WO2014155992A1 - 非水電解質二次電池 - Google Patents
非水電解質二次電池 Download PDFInfo
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- WO2014155992A1 WO2014155992A1 PCT/JP2014/001256 JP2014001256W WO2014155992A1 WO 2014155992 A1 WO2014155992 A1 WO 2014155992A1 JP 2014001256 W JP2014001256 W JP 2014001256W WO 2014155992 A1 WO2014155992 A1 WO 2014155992A1
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- carbonate
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- chain carbonate
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/056—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
- H01M10/0569—Liquid materials characterised by the solvents
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2220/00—Batteries for particular applications
- H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2220/00—Batteries for particular applications
- H01M2220/30—Batteries in portable systems, e.g. mobile phone, laptop
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2300/00—Electrolytes
- H01M2300/0017—Non-aqueous electrolytes
- H01M2300/0025—Organic electrolyte
- H01M2300/0028—Organic electrolyte characterised by the solvent
- H01M2300/0037—Mixture of solvents
- H01M2300/004—Three solvents
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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 technique for a non-aqueous electrolyte secondary battery including a negative electrode containing lithium titanate.
- non-aqueous electrolyte secondary batteries represented by lithium ion secondary batteries are frequently used in consumer applications such as small portable devices because of their high energy density.
- a typical lithium ion secondary battery includes a transition metal oxide such as LiCoO 2 as a positive electrode active material, a carbon material such as graphite as a negative electrode active material, and an electrolyte salt such as LiPF 6 as an electrolytic solution and a nonaqueous solvent such as a carbonate ester.
- LiPF 6 lithium ion secondary battery
- a non-aqueous electrolyte dissolved in is used.
- lithium titanate in which lithium ion insertion / extraction reactions occur at a noble potential compared to a carbon material of about 1.5 V with respect to the lithium potential, has been proposed as a negative electrode active material.
- lithium titanate is used as a negative electrode active material, and a non-aqueous electrolyte using a mixed solvent of a cyclic carbonate such as propylene carbonate and a chain carbonate such as diethyl carbonate as a non-aqueous solvent of a non-aqueous electrolyte.
- Secondary batteries have been proposed.
- Patent Document 2 discloses a non-aqueous electrolyte secondary that uses lithium titanate as a negative electrode active material and a mixed solvent of cyclic carbonate, dimethyl carbonate, and ethyl methyl carbonate as a non-aqueous solvent for a non-aqueous electrolyte. Batteries have been proposed.
- non-aqueous electrolyte secondary batteries will be made medium and large in size and applied as power storage equipment power supplies or in-vehicle power supplies such as HEVs.
- high reliability is required and excellent cycle characteristics are required.
- the negative electrode active material is lithium titanate
- gas generation due to decomposition of the nonaqueous electrolyte increases during charge / discharge of the nonaqueous electrolyte secondary battery depending on the type and mixing ratio of the nonaqueous solvent. This causes a decrease in reliability due to an increase in internal pressure of the secondary battery, and consequently a decrease in cycle characteristics.
- an object of the present invention is to provide a non-aqueous electrolyte secondary battery that suppresses gas generation due to decomposition of the non-aqueous electrolyte and suppresses deterioration of cycle characteristics.
- a nonaqueous electrolyte secondary battery includes a positive electrode, a negative electrode including lithium titanate, a separator interposed between the positive electrode and the negative electrode, a nonaqueous electrolyte including an electrolyte salt and a nonaqueous solvent
- the non-aqueous solvent is propylene carbonate, a linear carbonate A represented by the general formula R 1 OCOOR 2 (R 1 and R 2 are alkyl groups having 2 or more carbon atoms), and a general formula R 3 OCOOR 4 ( R 3 is a methyl group and R 4 is an alkyl group), and the volume fraction of propylene carbonate in the non-aqueous solvent is in the range of 25 to 33% by volume.
- the volume fraction of the chain carbonate A is 65 to 74% by volume
- the volume fraction of the chain carbonate B in the non-aqueous solvent is 1 to 10% by volume.
- non-aqueous electrolyte secondary battery that suppresses gas generation due to decomposition of the non-aqueous electrolyte and suppresses deterioration of cycle characteristics.
- FIG. 6 is a diagram showing the results of cycle characteristics of test cells 1 to 5;
- FIG. 6 is a graph showing the results of cell volume increase rates of test cells 1 to 5; It is a figure which shows the result of the cell volume increase rate of the test cells 6-13.
- FIG. 1 is a schematic cross-sectional view showing an example of the configuration of the nonaqueous electrolyte secondary battery according to this embodiment.
- a nonaqueous electrolyte secondary battery 30 shown in FIG. 1 includes a negative electrode 1, a positive electrode 2, a separator 3 interposed between the negative electrode 1 and the positive electrode 2, a nonaqueous electrolyte (electrolytic solution), and a cylindrical battery case. 4 and a sealing plate 5.
- the nonaqueous electrolyte is injected into the battery case 4.
- the negative electrode 1 and the positive electrode 2 are wound with a separator 3 interposed therebetween, and constitute a wound electrode group together with the separator 3.
- An upper insulating plate 6 and a lower insulating plate 7 are attached to both ends in the longitudinal direction of the wound electrode group and are accommodated in the battery case 4.
- One end of a positive electrode lead 8 is connected to the positive electrode 2, and the other end of the positive electrode lead 8 is connected to a positive electrode terminal 10 provided on the sealing plate 5.
- One end of a negative electrode lead 9 is connected to the negative electrode 1, and the other end of the negative electrode lead 9 is connected to the inner bottom of the battery case 4.
- the lead and the member are connected by welding or the like.
- the open end of the battery case 4 is caulked to the sealing plate 5, and the battery case 4 is sealed.
- the negative electrode 1 includes a negative electrode current collector and a negative electrode active material layer provided on the negative electrode current collector.
- the negative electrode active material layer is preferably disposed on both sides of the negative electrode current collector, but may be provided on one side of the negative electrode current collector.
- the negative electrode active material layer includes a negative electrode active material, and in addition, a negative electrode additive and the like may be added.
- the negative electrode active material contains lithium titanate.
- Lithium titanate is preferably lithium titanate represented by the chemical formula Li 4 + x Ti 5 O 12 (0 ⁇ x ⁇ 3), for example, from the viewpoint of suppressing gas generation and cycle characteristic deterioration, Li and more preferably lithium titanate expressed by 4 Ti 5 O 12.
- lithium titanate may be used in which a part of Ti or Li is replaced with another element such as Fe or Mn.
- Na, K, Si, B, Al, P, Cl, and Mb may be contained.
- the negative electrode active material may contain a known negative electrode active material used for nonaqueous electrolyte secondary batteries such as lithium ion batteries in addition to the above lithium titanate, and includes, for example, a carbon-based active material and silicon. Examples thereof include silicon-based active materials. Examples of the carbon-based active material include artificial graphite, natural graphite, non-graphitizable carbon, and graphitizable carbon. Examples of the silicon-based active material include silicon, silicon compounds, partially substituted products and solid solutions thereof. As the silicon compound, for example, silicon oxide represented by SiO a (0.05 ⁇ a ⁇ 1.95) is preferable.
- the negative electrode additive is, for example, a binder or a conductive agent.
- the conductive agent include carbon black including acetylene black, graphite, and fibrous graphite.
- the binder include fluorine resins such as polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and fluorine rubber, styrene-butadiene rubber, polyacrylic acid, and the like.
- the negative electrode current collector is made of, for example, a known conductive material used for a nonaqueous electrolyte secondary battery such as a lithium ion battery, and examples thereof include a nonporous conductive substrate such as a metal foil.
- a metal foil for example, a copper foil or an aluminum foil is preferable.
- the thickness of the negative electrode current collector is preferably in the range of about 1 ⁇ m to 500 ⁇ m, for example.
- the nonaqueous electrolyte used in the present embodiment includes a supporting electrolyte salt and a nonaqueous solvent.
- the non-aqueous solvent includes propylene carbonate, a chain carbonate A represented by the general formula R 1 OCOOR 2 (R 1 and R 2 are alkyl groups having 2 or more carbon atoms), and a general formula R 3 OCOOR 4 (R 3 Is a chain carbonate B represented by a methyl group and R 4 is an alkyl group).
- Propylene carbonate is a suitable non-aqueous solvent from the viewpoint of viscosity, electrical conductivity, etc., but it is considered that gas generation occurs due to decomposition of propylene carbonate by reaction with lithium titanate during charging and discharging. .
- ethylene carbonate which is widely used as a non-aqueous electrolyte solvent for batteries using carbon-based negative electrodes such as graphite
- gas generation is reduced, but it remains one of the problems.
- chain carbonate A and chain carbonate B are added, gas generation can be further reduced. This is considered due to the following effects.
- chain carbonate A and chain carbonate B When chain carbonate A and chain carbonate B are added, they react with lithium titanate and decompose before propylene carbonate, so that a film is formed on lithium titanate. Since this coating protects the lithium titanate surface, decomposition of propylene carbonate is suppressed, so that it is considered that gas generation due to decomposition of the nonaqueous electrolyte can be suppressed as compared with the case of using propylene carbonate alone as a nonaqueous solvent. .
- the chain carbonate B has an alkyl group having 2 or more carbon atoms as an alkyl group bonded to both ends of the carbonate group, whereas the chain carbonate A has a methyl group having 1 carbon atom. Have one or more.
- This methyl group has a smaller steric hindrance than the alkyl group having 2 or more carbon atoms, and the chain carbonate B is more reactive than the chain carbonate A. From this, it is considered that a film mainly derived from the chain carbonate B is formed on the lithium titanate because it reacts and decomposes preferentially over the chain carbonate A having no methyl group. .
- the decomposition of the nonaqueous electrolyte is more effective than the case where the mixed solvent of propylene carbonate and chain carbonate A is a nonaqueous solvent. It is thought that gas is suppressed.
- propylene carbonate is a high dielectric constant solvent, it has the effect of dissociating the anion and cation of the supporting electrolyte salt, which is a solute, and increasing the conductivity due to ions. Since the dissociation of the electrolyte salt is suppressed, the conductivity of the non-aqueous electrolyte is lowered, and the battery performance is similarly lowered.
- the content of the chain carbonate A the direct influence by the size is small, but the content of the propylene carbonate and the chain carbonate B relatively increases and decreases, which causes the battery performance deterioration for the above reason. Become.
- the volume fraction of propylene carbonate in the non-aqueous solvent is in the range of 25 to 33% by volume, and the volume fraction of the chain carbonate A in the non-aqueous solvent is in the range of 65 to 74% by volume.
- the volume fraction of the chain carbonate B is in the range of 1 to 10% by volume.
- the volume fraction of propylene carbonate in the non-aqueous solvent is in the range of 25 to 33% by volume, and the volume fraction of chain carbonate A in the non-aqueous solvent is 65 to 74 volumes.
- the volume fraction of the chain carbonate B in the nonaqueous solvent is in the range of 1 to 10% by volume, thereby suppressing gas generation due to decomposition of the nonaqueous electrolyte and suppressing deterioration of cycle characteristics. It becomes possible.
- the volume fraction of propylene carbonate in the non-aqueous solvent is less than 25% by volume, the conductivity of the non-aqueous electrolyte is decreased due to an increase in the viscosity of the non-aqueous electrolyte or a decrease in the dissociation degree of the supporting electrolyte salt.
- the battery performance of the nonaqueous electrolyte secondary battery is degraded.
- the volume fraction of propylene carbonate in the non-aqueous solvent exceeds 33% by volume, the amount of reaction with lithium titanate increases, so that more propylene carbonate is decomposed and more gas is generated. It is.
- volume fraction of the chain carbonate A in the non-aqueous solvent is less than 65% by volume or the volume fraction of the chain carbonate B is less than 1% by volume, the decomposition of propylene carbonate is not sufficiently suppressed, and gas generation and Deterioration of cycle characteristics cannot be suppressed.
- the volume fraction of the linear carbonate A in the non-aqueous solvent is more than 75% by volume, the volume fraction of the propylene carbonate is relatively less than 25% by volume, which leads to a decrease in battery performance for the above reason. .
- the volume fraction of the chain carbonate B is more than 10% by volume, an increase in gas generation or a decrease in cycle characteristics due to the decomposition of the chain carbonate B itself cannot be suppressed.
- the chain carbonate A represented by the general formula R 1 OCOOR 2 (R 1 and R 2 are alkyl groups having 2 or more carbon atoms) is, for example, diethyl carbonate, ethyl isopropyl carbonate, dipropyl carbonate, diisopropyl carbonate, dibutyl carbonate, And a mixture containing at least two of them, and from the viewpoint of suppressing the deterioration of cycle characteristics, and also from the viewpoint of viscosity and the like affecting the conductivity of the nonaqueous electrolyte, it should be diethyl carbonate. preferable.
- Examples of the chain carbonate B represented by the general formula R 3 OCOOR 4 (R 3 is a methyl group, R 4 is an alkyl group) include dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, and the like. From the viewpoint of reducing gas generation due to decomposition of the electrolyte, dimethyl carbonate, ethyl methyl carbonate, a mixture thereof, and the like are preferable. Furthermore, it is more preferable that it is a dimethyl carbonate considered that the both terminal is a methyl group and is more reactive.
- the non-aqueous solvent of the present embodiment is not prevented from containing other than those specifically described above, and examples thereof include cyclic ethers such as tetrahydrofuran (THF) and 2-methyltetrahydrofuran (2MeTHF), and dimethoxyethane. It may contain a chain ether such as (DME), ⁇ -butyrolactone (GBL), acetonitrile (AN), sulfolane (SL), various ionic liquids, various room temperature molten salts, and the like.
- cyclic ethers such as tetrahydrofuran (THF) and 2-methyltetrahydrofuran (2MeTHF), and dimethoxyethane.
- It may contain a chain ether such as (DME), ⁇ -butyrolactone (GBL), acetonitrile (AN), sulfolane (SL), various ionic liquids, various room temperature molten salts, and the like.
- DME
- the supporting electrolyte salt used in the present embodiment is not particularly limited.
- LiClO 4 , LiBF 4 , LiAsF 6 , LiPF 6 , LiPF (CF 3 ) 5 , LiPF 2 (CF 3 ) 4 , LiPF 3 ( CF 3 ) 3 , LiPF 4 (CF 3 ) 2 , LiPF 5 (CF 3 ), LiPF 3 (C 2 F 5 ) 3 , LiCF 3 SO 3 , LiN (CF 3 SO 2 ) 2 , LiN (C 2 F 5 SO 2 ) 2 , LiN (C 2 F 5 CO) 2 , LiI, LiAlCl 4 , LiBC 4 O 8 and the like can be used alone or in admixture of two or more.
- the ion conductivity of the nonaqueous electrolyte uses LiPF 6 from becoming better.
- the supporting electrolyte salt concentration is preferably 0.5 to 2.0 mol / L. Further, it is more preferably 1.5 to 2.0 mol / L.
- carbonates such as vinylene carbonate and butylene carbonate in the electrolyte salt, compounds having a benzene ring such as biphenyl and cyclohexylbenzene, sulfur-containing compounds such as propane sultone, propene sultone, and ethylene sulfide, hydrogen fluoride, triazole type At least one selected from the group consisting of cyclic compounds, fluorine-containing esters, hydrogen fluoride complexes of tetraethylammonium fluoride or derivatives thereof, phosphazenes and derivatives thereof, amide group-containing compounds, imino group-containing compounds, or nitrogen-containing compounds. It can be used even if it contains seeds. Moreover, CO 2, NO 2, CO , also contain at least one selected from such SO 2 may be used.
- the positive electrode 2 includes a positive electrode current collector and a positive electrode active material layer.
- the positive electrode active material layer is preferably disposed on both sides of the positive electrode current collector, but may be disposed only on one side of the positive electrode current collector.
- the positive electrode active material layer contains a positive electrode active material, and in addition, a positive electrode additive may be added.
- the positive electrode active material examples include known positive electrode active materials used for non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries, and include lithium-containing composite metal oxides, lithium cobalt oxide (LiCoO 2 ), and nickel cobalt. Examples thereof include layered oxides such as lithium manganate (LiNiCoMnO 2 ) and nickel cobalt lithium aluminate (LiNiCoAlO 2 ), and spinel composite oxides such as lithium manganate (LiMn 2 O 4 ).
- the volume energy density is high lithium cobaltate (LiCoO 2), lithium nickel cobalt manganese oxide (LiNiCoMnO 2), include layered oxides such as lithium nickel cobalt aluminate (LiNiCoAlO 2).
- the positive electrode additive is, for example, a binder or a conductive agent.
- the same material as that used for the negative electrode 1 can be used for the binder and the conductive agent.
- the positive electrode current collector is made of, for example, a known conductive material used for a non-aqueous electrolyte secondary battery such as a lithium ion battery, and examples thereof include a nonporous conductive substrate such as a metal foil.
- a metal foil for example, an aluminum foil is preferable.
- the thickness of the positive electrode current collector is preferably in the range of, for example, about 1 ⁇ m or more and 500 ⁇ m or less.
- the separator 3 for example, a microporous film such as polyolefin or aramid resin or a non-woven fabric having a predetermined air permeability, mechanical strength, insulation, etc., or a sheet obtained by beating and papermaking cellulose fibers, etc. are used.
- the thickness of the separator 3 is preferably in the range of about 10 ⁇ m to 300 ⁇ m, for example.
- the porosity of the separator 3 is preferably in the range of about 30% to 70%. The porosity is a percentage of the total volume of the pores of the separator 3 with respect to the volume of the separator 3.
- the nonaqueous electrolyte secondary battery 30 in FIG. 1 is a cylindrical battery including a wound electrode group, but the battery shape is not particularly limited.
- the battery is a square battery, a flat battery, or a coin battery.
- a laminated film pack battery or the like may be used.
- LiNi 0.80 Co 0.15 Al 0.05 O 2 was prepared as a positive electrode material.
- an alkaline solution containing sodium hydroxide was dropped into an aqueous solution in which nickel sulfate and cobalt sulfate in a predetermined ratio were dissolved to obtain a precipitate of hydroxide.
- This hydroxide was dispersed in an aqueous NaAlO 2 solution and neutralized with sulfuric acid, so that aluminum hydroxide was uniformly deposited on the surface of the hydroxide. Thereafter, in an air atmosphere, and calcined at 700 ° C. 10 hours, an oxide of ternary [Ni 0.80 Co 0.15 Al 0.05] to give the O.
- lithium hydroxide monohydrate powder was mixed with the obtained oxide so that the ratio of the number of moles of Ni, Co, and Al combined to the number of moles of Li was 1: 1, and an oxygen atmosphere
- the temperature was raised to 750 ° C. in 10 hours, and heat treatment was performed at 750 ° C. for 36 hours to obtain the target LiNi 0.80 Co 0.15 Al 0.05 O 2 .
- the positive electrode active material LiNi 0.80 Co 0.15 Al 0.05 O 2 obtained as described above, acetylene black powder as a conductive agent, and polyvinylidene fluoride (PVdF) as a binder, are mixed so that the mass ratio of the active material, the conductive agent, and the binder is 100: 3: 4, and then N-methyl-2-pyrrolidone as a dispersion medium is added and kneaded. A slurry was prepared.
- This positive electrode slurry was applied to both surfaces of an aluminum foil (thickness 15 ⁇ m) as a positive electrode current collector and dried to produce a positive electrode active material layer on the aluminum foil, and then rolled with a rolling roller to produce a positive electrode.
- a positive electrode lead made of aluminum was attached to the obtained positive electrode.
- Li 4 Ti 5 O 12 was prepared as a negative electrode material. After mixing titanium dioxide and lithium hydroxide, heat treatment was performed in air at 850 ° C. for 15 hours to obtain the target Li 4 Ti 5 O 12 .
- Test cell A positive electrode, a negative electrode, and a separator were interposed between the positive electrode and the negative electrode prepared as described above, and the obtained laminate was wound to prepare an electrode group.
- the electrode group is accommodated in an aluminum laminate film container as an outer package, and the nonaqueous electrolytes 1 to 5 are injected into the aluminum laminate film container containing the electrode group, and then the aluminum laminate film container Test cells 1 to 5 were prepared by heat-sealing and sealing the openings.
- the positive electrode lead and the negative electrode lead were taken out of the container through the heat-sealed portion while maintaining hermeticity.
- Test cells 1 to 5 were housed in a constant temperature bath at 20 ° C. and charged / discharged by the following constant current / constant voltage method. Each of the test cells 1 to 5 was charged at a constant current of 1C rate (1C is a current value that can use up the entire battery capacity in 1 hour) until the battery voltage reaches 2.8V. After the battery voltage reached 2.8V, each test cell was charged at a constant voltage of 2.8V until the current value reached 0.05C. Next, after resting for 20 minutes, the test cell after charging was discharged at a high rate constant current of C rate until the battery voltage became 1.5V. Such charging / discharging was repeated 800 cycles.
- 1C rate 1C is a current value that can use up the entire battery capacity in 1 hour
- the ratio of the total discharge capacity of each subsequent cycle to the total discharge capacity of the first cycle (value obtained as a percentage value) was calculated, and these are summarized in FIG. 2 as the discharge capacity maintenance ratio. It can be said that the lower the discharge capacity retention rate, the lower the cycle characteristics.
- FIG. 2 is a diagram showing the results of the cycle characteristics of the test cells 1 to 5
- FIG. 3 is a diagram showing the results of the cell volume increase rate of the test cells 1 to 5.
- test cell 2 using a mixed solvent of 25% by volume of propylene carbonate, 70% by volume of diethyl carbonate and 5% by volume of dimethyl carbonate, and 25% by volume of propylene carbonate In the test cell 3 using a mixed solvent of 65% by volume of diethyl carbonate and 10% by volume of dimethyl carbonate, gas generation was suppressed from other test cells, and 25% by volume of propylene carbonate and 75% by volume of diethyl carbonate. Like the test cell 1 using the mixed solvent, the deterioration of the cycle characteristics was suppressed.
- test cell 4 using a mixed solvent of 25% by volume of propylene carbonate, 60% by volume of diethyl carbonate and 15% by volume of dimethyl carbonate, 25% by volume of propylene carbonate, 55% by volume of diethyl carbonate, and dimethyl carbonate
- test cell 5 using a mixed solvent of 20% by volume, gas generation was increased as compared with the test cell 1 to which dimethyl carbonate was not added, and deterioration in cycle characteristics could not be suppressed.
- Example 2 (6) 25% by volume of propylene carbonate, 75% by volume of diethyl carbonate, (7) 33% by volume of propylene carbonate, 66% by volume of diethyl carbonate, (8) 40% by volume of propylene carbonate, 60% by volume of diethyl carbonate (9) 45% by volume of propylene carbonate, 55% by volume of diethyl carbonate, (10) 50% by volume of propylene carbonate, 50% by volume of diethyl carbonate, (11) 55% by volume of propylene carbonate, 45% by volume of diethyl carbonate %, (12) 60% by volume of propylene carbonate, 40% by volume of diethyl carbonate, (13) lithium hexafluorophosphate (based on a mixed solvent of 90% by volume of propylene carbonate and 10% by volume of diethyl carbonate ( L PF 6) was dissolved to a concentration of 1.2 mol / L, except that to prepare a non-aqueous electrolyte 6-13
- the volume of the test cells 6 to 13 before charging / discharging was measured. Then, charging and discharging were repeated 300 cycles by the same constant current and constant voltage method as described above, and the volumes of the test cells 6 to 13 after 300 cycles were measured.
- the ratio of the volume of the test cells 6 to 13 after 300 cycles with respect to the volume of the test cells 6 to 13 before charging / discharging was calculated and summarized as the cell volume increase rate in FIG.
- FIG. 4 is a diagram showing the results of the cell volume increase rate of the test cells 6 to 13.
- test cells 6 and 7 using a mixed solvent with propylene carbonate being 33% by volume or less are more gas than other test cells using a mixed solvent with propylene carbonate being more than 33% by volume. Occurrence was suppressed.
- test cell 3 using a mixed solvent of 10% by volume and 10% by volume of dimethyl carbonate gas generation increased.
- propylene carbonate is mainly contained in a range of 25 to 33% by volume, and dimethyl carbonate (that is, general formula R 3 OCOOR 4 (R 3 is a methyl group, R 3 4 is a chain carbonate B) represented by an alkyl group) in the range of 1 to 10% by volume.
- dimethyl carbonate that is, general formula R 3 OCOOR 4 (R 3 is a methyl group, R 3 4 is a chain carbonate B) represented by an alkyl group
- diethyl carbonate namely, linear carbonate A represented by the general formula R 1 OCOOR 2 (R 1 and R 2 are alkyl groups having 2 or more carbon atoms)
- R 1 OCOOR 2 R 1 and R 2 are alkyl groups having 2 or more carbon atoms
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Abstract
Description
[正極活物質の作製]
正極材料としてLiNi0.80Co0.15Al0.05O2を準備した。まず、所定比率の硫酸ニッケルと硫酸コバルトを溶解した水溶液に、水酸化ナトリウムを含むアルカリ溶液を滴下して水酸化物の沈殿を得た。この水酸化物をNaAlO2水溶液中に分散させ、硫酸を用いて中和することにより水酸化アルミニウムを水酸化物の表面に均一に析出させた。その後、空気雰囲気中、700℃で10時間焼成し、3元系の酸化物である[Ni0.80Co0.15Al0.05]Oを得た。さらに、得られた酸化物に、Ni、Co、Alを合わせたモル数とLiのモル数との比が1:1になるように水酸化リチウム一水和物の粉末を混合し、酸素雰囲気中で750℃まで10時間で昇温し、750℃で熱処理を36時間行うことにより、目的とするLiNi0.80Co0.15Al0.05O2を得た。
上記のようにして得られた正極活物質(LiNi0.80Co0.15Al0.05O2)と、導電剤としてのアセチレンブラック粉末と、結着剤としてのポリフッ化ビニリデン(PVdF)とを、活物質と導電剤と結着剤との質量比が100:3:4の割合になるように混合した後、分散媒としてのN-メチル-2-ピロリドンを添加して混練し、正極スラリーを調製した。この正極スラリーを、正極集電体としてのアルミニウム箔(厚み15μm)の両面に塗布、乾燥し、アルミニウム箔上に正極活物質層を作製した後、圧延ローラにより圧延し、正極を作製した。得られた正極にはアルミニウム製の正極リードを取り付けた。
負極材料としてLi4Ti5O12を準備した。二酸化チタンと水酸化リチウムを混合したのち、空気中にて850℃で15時間加熱処理することにり、目的とするLi4Ti5O12を得た。
この負極活物質(Li4Ti5O12)と、導電剤としてのアセチレンブラック粉末と、結着剤としてのポリフッ化ビニリデン(PVdF)とを、活物質と導電剤と結着剤との質量比が100:3:4の割合になるように混合した後、分散媒としてのN-メチル-2-ピロリドンを添加して混練し、負極スラリーを調製した。この負極スラリーを、負極集電体としてのアルミニウム箔(厚み15μm)の両面に塗布、乾燥し、アルミニウム箔上に負極活物質層を作製した後、圧延ローラにより圧延し、負極を作製した。得られた負極にはアルミニウム製の負極リードを取り付けた。
プロピレンカーボネートを25体積%に固定し、(1)ジエチルカーボネート75体積%、(2)ジエチルカーボネート70体積%とジメチルカーボネート5体積%、(3)ジエチルカーボネート65体積%とジメチルカーボネート10体積%、(4)ジエチルカーボネート60体積%とジメチルカーボネート15体積%、(5)ジエチルカーボネート55体積%とジメチルカーボネート20体積%で混合した混合溶媒に対し、支持電解質塩としての六フッ化リン酸リチウム(LiPF6)を1.2mol/Lの濃度になるように溶解させて、非水電解質1~5を調製した。
上記のように作製した正極、負極、正極と負極との間にセパレータを介在させて積層し、得られた積層物を捲回して、電極群を作製した。該電極群を外装体としてのアルミラミネートフィルム製容器に収容し、前述の非水電解質1~5を、前記の電極群を収容したアルミラミネートフィルム製容器に注液した後、アルミラミネートフィルム製容器の開口部を加熱融着して密閉し、試験セル1~5を作製した。正極リードおよび負極リードは前記加熱融着部分を通して、密閉性を保持した状態で容器外部に取り出した。
試験セル1~5を20℃の恒温槽に収容し、以下のような定電流定電圧方式で充放電した。各試験セル1~5を、電池電圧が2.8Vになるまで1Cレート(1Cとは1時間で全電池容量を使い切ることができる電流値)の定電流で充電した。電池電圧が2.8Vに達した後は、電流値が0.05Cになるまで、各試験セルを2.8Vの定電圧で充電した。次に、20分間休止した後、充電後の試験セルを、Cレートのハイレートの定電流で、電池電圧が1.5Vになるまで放電した。このような充放電を800サイクル繰り返した。1サイクル目の全放電容量に対するその後の各サイクルの全放電容量の割合(百分率値で求めた値)を算出し、これを放電容量維持率として図2にまとめた。放電容量維持率が低い程、サイクル特性が低下したと言える。
充放電前の試験セル1~5の体積を測定した。そして、前述と同様の定電流定電圧方式で充放電を300サイクル繰り返し、300サイクル後の試験セル1~5の体積を測定した。充放電前の試験セル1~5の体積に対する300サイクル後の試験セル1~5の体積の割合(百分率値で求めた値)を算出し、これをセル体積増加率として図3にまとめた。セル体積増加率が大きいほど、試験セル内部でのガス発生により電池が膨れたと言える。
(6)プロピレンカーボネートを25体積%、ジエチルカーボネートを75体積%、(7)プロピレンカーボネートを33体積%、ジエチルカーボネートを66体積%、(8)プロピレンカーボネートを40体積%、ジエチルカーボネートを60体積%、(9)プロピレンカーボネートを45体積%、ジエチルカーボネートを55体積%、(10)プロピレンカーボネートを50体積%、ジエチルカーボネートを50体積%、(11)プロピレンカーボネートを55体積%、ジエチルカーボネートを45体積%、(12)プロピレンカーボネートを60体積%、ジエチルカーボネートを40体積%、(13)プロピレンカーボネートを90体積%、ジエチルカーボネートを10体積%で混合した混合溶媒に対し、六フッ化リン酸リチウム(LiPF6)を1.2mol/Lの濃度になるように溶解させて、非水電解質6~13を調製したこと以外は、実施例1と同様の試験セルを作製した。これらを試験セル6~13とした。
Claims (3)
- 正極と、チタン酸リチウムを含む負極と、前記正極と前記負極との間に介在するセパレータと、電解質塩及び非水溶媒を含む非水電解質と、を備える非水電解質二次電池であって、
前記非水溶媒は、プロピレンカーボネートと、一般式R1OCOOR2(R1及びR2は炭素数2以上のアルキル基)で表される鎖状カーボネートAと、一般式R3OCOOR4(R3はメチル基、R4はアルキル基)で表される鎖状カーボネートBとを含み、
前記非水溶媒中の前記プロピレンカーボネートの体積分率は25~33体積%の範囲であり、前記非水溶媒中の前記鎖状カーボネートAの体積分率は65~74体積%の範囲であり、前記非水溶媒中の前記鎖状カーボネートBの体積分率は1~10体積%の範囲であることを特徴とする非水電解質二次電池。 - 前記鎖状カーボネートBは、ジメチルカーボネート、エチルメチルカーボネート、又はそれらの混合物から選択されることを特徴とする請求項1記載の非水電解質二次電池。
- 前記鎖状カーボネートAはジエチルカーボネートであることを特徴とする請求項1記載の非水電解質二次電池。
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WO2021132203A1 (ja) * | 2019-12-27 | 2021-07-01 | パナソニックIpマネジメント株式会社 | 非水電解質二次電池用セパレータ、非水電解質二次電池、及び非水電解質二次電池用セパレータの製造方法 |
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