (3) was prepared in the same manner as the positive electrode active material powder (1).
- Positive Electrode Active Material Powder (4) Sucrose (carbon precursor) was diluted with acetone to prepare a carbon precursor solution containing 20% by weight of sucrose. Using this carbon precursor solution, a positive electrode active material powder (4) was prepared in the same manner as the positive electrode active material powder (1).
- a positive electrode (1) is produced using the positive electrode active material powder (1)
- a positive electrode (2) is produced using the positive electrode active material powder (2)
- a positive electrode (3) is produced using the positive electrode active material powder (3).
- a positive electrode (4) was prepared using the positive electrode active material powder (4). The configuration other than the positive electrode active material powder was the same. Specifically, it was produced as follows.
- positive electrode active material powder (1), (2), (3) or (4), acetylene black (conducting aid), and polyvinylidene fluoride (PVDF ((CH 2 CF 2 ) n )) (binder) Were mixed so that the positive electrode active material powder was 88 to 95% by weight and the conductive assistant was 3.5 to 4.5% by weight with respect to the total of 100% by weight.
- a positive electrode active material paste was prepared by adding N-methylpyrrolidone to this mixed powder and kneading. The positive electrode active material paste was applied onto an aluminum foil (positive electrode current collector sheet), and the coating film was dried to form a positive electrode active material layer on the positive electrode current collector sheet, thereby producing positive electrodes (1) to (4). .
- a lithium ion secondary battery (1) was produced using the positive electrode (1), a lithium ion secondary battery (2) was produced using the positive electrode (2), and a lithium ion secondary battery (2) was produced using the positive electrode (3).
- a secondary battery (3) was produced, and a lithium ion secondary battery (4) was produced using the positive electrode (4).
- the configuration other than the positive electrode was the same. Specifically, it was produced as follows. A power generation element in which the positive electrode (1), the positive electrode (2), the positive electrode (3) or the positive electrode (4), a polyolefin separator (shutdown temperature around 120 ° C), and a carbonaceous negative electrode are laminated, and a safety valve is attached to the lid member.
- Lithium ion secondary batteries (1) to (4) were prepared by storing in a battery container provided and injecting a non-aqueous electrolyte into the battery container.
- Overcharge test (1) (Reference experiment) The overcharge test of the fabricated lithium ion secondary batteries (1) to (4) was performed. Specifically, the test was conducted as follows. First, after charging for 6 hours with a charging current of 50 A and an upper limit voltage of 3.5 V, the prepared battery was fully charged, and then an overcharge test was performed. In the overcharge test, CCCV (Constant-Current-Constant-Voltage) charge was performed with a charge current of 50 A which is 1 ItA (1 CA) and a test upper limit voltage of 10 V. In the overcharge test, the voltage between the positive external connection terminal and the negative external connection terminal and the current flowing between these external connection terminals were measured. In the overcharge test, the temperature was measured by attaching a thermocouple to the battery container. The test results are shown in Table 1.
- CCCV Constant-Current-Constant-Voltage
- FIG. 8 The result of the overcharge test of the lithium ion secondary battery (1) is shown in FIG. 8, and the result of the overcharge test of the lithium ion secondary battery (3) is shown in FIG.
- the horizontal axes in FIGS. 8 and 9 indicate the test time when the overcharge test is started as 0 minutes.
- FIG.8 (c) and FIG.9 (c) showed the temperature rise amount from the time of starting an overcharge test.
- the voltage between the positive electrode and the negative electrode increased to about 5.5 V and became almost constant.
- the voltage rapidly increased from about 12 minutes, and the voltage between the positive electrode and the negative electrode reached the test upper limit voltage around 13 minutes.
- the temperature rise of the battery (1) is about 30 ° C., and the battery internal temperature is considered not to reach the shutdown temperature of the separator.
- the safety valve never opened.
- the voltage between the positive electrode and the negative electrode gradually increases, and the current flowing between the positive electrode and the negative electrode gradually decreases. Therefore, when the battery is overcharged, the internal resistance of the battery gradually increases. It is thought that.
- the overcharge test of the lithium ion secondary battery (2) the same voltage behavior, current behavior, and temperature behavior as in the overcharge test of the battery (1) were shown.
- the positive electrode (1), (3) was taken out from the lithium ion secondary battery (1), (3) after the overcharge test, and the electrical resistivity of the positive electrode (1), (3) was measured using a four-terminal method. . In addition, the electrical resistivity of the positive electrodes (1) and (3) before battery incorporation was also measured. Further, the separator was taken out from the lithium ion secondary batteries (1) and (3) after the overcharge test, and an air permeability resistance test was performed. Moreover, the air permeability resistance test was done also about the separator before battery installation. The air resistance test was performed using an air resistance tester (Gurley tester). This test measures the time required for permeation of a defined volume of air per unit area. These test results are shown in Table 2.
- the resistivity of the positive electrode (1) after the overcharge test was 500 ⁇ ⁇ m or more, which was significantly higher than that of the positive electrode (1) before incorporating the battery.
- the resistivity of the positive electrode (3) after the overcharge test was about 9 ⁇ ⁇ m, and the increase in the resistivity of the positive electrode (3) was found to be small. From this, it was found that the increase in the internal resistance of the battery (1) in the overcharge test was caused by the increase in the internal resistance of the positive electrode (1). On the other hand, it was found that the increase in the internal resistance of the battery (3) in the overcharge test was not due to the increase in the internal resistance of the positive electrode (3).
- the air resistance of the separator of the battery (1) after the overcharge test was about 1.3 times the air resistance of the unused separator.
- the value of the air resistance was too large to be measured. From this, in the overcharge test for battery (1), it was found that the battery internal temperature did not reach the shutdown temperature of the separator. It was also found that the increase in the internal resistance of the battery (1) in the overcharge test was not caused by the clogging of the separator pores. Also, in the overcharge test for battery (3), it was found that the battery internal temperature reached the shutdown temperature of the separator. For this reason, it is considered that the pores of the separator are blocked, the conduction ion passage path in the battery is blocked, the voltage between the positive electrode and the negative electrode rapidly increases, and the current rapidly decreases.
- the positive electrode (2) and the separator were taken out from the battery (2) after the overcharge test, and the electrical resistivity of the positive electrode (2) was measured and the air permeability resistance test of the separator was performed.
- the separator was not shut down as in the case of the battery (1).
- the electrical resistivity of the positive electrode (2) was increased as in the case of the battery (1). From this, it is considered that the same phenomenon as in the battery (1) occurred in the battery (2).
- the positive electrode (4) and the separator were taken out from the battery (4) after the overcharge test, and the electrical resistivity of the positive electrode (4) was measured and the air permeability resistance test of the separator was performed. As a result of the air permeability resistance test of the battery (4), the separator was shut down as in the case of the battery (3). From this, it is considered that the same phenomenon as in the battery (3) occurred in the battery (4).
- FIG. 10A is a TEM image of the positive electrode active material powder (1)
- FIG. 10B is an enlarged image of a range C surrounded by a broken line in FIG. 10A.
- FIG. 10 shows that the thickness of the carbonaceous film is about 4 nm.
- a carbonaceous film has two or more basic structural units 10 (BSU) of the structure where the some carbon hexagonal mesh surface 4 was folded.
- the carbonaceous film had an oriented structure in which the basic structural units 10 were oriented. From this, it was found that the carbonaceous film is graphitizable carbon (soft carbon).
- the average size of the plurality of carbon hexagonal mesh surfaces 4 was about 4.5 nm.
- the carbonaceous film contained in the positive electrode active material powder (2) was directly observed. Although not shown, the carbonaceous film has an oriented structure in which the basic structural units 10 are oriented, and is easily graphitizable carbon (soft carbon). In addition, the average size of the plurality of carbon hexagonal mesh surfaces 4 was about 3.2 nm.
- FIG.11 (a) is a TEM image of positive electrode active material powder (3)
- FIG.11 (b) is an enlarged image of the range D enclosed with the broken line of Fig.11 (a). From FIG. 11, it was found that the carbonaceous film had a structure in which small carbon hexagonal mesh surfaces 4 were complicated. This indicates that the carbonaceous film is non-graphitizable carbon (hard carbon). Moreover, the average size of the plurality of carbon hexagonal mesh surfaces 4 was about 1.5 nm. The carbonaceous film contained in the positive electrode active material powder (4) was directly observed.
- the carbonaceous film is non-graphitizable carbon (hard carbon) having a structure in which small carbon hexagonal mesh surfaces 4 are intricately interlaced, and the average size of the plurality of carbon hexagonal mesh surfaces 4 is about 1. It was 6 nm.
- the positive electrode (6) which has the carbon layer 42b formed using the non-graphitizable carbon (hard carbon) powder by the same method was produced, and the beaker cell (2) was produced.
- the non-graphitizable carbon powder Carbotron P (manufactured by Kureha Battery Materials Japan) was used.
- the positive electrode (7) which has the carbon layer 42c formed using the graphite powder by the same method was produced, and the beaker cell (3) was produced.
- As the graphite powder KGNJ-9 (manufactured by MT Carbon Co., Ltd.) prepared by firing coke carbon was used.
- the produced carbon layers 42a, 42b, and 42c all had high conductivity.
- the nonaqueous electrolyte 15, carbonate-based solvent and (EC:: DEC 3 7 ), LiPF 6 was used electrolytic solution 1M containing the LiPF 6 as the electrolyte.
- the test upper limit voltage was set to 7 V, the charging voltage was applied between the positive electrode and the negative electrode, and a constant current of 10 mA was passed.
- the test results are shown in FIG.
- the terminal voltage rose to about 5.3V in the test time of about 0 to 10 seconds, and the test time of about 10 to 220 seconds.
- the terminal voltage gradually increased to about 6V. Thereafter, the terminal voltage rose rapidly and reached the test upper limit voltage.
- the terminal voltage rises to about 6.2V in the test time of about 0 to 15 seconds, and then the terminal voltage becomes constant. It was.
- the terminal voltage rapidly increased to about 5.0 V in the test time of about 0 to 2 seconds, and the terminal was reached in the test time of about 2 to 275 seconds.
- the voltage gradually increased to about 6.2V.
- the terminal voltage was constant at about 6.2V.
- the terminal voltage reached the test upper limit voltage.
- Soft carbon increases in resistance while the terminal voltage rises from about 5.3V to about 6V, and when the terminal voltage exceeds about 6V, the increase in resistance of the soft carbon ends, and current flows in the carbon layer 42a. It is considered that the terminal voltage has reached the test upper limit voltage.
- the test time in the test time of about 10 to 220 seconds, it is considered that the soft carbon was oxidized by LiPF 6 in the electrolyte.
- the beaker cell (2) using hard carbon for the carbon layer 42 of the positive electrode the hard carbon did not participate in the electrochemical reaction, and the terminal voltage continued to rise and the terminal voltage became constant at about 6.2V.
- the increase in the internal resistance of the lithium ion secondary battery (1) measured in the overcharge test (1) and the positive electrode (1
- the increase in electrical resistance is considered to be due to the increase in resistance of the carbonaceous film, which is graphitizable carbon (soft carbon).
- the carbonaceous film and the conductive additive 7 are non-graphitizable carbon, so the battery is overcharged and the potential of the positive electrode is high.
- Overcharge test (2) Using the positive electrode active material powder (1) prepared in the positive electrode active material powder preparation experiment, a positive electrode (8) was produced, and a beaker cell (4) was produced. Specifically, it was produced as follows. Positive electrode active material powder (1), soft carbon powder (conducting aid), and binder (PVDF) total 100% by weight, positive electrode active material powder is 91% by weight, soft carbon powder is 4% by weight Then, the binder was mixed so as to be 5% by weight. KANJ-9 (manufactured by MT Carbon Co., Ltd.), a coke-based soft carbon, was used as the soft carbon powder. A positive electrode active material paste was prepared by adding N-methylpyrrolidone to this mixed powder and kneading.
- This positive electrode active material paste was applied onto an aluminum foil (positive electrode current collector sheet) (amount applied: about 10.5 mg), and a positive electrode active material layer 1 was formed on the positive electrode current collector sheet 3 to produce a positive electrode (8). .
- a charge / overcharge test was conducted using a beaker cell (4).
- the test upper limit voltage was set to 7.5 V
- the charge voltage was applied between the positive electrode and the negative electrode, and a constant current of about 0.6 C was passed.
- the results of the charge / overcharge test are shown in FIG.
- the terminal voltage was stable at about 3.8 V in the charging range of about 0 to 4350 seconds. If the battery is overcharged beyond the fully charged state, the terminal voltage rises in about 4350-6520 seconds, the terminal voltage becomes constant in about 6520-7760 seconds, and then the terminal voltage rises to reach the test upper limit voltage. did. Thus, it was confirmed that the internal resistance of the battery was increased even when no separator was provided.
- the positive electrode active material layer 1 of the positive electrode (8) contained in the beaker cell (4) contains soft carbon as a conductive additive and does not contain acetylene black.
- the carbonaceous film on the surface of the positive electrode active material powder (1) is graphitizable carbon (soft carbon). Therefore, in the overcharged state, the graphitizable carbon is electrochemically oxidized to increase the resistance of the carbonaceous film and the conductive additive, and the internal resistance of the beaker cell (4) is increased as shown in FIG. It is thought that it rose.
- the region where the terminal voltage is constant for about 6520 to 7760 seconds is considered to be a region where soft carbon is electrochemically oxidized.
- the positive electrode active material layer 1 has a structure in which the carbonaceous film of the positive electrode active material powder is graphitizable carbon and the conductive additive is graphitizable carbon. It was found that the resistance of the material layer 1 can be quickly increased, and the current accompanying heat generation can be prevented from flowing through the positive electrode active material layer 1. Therefore, it has been found that by configuring the positive electrode active material layer 1 as described above, the heat generation of the battery in an overcharged state can be suppressed, and the internal pressure of the battery can be increased to prevent the battery from bursting. .
- Overcharge test (3) Beaker cells (5) to (8) were prepared using a mixed powder of soft carbon and hard carbon as a conductive additive (4 wt%). Other configurations were made in the same manner as the beaker cell (4). In the beaker cell (5), a mixed powder of 80 wt% soft carbon + 20 wt% hard carbon is used as a conductive assistant, and in the beaker cell (6), a mixed powder of 85 wt% soft carbon + 15 wt% hard carbon is used as a conductive assistant.
- a mixed powder of 90 wt% soft carbon + 10 wt% hard carbon was used as a conductive assistant
- Beaker Cell (8) a mixed powder of 95 wt% soft carbon + 5 wt% hard carbon was used as a conductive assistant.
- the mixed powder was prepared using KANJ-9 (manufactured by MT Carbon Co., Ltd.), a soft carbon powder, and Carbotron P (manufactured by Kureha Battery Materials Japan Co., Ltd.), a hard carbon powder. did.
- the terminal voltage did not reach the test upper limit voltage within a predetermined time. In these cells, it is considered that the positive electrode active material layer was not increased in resistance because the positive electrode active material layer was formed using a conductive additive having a relatively large proportion of hard carbon. In the tests of the beaker cells (7) and (8), the terminal voltage reached the test upper limit voltage within a predetermined time. In these cells, since the positive electrode active material layer was formed using a conductive additive having a relatively small proportion of hard carbon and a large proportion of soft carbon, it is considered that the resistance of the positive electrode active material layer was increased.
- Positive electrode active material layer 2 Undercoat layer 3: Positive electrode current collector sheet 4: Carbon hexagonal mesh surface 5: Positive electrode 6: Positive electrode active material particles 7: Conductive aid 8: Carbonaceous coating 9: Pore 10: Basic structural unit (BSU) 11: Battery case 12: Lid member 13: Positive electrode connection member 14: Negative electrode connection member 15: Nonaqueous electrolyte 16a, 16b: Screw member 18a, 18b: External connection terminal 20a, 20b: External insulation member 21a, 21b: Internal insulation member 22: Power generation element 25: Shrink film 30: Non-aqueous electrolyte secondary battery 32: Negative electrode 34: Separator 36: Negative electrode active material layer 38: Negative electrode current collector sheet 40a, 40b: Clip 41: Aluminum foil 42: Carbon layer 43: Positive electrode 45: B Seru
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Abstract
Description
リチウムイオン二次電池は一般的には、電解液としてリチウム塩を非水溶媒に溶解させた非水電解液が用いられている。
これらの非水電解液は可燃性の材料であることから、従来の電池には安全弁やセパレータ等の安全機構が設けられている。
過充電などによって電池が発熱するなどの異常な状態に見舞われた際、電池の破裂を防止するために安全弁を開裂させて、高くなった電池内圧を逃がす構造にしている。
また、過充電などによって電池が発熱などの異常な状態に見舞われた際、反応がさらに進んでしまうのを防止する為、120℃程度の温度に達するとセパレータに形成している細孔を閉塞(シャットダウン)させて、電池内の伝導イオンの通過経路を止めてしまう構造にしている。
炭素材料は、一般的に、黒鉛、フラーレンなどの一定の結晶構造を有するものと、非晶質炭素(微晶質炭素)とに分類することができる。また、非晶質炭素は、一般的に易黒鉛化性炭素(ソフトカーボン)と難黒鉛化性炭素(ハードカーボン)とに分類することができる。
易黒鉛化性炭素は、高温処理により黒鉛になりやすい炭素材料である。また、易黒鉛化性炭素は、一般的に、複数の基本構造単位(BSU)が集合した非晶質炭素であり、複数の基本構造単位が配向した配向組織を有する。基本構造単位は、複数の炭素六角網面が積層した構造単位であり、微視的に黒鉛類似構造を有する。また、一般的に、ピッチ類を熱処理した炭素材料、易黒鉛化性コークス類などが易黒鉛化性炭素に分類される(例えば、特許文献2参照)。
難黒鉛化性炭素は、高温処理の際に黒鉛化の進行が遅い炭素材料である。また、難黒鉛化性炭素は、一般的に、複数の基本構造単位が集合した非晶質炭素であり、複数の基本構造単位が配向していない無配向組織を有する。また、一般的に、熱硬化性樹脂を熱処理した炭素材料、カーボンブラック、難黒鉛化性コークス、植物系原料を熱処理した炭素材料などが難黒鉛化炭素に分類される(例えば、特許文献2参照)。
また、過充電の異常状態を止める機構として、セパレータの導電イオン通過経路を熱によって閉塞させる方法では、セパレータ材料種が限定されてしまうことに加え、発熱が過度に進行した場合、セパレータ全体が収縮する等で、正負極間の短絡を防ぐ機能が損なわれ異常状態を止める機能が働かなくなる可能性がある。
過充電時における保護機能の安全性の要求が高まる中で、安全弁やセパレータの保護機構に加えてさらなる安全機構の必要性が生じている。
本発明は、このような事情に鑑みてなされたものであり、新たな過充電保護機能を有する非水電解質二次電池用正極を提供する。
前記正極活物質層は正極活物質粒子の表面に設けられた炭素質被膜を含み、かつ、複数の正極活物質粒子の粒間に配置された導電助剤を0wt%以上20wt%以下で含むため、炭素質被膜又は導電助剤を電子伝導経路とすることができ、電極反応に伴う電子の授受を速やかに行うことができる。このため、電池特性を向上させることができる。また、正極活物質粒子に導電率の比較的低い材料を用いることが可能になる。
このため、非水電解質二次電池が過充電状態になったときに電子伝導経路である炭素質被膜及び導電助剤を高抵抗化することができ、過充電状態における電池内を流れる充電電流を速やかに少なくすることができる。このことにより、電解液の電気化学反応に伴う発熱や炭素質被膜又は導電助剤に電流が流れることによる発熱を抑制することができ、電池が高温になることを抑えることができ、電解液が沸騰することを抑制することができる。その結果として、過充電により電池の内圧が上昇することを抑制することができ、電池の破裂を防止することができる。つまり、本発明の正極を用いると、正極活物質層が安全性向上メカニズムを有する電池を作製することができる。
また、シャットダウン機構を有さないセパレータを使用して電池を作製することが可能になるため、電池の耐熱性を向上させることが可能になる。また、保護回路の簡略化することが可能になる。さらに、大型の電池の安全性を向上させることが可能になる。
本発明の正極に含まれる炭素質被膜及び導電助剤は、ピッチ系材料を焼成したもの(ピッチ系炭素材料)であることが好ましい。このことにより、非水電解質二次電池が過充電状態になったときに、炭素質被膜及び導電助剤を高抵抗化することができる。
本発明の正極に含まれる炭素質被膜及び導電助剤は、1.8g/cm3以上2.1g/cm3以下の材料密度を有することが好ましい。このことにより、非水電解質二次電池が過充電状態になったときに、炭素質被膜及び導電助剤を高抵抗化することができる。
本発明の正極は、正極集電シートをさらに備えることが好ましく、正極活物質層は、正極集電シート上に設けられたことが好ましい。このことにより、正極集電シートと正極活物質との間の導電距離を短くすることができ、電極反応に伴う電子の授受を速やかに行うことができる。
本発明の正極に含まれる正極活物質層は難黒鉛化炭素(ハードカーボン)及び黒鉛を実質的に含まないことが好ましい。このことにより、非水電解質二次電池が過充電状態になったときに、正極活物質層を高抵抗化させることができ、過充電状態の電池の発熱を抑制することができる。
本発明の非水電解質二次電池によれば、非水電解質二次電池が過充電状態になったときに正極活物質層を高抵抗化することができ、電池が高温になることを抑制することができる。このため、過充電により電池の内圧が上昇することを抑制することができ、電池の破裂を防止することができる。
本発明の二次電池において、負極活物質は炭素材料であることが好ましく、非水電解質は非水溶媒にリチウム塩が溶解した電解液であることが好ましく、炭素質被膜及び導電助剤は、過充電状態において、電気化学的に分解又は反応し高抵抗化する易黒鉛化性炭素であることが好ましい。このことにより、非水電解質二次電池が過充電状態になったときに電池が高温になることを抑制することができる。このため、過充電により電池の内圧が上昇することを抑制することができ、電池の破裂を防止することができる。
本実施形態の非水電解質二次電池30は、本実施形態の正極5と、負極活物質を有する負極32と、正極5と負極32とに挟まれたセパレータ34と、非水電解質15と、正極5と負極32とセパレータ34と非水電解質15とを収容する電池ケース11とを備えることを特徴とする。
以下、本実施形態の非水電解質二次電池用正極5及び非水電解質二次電池30について説明する。
非水電解質二次電池用正極5は、非水電解質二次電池30を構成する正極又は非水電解質二次電池30の製造に用いられる正極である。
非水電解質二次電池用正極5は、複数の正極活物質粒子6を含む正極活物質層1を備える。また、正極5は、正極集電シート3を備えることができ、正極活物質層1は正極集電シート3上に設けることができる。正極5は、例えば、図1(a)(b)に示したような構造を有することができる。正極集電シート3は、例えば、アルミニウム箔などの金属箔とすることができる。また、正極5は、正極集電シート3と正極活物質層1との間に下地層2を備えてもよい。下地層2は、例えば、図1(c)のように設けることができる。
正極活物質層1は、正極活物質粒子6の表面に設けられた炭素質被膜8と、複数の正極活物質粒子6の粒間に配置された導電助剤7との両方を有することができる。この場合、炭素質被膜8と導電助剤7の両方が易黒鉛化性炭素である。例えば、正極活物質層1は、図2のような微細構造を有することができる。このような正極活物質層1は、例えば、炭素質被膜8を形成した正極活物質粉末と、導電助剤7と、バインダーとを混合してペーストを調製し、このペーストを正極集電シート3上に塗布することにより形成することができる。ペーストの調製に用いる溶剤としては、ジメチルホルムアミド、N-メチルピロリドン、イソプロパノール、トルエン等が挙げられる。また、正極活物質層1は、0wt%以上20wt%以下の導電助剤を含むことができる。導電助剤は出力の向上に効果が見込めるが、多すぎると電極の体積当たりの容量が減ってしまうため20wt%以下にするのが好ましい。
導電助剤7は、例えば、易黒鉛化性炭素であるコークス系ソフトカーボンを用いることができる。
正極活物質層1に含まれる炭素質被膜8及び導電助剤7の合計量のうち90%以上は、易黒鉛化性炭素であってもよい。このことは、正極活物質層1の透過型電子顕微鏡写真に含まれる炭素質被膜8及び導電助剤7の合計量のうち90%以上が易黒鉛化性炭素であることを確認することにより確かめることができる。また、X線回折測定により確認することもできる。
また、炭素質被膜8及び導電助剤7は、1.8g/cm3以上2.1g/cm3以下の材料密度を有する易黒鉛化性炭素であってもよい。一般的に、易黒鉛化性炭素は、難黒鉛化性炭素に比べ大きい材料密度を有するため、このことを調べることにより易黒鉛化性炭素であるか否かを確認することができる。
なお、下地層2は、易黒鉛化性炭素の粉末とバインダーとを混合してペーストを調製し、このペーストを正極集電シート3上に塗布することにより形成することができる。また、正極活物質層1は、下地層2上に形成することができる。
なお、後述する電圧印加実験により、難黒鉛化性炭素及び黒鉛は、過充電状態において高抵抗化しないことが明らかになった。
また、正極活物質粒子6は、YxM2(PO4)3で表すことができるNASICON型化合物の粒子であってもよい。NASICON型化合物は、菱面体晶を有し、例えば、Li3+xFe2(PO4)3、Li2+xFeTi(PO4)3、LixTiNb(PO4)3およびLi1+xFeNb(PO4)3などが挙げられる。
また、正極活物質粒子6は、リチウムイオンを可逆的に吸蔵・放出することが可能なリチウム遷移金属複合酸化物(層状系、スピネル等)の粒子であってもよい。
また、正極活物質層1は、上述の正極活物質粒子6を一種単独で含有してもよく、複数種を含有してもよい。
また、正極活物質層1は、上述の正極活物質粒子6を一種単独で含有してもよく、複数種を含有してもよい。
非水電解質二次電池30は、上述の正極5と、負極32と、正極5と負極32とに挟まれたセパレータ34と、非水電解質15と、正極5と負極32とセパレータ34と非水電解質15とを収容する電池ケース11とを備える。非水電解質二次電池30は、例えば、リチウムイオン二次電池、ナトリウムイオン二次電池などである。
負極活物質層36は、負極活物質、導電剤、結着剤などを含むことができる。
負極活物質は、例えば、グラファイト(黒鉛)、部分黒鉛化した炭素、ハードカーボン、ソフトカーボン、LiTiO4、Sn、Siなどが挙げられる。また、負極活物質層36は、上述の負極活物質を一種単独で含有してもよく、複数種を含有してもよい。
セパレータ34は、短絡電流が流れることを防止でき、正極-負極間を伝導するイオンが透過可能なものであれば特に限定されないが、例えばポリオレフィンの微多孔性フィルム、セルロースシート、アラミドシートとすることができる。
電池ケース11は、正極5、負極32、セパレータ34、非水電解質15を収容する容器である。また、電池ケース11は、蓋部材12により塞がれた開口を有してもよい。このことにより、電池ケース11内に発電要素22を収容することができる。
非水電解質15に含まれる非水溶媒には、カーボネート化合物(環状カーボネート化合物、鎖状カーボネート化合物など)、ラクトン、エーテル、エステルなどを使用することができ、これら溶媒の2種類以上を混合して用いることもできる。これらの中では特に環状カーボネート化合物と鎖状カーボネート化合物を混合して用いることが好ましい。
非水電解質15に含まれる電解質塩としては、例えば、LiCF3SO3、LiAsF6、LiClO4、LiBF4、LiPF6、LiBOB、LiN(CF3SO2)2、LiN(C2F5SO2)等を挙げることができる。
また、非水電解質15には、必要に応じて難燃化剤等の添加剤を配合してもよい。
異なる炭素前駆体を用いてリン酸鉄リチウム(LiFePO4)粉末の表面上に炭素質被膜(導電性被膜)を形成し、正極活物質粉末(1)~(4)を調製した。具体的には以下のように調製した。
(1)正極活物質の前処理
正極活物質材料であるリン酸鉄リチウム試薬(株式会社 豊島製作所製)を350℃、窒素雰囲気下で5時間加熱乾燥し、表面の吸着水などを除去した。
(2)炭素前駆体溶液の調製
エチレンタールピッチ(炭素前駆体)をアセトンで希釈し、20重量%のエチレンタールピッチを含む炭素前駆体溶液を調製した。
(3)正極活物質への炭素前駆体付着処理
上記の炭素前駆体溶液100gに、前処理後の正極活物質材料480gを加え、プラネタリミキサにて20rpm、1時間の混練処理を露点管理されたドライボックス内にて行った。その後、溶剤除去が可能なオーブン内にて40℃に加熱し、希釈溶媒であるアセトンを除去し、炭素含有量4重量%の混合体を調製した。
(4)炭素化処理
上記の混合体を、電気炉にて窒素雰囲気下、700℃、2時間の炭素化処理を行い、正極活物質粉末(1)を調製した。
キノリン不溶分を含まない改質エチレンタールピッチ(炭素前駆体)をアセトンで希釈し、20重量%の改質エチレンタールピッチを含む炭素前駆体溶液を調製した。この炭素前駆体溶液を用いて正極活物質粉末(1)と同様の方法で正極活物質粉末(2)を調製した。
ピレン(炭素前駆体)をアセトンで希釈し、20重量%のピレンを含む炭素前駆体溶液を調製した。この炭素前駆体溶液を用いて正極活物質粉末(1)と同様の方法で正極活物質粉末(3)を調製した。
スクロース(炭素前駆体)をアセトンで希釈し、20重量%のスクロースを含む炭素前駆体溶液を調製した。この炭素前駆体溶液を用いて正極活物質粉末(1)同様の方法で正極活物質粉末(4)を調製した。
正極活物質粉末(1)を用いて正極(1)を作製し、正極活物質粉末(2)を用いて正極(2)を作製し、正極活物質粉末(3)を用いて正極(3)を作製し、正極活物質粉末(4)を用いて正極(4)を作製した。正極活物質粉末以外の構成は同じにした。具体的には以下のように作製した。
まず、正極活物質粉末(1)、(2)、(3)又は(4)と、アセチレンブラック(導電助剤)と、ポリフッ化ビニリデン(PVDF ((CH2CF2)n))(バインダー)とを、合計100重量%に対し、正極活物質粉末が88~95重量%となり、導電助剤が3.5~4.5重量%となるように混合した。この混合粉末にN-メチルピロリドンを加えて混練することにより正極活物質ペーストを調製した。この正極活物質ペーストをアルミニウム箔(正極集電シート)上に塗布し、塗布膜を乾燥させることにより正極集電シート上に正極活物質層を形成し正極(1)~(4)を作製した。
正極(1)、正極(2)、正極(3)又は正極(4)と、ポリオレフィン製のセパレータ(シャットダウン温度120℃付近)と、炭素質負極とを積層した発電要素を、蓋部材に安全弁を備えた電池容器に収容し、非水電解液を電池容器内に注入することによりリチウムイオン二次電池(1)~(4)を作製した。非水電解液には、カーボネート系溶媒(EC:DEC:EMC=1:1:1)と、添加剤(電解液100重量部に対してVCを1重量部、FECを1重量部)と、電解質であるLiPF6とを含む1MのLiPF6電解液を用いた。
作製したリチウムイオン二次電池(1)~(4)の過充電試験を行った。具体的には以下のようにして試験を行った。
まず、充電電流を50A、上限電圧を3.5Vとして6時間の充電を行い作製した電池を満充電状態にした後、過充電試験を行った。過充電試験では、充電電流を1ItA(1CA)である50Aとし、試験上限電圧を10Vとして、CCCV (Constant-Current-Constant-Voltage) 充電を行った。なお、過充電試験では、正極の外部接続端子と負極の外部接続端子との間の電圧と、これらの外部接続端子間に流れる電流を測定した。また、過充電試験では、電池容器に熱電対を取り付けて温度を測定した。
この試験結果を表1に示す。
電池(3)では、図9(a)に示した電圧曲線のように過充電状態で充電を続けると、正極-負極間の電圧は、約5.5Vまで上昇した後ほぼ一定となった。そして約12分から電圧は急上昇し、13分付近で正極-負極間の電圧は試験上限電圧に達した。
また、電池(3)では、図9(b)に示した電流曲線のように13分付近で正極-負極間の電流は急降下しほとんど流れなくなった。
また、電池(3)では、図9(c)のように、電池容器の温度上昇量は、約90℃に達した。なお、電池(3)では安全弁が開き、電池容器中の電解液が噴出した。
電池(3)では、12~13分で正極-負極間の電圧が急上昇し、電流が急降下しているため、電池内部の温度が120℃以上に達し、セパレータの細孔がシャットダウンし、電池内の伝導イオンの通過経路が止まったと考えられる。
なお、リチウムイオン二次電池(4)の過充電試験でも、電池(3)の過充電試験と同様の電圧挙動、電流挙動、温度挙動を示した。
また、電池(1)では、図8(b)に示した電流曲線のように正極-負極間の電圧が7~10分付近で試験上限電圧に達すると、正極-負極間に流れる電流は徐々に減少し試験時間が12~14分でほとんど流れなくなった。セパレータのシャットダウン時にみられるような急に電流が流れなくなるような現象とは異なる挙動を示していた。
また、電池(1)では、図8(c)に示した温度上昇量曲線のように、10~12分までは電池温度が徐々に上昇したが、その後はほぼ一定となった。電池(1)の温度上昇量は30℃程度であり、電池内部温度はセパレータのシャットダウン温度まで到達していないと考えられる。なお、電池(1)では、安全弁が開くことはなかった。
電池(1)では、正極-負極間の電圧は徐々に上昇し、正極-負極間に流れる電流は徐々に減少しているため、電池が過充電状態になると、電池の内部抵抗が徐々に上昇すると考えられる。
なお、リチウムイオン二次電池(2)の過充電試験でも、電池(1)の過充電試験と同様の電圧挙動、電流挙動、温度挙動を示した。
過充電試験後のリチウムイオン二次電池(1)、(3)から正極(1)、(3)を取り出し、正極(1)、(3)の電気抵抗率を四端子法を用いて測定した。また、電池組み込み前の正極(1)、(3)の電気抵抗率も測定した。
また、過充電試験後のリチウムイオン二次電池(1)、(3)からセパレータを取り出し、透気抵抗度試験を行った。また、電池組み込み前のセパレータについても、透気抵抗度試験を行った。透気抵抗度試験は、透気抵抗度試験機(ガーレー試験機)を用いて測定を行った。この試験は、単位面積当たりを規定された体積の空気が透過するのに要する時間を測定するものである。
これらの試験結果を表2に示す。
このことから電池(1)についての過充電試験における電池の内部抵抗の上昇は、正極(1)の内部抵抗の上昇に起因することがわかった。
一方、電池(3)についての過充電試験における電池の内部抵抗の上昇は、正極(3)の内部抵抗の上昇によるものではないことがわかった。
このことから電池(1)についての過充電試験では、電池内部温度がセパレータのシャットダウン温度まで到達していないことがわかった。また、過充電試験における電池(1)の内部抵抗の上昇は、セパレータの細孔の閉塞に起因しないことがわかった。
また、電池(3)についての過充電試験では、電池内部温度がセパレータのシャットダウン温度まで到達したことがわかった。このため、セパレータの細孔が閉塞して電池内の伝導イオンの通過経路が遮断され、正極-負極間の電圧が急上昇し、電流が急降下したと考えられる。
また、過充電試験後の電池(4)から正極(4)及びセパレータを取り出し、正極(4)の電気抵抗率の測定及びセパレータの透気抵抗度試験を行った。電池(4)の透気抵抗度試験の結果は、電池(3)と同じように、セパレータがシャットダウンしていた。このことから、電池(4)でも、電池(3)と同じような現象が起きたと考えられる。
透過型電子顕微鏡を用いて、正極活物質粉末(1)に含まれる炭素質被膜の直接観察を行った。また、正極活物質粉末(3)に含まれる炭素質被膜の直接観察を行った。なお、薄片処理はしていない。
図10(a)は、正極活物質粉末(1)のTEM像であり、図10(b)は、図10(a)の破線で囲んだ範囲Cの拡大像である。
図10から炭素質被膜の厚さは、約4nmであることがわかった。また、炭素質被膜は、複数の炭素六角網面4が折り重なった構造の基本構造単位10(BSU)を複数有することがわかった。また、複数の基本構造単位10は、正極活物質粒子6の表面に対向するように配向しており、炭素質被膜は、基本構造単位10が配向した配向組織を有することがわかった。このことから、炭素質被膜は、易黒鉛化性炭素(ソフトカーボン)であることがわかった。
また、複数の炭素六角網面4の平均サイズは、約4.5nmであった。
正極活物質粉末(2)に含まれる炭素質被膜の直接観察を行った。図示はしないが、炭素質被膜は、基本構造単位10が配向した配向組織を有しており、易黒鉛化性炭素(ソフトカーボン)であった。また、複数の炭素六角網面4の平均サイズは、約3.2nmであった。
図11から炭素質被膜は、小さな炭素六角網面4が複雑に入り組んだ構造を有することがわかった。このことから炭素質被膜は、難黒鉛化性炭素(ハードカーボン)であることがわかった。また、複数の炭素六角網面4の平均サイズは、約1.5nmであった。
正極活物質粉末(4)に含まれる炭素質被膜の直接観察を行った。図示はしないが、炭素質被膜は、小さな炭素六角網面4が複雑に入り組んだ構造の難黒鉛化性炭素(ハードカーボン)であり、複数の炭素六角網面4の平均サイズは、約1.6nmであった。
過充電状態における炭素質被膜の電気的特性を調べるために、異なる種類のカーボン層42を有する正極(5)~(7)を作製し、この正極(5)~(7)を用いて図12に示したようなビーカーセル(1)~(3)を作製し、過充電試験を想定した電圧印加実験を行った。易黒鉛化性炭素(ソフトカーボン)粉末とバインダー(PVDF)とを混合して調製したペーストをアルミニウム箔41上に塗布してカーボン層42aを形成して正極(5)を作製し、この正極(5)を用いてビーカーセル(1)を作製した。易黒鉛化性炭素粉末には、コークス系ソフトカーボンであるKANJ-9(エム・ティー・カーボン株式会社製)を用いた。
また、同様の方法で難黒鉛化性炭素(ハードカーボン)粉末を用いて形成したカーボン層42bを有する正極(6)を作製し、ビーカーセル(2)を作製した。難黒鉛化性炭素粉末には、カーボトロンP(株式会社クレハ・バッテリー・マテリアルズ・ジャパン製)を用いた。
さらに同様の方法でグラファイト粉末を用いて形成したカーボン層42cを有する正極(7)を作製し、ビーカーセル(3)を作製した。グラファイト粉末には、コークス系カーボンを焼成して作成したKGNJ-9(エム・ティー・カーボン株式会社製)を用いた。
作製したカーボン層42a、42b、42cは、いずれも高い導電率を有していた。
なお、非水電解質15には、カーボネート系溶媒(EC:DEC =3:7)と、電解質であるLiPF6とを含む1MのLiPF6電解液を用いた。負極32には、金属リチウム箔を用いた。電圧印加実験では、試験上限電圧を7Vとして、充電電圧を正極と負極の間に印加し10mAの定電流を流すことにより行った。
ハードカーボンのカーボン層42bを有する正極(6)を用いたビーカーセル(2)では、試験時間約0~15秒で、端子電圧が約6.2Vまで上昇し、その後、端子電圧は一定となった。
グラファイトのカーボン層42cを有する正極(7)を用いたビーカーセル(3)では、試験時間約0~2秒で、端子電圧が約5.0Vまで急上昇し、試験時間約2~275秒で端子電圧は徐々に約6.2Vまで上昇した。そして、端子電圧は、約6.2Vで一定となった。
正極のカーボン層42にハードカーボンを用いたビーカーセル(2)では、ハードカーボンが電気化学反応に関与することなく、端子電圧が上がり続けて端子電圧が約6.2Vで一定となった。
また、正極のカーボン層42にグラファイトを用いたビーカーセル(3)では、グラファイトが約5.0Vで電気化学反応に関与していていることが観察されるものの、グラファイトの構造が安定なためにカーボン層42の高抵抗化には至らず、端子電圧が約6.2Vで一定となった。
なお、端子電圧が約6.2Vで一定である領域では、カーボネート系溶媒が電気化学的に反応していると考えられる。
また、上記電圧印加実験の結果から、難黒鉛化炭素(ハードカーボン)及びグラファイトは、過充電状態で高抵抗化しないことがわかった。このことから、上記過充電試験(1)のリチウムイオン二次電池(3)では、炭素質被膜及び導電助剤7が難黒鉛化炭素であるため、電池が過充電状態となり正極の電位が高くなった場合でも炭素質被膜及び導電助剤7が高い導電率を有すると考えられる。このため、過充電状態でも正極活物質層1には炭素質被膜及び導電助剤7を介して電流が流れると考えられ、正極活物質層1において非水電解質15に含まれる電解質や非水溶媒が電気化学的に分解又は反応し発熱すると考えられる。また、この場合、炭素質被膜及び導電助剤7に電流が流れ発熱すると考えられる。これらの発熱により電解液15が沸騰し電池の安全弁が開いたと考えられる。
上記正極活物質粉末調製実験で調製した正極活物質粉末(1)を用いて正極(8)を作製し、ビーカーセル(4)を作製した。具体的には以下のように作製した。
正極活物質粉末(1)と、ソフトカーボン粉末(導電助剤)と、バインダー(PVDF)とを、合計100重量%に対し、正極活物質粉末が91重量%となり、ソフトカーボン粉末が4重量%となり、バインダーが5重量%となるように混合した。ソフトカーボン粉末には、コークス系ソフトカーボンであるKANJ-9(エム・ティー・カーボン株式会社製)を用いた。この混合粉末にN-メチルピロリドンを加えて混練することにより正極活物質ペーストを調製した。この正極活物質ペーストをアルミニウム箔(正極集電シート)上に塗布し(塗布量:約10.5mg)、正極集電シート3上に正極活物質層1を形成し正極(8)を作製した。
この正極(8)を用いてビーカーセル(4)を作製した。なお、非水電解液15には、カーボネート系溶媒(EC:DEC=3:7)と、電解質であるLiPF6とを含む1MのLiPF6電解液を用いた。負極32には、金属リチウム箔を用いた。また、セパレータは設けていない。
充電・過充電試験の結果を図14に示す。
ビーカーセル(4)の試験では、約0~4350秒の充電領域では、端子電圧が約3.8Vで安定していた。満充電状態を超えて過充電をすると、約4350~6520秒で端子電圧は上昇していき、約6520~7760秒で端子電圧が一定になり、その後、端子電圧が上昇し試験上限電圧に達した。このことにより、セパレータを設けない場合でも、電池の内部抵抗が上昇することが確認できた。
ソフトカーボンとハードカーボンの混合粉末を導電助剤(4wt%)として用いてビーカーセル(5)~(8)を作製した。その他の構成は、ビーカーセル(4)と同様に作製した。ビーカーセル(5)では80wt%ソフトカーボン+20wt%ハードカーボンの混合粉末を導電助剤として用い、ビーカーセル(6)では85wt%ソフトカーボン+15wt%ハードカーボンの混合粉末を導電助剤として用い、ビーカーセル(7)では90wt%ソフトカーボン+10wt%ハードカーボンの混合粉末を導電助剤として用い、ビーカーセル(8)では、95wt%ソフトカーボン+5wt%ハードカーボンの混合粉末を導電助剤として用いた。なお、混合粉末は、ソフトカーボン粉末であるKANJ-9(エム・ティー・カーボン株式会社製)と、ハードカーボン粉末であるカーボトロンP(株式会社クレハ・バッテリー・マテリアルズ・ジャパン製)を用いて調製した。
ビーカーセル(7)、(8)の試験では、所定の時間内に端子電圧が試験上限電圧に達した。これらのセルでは、ハードカーボンの割合が比較的小さく、ソフトカーボンの割合が大きい導電助剤を用いて正極活物質層を形成したため、正極活物質層が高抵抗化したと考えられる。
Claims (9)
- 複数の正極活物質粒子を含む正極活物質層を備え、
前記正極活物質層は、前記正極活物質粒子の表面に設けられた炭素質被膜を含み、かつ、複数の正極活物質粒子の粒間に配置された導電助剤を0wt%以上20wt%以下で含み、
前記炭素質被膜及び前記導電助剤の少なくとも一方は、易黒鉛化性炭素であることを特徴とする非水電解質二次電池用正極。 - 前記炭素質被膜及び前記導電助剤は、複数の炭素六角網面が積層した構造の基本構造単位が複数集合した非晶質炭素であり、複数の基本構造単位が配向した配向組織を有する請求項1に記載の正極。
- 前記炭素質被膜及び前記導電助剤は、ピッチ系材料を焼成したものである請求項1又は2に記載の正極。
- 前記正極活物質層に含まれる前記炭素質被膜及び前記導電助剤の合計量のうち90%以上は、易黒鉛化性炭素である請求項1~3のいずれか1つに記載の正極。
- 前記炭素質被膜及び前記導電助剤は、1.8g/cm3以上2.1g/cm3以下の材料密度を有する請求項1~4のいずれか1つに記載の正極。
- 前記正極活物質粒子は、オリビン型化合物の粒子又はNASICON型化合物の粒子である請求項1~5のいずれか1つに記載の正極。
- 正極集電シートをさらに備え、
前記正極活物質層は、前記正極集電シート上に設けられた請求項1~6のいずれか1つに記載の正極。 - 請求項1~7のいずれか1つに記載の正極と、負極活物質を有する負極と、前記正極と前記負極とに挟まれたセパレータと、非水電解質と、前記正極と前記負極と前記セパレータと前記非水電解質とを収容する電池ケースとを備える非水電解質二次電池。
- 前記負極活物質は、炭素材料であり、
前記非水電解質は、非水溶媒にリチウム塩が溶解した電解液であり、
前記炭素質被膜及び前記導電助剤は、過充電状態において、電気化学的に分解又は反応し高抵抗化する易黒鉛化性炭素である請求項8に記載の非水電解質二次電池。
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Publication number | Publication date |
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EP3457473A4 (en) | 2019-10-30 |
CN109155402A (zh) | 2019-01-04 |
EP3457473A1 (en) | 2019-03-20 |
US20190288275A1 (en) | 2019-09-19 |
KR20190006989A (ko) | 2019-01-21 |
US11652202B2 (en) | 2023-05-16 |
JPWO2017195330A1 (ja) | 2019-03-07 |
JP6991583B2 (ja) | 2022-01-12 |
CN109155402B (zh) | 2023-04-28 |
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