WO2015046492A1 - リチウムイオン二次電池用電極およびリチウムイオン二次電池 - Google Patents
リチウムイオン二次電池用電極およびリチウムイオン二次電池 Download PDFInfo
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- WO2015046492A1 WO2015046492A1 PCT/JP2014/075823 JP2014075823W WO2015046492A1 WO 2015046492 A1 WO2015046492 A1 WO 2015046492A1 JP 2014075823 W JP2014075823 W JP 2014075823W WO 2015046492 A1 WO2015046492 A1 WO 2015046492A1
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
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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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- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- 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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- H01M4/02—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
- H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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- H01M4/36—Selection of substances as active materials, active masses, active liquids
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- 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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- 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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- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
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- H01M4/64—Carriers or collectors
- H01M4/66—Selection of materials
- H01M4/661—Metal or alloys, e.g. alloy coatings
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- H—ELECTRICITY
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- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- 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
- H01M10/0566—Liquid materials
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- H—ELECTRICITY
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/028—Positive electrodes
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- H01M2220/00—Batteries for particular applications
- H01M2220/30—Batteries in portable systems, e.g. mobile phone, laptop
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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 an electrode for a lithium ion secondary battery in which measures against overcharge are taken, and a lithium ion secondary battery including the electrode for a lithium ion secondary battery.
- lithium ion secondary batteries lithium having a high chemical activity, a highly flammable electrolyte, and a lithium transition metal composite oxide having low stability in an overcharged state are used as battery materials. It is known that if the charging is further continued in the overcharged state, there is a problem that a chemical reaction between the battery materials rapidly proceeds and the battery generates heat. For this reason, it is necessary to quickly stop charging before reaching an overcharged state, and a mechanism is employed in which an external circuit performs voltage monitoring, charging stop, and the like. Such a mechanism for preventing the heat generation of the battery is provided not only in the external circuit of the battery but also in the battery as described below.
- Patent Document 1 discloses an electrolyte additive that suppresses overcharging by increasing the internal resistance of the battery by oxidizing and polymerizing a material added to the electrolyte due to a voltage increase associated with overcharging.
- Patent Document 2 discloses a technique of increasing the electrode resistance due to a temperature increase associated with overcharging and suppressing overcharging. Specifically, in an electrode in which an electrode mixture layer made of a positive electrode material or a negative electrode material is laminated on a current collector, thermal expansion occurs in the electrode mixture layer or along the interface between the electrode mixture layer and the current collector. Microcapsules are contained. When the overcharged state is reached, the microcapsule foams to separate the electrode mixture layer and the current collector, thereby increasing the electrode resistance.
- Patent Document 3 discloses a positive electrode in which a compound contained in a positive electrode mixture decomposes due to an increase in voltage due to overcharge to generate gas, and the internal resistance of the battery increases to suppress further overcharge.
- a positive electrode having a two-layer structure having a second layer composed of a conductive agent and a binder is disclosed.
- the positive electrode configured in this way becomes a high potential due to overcharging, a substance that decomposes at a high potential is decomposed to generate gas.
- the first layer is structurally destroyed and acts to cause interface failure between the first layer and the second layer.
- the internal resistance of the battery increases, thereby blocking the charging current and suppressing overcharge. To do.
- Japanese Patent No. 3938194 Japanese Patent No. 4727021 Japanese Unexamined Patent Publication No. 2008-181830 Japanese Patent No. 4236308
- Patent Document 1 when an additive that suppresses overcharge is mixed in the electrolytic solution, there is a problem that the electrolyte ion conductivity in the electrolytic solution decreases. Further, there is a problem that the reaction of the additive occurs during high-temperature storage, and the battery cycle life and high-temperature storage characteristics deteriorate.
- Patent Document 2 when a microcapsule that thermally expands due to an increase in temperature due to overcharge is introduced into the positive electrode, the microcapsule gradually expands during high temperature storage to increase the positive electrode resistance. There is a problem that the life and high-temperature storage characteristics deteriorate.
- Patent Document 3 when a compound that generates gas by being decomposed by an increase in voltage due to overcharge is introduced into the positive electrode mixture, the amount of active material in the positive electrode mixture decreases, so the positive electrode capacity is There is a problem of lowering.
- Patent Document 4 when a compound that generates gas by being decomposed by a voltage increase due to overcharging is introduced into the first positive electrode layer on the current collector, the cost increases due to the introduction of the gas generating material. There are also challenges.
- the present invention has been made in view of such problems, and an electrode for a lithium ion secondary battery that suppresses generation of heat when an overcharged state is achieved while suppressing manufacturing cost, and the lithium ion It aims at provision of a lithium ion secondary battery provided with the electrode for secondary batteries.
- An electrode for a lithium ion secondary battery includes a positive electrode current collector, a first binder that is a synthetic polymer having an ester bond, and a first conductive agent, A positive electrode first layer formed on the positive electrode current collector, a positive electrode active material, a second binder, and a second conductive agent, and the positive electrode current collector of the positive electrode first layer is formed. And a positive electrode second layer formed on a surface opposite to the opposite surface.
- the synthetic polymer may be any one of polyester, polyurethane, and polyester urethane.
- the lithium ion secondary battery which concerns on the 2nd aspect of this invention is equipped with the electrode for lithium ion secondary batteries which concerns on the said 1st aspect, the negative electrode which occludes and discharge
- the first binder when the potential difference between the lithium ion secondary battery electrode and the negative electrode is 4.33 V or more and 4.76 V or less, the first binder starts to be altered. The electric resistance value of the first binder may be increased.
- the first binder may be altered by oxidative polymerization or oxidative decomposition.
- the electrode for a lithium ion secondary battery and the lithium ion secondary battery it is possible to suppress the generation of heat when an overcharged state is achieved while suppressing the manufacturing cost.
- the positive electrode 1 of the present embodiment includes a positive electrode current collector 10, a first binder and a first conductive agent, and a positive electrode first formed on the positive electrode current collector 10.
- a positive electrode first layer 11 having a positive electrode active material, a second binder, and a second conductive agent and formed on the positive electrode first layer 11 on the side opposite to the positive electrode current collector 10; And two layers 12.
- the positive electrode 1 has a two-layer configuration in which a positive electrode first layer 11 and a positive electrode second layer 12 are formed on a positive electrode current collector 10.
- the configuration of the positive electrode 1 will be described.
- the positive electrode current collector 10 is not particularly limited, and a material in which a known material such as aluminum, stainless steel, or nickel-plated steel is formed into a plate shape can be used.
- the first binder contained in the positive electrode first layer 11 is a synthetic polymer that changes in quality when the lithium ion secondary battery is overcharged, such as oxidative polymerization, oxidative decomposition, or foaming. It is necessary to be a synthetic polymer that changes in quality due to the above. As this synthetic polymer, it is preferable to use a resin having an ester bond in the main chain, and specifically, any one of polyester, polyurethane, and polyester urethane can be used. As the first conductive agent contained in the positive electrode first layer 11, known materials such as acetylene black, ketjen black, carbon black, graphite (graphite), and carbon nanotube can be used.
- the positive electrode first layer 11 is prepared by mixing the first binder and the first conductive agent in a single solvent or a mixed solvent such as methyl ethyl ketone and toluene, and then applying and drying on the positive electrode current collector 10. Can be formed.
- the positive electrode active material contained in the positive electrode second layer 12 is not particularly limited, and a conventionally known active material can be used.
- the positive electrode active material include a lithium transition metal composite oxide capable of releasing lithium ions.
- the lithium transition metal composite oxide include LiNiO 2 , LiMnO 2 , LiCoO 2 , LiFePO 4, and the like.
- a mixture of a plurality of lithium transition metal oxides can be used.
- the second binder contained in the positive electrode second layer 12 polyvinylidene fluoride (PVDF) or the like can be used as in the conventional case.
- PVDF polyvinylidene fluoride
- As a 2nd electrically conductive agent contained in the positive electrode 2nd layer 12, graphite, aluminum, etc. can be used like the past.
- the positive electrode second layer 12 is laminated on the positive electrode first layer 11 after mixing the positive electrode active material, the second binder, and the second conductive agent in a solvent such as N-methylpyrrolidone (NMP). It can be formed by coating and drying.
- NMP N-methylpyrrolidone
- the positive electrode first layer 11 and the positive electrode second layer 12 are produced in a continuous manufacturing process, it is necessary to dry the positive electrode first layer 11 in a short time. It is desirable to select a low boiling point solvent as the solvent for the liquid composition. Therefore, it is preferable to select a resin that dissolves in the low-boiling solvent as the first binder of the positive electrode first layer 11.
- the positive electrode 1 As shown in FIG. 2, the positive electrode 1 according to the present embodiment configured as described above includes a negative electrode 20, a separator 21 for preventing contact between the positive electrode 1 and the negative electrode 20, a positive electrode 1, a negative electrode 20, and a separator.
- the lithium ion secondary battery 2 which concerns on this embodiment is comprised with the nonaqueous electrolyte solution 22 in which 21 is immersed.
- a configuration other than the positive electrode 1 in the lithium ion secondary battery 2 will be described.
- the negative electrode active material contained in the negative electrode 20 is not particularly limited, and can absorb and release lithium ions such as metal materials such as lithium, alloy materials containing silicon, tin, and the like, and carbon materials such as graphite and coke. The compounds can be used alone or in combination.
- the negative electrode 20 can be formed by pressing a lithium foil on a negative electrode current collector such as copper.
- a negative electrode made of a metal such as copper is mixed after mixing the negative electrode active material, the binder, the conductive additive, etc. in a solvent such as water or N-methylpyrrolidone.
- the negative electrode 20 can be formed by applying and drying on a current collector.
- the binder is preferably a chemically and physically stable material such as polyvinylidene fluoride, polytetrafluoroethylene, EPDM, SBR, NBR, or fluororubber.
- the conductive assistant include ketjen black, acetylene black, carbon black, graphite, carbon nanotube, and amorphous carbon.
- the negative electrode current collector is not particularly limited, and a current collector formed from a copper foil or the like can be used.
- the nonaqueous electrolytic solution 22 is not particularly limited, and includes an electrolytic solution in which a supporting salt is dissolved in a solvent such as an organic solvent, an ionic liquid that is an electrolyte and solvent, an electrolytic solution in which a supporting salt is further dissolved in the ionic liquid, and the like.
- a solvent such as an organic solvent, an ionic liquid that is an electrolyte and solvent, an electrolytic solution in which a supporting salt is further dissolved in the ionic liquid, and the like.
- a solvent such as an organic solvent, an ionic liquid that is an electrolyte and solvent, an electrolytic solution in which a supporting salt is further dissolved in the ionic liquid, and the like.
- organic solvent carbonates, halogenated hydrocarbons, ethers, ketones, nitriles, lactones, oxolane compounds and the like can be used.
- a mixed solvent such as propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane
- the supporting salt used for the nonaqueous electrolytic solution 22 is not particularly limited.
- the ionic liquid used for the non-aqueous electrolyte solution 22 is not particularly limited as long as it is a salt that is liquid at room temperature. Examples thereof include phosphonium salts. Further, it is more preferable that the ionic liquid is electrochemically stable in a wide potential region.
- the separator 21 include a microporous film or nonwoven fabric made of polyolefin such as polyethylene and polypropylene, or an aromatic polyamide resin, and a porous resin coat containing inorganic ceramic powder.
- the positive electrode 1, the negative electrode 20, the non-aqueous electrolyte solution 22, and the separator 21 are accommodated in a positive electrode case 24 and a negative electrode case 25 shown in FIG. Type lithium ion secondary battery 2 can be produced. Cases 24 and 25 are formed of a metal plate or the like.
- the positive electrode case 24 and the negative electrode case 25 are sealed with an insulating gasket 26.
- Example 2 Hereinafter, although the Example and comparative example of the lithium ion secondary battery 2 of this invention are demonstrated in detail, this lithium ion secondary battery is not limited to this.
- Example 1 First, 30 parts by mass of acetylene black (HS-100, manufactured by Denki Kagaku Kogyo) and 70 parts by mass of polyester A (molecular weight: 17,000, Tg (glass transition point): 67 ° C., first binder) It added to the mixed solvent of methyl ethyl ketone (MEK) and toluene, the dispersion process was performed, and the homogeneous paste was prepared. This paste was applied on an aluminum foil current collector (thickness 20 ⁇ m (micrometer), positive electrode current collector) and subjected to a drying treatment to obtain a positive electrode first layer. The film thickness of the positive electrode first layer after the drying treatment was 1 to 2 ⁇ m.
- MEK methyl ethyl ketone
- the obtained positive electrode was punched into a diameter of 13.5 mm, and a lithium foil having a diameter of 15 mm was prepared as a negative electrode.
- the positive electrode and the negative electrode were sandwiched through a polyolefin or polyethylene separator (Hypore, manufactured by Asahi Kasei E-Materials).
- LiPF 6 lithium hexafluorophosphate
- a non-aqueous electrolyte prepared by adding 2% by weight of vinylene carbonate was injected to produce a coin-type battery 2.
- Example 2 The same procedure as in Example 1 was conducted except that polyester B (molecular weight: 15,000, Tg: 60 ° C.) different from polyester A was used instead of polyester A as the first binder of the positive electrode first layer. Thus, a battery 2 was produced.
- polyester B molecular weight: 15,000, Tg: 60 ° C.
- Example 3 A battery 2 was produced in the same manner as in Example 1 except that polyester C (molecular weight: 23,000, Tg: 67 ° C.) was used as the first binder for the positive electrode first layer.
- polyester C molecular weight: 23,000, Tg: 67 ° C.
- Example 4 A battery 2 was produced in the same manner as in Example 1 except that polyester D (molecular weight: 18,000, Tg: 68 ° C.) was used as the first binder of the positive electrode first layer.
- polyester D molecular weight: 18,000, Tg: 68 ° C.
- Example 5 A battery 2 was produced in the same manner as in Example 1 except that polyester E (molecular weight: 22,000, Tg: 72 ° C.) was used as the first binder of the positive electrode first layer.
- polyester E molecular weight: 22,000, Tg: 72 ° C.
- Example 6 A battery 2 was produced in the same manner as in Example 1 except that polyester F (molecular weight: 14,000, Tg: 71 ° C.) was used as the first binder for the positive electrode first layer.
- polyester F molecular weight: 14,000, Tg: 71 ° C.
- Example 7 A battery 2 was produced in the same manner as in Example 1 except that polyester G (molecular weight: 11,000, Tg: 36 ° C.) was used as the first binder for the positive electrode first layer.
- polyester G molecular weight: 11,000, Tg: 36 ° C.
- Example 8 A battery 2 was produced in the same manner as in Example 1 except that polyester H (molecular weight: 18,000, Tg: 84 ° C.) was used as the first binder for the positive electrode first layer.
- polyester H molecular weight: 18,000, Tg: 84 ° C.
- Example 9 A battery 2 was produced in the same manner as in Example 1 except that the above-mentioned polyester F was used as the first binder of the positive electrode first layer, and the first binder was equivalently crosslinked with hexamethylene diisocyanate. .
- Example 10 A battery 2 was prepared in the same manner as in Example 1 except that polyurethane A (molecular weight: 20,000, Tg: 68 ° C.) was used as the first binder of the positive electrode first layer and equivalent crosslinking was performed with hexamethylene diisocyanate. Produced.
- polyurethane A molecular weight: 20,000, Tg: 68 ° C.
- Example 11 A battery 2 was prepared in the same manner as in Example 1 except that polyurethane B (molecular weight: 30,000, Tg: 46 ° C.) was used as the first binder of the positive electrode first layer and equivalent crosslinking was performed with hexamethylene diisocyanate. Produced.
- polyurethane B molecular weight: 30,000, Tg: 46 ° C.
- Example 12 Battery 2 was prepared in the same manner as in Example 1 except that polyester urethane A (molecular weight: 40,000, Tg: 83 ° C.) was used as the first binder of the positive electrode first layer and equivalent crosslinking was performed with hexamethylene diisocyanate. Was made.
- polyester urethane A molecular weight: 40,000, Tg: 83 ° C.
- Example 13 Battery 2 was prepared in the same manner as in Example 1 except that polyester urethane B (molecular weight: 25,000, Tg: 73 ° C.) was used as the first binder of the positive electrode first layer and equivalent crosslinking was performed with hexamethylene diisocyanate. Was made.
- polyester urethane B molecular weight: 25,000, Tg: 73 ° C.
- Example 1 Without forming the first positive electrode layer, 92 parts by weight of LiMnO 2 (manufactured by Nippon Kagaku Sangyo) on an aluminum foil current collector (thickness 20 ⁇ m, positive current collector), acetylene black (HS-100, electrochemical) Example 1 except that a positive electrode having a positive electrode second layer formed from 5 parts by weight of industrial) and 3 parts by weight of polyvinylidene fluoride (# 7200, manufactured by Kureha Battery Materials Japan) was used. A battery 100 was produced in the same manner as described above.
- Example 2 A battery was prepared in the same manner as in Example 1 except that acrylic polyol A (molecular weight: 10,000, Tg: 88 ° C.) was used for the first binder of the positive electrode first layer and equivalent crosslinking was performed with hexamethylene diisocyanate. Produced.
- acrylic polyol A molecular weight: 10,000, Tg: 88 ° C.
- Example 3 A battery was prepared in the same manner as in Example 1 except that acrylic polyol B (molecular weight: 37,000, Tg: 77 ° C.) was used as the first binder for the positive electrode first layer and equivalent crosslinking was performed with hexamethylene diisocyanate. Produced.
- acrylic polyol B molecular weight: 37,000, Tg: 77 ° C.
- Example 4 A battery was prepared in the same manner as in Example 1 except that acrylic polyol C (molecular weight: 23,000, Tg: 60 ° C.) was used for the first binder of the positive electrode first layer and equivalent crosslinking was performed with hexamethylene diisocyanate. Produced.
- acrylic polyol C molecular weight: 23,000, Tg: 60 ° C.
- Example 5 A battery was prepared in the same manner as in Example 1 except that acrylic polyol D (molecular weight: 16,000, Tg: 52 ° C.) was used as the first binder for the positive electrode first layer and equivalent crosslinking was performed with hexamethylene diisocyanate. Produced.
- acrylic polyol D molecular weight: 16,000, Tg: 52 ° C.
- Example 6 A battery was fabricated in the same manner as in Example 1, except that acrylic polyol A was used for the first binder of the positive electrode first layer and 5 wt% of lithium carbonate was further added.
- a two-electrode cell (comparative battery 100) was prepared using the first positive electrode layer as a working electrode (positive electrode) and lithium metal as a counter electrode (negative electrode).
- a potentio / galvanostat device (type 1287, manufactured by Solartron) and a frequency response analyzer (type 1260, manufactured by Solartron)
- a sweep rate of 5 mV / s (millivolt per second) and a potential range of 3.0 to 5.0 V
- the potential difference between the positive electrode and the negative electrode was measured while sweeping, and cyclic voltammetry (CV) measurement was performed.
- CV cyclic voltammetry
- the voltage at which the oxidation current was observed at 0.05 mA / cm 2 was used as the oxidation start potential (altering)
- the potential to start When the potential difference between the positive electrode and the negative electrode becomes large and the first binder reaches the oxidation start potential, the first binder starts to change and the electric resistance value of the first binder becomes growing.
- Table 1 shows the CV characteristics of the batteries of Examples and Comparative Examples.
- the oxidation start potential in the table is the potential (V) with respect to the negative electrode made of lithium metal (Li).
- V potential
- the positive electrode first layer caused an oxidation reaction from a relatively low potential of 4.5 V or less.
- the positive electrode first layer causes an oxidation reaction at a relatively high potential of 4.5 V or higher.
- the oxidation start potential of the first binder is decreased from 4.8 V of Comparative Example 2 to 4.46 V. I understood that.
- the acrylic polyol of the first binder was thermally crosslinked, but it was found that the oxidation initiation potential of the first binder was 4.8 V or more. Furthermore, in the battery 2 of Example 9 which has the 1st binder which heat-crosslinked polyester F, it turned out that an oxidation start potential exists in 4.5V vicinity. That is, in the batteries 2 of Examples 1 to 13, the oxidation start potential of the first binder is 4.3 V or more and 4.8 V or less, and more specifically 4.33 V or more and 4.76 or less.
- the voltage drop of the battery 2 of Examples 1 to 9 using polyester A to polyester H as the first binder of the positive electrode first layer was 0.4 to 0.6 V, polyurethane A and B, polyester urethane
- the drop voltage of the battery 2 of Examples 10 to 13 using A and B was 0.4 to 0.5V. From the above, when a positive electrode first layer having a first binder having an oxidation start potential is introduced in the vicinity of 4.4 to 4.8 V, the voltage drop immediately after the start of discharge in the charge / discharge test after the overcharge test is Compared with the battery of Comparative Example 6 having the first binder to which lithium carbonate was added, a substantially equivalent 0.4 to 0.6 V was exhibited. Therefore, the positive electrode first layer in the batteries 2 of Examples 1 to 13 has an increase in internal resistance as well as the positive electrode first layer having the first binder to which lithium carbonate is added, and the effect of suppressing overcharge. I think there is.
- the battery 100 of the comparative example that does not have the positive electrode first layer it has an oxidation start potential of 4.3 V or more, and further, 4.8 V or less, which is the oxidative decomposition start potential of the electrolyte
- the first binder is altered when it is overcharged. It has been found that resistance increases. By increasing the resistance of the first binder, the increasing speed of the potential difference between the positive electrode and the negative electrode is reduced.
- the internal resistance of the batteries 2 of Examples 1 to 13 increased almost equally as compared with the positive electrode first layer having the first binder to which lithium carbonate was added. Therefore, in the batteries 2 of Examples 1 to 13, the temperature rise can be mitigated by the resistance rise, and the shutdown function by the separator can be expressed more accurately. Further, it was confirmed that the discharge capacity and the cycle performance of the batteries 2 of Examples 1 to 13 were substantially the same as those of the comparative battery 100 having no positive electrode first layer. It was also found that the positive electrode first layer having the first binder to which lithium carbonate was added exhibited battery performance higher than the capacity ratio of the 4C discharge capacity to the 0.2C discharge capacity. Therefore, the positive electrode included in the battery 2 of Examples 1 to 13 is excellent in both overcharge suppression capability and battery performance.
- the production cost can be reduced by not using a material that generates gas for the positive electrode 1.
- the first binder is altered and the resistance is increased, and the rate of increase in the potential difference between the positive electrode 1 and the negative electrode 20 is alleviated, resulting in an overcharged state. Heat generation can be suppressed.
- the present inventors have not introduced a compound that generates gas by being decomposed by a voltage increase accompanying overcharge in the positive electrode first layer, and a voltage increase accompanying overcharge.
- the positive electrode first layer has only the first conductive agent that is a conductive filler and the first binder.
- the drying time of the positive electrode first layer can be shortened, and the positive electrode first layer and the positive electrode second layer are continuously formed. Cost reduction by coating is also possible.
- the coating and drying process of the positive electrode first layer can be completed in a very short time. Therefore, a positive electrode 1st layer and a positive electrode 2nd layer can be produced in a continuous manufacturing process, and the raise of electrode manufacturing cost can also be suppressed.
Abstract
Description
本願は、2013年9月30日に日本に出願された特願2013-203874号に基づき優先権を主張し、その内容をここに援用する。
このような電池の発熱を防止する機構は、電池の外部回路だけでなく、以下に説明するように電池の内部にも設けられるようになっている。
特許文献2では、過充電に伴う温度上昇により電極抵抗を上昇させ、過充電を抑止する手法が開示されている。具体的には、正極材料又は負極材料からなる電極合剤層を集電体上に積層する電極において、電極合剤層中、又は電極合剤層と集電体との界面に沿って熱膨張性マイクロカプセルを含有させる。過充電状態になったときにマイクロカプセルが発泡して電極合剤層と集電体とを離間させたりすることで、電極抵抗が上昇する。
特許文献4では、正極集電体、導電剤、結着剤と過充電状態での高電位で分解する物質とから形成された第一層、および、第一層上に形成された正極活物質と導電剤と結着剤とからなる第二層を有する二層構造の正極が開示されている。このように構成された正極は、過充電により高電位となった場合に、高電位で分解する物質が分解されてガスを発生する。
その結果、第一層を構造破壊するとともに、第一層と第二層との界面破壊を生じるように作用し、電池の内部抵抗が上昇することで、充電電流を遮断し、過充電を抑制する。
また、特許文献2に示すように過充電に伴う温度上昇により熱膨張するマイクロカプセルを正極内に導入した場合も、高温保管時にマイクロカプセルが徐々に膨張して正極抵抗を上昇させる為、電池サイクル寿命、高温保存特性が低下するという課題がある。
また、特許文献4に示すように過充電に伴う電圧上昇により分解されてガスを発生する化合物を集電体上の正極第一層内に導入した場合、ガス発生材料導入によりコストが上昇するという課題もある。
上記第一態様において、前記合成高分子は、ポリエステル、ポリウレタン、およびポリエステルウレタンのいずれか一つであってもよい。
上記第二態様において、前記リチウムイオン二次電池用電極と前記負極との間の電位差が4.33V以上4.76V以下になったときに、前記第一の結着剤が変質を開始して前記第一の結着剤の電気抵抗値が大きくなってもよい。
上記第二態様において、前記第一の結着剤は、酸化重合または酸化分解によって変質してもよい。
図1に示すように、本実施形態の正極1は、正極集電体10と、第一の結着剤および第一の導電剤を有し、正極集電体10上に形成された正極第一層11と、正極活物質、第二の結着剤、および第二の導電剤を有し、正極第一層11上であって正極集電体10とは反対側に形成された正極第二層12とを備えている。
正極1は、正極集電体10上に正極第一層11及び正極第二層12が形成された2層構成を有する。
以下、正極1の構成について説明する。
正極集電体10は、特に限定されず、アルミニウム、ステンレス鋼、ニッケルメッキ鋼等の公知の材質を板状に形成した材料を使用することができる。
正極第一層11に含まれる第一の導電剤は、例えばアセチレンブラック、ケッチェンブラック、カーボンブラック、グラファイト(黒鉛)、カーボンナノチューブ等の公知の材料を使用することができる。
正極第二層12に含まれる第二の結着剤としては、従来と同様にポリビニリデンフルオライド(PVDF)等を用いることができる。正極第二層12に含まれる第二の導電剤としては、従来と同様にグラファイト、アルミニウム等を用いることができる。
以下、リチウムイオン二次電池2における正極1以外の構成について説明する。
負極20に含まれる負極活物質は、特に限定されず、リチウム等の金属材料、ケイ素、スズ等を含有する合金系材料、グラファイト、コークス等の炭素材料のような、リチウムイオンを吸蔵・放出できる化合物を単独または組み合わせて用いることができる。また、負極活物質としてリチウム金属箔を用いる場合、銅等の負極集電体上にリチウム箔を圧着して負極20を形成することができる。また負極活物質として合金材料、炭素材料を用いる場合は、負極活物質、結着材、導電助剤等を水、N-メチルピロリドン等の溶媒中で混合した後、銅等の金属製の負極集電体上に塗布、乾燥することで負極20を形成することができる。
負極集電体は、特に限定されず、銅箔などから形成される集電体を使用することができる。
非水電解液22は、特に限定されず、有機溶媒などの溶媒に支持塩を溶解させた電解液、電解質兼溶媒であるイオン液体、そのイオン液体にさらに支持塩を溶解させた電解液等を挙げることができる。
有機溶媒としては、カーボネート類、ハロゲン化炭化水素、エーテル類、ケトン類、ニトリル類、ラクトン類、オキソラン化合物等を用いることができる。また、プロピレンカーボネート、エチレンカーボネート、1,2-ジメトキシエタン、ジメチルカーボネート、ジエチルカーボネート、エチルメチルカーボネート等の混合溶媒を用いることもできる。
非水電解液22に用いられるイオン液体も、常温で液体である塩であれば特に限定されず、例えばアルキルアンモニウム塩、ピロリジニウム塩、ピラゾリウム塩、ピペリジニウム塩、イミダゾリウム塩、ピリジニウム塩、スルホニウム塩、ホスホニウム塩などを挙げることができる。また、イオン液体は、広い電位領域において電気化学的に安定であるとさらに好ましい。
セパレータ21としては、ポリエチレン、ポリプロピレンなどのポリオレフィン製や芳香族ポリアミド樹脂製の微孔膜または不織布、無機セラミック粉末を含む多孔質の樹脂コートなどを挙げることができる。
前記正極1、負極20、非水電解液22、およびセパレータ21を、電解液の漏洩防止、外気進入の防止等を目的とした図2に示す正極ケース24および負極ケース25に収納して、コイン型のリチウムイオン二次電池2を作製することができる。ケース24、25は、金属板などで形成される。
なお、正極ケース24と負極ケース25との間は、絶縁性を有するガスケット26で封止する。
以下、本発明のリチウムイオン二次電池2の実施例および比較例について詳細に説明するが、本リチウムイオン二次電池はこれに限定されない。
まず、アセチレンブラック(HS-100、電気化学工業製)30質量部、及びポリエステルA(分子量:17,000、Tg(ガラス転移点):67℃、第一の結着剤)70質量部を、メチルエチルケトン(MEK)とトルエンとの混合溶媒に添加し、分散処理を行い、均質なペーストを調製した。このペーストをアルミニウム箔製の集電体(厚さ20μm(マイクロメートル)、正極集電体)上に塗布し、乾燥処理を行うことで、正極第一層を得た。乾燥処理後の正極第一層の膜厚は、1~2μmであった。
正極の密度が約2.6g/cm2になるように、乾燥処理後の正極を加圧処理した。
そこに、エチレンカーボネートとジエチルカーボネートとを体積比で3:7に混合した混合有機溶媒中にLiPF6(ヘキサフルオロリン酸リチウム)が1モル/Lの濃度になるように添加した。さらに、ビニレンカーボネートを重量比で2%添加して調製した非水電解液を注入し、コイン型の電池2を作製した。
正極第一層の第一の結着剤に、ポリエステルAに代えて、ポリエステルAとは異なるポリエステルB(分子量:15,000、Tg:60℃)を使用した以外は、実施例1と同様にして電池2を作製した。
正極第一層の第一の結着剤にポリエステルC(分子量:23,000、Tg:67℃)を使用した以外は、実施例1と同様にして電池2を作製した。
正極第一層の第一の結着剤にポリエステルD(分子量:18,000、Tg:68℃)を使用した以外は、実施例1と同様にして電池2を作製した。
正極第一層の第一の結着剤にポリエステルE(分子量:22,000、Tg:72℃)を使用した以外は、実施例1と同様にして電池2を作製した。
正極第一層の第一の結着剤にポリエステルF(分子量:14,000、Tg:71℃)を使用した以外は、実施例1と同様にして電池2を作製した。
正極第一層の第一の結着剤にポリエステルG(分子量:11,000、Tg:36℃)を使用した以外は、実施例1と同様にして電池2を作製した。
正極第一層の第一の結着剤にポリエステルH(分子量:18,000、Tg:84℃)を使用した以外は、実施例1と同様にして電池2を作製した。
正極第一層の第一の結着剤に前述のポリエステルFを使用し、その第一の結着剤をヘキサメチレンジイソシアネートで当量架橋した以外は、実施例1と同様にして電池2を作製した。
正極第一層の第一の結着剤にポリウレタンA(分子量:20,000、Tg:68℃)を使用し、ヘキサメチレンジイソシアネートで当量架橋した以外は、実施例1と同様にして電池2を作製した。
正極第一層の第一の結着剤にポリウレタンB(分子量:30,000、Tg:46℃)を使用し、ヘキサメチレンジイソシアネートで当量架橋した以外は、実施例1と同様にして電池2を作製した。
正極第一層の第一の結着剤にポリエステルウレタンA(分子量:40,000、Tg:83℃)を使用し、ヘキサメチレンジイソシアネートで当量架橋した以外は、実施例1と同様にして電池2を作製した。
正極第一層の第一の結着剤にポリエステルウレタンB(分子量:25,000、Tg:73℃)を使用し、ヘキサメチレンジイソシアネートで当量架橋した以外は、実施例1と同様にして電池2を作製した。
正極第一層を形成することなく、アルミニウム箔製の集電体(厚さ20μm、正極集電体)上にLiMnO2(日本化学産業製)92重量部、アセチレンブラック(HS-100、電気化学工業製)5重量部、及びポリフッ化ビニリデン(♯7200、クレハ・バッテリー・マテリアルズ・ジャパン製)3重量部から形成される正極第二層を形成した正極を使用したこと以外は、実施例1と同様にして電池100を作製した。
正極第一層の第一の結着剤にアクリルポリオールA(分子量:10,000、Tg:88℃)を使用し、ヘキサメチレンジイソシアネートで当量架橋した以外は、実施例1と同様にして電池を作製した。
正極第一層の第一の結着剤にアクリルポリオールB(分子量:37,000、Tg:77℃)を使用し、ヘキサメチレンジイソシアネートで当量架橋した以外は、実施例1と同様にして電池を作製した。
正極第一層の第一の結着剤にアクリルポリオールC(分子量:23,000、Tg:60℃)を使用し、ヘキサメチレンジイソシアネートで当量架橋した以外は、実施例1と同様にして電池を作製した。
正極第一層の第一の結着剤にアクリルポリオールD(分子量:16,000,Tg:52℃)を使用し、ヘキサメチレンジイソシアネートで当量架橋した以外は、実施例1と同様にして電池を作製した。
正極第一層の第一の結着剤にアクリルポリオールAを使用し、さらに炭酸リチウムを5wt%添加した以外は、実施例1と同様にして電池を作製した。
正極評価として、正極第一層の電気化学的挙動の調査を行った。具体的には、上記正極第一層を作用極(正極)、リチウム金属を対極(負極)とした2極セル(比較例の電池100)を作製した。ポテンショ/ガルバノスタット装置(1287型、Solartron社製)と周波数応答アナライザ(1260型、Solartron社製)とを用いて、掃引速度5mV/s(ミリボルト毎秒)、電位範囲3.0~5.0Vで掃引しつつ正極と負極との間の電位差を測定し、サイクリックボルタンメトリー(CV)測定を実施した。
上記の電池100のCV測定において、酸化電流が0.05mA/cm2観測された時点の電圧(前述の電位差)を、正極第一層が含有する第一の結着剤の酸化開始電位(変質を開始する電位)とした。
正極と負極との間の電位差が大きくなり第一の結着剤が酸化開始電位に達したときに、第一の結着剤が変質を開始して第一の結着剤の電気抵抗値が大きくなる。
実施例の電池2を使用し、定電流、定電圧充電にて4.3Vまで充電し、定電流放電にて3.0Vまで放電した。まず、0.1Cでの充放電を2回繰り返した後、0.2Cで充電した。その後、0.2C、1C、2C、4C、6C、10C放電の順番で測定を行い、放電容量レート特性を得た。なお、定電圧充電により0.01mAまで電流値が低下した後、定電流放電に移行するように設定した。
電池2を使用し、0.1Cでの充放電を2回繰り返した後、0.2C充電、1C放電の繰り返しによるサイクル特性評価を実施した。なお、定電圧充電により0.01mAまで電流値が低下した後、定電流放電に移行するように設定した。
上記放電容量評価と同様に、実施例の電池2を使用し、定電流、定電圧充電にて4.3Vまで充電し、定電流放電にて3.0Vまで放電した。
初めに、0.1Cによるならし充放電を2回行った。次に、充放電1回目として、4.3V、0.2C充放電を1度実施した。その後、充放電2回目として、0.2C充電で4.8Vまで定電流、定電圧充電を行うことで過充電を実施し、0.2C放電を行った。さらに、充放電3回目として、4.3V、0.2C充放電を1度実施した。充放電3回目の0.2C放電開始後60秒経過時の降下電圧値を、降下電圧と規定した。
表1に、実施例および比較例の電池のCV特性を示す。表中の酸化開始電位は、リチウム金属(Li)製の負極に対する電位(V)である。実施例1から6、10から13の電池2では、正極第一層が4.5V以下の比較的低電位から酸化反応を生じることが分かった。実施例7および8の電池2では、正極第一層が4.5V以上の比較的高電位で酸化反応を生じることが分かった。
アクリルポリオールAに炭酸リチウムを添加した第一の結着剤を有する比較例6の電池では、第一の結着剤の酸化開始電位が、比較例2の4.8Vから4.46Vに低下することが分かった。
比較例2から5の電池では、第一の結着剤のアクリルポリオールを熱架橋しているが、第一の結着剤の酸化開始電位は4.8V以上であることが分かった。さらに、ポリエステルFを熱架橋した第一の結着剤を有する実施例9の電池2では、4.5V付近に酸化開始電位が存在することが分かった。
すなわち、実施例1から13の電池2では、第一の結着剤の酸化開始電位は4.3V以上4.8V以下であり、より詳しくは4.33V以上4.76以下である。
表2に示す実施例および比較例の電池の放電特性から、正極第一層を備えない比較例1の電池100と比較して、実施例1から13の電池2は、ほぼ同程度の0.2C放電容量を発揮することが分かった。
また、0.2C放電容量に対する4C放電容量の容量比も、実施例1から13のいずれの電池2においても0.76~0.80であり、比較例1の電池100、および比較例2から6の電池とほぼ同程度の4C放電容量を発揮することが分かった。
さらに、50サイクルの容量維持率も、正極第一層の存在有無に関わらず、92~95%を発揮することが分かった。一方で、アクリルポリオールAに炭酸リチウムを添加した正極第一層を有する電池では、0.2C放電容量に対する4C放電容量の容量比が0.73であることが分かった。よって、炭酸リチウムを添加した第一の結着剤を有する正極第一層と比較して、実施例1から13に示すような炭酸リチウムを添加しない正極第一層が、高い電池特性を示すことが分かった。
表3に示す電池および比較例の電池の過充電特性から、正極第一層を備えない正極を有する比較例1の電池100の場合には、降下電圧は0.2Vであった。また、正極第一層の第一の結着剤にアクリルポリオールAからアクリルポリオールDを採用し、正極第二層を積層した正極を使用した場合にも、降下電圧はほぼ同等の0.2~0.3Vであった。さらに、アクリルポリオールAに炭酸リチウムを添加した正極第一層に正極第二層を積層した正極を使用した比較例6の電池の場合には、降下電圧は0.6Vであった。
一方で、正極第一層の第一の結着剤にポリエステルAからポリエステルHを用いた実施例1から9の電池2の降下電圧は0.4~0.6V、ポリウレタンAおよびB、ポリエステルウレタンAおよびBを用いた実施例10から13の電池2の降下電圧は0.4~0.5Vであった。以上より、4.4~4.8V付近に酸化開始電位を有する第一の結着剤を有する正極第一層を導入した場合、過充電試験後の充放電試験における放電開始直後の降下電圧が、炭酸リチウムを添加した第一の結着剤を有する比較例6の電池と比較して、ほぼ同等の0.4~0.6Vを示した。
よって、実施例1から13の電池2における正極第一層が、炭酸リチウムを添加した第一の結着剤を有する正極第一層と同様に内部抵抗の上昇が大きく、過充電を抑制する効果があると考える。
また、炭酸リチウムを添加した第一の結着剤を有する正極第一層と比較して、実施例1から13の電池2がほぼ同等に内部抵抗が上昇することも分かった。よって、実施例1から13の電池2では、抵抗上昇によって温度上昇を緩和できて、セパレータによるシャットダウン機能をより正確に発現できる。
また、正極第一層を有しない比較例の電池100と比較して、実施例1から13の電池2の放電容量、サイクル性能がほぼ同等であることを確認した。さらに、炭酸リチウムを添加した第一の結着剤を有する正極第一層の0.2C放電容量に対する4C放電容量の容量比よりも高い電池性能を示すことも分かった。よって、実施例1から13の電池2が備える正極は、過充電抑制能力と電池性能との両方に優れる。
前記構成を採用することで、正極第一層用の調液工程を煩雑化することなく、添加材料導入によるコスト上昇を回避しながら、安全性を向上させることが可能である。
前記第一の結着剤として、低沸点溶媒に溶解可能な結着剤を採用することで、正極第一層の乾燥時間を短縮化できて、正極第一層と正極第二層との連続塗工によるコスト低減も可能である。
2電池(リチウムイオン二次電池)
10 正極集電体
11 正極第一層
12 正極第二層
20 負極
22 非水電解液
Claims (5)
- 正極集電体と、
エステル結合を有する合成高分子である第一の結着剤、および第一の導電剤を有し、前記正極集電体上に形成された正極第一層と、
正極活物質、第二の結着剤、および第二の導電剤を有し、前記正極第一層の前記正極集電体が形成された面とは反対の面に形成された正極第二層と、
を備えるリチウムイオン二次電池用電極。 - 前記合成高分子は、ポリエステル、ポリウレタン、およびポリエステルウレタンのいずれか一つである請求項1に記載のリチウムイオン二次電池用電極。
- 請求項1または2に記載されたリチウムイオン二次電池用電極と、
リチウムイオンを吸蔵及び放出する負極と、
非水電解液と、
を備えるリチウムイオン二次電池。 - 前記リチウムイオン二次電池用電極と前記負極との間の電位差が4.33V以上4.76V以下になったときに、前記第一の結着剤が変質を開始して前記第一の結着剤の電気抵抗値が大きくなる請求項3に記載のリチウムイオン二次電池。
- 前記第一の結着剤は、酸化重合または酸化分解によって変質する請求項3または4に記載のリチウムイオン二次電池。
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JP2015539413A JPWO2015046492A1 (ja) | 2013-09-30 | 2014-09-29 | リチウムイオン二次電池用電極およびリチウムイオン二次電池 |
KR1020167008283A KR20160065106A (ko) | 2013-09-30 | 2014-09-29 | 리튬 이온 이차 전지용 전극 및 리튬 이온 이차 전지 |
CN201480053737.8A CN105580167A (zh) | 2013-09-30 | 2014-09-29 | 锂离子二次电池用电极和锂离子二次电池 |
US15/083,674 US20160211523A1 (en) | 2013-09-30 | 2016-03-29 | Electrode for lithium ion secondary cells, and lithium ion secondary cell |
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US11316150B2 (en) | 2017-06-23 | 2022-04-26 | Lg Energy Solution, Ltd. | Cathode for lithium secondary battery and lithium secondary battery comprising the same |
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US10038193B1 (en) | 2017-07-28 | 2018-07-31 | EnPower, Inc. | Electrode having an interphase structure |
KR102237952B1 (ko) * | 2017-07-28 | 2021-04-08 | 주식회사 엘지화학 | 이차전지용 양극 및 이를 포함하는 리튬 이차전지 |
JP6816696B2 (ja) * | 2017-10-13 | 2021-01-20 | トヨタ自動車株式会社 | 負極、およびそれを備える非水電解質二次電池 |
US10991942B2 (en) | 2018-03-23 | 2021-04-27 | EnPower, Inc. | Electrochemical cells having one or more multilayer electrodes |
US11245106B2 (en) * | 2018-04-12 | 2022-02-08 | Samsung Sdi Co., Ltd. | Electrode assembly and rechargeable battery including same |
US10998553B1 (en) | 2019-10-31 | 2021-05-04 | EnPower, Inc. | Electrochemical cell with integrated ceramic separator |
CN111781252A (zh) * | 2020-06-18 | 2020-10-16 | 合肥国轩高科动力能源有限公司 | 一种锂离子电池粘结剂电化学稳定性的检测方法 |
US11594784B2 (en) | 2021-07-28 | 2023-02-28 | EnPower, Inc. | Integrated fibrous separator |
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- 2014-09-29 CN CN201480053737.8A patent/CN105580167A/zh active Pending
- 2014-09-29 KR KR1020167008283A patent/KR20160065106A/ko not_active Application Discontinuation
- 2014-09-29 JP JP2015539413A patent/JPWO2015046492A1/ja not_active Withdrawn
- 2014-09-29 TW TW103133676A patent/TW201539845A/zh unknown
- 2014-09-29 WO PCT/JP2014/075823 patent/WO2015046492A1/ja active Application Filing
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2016
- 2016-03-29 US US15/083,674 patent/US20160211523A1/en not_active Abandoned
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US20160211523A1 (en) | 2016-07-21 |
JPWO2015046492A1 (ja) | 2017-03-09 |
TW201539845A (zh) | 2015-10-16 |
KR20160065106A (ko) | 2016-06-08 |
CN105580167A (zh) | 2016-05-11 |
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