CN1698232A - Nonaqueous electrolytic solution and lithium secondary battery - Google Patents
Nonaqueous electrolytic solution and lithium secondary battery Download PDFInfo
- Publication number
- CN1698232A CN1698232A CNA200480000437XA CN200480000437A CN1698232A CN 1698232 A CN1698232 A CN 1698232A CN A200480000437X A CNA200480000437X A CN A200480000437XA CN 200480000437 A CN200480000437 A CN 200480000437A CN 1698232 A CN1698232 A CN 1698232A
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- CN
- China
- Prior art keywords
- carbonate
- electrolyte solution
- lithium salt
- lithium
- mol
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
- 239000008151 electrolyte solution Substances 0.000 title claims abstract description 68
- 229910052744 lithium Inorganic materials 0.000 title claims abstract description 60
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 title claims abstract description 59
- 229910003002 lithium salt Inorganic materials 0.000 claims abstract description 77
- 159000000002 lithium salts Chemical class 0.000 claims abstract description 77
- KMTRUDSVKNLOMY-UHFFFAOYSA-N Ethylene carbonate Chemical compound O=C1OCCO1 KMTRUDSVKNLOMY-UHFFFAOYSA-N 0.000 claims abstract description 58
- VAYTZRYEBVHVLE-UHFFFAOYSA-N 1,3-dioxol-2-one Chemical compound O=C1OC=CO1 VAYTZRYEBVHVLE-UHFFFAOYSA-N 0.000 claims abstract description 46
- 239000002904 solvent Substances 0.000 claims abstract description 37
- 229910001290 LiPF6 Inorganic materials 0.000 claims abstract description 31
- 229910001496 lithium tetrafluoroborate Inorganic materials 0.000 claims abstract description 29
- RUOJZAUFBMNUDX-UHFFFAOYSA-N propylene carbonate Chemical compound CC1COC(=O)O1 RUOJZAUFBMNUDX-UHFFFAOYSA-N 0.000 claims abstract description 26
- 150000001875 compounds Chemical class 0.000 claims abstract description 13
- BVKZGUZCCUSVTD-UHFFFAOYSA-L Carbonate Chemical compound [O-]C([O-])=O BVKZGUZCCUSVTD-UHFFFAOYSA-L 0.000 claims abstract description 8
- 239000011255 nonaqueous electrolyte Substances 0.000 claims description 53
- 150000005678 chain carbonates Chemical class 0.000 claims description 44
- IEJIGPNLZYLLBP-UHFFFAOYSA-N dimethyl carbonate Chemical group COC(=O)OC IEJIGPNLZYLLBP-UHFFFAOYSA-N 0.000 claims description 29
- 229910013872 LiPF Inorganic materials 0.000 claims description 27
- 101150058243 Lipf gene Proteins 0.000 claims description 27
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical group CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 claims description 21
- 125000004432 carbon atom Chemical group C* 0.000 claims description 19
- OIFBSDVPJOWBCH-UHFFFAOYSA-N Diethyl carbonate Chemical compound CCOC(=O)OCC OIFBSDVPJOWBCH-UHFFFAOYSA-N 0.000 claims description 18
- 125000002947 alkylene group Chemical group 0.000 claims description 17
- 229910013075 LiBF Inorganic materials 0.000 claims description 12
- 229910052731 fluorine Inorganic materials 0.000 claims description 12
- 239000003575 carbonaceous material Substances 0.000 claims description 11
- 125000001153 fluoro group Chemical group F* 0.000 claims description 9
- 229910052751 metal Inorganic materials 0.000 claims description 9
- 239000002184 metal Substances 0.000 claims description 9
- 239000007774 positive electrode material Substances 0.000 claims description 9
- 150000001491 aromatic compounds Chemical class 0.000 claims description 7
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- HHNHBFLGXIUXCM-GFCCVEGCSA-N cyclohexylbenzene Chemical compound [CH]1CCCC[C@@H]1C1=CC=CC=C1 HHNHBFLGXIUXCM-GFCCVEGCSA-N 0.000 claims description 6
- TXCDCPKCNAJMEE-UHFFFAOYSA-N dibenzofuran Chemical compound C1=CC=C2C3=CC=CC=C3OC2=C1 TXCDCPKCNAJMEE-UHFFFAOYSA-N 0.000 claims description 6
- ZUOUZKKEUPVFJK-UHFFFAOYSA-N diphenyl Chemical compound C1=CC=CC=C1C1=CC=CC=C1 ZUOUZKKEUPVFJK-UHFFFAOYSA-N 0.000 claims description 6
- USIUVYZYUHIAEV-UHFFFAOYSA-N diphenyl ether Chemical compound C=1C=CC=CC=1OC1=CC=CC=C1 USIUVYZYUHIAEV-UHFFFAOYSA-N 0.000 claims description 6
- YTZKOQUCBOVLHL-UHFFFAOYSA-N tert-butylbenzene Chemical compound CC(C)(C)C1=CC=CC=C1 YTZKOQUCBOVLHL-UHFFFAOYSA-N 0.000 claims description 6
- 239000011149 active material Substances 0.000 claims description 5
- 229910052723 transition metal Inorganic materials 0.000 claims description 4
- QHTJSSMHBLGUHV-UHFFFAOYSA-N 2-methylbutan-2-ylbenzene Chemical compound CCC(C)(C)C1=CC=CC=C1 QHTJSSMHBLGUHV-UHFFFAOYSA-N 0.000 claims description 3
- 229910000552 LiCF3SO3 Inorganic materials 0.000 claims description 3
- 235000010290 biphenyl Nutrition 0.000 claims description 3
- 239000004305 biphenyl Substances 0.000 claims description 3
- 238000005984 hydrogenation reaction Methods 0.000 claims description 3
- 229910000625 lithium cobalt oxide Inorganic materials 0.000 claims description 2
- 229910002102 lithium manganese oxide Inorganic materials 0.000 claims description 2
- BFZPBUKRYWOWDV-UHFFFAOYSA-N lithium;oxido(oxo)cobalt Chemical compound [Li+].[O-][Co]=O BFZPBUKRYWOWDV-UHFFFAOYSA-N 0.000 claims description 2
- VLXXBCXTUVRROQ-UHFFFAOYSA-N lithium;oxido-oxo-(oxomanganiooxy)manganese Chemical compound [Li+].[O-][Mn](=O)O[Mn]=O VLXXBCXTUVRROQ-UHFFFAOYSA-N 0.000 claims description 2
- URIIGZKXFBNRAU-UHFFFAOYSA-N lithium;oxonickel Chemical compound [Li].[Ni]=O URIIGZKXFBNRAU-UHFFFAOYSA-N 0.000 claims description 2
- 239000002905 metal composite material Substances 0.000 claims description 2
- 150000003624 transition metals Chemical class 0.000 claims description 2
- 239000003125 aqueous solvent Substances 0.000 claims 2
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- 238000009831 deintercalation Methods 0.000 claims 1
- 238000009830 intercalation Methods 0.000 claims 1
- 238000007600 charging Methods 0.000 abstract description 42
- 238000003860 storage Methods 0.000 abstract description 15
- 238000005549 size reduction Methods 0.000 abstract 1
- 229940021013 electrolyte solution Drugs 0.000 description 88
- 230000000052 comparative effect Effects 0.000 description 28
- 239000007789 gas Substances 0.000 description 28
- -1 cyclic carboxylic acid esters Chemical class 0.000 description 23
- 239000000203 mixture Substances 0.000 description 20
- 229910052782 aluminium Inorganic materials 0.000 description 14
- 238000004519 manufacturing process Methods 0.000 description 13
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 11
- 238000012360 testing method Methods 0.000 description 11
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 10
- 229910002804 graphite Inorganic materials 0.000 description 10
- 239000010439 graphite Substances 0.000 description 10
- 239000010409 thin film Substances 0.000 description 10
- 125000004122 cyclic group Chemical group 0.000 description 9
- PXHVJJICTQNCMI-UHFFFAOYSA-N nickel Substances [Ni] PXHVJJICTQNCMI-UHFFFAOYSA-N 0.000 description 9
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 3
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- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 2
- 229910017199 LixMn1-yMyO2 Inorganic materials 0.000 description 2
- 229910014223 LixNi1-yMyO2 Inorganic materials 0.000 description 2
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- 125000000217 alkyl group Chemical group 0.000 description 2
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- 229910052788 barium Inorganic materials 0.000 description 1
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- BECPQYXYKAMYBN-UHFFFAOYSA-N casein, tech. Chemical compound NCCCCC(C(O)=O)N=C(O)C(CC(O)=O)N=C(O)C(CCC(O)=N)N=C(O)C(CC(C)C)N=C(O)C(CCC(O)=O)N=C(O)C(CC(O)=O)N=C(O)C(CCC(O)=O)N=C(O)C(C(C)O)N=C(O)C(CCC(O)=N)N=C(O)C(CCC(O)=N)N=C(O)C(CCC(O)=N)N=C(O)C(CCC(O)=O)N=C(O)C(CCC(O)=O)N=C(O)C(COP(O)(O)=O)N=C(O)C(CCC(O)=N)N=C(O)C(N)CC1=CC=CC=C1 BECPQYXYKAMYBN-UHFFFAOYSA-N 0.000 description 1
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- 230000015556 catabolic process Effects 0.000 description 1
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- 238000000576 coating method Methods 0.000 description 1
- 229910017052 cobalt Inorganic materials 0.000 description 1
- 239000010941 cobalt Substances 0.000 description 1
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 1
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- 238000013461 design Methods 0.000 description 1
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- NKDDWNXOKDWJAK-UHFFFAOYSA-N dimethoxymethane Chemical compound COCOC NKDDWNXOKDWJAK-UHFFFAOYSA-N 0.000 description 1
- VUPKGFBOKBGHFZ-UHFFFAOYSA-N dipropyl carbonate Chemical compound CCCOC(=O)OCCC VUPKGFBOKBGHFZ-UHFFFAOYSA-N 0.000 description 1
- 230000005593 dissociations Effects 0.000 description 1
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- 239000000945 filler Substances 0.000 description 1
- NBVXSUQYWXRMNV-UHFFFAOYSA-N fluoromethane Chemical compound FC NBVXSUQYWXRMNV-UHFFFAOYSA-N 0.000 description 1
- 239000011521 glass Substances 0.000 description 1
- VANNPISTIUFMLH-UHFFFAOYSA-N glutaric anhydride Chemical compound O=C1CCCC(=O)O1 VANNPISTIUFMLH-UHFFFAOYSA-N 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 229920003063 hydroxymethyl cellulose Polymers 0.000 description 1
- 229940031574 hydroxymethyl cellulose Drugs 0.000 description 1
- 238000011065 in-situ storage Methods 0.000 description 1
- 229910052738 indium Inorganic materials 0.000 description 1
- 230000005764 inhibitory process Effects 0.000 description 1
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- 239000011229 interlayer Substances 0.000 description 1
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- 229910052745 lead Inorganic materials 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- MHCFAGZWMAWTNR-UHFFFAOYSA-M lithium perchlorate Chemical compound [Li+].[O-]Cl(=O)(=O)=O MHCFAGZWMAWTNR-UHFFFAOYSA-M 0.000 description 1
- 229910001486 lithium perchlorate Inorganic materials 0.000 description 1
- ACFSQHQYDZIPRL-UHFFFAOYSA-N lithium;bis(1,1,2,2,2-pentafluoroethylsulfonyl)azanide Chemical compound [Li+].FC(F)(F)C(F)(F)S(=O)(=O)[N-]S(=O)(=O)C(F)(F)C(F)(F)F ACFSQHQYDZIPRL-UHFFFAOYSA-N 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 239000011777 magnesium Substances 0.000 description 1
- FPYJFEHAWHCUMM-UHFFFAOYSA-N maleic anhydride Chemical compound O=C1OC(=O)C=C1 FPYJFEHAWHCUMM-UHFFFAOYSA-N 0.000 description 1
- 230000010534 mechanism of action Effects 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 239000007769 metal material Substances 0.000 description 1
- 229920000609 methyl cellulose Polymers 0.000 description 1
- MBABOKRGFJTBAE-UHFFFAOYSA-N methyl methanesulfonate Chemical compound COS(C)(=O)=O MBABOKRGFJTBAE-UHFFFAOYSA-N 0.000 description 1
- 229940017219 methyl propionate Drugs 0.000 description 1
- 239000001923 methylcellulose Substances 0.000 description 1
- 235000010981 methylcellulose Nutrition 0.000 description 1
- JCDWETOKTFWTHA-UHFFFAOYSA-N methylsulfonylbenzene Chemical compound CS(=O)(=O)C1=CC=CC=C1 JCDWETOKTFWTHA-UHFFFAOYSA-N 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- PYLWMHQQBFSUBP-UHFFFAOYSA-N monofluorobenzene Chemical compound FC1=CC=CC=C1 PYLWMHQQBFSUBP-UHFFFAOYSA-N 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- KSEMETYAQIUBQB-UHFFFAOYSA-N n,n-diethylmethanesulfonamide Chemical compound CCN(CC)S(C)(=O)=O KSEMETYAQIUBQB-UHFFFAOYSA-N 0.000 description 1
- WCFDSGHAIGTEKL-UHFFFAOYSA-N n,n-dimethylmethanesulfonamide Chemical compound CN(C)S(C)(=O)=O WCFDSGHAIGTEKL-UHFFFAOYSA-N 0.000 description 1
- UUIQMZJEGPQKFD-UHFFFAOYSA-N n-butyric acid methyl ester Natural products CCCC(=O)OC UUIQMZJEGPQKFD-UHFFFAOYSA-N 0.000 description 1
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 description 1
- 239000004745 nonwoven fabric Substances 0.000 description 1
- TVMXDCGIABBOFY-UHFFFAOYSA-N octane Chemical compound CCCCCCCC TVMXDCGIABBOFY-UHFFFAOYSA-N 0.000 description 1
- BHVICADLOSIXKE-UHFFFAOYSA-N oxaldehydoyl 2-oxoacetate Chemical compound O=CC(=O)OC(=O)C=O BHVICADLOSIXKE-UHFFFAOYSA-N 0.000 description 1
- MHYFEEDKONKGEB-UHFFFAOYSA-N oxathiane 2,2-dioxide Chemical compound O=S1(=O)CCCCO1 MHYFEEDKONKGEB-UHFFFAOYSA-N 0.000 description 1
- 239000001254 oxidized starch Substances 0.000 description 1
- 235000013808 oxidized starch Nutrition 0.000 description 1
- MCXSFYZQNOWAKR-UHFFFAOYSA-N oxolan-2-ylmethyl hydrogen carbonate Chemical compound OC(=O)OCC1CCCO1 MCXSFYZQNOWAKR-UHFFFAOYSA-N 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 238000012856 packing Methods 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- RGSFGYAAUTVSQA-UHFFFAOYSA-N pentamethylene Natural products C1CCCC1 RGSFGYAAUTVSQA-UHFFFAOYSA-N 0.000 description 1
- 125000004817 pentamethylene group Chemical group [H]C([H])([*:2])C([H])([H])C([H])([H])C([H])([H])C([H])([H])[*:1] 0.000 description 1
- 125000006551 perfluoro alkylene group Chemical group 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 1
- 239000010452 phosphate Substances 0.000 description 1
- 229910052698 phosphorus Inorganic materials 0.000 description 1
- 238000007747 plating Methods 0.000 description 1
- 229920000058 polyacrylate Polymers 0.000 description 1
- 229920002857 polybutadiene Polymers 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 229920001343 polytetrafluoroethylene Polymers 0.000 description 1
- 239000004810 polytetrafluoroethylene Substances 0.000 description 1
- 229920002451 polyvinyl alcohol Polymers 0.000 description 1
- 235000019422 polyvinyl alcohol Nutrition 0.000 description 1
- QQONPFPTGQHPMA-UHFFFAOYSA-N propylene Natural products CC=C QQONPFPTGQHPMA-UHFFFAOYSA-N 0.000 description 1
- 125000004805 propylene group Chemical group [H]C([H])([H])C([H])([*:1])C([H])([H])[*:2] 0.000 description 1
- 239000002516 radical scavenger Substances 0.000 description 1
- 230000009257 reactivity Effects 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 150000003839 salts Chemical class 0.000 description 1
- 229910052709 silver Inorganic materials 0.000 description 1
- 238000001228 spectrum Methods 0.000 description 1
- 238000004544 sputter deposition Methods 0.000 description 1
- 239000008107 starch Substances 0.000 description 1
- 235000019698 starch Nutrition 0.000 description 1
- 229910052712 strontium Inorganic materials 0.000 description 1
- 229920003048 styrene butadiene rubber Polymers 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 229940014800 succinic anhydride Drugs 0.000 description 1
- HXJUTPCZVOIRIF-UHFFFAOYSA-N sulfolane Chemical compound O=S1(=O)CCCC1 HXJUTPCZVOIRIF-UHFFFAOYSA-N 0.000 description 1
- MBDNRNMVTZADMQ-UHFFFAOYSA-N sulfolene Chemical compound O=S1(=O)CC=CC1 MBDNRNMVTZADMQ-UHFFFAOYSA-N 0.000 description 1
- 229910052717 sulfur Inorganic materials 0.000 description 1
- 239000011593 sulfur Substances 0.000 description 1
- 229910052715 tantalum Inorganic materials 0.000 description 1
- GUVRBAGPIYLISA-UHFFFAOYSA-N tantalum atom Chemical compound [Ta] GUVRBAGPIYLISA-UHFFFAOYSA-N 0.000 description 1
- YLQBMQCUIZJEEH-UHFFFAOYSA-N tetrahydrofuran Natural products C=1C=COC=1 YLQBMQCUIZJEEH-UHFFFAOYSA-N 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- 238000007740 vapor deposition Methods 0.000 description 1
- 239000011800 void material Substances 0.000 description 1
- 239000011701 zinc Substances 0.000 description 1
Classifications
-
- 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
-
- 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
Abstract
An object of the invention is to provide such a battery that has a high capacity, is excellent in storage characteristics, cycle characteristics and continuous charging characteristics, and is small in gas generation amount, whereby size reduction and improvement in performance of a lithium secondary battery can be attained. The present invention relates to a nonaqueous electrolytic solution comprising a lithium salt and a nonaqueous solvent dissolving the same, wherein the electrolytic solution contains, as the lithium salt, LiPF6 in a concentration of from 0.2 to 2 mole/L, and LiBF4 and/or a compound represented by the following formula (1) in a molar ratio of from 0.005 to 0.4 with respect to LiPF6, and the nonaqueous solvent mainly comprises (1) ethylene carbonate and/or propylene carbonate, (2-1) a symmetric linear carbonate, (2-2) an asymmetric linear carbonate, and (3) vinylene carbonate.
Description
Technical Field
The present invention relates to a nonaqueous electrolyte solution and a lithium secondary battery using the same. More particularly, the present invention relates to a lithium secondary battery having a high capacity and excellent storage characteristics, cycle characteristics and sustained discharge characteristics, and generating a small amount of gas.
Background
In recent years, with the reduction in weight and size of electric appliances, lithium secondary batteries having high energy density have been developed.
Generally, an electrolyte solution used in a lithium secondary battery is mainly composed of a lithium salt and a nonaqueous solvent. Examples of the main component of the nonaqueous solvent include cyclic carbonates such as ethylene carbonate and propylene carbonate; chain carbonates such as dimethyl carbonate and ethyl methyl carbonate; and cyclic carboxylic acid esters such as gamma-butyrolactone and gamma-valerolactone.
In order to improve characteristics of the secondary battery, such as load characteristics, cycle characteristics, storage characteristics, and low-temperature characteristics, many studies have been made on nonaqueous solvents and lithium salts.
For example, patent document 1 discloses the following: when a mixture of an asymmetric chain carbonate and a cyclic carbonate having a double bond is used as a nonaqueous solvent, the cyclic carbonate having a double bond mainly reacts with a negative electrode to form a high-quality thin film on the surface of the negative electrode, thereby preventing the asymmetric chain carbonate from forming an insulator thin film on the surface of the negative electrode and improving cycle characteristics.
In the case of using a composition containing only LiPF6In a secondary battery using as an electrolyte solution of lithium salt, by LiPF6Dissociation of (1) ) Thus formed PF5Leading to the breakage of C — O bonds in the carbonate, which in turn decomposes the carbonate (self-discharge), thereby causing a decrease in battery capacity upon storage. However, patent document 2 discloses the following: in the presence of a catalyst containing LiPF6And LiBF4In the secondary battery using the electrolyte solution of (2), from LiBF4Formed anion (BF)4 -) Inhibition by LiPF6Formed PF6 -The electrolyte solution is stabilized, whereby the battery capacity can be prevented from being reduced during storage. Patent document 2 also discloses that a mixture of cyclic carbonate and chain carbonate is used as a nonaqueous solvent, and in examples thereof, a mixture of ethylene carbonate and diethyl carbonate is used.
Patent document 3 discloses the following: in a lithium secondary battery using aluminum as a current collector, high ion conductivity can be secured, and electricity containing perfluoroalkylene disulfonylimide salt as a lithium salt is usedThe electrolyte solution can prevent the aluminum from being corroded. Patent document 3 also discloses that the cyclic imide salt may be replaced with other lithium salts (e.g., LiBF)4And LiPF6) Mixed and used, and preferably used in a proportion of 10 mol times as much as that of the other lithium salt.
However, the demand for high-performance lithium secondary batteries has been increasing in recent years, and such lithium secondary batteries are required to have high capacity and improved high-temperature storage characteristics and cycle characteristics.
As a measure for increasing the capacity of the battery, a design scheme of packing as much electrode active material as possible in a limited battery volume, for example, compressing the electrode active material to increase the density thereof, is generally employed. However, other problems arise in increasing the battery capacity. For example, once the void in the battery is reduced, the internal pressure of the battery significantly increases due to the formation of gas, even if only a small amount of gas is formed due to the decomposition of the electrolyte solution.
When a battery is used as a backup power source in case of power failure or a power source of a portable device, a continuous charging method is employed in which a weak current is supplied to the battery to compensate for self-discharge of the battery, thereby maintaining a charged state. In the continuous charging method, the electrode is generally in a high-activity state, thereby accelerating the reduction in the battery capacity, and gas is easily generated by the decomposition of theelectrolyte solution. In a cylindrical battery having a safety valve that functions when an abnormal increase in the battery internal pressure due to overcharge is detected, there are sometimes cases where the safety valve opens due to the formation of a large amount of gas. In prismatic cells without safety valves, the cells can swell or rupture under severe conditions due to the pressure of the gases formed.
Therefore, there is a strong demand for lithium secondary batteries that suppress the formation of gas during continuous charging, while suppressing the decrease in capacity.
In the lithium secondary battery disclosed in patent document 1, an electrolyte solution is used by mixing LiPF6Dissolved in a nonaqueous solvent containing (1) ethylene carbonate, (2) ethyl methyl carbonate and (3) vinylene carbonate, however, it has substantially no effect on preventing a decrease in capacity and a decrease in gas production rate upon continuous charging, although it can improve cycle characteristics.
Further, in the secondary battery disclosed in patent document 2, the inclusion of LiPF is employed6And LiBF4As an electrolyte solution of a lithium compound, however, when the battery is stored under high temperature conditions of 80 ℃ or more, the battery characteristics deteriorate and the cycle characteristics are insufficient.
Moreover, in the secondary battery disclosed in patent document 3, an electrolyte solution containing a specific cyclic imide salt as a lithium compound is used, however, when it is prepared into a battery having a high capacity, not all of the storage characteristics, cycle characteristics and continuous charging characteristics can be simultaneously maintained at a high level, and particularly, when the battery is stored under high-temperature conditions, the battery characteristics are degraded although aluminum can be prevented from being corroded.
[ patent document 1]
JP-A-11-185806
[ patent document 2]
JP-A-8-64237
[ patent document 3]
JP-W-11-512563
Disclosure of Invention
The present invention has been made in view of the foregoing circumstances of the prior art, and an object thereof is to provide a lithium secondary battery having a high capacity, excellent in storage characteristics, cycle characteristics and continuous charging characteristics, and small in gas production amount.
After earnest study, the inventor of the invention finds that the LiPF is prepared by mixing LiPF6And LiBF4And/or a lithium salt represented by the following formula (1) in a nonaqueous solvent containing a specific combination of various solvents, and a nonaqueous electrolyte solution having a small capacity decrease during continuous charging and a small gas production amount during continuous charging, and thus the present invention has been completed.
In a first aspect, the present invention relates to a nonaqueous electrolyte solution containing a lithium salt and a nonaqueous solvent in which the lithium salt is dissolved, wherein the electrolyte solution contains LiPF as the lithium salt at a concentration of 0.2 to 2 mol/L6And relative to LiPF6In a molar ratio of 0.005 to 0.4, and a LiBF4And/or a compound represented by the following formula (1); and the nonaqueous solvent mainly contains (1) ethylene carbonate and/or propylene carbonate, (2-1) a symmetrical chain carbonate, (2-2) an asymmetrical chain carbonate, and (3) vinylene carbonate.
In a second aspect, the present invention also relates to a nonaqueous electrolyte solution containing a lithium salt and a nonaqueous solvent in which the lithium salt is dissolved, wherein the electrolyte solution contains LiPF as the lithium salt at a concentration of 0.2 to 2 mol/L6And LiBF at a concentration of 0.001 to 0.3 mol/L4(ii) a And the nonaqueous solvent mainly contains (1) ethylene carbonate and/or propylene carbonate, (2-1) a symmetrical chain carbonate, and (2-2) an asymmetrical chainCyclic carbonate, and (3) vinylene carbonate.
In a third aspect, the present invention also relates to a nonaqueous electrolyte solution containing a lithium salt and a nonaqueous solvent in which the lithium salt is dissolved, wherein the electrolyte solution contains LiPF as the lithium salt at a concentration of 0.5 to 2.5 mol/L6And a compound represented by the following formula (1) at a concentration of 0.001 to 0.3 mol/L:
(wherein R represents a linear or branched alkylene group having 1 to 20 carbon atoms, which may be substituted with a fluorine atom, provided that the alkylene chain has not more than 12 carbon atoms except for the side chain).
Drawings
Fig. 1 is a schematic sectional view of a cylindrical battery prepared in the example.
In the drawing, numeral 1 represents a battery can, 2 represents a sealing plate, 3 represents an insulating gasket, 4 represents a spiral-shaped electrode assembly, 5 represents a positive electrode terminal, 6 represents a negative electrode terminal, 7 represents an insulating ring, and8 represents a current cut-off device.
Detailed Description
The nonaqueous electrolyte solution according to the present invention mainly contains a lithium salt and a nonaqueous solvent dissolving the lithium salt, and is characterized in that the present invention uses LiPF in combination as the lithium salt, similarly to the ordinary nonaqueous electrolyte solution6And LiBF4And/or a lithium salt represented by the following formula (1); comprising a specific concentration of LiPF6(ii) a And including with respect to LiPF6Is a specific ratio of LiBF4And/or a lithium salt represented by the following formula (1).
In the nonaqueous electrolyte solution, LiPF6The concentration of (B) is 0.2 to 2 mol/L. If LiPF6Too high or too low of a concentration of (B) is presentThe conductivity of the electrolyte solution is lowered to deteriorate the battery characteristics. Preferred is LiPF6Is 0.3 mol/L or more, particularly 0.6 mol/L or more, and preferably it is 1.8 mol/L or less, particularly 1.5 mol/L or less. In the aforementioned LiPF6In the concentration range, the upper limit and the lower limit may be arbitrarily combined.
If LiPF6When used in combination with a lithium salt represented by the following formula (1), LiPF is contained in a nonaqueous electrolyte solution6The concentration of (B) may be 0.5 to 2.5 mol/L. LiPF in this case is preferred6Is 0.6 mol/L or more, particularly 0.7 mol/L or more, and preferably 1.8 mol/L or less, particularly 1.5 mol/L or less. In the aforementioned LiPF6In the concentration range, the upper limit and the lower limit may be arbitrarily combined.
In the formula (1), R represents a straight-chain or branched alkylene group having 1 to 20 carbon atoms, preferably 2 to 12 carbon atoms, which may be substituted with a fluorine atom, provided that the alkylene group has 1 to 12 carbon atoms, preferably 2 to 8 carbon atoms, excluding the side chain. The alkyl group constituting the alkylene side chain generally has 1 to 8 carbon atoms, preferably 1 to 4 carbon atoms, and the alkyl group may be linear or branched.
Examples of the linear alkylene group include ethylene, trimethylene, tetramethylene and pentamethylene. Examples of branched alkylene groups include 1-methyl-ethylene (propylene), 2-methyl-trimethylene and neopentylene. The fluorine atom may be substituted for any hydrogen atom in the alkylene group, and in the case where the alkylene group is substituted with a fluorine atom, a perfluoroalkylene group in which all hydrogen atoms are substituted with fluorine atoms is preferable.
Specific examples of the lithium salt represented by the following formula (1) include cyclic lithium 1, 2-ethanedisulfonylimide, cyclic lithium 1, 3-propanedisulfonylimide, cyclic lithium 1, 2-perfluoroethanedisulfonylimide, cyclic lithium 1, 3-perfluoropropanedisulfonylimide, and cyclic lithium 1, 4-perfluorobutanedisulfonylimide. Among them, preferred are cyclic lithium 1, 2-perfluoroethanedisulfonimide and cyclic lithium 1, 3-perfluoropropanedisulfonimide.
LiBF4Or a lithium salt represented by the following formula (1) with respect to LiPF6Is generally 0.005 or more, preferably 0.01 or more, particularly preferably 0.05 or more, and is generally 0.4 or less, preferably 0.2 or less, more preferably 0.15 or less. In the aforementioned molar ratio range, the upper limit and the lower limit may be arbitrarily combined.
If the molar ratio is too large, there is a tendency that the battery characteristics are lowered; if the molar ratio is too small, it becomes difficult to suppress gas generation and capacity deterioration during continuous charging. If both contain LiBF4And a lithium salt represented by the following formula (1), the total amount of which satisfies the aforementioned range.
LiBF4Or the lithium salt represented by the following formula (1) is generally contained in the nonaqueous electrolyte solution in a concentration of 0.001 to 0.3 mol/L. If LiBF4Or, if the concentration of the lithium salt represented by the following formula (1) is too low, it becomes difficult to suppress gas generation and capacity deterioration during continuous charging.
If the concentration is too high, there is a tendency that the battery characteristics after high-temperature storage are lowered. Preferably LiBF4Or the concentration of the lithium salt represented by the following formula (1) is 0.01 mol/L or more, particularly preferably 0.02 mol/L or more, and most preferably 0.05 mol/L or more. The upper limit thereof is preferably 0.25 mol/L or less, and most preferably 0.18 mol/L or less. If both contain LiBF4And a lithium salt represented by the following formula (1), the total amount of which satisfies the aforementioned range.
If the electrolyte solution contains LiPF6And a lithium salt represented by the following formula (1) as a lithium salt, the lithium salt represented by the following formula (1) is in contrast to LiPF6The lower limit of the molar ratio of (b) may be arbitrarily determined, and is preferably 0.005 or more. If the molar ratio is less than the lower limit, there may be cases where it is difficult to sufficiently suppress gas generation and capacity deterioration during continuous charging, and therefore, it is preferable that the molar ratio is 0.01 or more, particularly 0.02 or more. Also, the upper limit of the molar ratio can be arbitrarily determined, but if the molar ratio is too large, there is a tendency that the battery characteristics after high-temperature storage are lowered,therefore, it is preferable that the molar ratio is 0.5 or less, particularly 0.2 or less.
When the electrolyte solution, as a lithium salt, contains LiPF6And a lithium salt represented by the following formula (1), LiPF6The total amount of the lithium salt represented by the following formula (1) and the lithium salt in the nonaqueous electrolyte solution is preferably 0.7 to 1.7 mol/L, and the concentration and the molar ratio thereof may be in the above range.
In the nonaqueous electrolyte solution of the present invention, except for LiPF6、LiBF4And other lithium salts may be used therefor in addition to the lithium salt represented by the following formula (1). Examples of other lithium salts include inorganic lithium salts, such as LiClO4(ii) a And fluorine-containing organic lithium salts such as LiN (CF)3SO2)2，LiN(C2F5SO2)2，LiCF3SO3，LiC(CF3SO2)3，LiPF4(CF3)2，LiPF4(C2F5)2，LiPF4(CF4SO2)2，LiPF4(C2F5SO2)2，LiBF2(CF3)2，LiBF2(C2F5)2，LiBF2(CF3SO2)2And LiBF2(C2F5SO2)2。
If an additional lithium salt is added, the concentration of the additional lithium saltin the electrolyte solution is preferably 0.5 mol/L or less, and particularly preferably 0.2 mol/L or less. The lower limit thereof may be arbitrarily determined, and in order to exert a certain effect by such addition, it is generally preferred that the lower limit is 0.01 mol/L or more, particularly 0.05 mol/L or more.
The solution contains LiN (CF) at a concentration of 0.001-0.2 mol/L3SO2)2、LiN(C2F5SO2)2And LiCF3SO3Of (b), especially LiN (CF)3SO2)2In the case of (3), gas generation during continuous charging can be further suppressed. If the concentration is too lowIt will not function. Preferably, the concentration is 0.003 mol/L or more, particularly preferably 0.005 mol/L or more, and most preferably 0.008 mol/L or more. The upper limit thereof is preferably 0.15 mol/L or less, and particularly preferably 0.1 mol/L or less.
The second feature of the present invention is that the nonaqueous solvent mainly contains (1) ethylene carbonate and/or propylene carbonate, (2-1) a symmetrical chain carbonate, (2-2) an asymmetrical chain carbonate, and (3) vinylene carbonate.
(1) Ethylene carbonate and/or propylene carbonate
Ethylene carbonate and propylene carbonate may be used alone or in admixture with each other, and it is preferred that ethylene carbonate be used alone or in admixture with propylene carbonate.
If ethylene carbonate is used in admixture with propylene carbonate, the volume ratio (EC/PC) of Ethylene Carbonate (EC) to Propylene Carbonate (PC) is generally 99/1 or less, preferably 95/5 or less, and generally 40/60 or more, preferably 50/50 or more.
If the amount of the propylene carbonate is too large, it is particularly not preferable in a battery using graphite as a negative electrode active material because the propylene carbonate is easily decomposed on the surface of graphite. In the present specification, the volume of the nonaqueous solvent is a volume at 25 ℃, and the volume of the ethylene carbonate is a volume at the melting point thereof.
(2) Chain carbonate
(2-1) symmetrical chain carbonate
Examples of symmetrical chain carbonates include dimethyl carbonate, diethyl carbonate and di-n-propyl carbonate. Among them, carbonates having 5 or less carbon atoms are preferable, and dimethyl carbonate and diethyl carbonate are particularly preferable. These carbonates may be used alone or in admixture of two or more thereof.
(2-2) an asymmetric chain carbonate
Examples of asymmetric chain carbonates include ethyl methyl carbonate, n-methyl propyl carbonate and n-ethyl propyl carbonate. Among them, carbonates having 5 or less carbon atoms are preferable, and ethyl methyl carbonate is particularly preferable. These carbonates may be used alone or in admixture of two or more thereof.
In the nonaqueous electrolyte solution, the volume ratio of the total amount of ethylene carbonate and propylene carbonate to the total amount of the symmetrical chain carbonate and the asymmetrical chain carbonate is generally 10/90 to 70/30, preferably 10/90 to 50/50, particularly preferably 10/90 to 45/55, and most preferably 15/85 to 40/60. If the total amount of the symmetrical chain carbonate and the asymmetrical chain carbonate is too small, the viscosity of the electrolyte solution increases; in contrast, if the total amount is too large, the degree of dissociation of the lithium salt decreases, and in both cases, there is a possibility that the conductivity of the electrolyte solution is decreased.
Examples of the combination ofethylene carbonate and chain carbonates include a combination of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate, a combination of ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate, and a combination of ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, which provide an electrolyte solution having a good balance between cycle characteristics and large-current discharge characteristics. In a preferred combination, various combinations obtained by further adding propylene carbonate to the aforementioned combination of ethylene carbonate and a chain carbonate are also included.
(3) Vinylene carbonate
The proportion of vinylene carbonate in the nonaqueous electrolyte solution other than the lithium salt is generally 0.01% by weight or more, preferably 0.1% by weight or more, particularly preferably 0.3% by weight or more, most preferably 0.5% by weight or more, and is generally 8% by weight or less, preferably 5% by weight or less, particularly preferably 3% by weight or less. In the above-mentioned proportion of vinylene carbonate, the lower limit and the upper limit may be arbitrarily combined.
It is considered that vinylene carbonate has a function of forming a thin film on the surface of the negative electrode to improve the cycle characteristics, and if the proportion of vinylene carbonate is too small, the cycle characteristics cannot be sufficiently improved. On the other hand, if the ratio is too large, the internal pressure of the battery may increase due to gas generated during storage at high temperature.
In the nonaqueous electrolyte solution of the present invention, it is preferable that the nonaqueous solvent is formed by mixing ethylene carbonate, propylene carbonate, a symmetrical chain carbonate and an asymmetrical chain carbonate, and vinylene carbonate as a maincomponent.
The total amount of ethylene carbonate, propylene carbonate, symmetrical chain carbonates and asymmetrical chain carbonates, and vinylene carbonate in the nonaqueous electrolyte solution other than the lithium salt is preferably 80% by weight or more. It is further preferable that the total amount is 90% by weight or more, and 93% by weight or more is particularly preferable. The nonaqueous electrolyte solution having the total amount in the aforementioned range is preferable because a good balance between the cycle characteristics and the large-current discharge characteristics can be achieved.
Examples of other nonaqueous solvents than vinylene carbonate, ethylene carbonate, propylene carbonate, symmetrical chain carbonates, and asymmetrical chain carbonates include cyclic carbonates having 5 or more carbon atoms, such as butylene carbonate; cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran; chain ethers such as dimethoxyethane and dimethoxymethane; cyclic carboxylic acid esters such as γ -butyrolactone and γ -valerolactone; and chain carboxylates such as methyl acetate, methyl propionate, ethyl propionate and methyl butyrate. These nonaqueous solvents may be used alone or as a mixture of two or more thereof. If the nonaqueous electrolyte solution contains these nonaqueous solvents, the proportion thereof in the nonaqueous electrolyte solution other than the lithium salt is generally 20% by weight or less.
The mechanism by which the nonaqueous electrolyte solution of the present invention produces less deteriorating effect on the discharge characteristics can be expected as follows, although the mechanism is not completely understood.
Vinylene carbonate forms a stable film on the surface of the negative electrode, thereby improving the cycle characteristics. However, since vinylene carbonate is easily reacted with a positive electrode material in a charged state and the positive electrode is always in a highly active state when constant-voltage continuous charging is performed, a reaction occurs between vinylene carbonate and the positive electrode material, so that the positive electrode active material may be deteriorated at an increased speed and the gas production amount may be increased. In addition, the constituent components of the thin film formed on the surface of the negative electrode are partially dissolved in the electrolyte solution, and the dissolved substances react with the surface of the positive electrode, resulting in accelerated deterioration of the active material of the positive electrode and generation of gas.
On the other hand, from LiBF4The above-mentioned reaction on the positive electrode is inhibited by the decomposed product of (b), and the formation of a thin film of vinylene carbonate on the surface of the negative electrode is not inhibited by the decomposed product of (b). In addition, partial LiBF4Is reduced on the surface of the negative electrode to form vinylene carbonate and LiBF on the negative electrode4The composite membrane of (3). The composite membrane is thermally stable and has excellent lithium ion permeability. Furthermore, the composite film is difficult to dissolve, and dissolution of the film components is suppressed, thereby suppressing side reactions inside the battery, and further suppressing degradation of the electrode active material, thereby maintaining good discharge characteristics.
And LiPF6In contrast, LiBF4Easily reacts with a charged anode material and promotes a side reaction with the anode material without containing vinylene carbonate, but when LiBF4When present with vinylene carbonate, it forms a stable thin film on the surface of the negative electrode, and the thin film suppresses side reactions with the negative electrode material.
As described above, by the reaction of vinylene carbonate with LiBF4The interaction between them can improve the cycle characteristics and prevent the deterioration of the discharge characteristics upon continuous charging.
Specifically, it is preferable that the proportion of vinylene carbonate in the nonaqueous electrolyte solution other than the lithium salt is 0.3% by weight or more, and LiBF is preferable4The concentration in the nonaqueous electrolyte solution is 0.02 mol/L or more because the effect of the present invention is remarkable as such.
Although the mechanism of action of the lithium salt represented by the following formula (1) is not completely understood, the lithium salt represented by the following formula (1) or a decomposition product derived from the lithium salt suppresses the positive electrode reactivity by adsorbing or coating the positive electrode active site, and further suppresses the side reaction of vinylene carbonate and other components of the electrolyte solution on the positive electrode. Further, it is also considered that the lithium salt represented by the following formula (1) does not inhibit the formation of a thin film of vinylene carbonate on the surface of the negative electrode, but promotes the formation of a stable thin film having excellent lithium ion permeability, and therefore, it is possible to improve cycle characteristics, suppress gas generation during continuous charging, and improve discharge characteristics during continuous charging.
The nonaqueous electrolyte solution of the present invention may contain other components, for example, well-known adjuvants such as an overcharge preventing agent, a dehydrating agent and an acid scavenger, as required.
Examples of the overcharge preventing agent include aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partial hydrogenation products of terphenyl, cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, diphenyl ether and dibenzofuran; partially fluorinated products of the foregoing aromatic compounds, such as 2-fluorobiphenyl, o-cyclohexylfluorobenzene and p-cyclohexylfluorobenzene; and fluorine-containing anisole compounds such as 2, 4-difluoroanisole, 2, 5-difluoroanisole and 2, 6-difluoroanisole. Among them, fluorine-free substituted aromatic compounds are preferable.
These aromatic compounds may be used alone or in admixture of two or more thereof. If a mixture of two or more thereof is used, it is particularly preferably selected from among oxygen-free aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partial hydrogenation products of terphenyl, cyclohexylbenzene, tert-butylbenzene and tert-amylbenzene, used in admixture with oxygen-containing aromatic compounds such as diphenyl ether and dibenzofuran. If the nonaqueous electrolyte solution contains an overcharge inhibitor, the concentration thereof is generally 0.1 to 5% by weight. It is preferable to include an overcharge inhibitor in the nonaqueous electrolyte solution because it is possible to prevent the battery from being ruptured and ignited by overcharge, thereby improving the safety of the battery.
In general, since the overcharge inhibitor reacts more easily on the positive and negative electrodes than the nonaqueous solvent constituting the nonaqueous electrolyte solution, it reacts with highly active sites of the electrodes during continuous charging and high-temperature storage, increases the internal resistance of the battery and generates gas, thereby causing significant deterioration of discharge characteristics during continuous charging and high-temperature storage. However, it is still preferable to add an overcharge inhibitor to the nonaqueous electrolyte solution of the present invention because deterioration of the discharge characteristics can be suppressed.
Examples of the auxiliary agent for improving the capacity retention characteristics and the cycle characteristics after high-temperature storage include carbonate compounds such as vinyl ethylene carbonate, ethylene fluorocarbon, propylene trifluorocarbonate, phenyl ethylene carbonate, tetrahydrofurfuryl carbonate and spiro-dimethylene carbonate; carboxylic acid anhydrides such as succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, glyoxylic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic anhydride and phenylsuccinic anhydride; sulfur-containing compounds, such as ethylene sulfite, 1, 3-propanesultone, 1, 4-butanesultone, methyl methanesulfonate, butanediol methanesulfonate diester, sulfolane, cyclobutanesulfoxide (sulfolene), dimethylsulfone, diphenylsulfone, methylphenylsulfone, dibutylenesulfide, dicyclohexyldisulfide, tetramethylthiuram monosulfide, N, N-dimethylmethanesulfonamide, and N, N-diethylmethanesulfonamide; nitrogen-containing compounds such as 1-methyl-2-pyrrolidone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1, 3-dimethyl-2-imidazolidinone, and N-methylsuccinimide; hydrocarbon compounds such as heptane, octane and cycloheptane; and fluorine-containing compounds such as fluorobenzene, difluorobenzene, hexafluorobenzene and trifluorotoluene. These compounds may be used alone or in admixture of two or more thereof. If the nonaqueous electrolyte solution contains the auxiliary, the concentration thereof is generally 0.1 to 5% by weight.
The nonaqueous electrolyte solution of the present invention can be prepared by mixing LiPF6、LiBF4And/or a lithium salt represented by the following formula (1) and, if necessary, other compounds are dissolved in a nonaqueous solvent mainly containing (1) ethylene carbonate and/or propylene carbonate, (2-1) a symmetrical chain carbonate, (2-2) an asymmetrical chain carbonate, and (3) vinylene carbonate. In preparing the nonaqueous electrolyte solution, it is preferable that the raw materials are dehydrated in advance, and it is generally preferable that they are dehydrated in advance to 50ppm or less, more preferably to 30ppm or lessAnd is smaller.
The nonaqueous electrolyte solution of the present invention is suitably used as an electrolyte solution for a secondary battery, particularly a lithium secondary battery. The lithium secondary battery of the present invention using the electrolyte solution will be described below.
The lithium secondary battery of the present invention is the same as a known lithium secondary battery except for the electrolytic solution, and has a structure in which a positive electrode and a negative electrode are housed in a case through a porous film impregnated with the electrolytic solution of the present invention. Therefore, the secondary battery may have any shape, such as a cylindrical shape, a prismatic shape, a sheet shape, a coin shape, and a large-sized shape.
As described above, the lithium secondary battery using the electrolyte solution of the present invention forms a small amount of gas in a continuously charged state. Therefore, if the electrolyte solution of the present invention is used for a battery having a current breaker that functions due to an increase in the internal pressure of the battery under abnormal conditions (such as overcharge), it is possible to prevent abnormal operation of the current breaker from occurring under a continuous charging condition.
The problem of expansion of the battery caused by an increase in the internal pressure of the battery easily occurs in a battery in which the case is formed of metal aluminum or an aluminum alloy having a thickness of 0.5mm or less, particularly 0.4mm or less, and a battery having a volume capacity density of 110mAh/cc or more, particularly 130mAh/cc or more, particularly 140mAh/cc or more, but the expansion of the battery can be prevented by using the electrolyte solution of the present invention.
Examples of the negative electrode active material include carbonaceous materials and metal compounds capable of inserting and extracting lithium, metallic lithium and lithium alloys. These materials may be used alone or in admixture of two or more thereof.
Among them, carbonaceous materials are preferable, and graphite or graphite materials coated with amorphous (as compared with graphite) carbon on the surface thereof are particularly preferable.
The d value (interlayer spacing) of the lattice plane (002 plane) of graphite is measured by X-ray diffraction method according to JSPS method, and the d value of graphite is preferably 0.335 to 0.338nm, particularly preferably 0.335 to 0.337 nm. The crystallite size (Lc) as determined by X-ray diffraction method according to JSPs is preferably 30nm or more, more preferably 50nm or more, particularly preferably 100nm or more. The ash content is preferably 1% by weight or less, more preferably 0.5% by weight or less, and particularly preferably 0.1% by weight or less.
It is preferable that the graphite material having its surface coated with amorphous carbon has a structure in which: wherein graphite having a lattice plane (002 plane) with a d value of 0.335 to 0.338nm in X-ray diffraction is used as a core material, and a carbonaceous material having a lattice plane (002 plane) with a d value larger than that of the core material in X-ray diffraction is attached to the core material, and the weight ratio of the core material to the carbonaceous material having a lattice plane (002 plane) with a d value larger than that of the core material in X-ray diffraction is 99/1 to 80/20. With this material, a negative electrode having a highcapacity and being difficult to react with an electrolyte solution can be produced.
The particle diameter of the carbonaceous material is preferably 1 μm or more, more preferably 3 μm or more, particularly preferably 5 μm or more, and most preferably 7 μm or more in terms of the median diameter obtained by the laser diffraction and scattering method. The upper limit thereof is preferably 100 μm or less, more preferably 50 μm or less, particularly preferably 40 μm or less, and most preferably 30 μm or less.
The BET specific surface area of the carbonaceous material is preferably 0.3m2A,/g or more, more preferably 0.5m2A specific ratio of 0.7 m/g or more2A/g or more, most preferably 0.8m2(ii) a/g or greater. The upper limit is preferably 25.0m2A,/g or less, more preferably 20.0m2A specific ratio of 15.0 m/g or less2A/g or less, most preferably 10.0m2(ii) g or less.
The carbonaceous material preferably has an R value (═ I) of 0.01 to 0.7B/IA) R represents a peak PAPeak intensity of (1)AAnd peak PBPeak intensity of (1)BWherein peak P isAThe Raman spectrum obtained by using an argon laser is 1570-1620 cm-1Peak of range, peak PBIs positioned at 1300-1400 cm in the spectrum-1Peak of the range. It is located at 1570-1620 cm-1The half-value width of the peak of the range is preferably 26cm-1Or less, particularly preferably 25cm-1Or smaller.
Examples of the metal compound capable of inserting and extracting lithium include compounds containing metals such as Ag, Zn, Al, Ga, In, Si, Ge, Sn, Pb, P, Sb, Bi, Cu, Ni, Sr, and Ba, and these metals may be used In the form of a simple substance, an oxide, or an alloy with lithium. In the present invention, a compound containing an element selected from Si, Sn, Ge, and Al is preferable, and an oxide or a lithium alloy of a metal selected from Si, Sn, and Al is more preferable.
A metal compound capable of inserting and extracting lithium, or an oxide thereof or a lithium alloy thereof generally has a larger capacity per unit weight than a carbonaceous material represented by graphite, and therefore, is preferable for a lithium secondary battery required to have a higher capacity.
Examples of the positive active material include materials capable of inserting and extracting lithium, for example, lithium transition metal composite oxides such as lithium-cobalt oxide, lithium-nickel oxide, and lithium-manganese oxide, and composite oxides obtained by substituting a part of transition metals in the aforementioned composite oxides with other metals. Examples of these compounds include LixCoO2、LixNiO2、LixMnO2、LixCo1-yMyO2、LixNi1-yMyO2And LixMn1-yMyO2Wherein M represents at least one selected from the group consisting of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, V, Sr and Ti, x is 0.4. ltoreq. x.ltoreq.1.2, and y is 0. ltoreq. y.ltoreq.0.6.
Specifically, compounds obtained by substituting part of cobalt, nickel or manganese with other metals, such as Li, are preferablexCo1-yMyO2、LixNi1-yMyO2And LixMn1-yMyO2Because of its structural stability. The positive electrode active material may be used alone or as a mixture of a plurality of the positive electrode active materials.
The binder used to bind theactive material may be any material that is stable to the solvent used in preparing the electrode and to the electrolyte solution. Examples thereof include fluorine resins such as polyvinylidene fluoride and polytetrafluoroethylene; polyolefins such as polyethylene and polypropylene; polymers having unsaturated bonds and copolymers thereof such as styrene-butadiene rubber, isoprene rubber and butadiene rubber; and acrylic polymers and copolymers thereof, such as ethylene-acrylic acid copolymers, ethylene-methacrylic acid copolymers.
In order to improve mechanical strength and conductivity, the electrode may contain a thickener, a conductive material, a filler, and the like.
Examples of the thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, starch phosphate and casein.
Examples of the conductive material include metallic materials such as copper and nickel, and carbon materials such as graphite and carbon black.
The electrode may be prepared according to a conventional method. For example, a binder, a thickener, a conductive material, a solvent, and the like are added to a negative electrode or positive electrode active material to form a slurry; the slurry is coated on a current collector, and then dried and pressed to prepare an electrode.
The density of the anode active material layer after drying and pressing is generally 1.45g/cm3Or more, preferably 1.55g/cm3Or more, particularly preferably 1.60g/cm3Or larger. It is preferable that the density of the anode active material layer is as high as possible because the capacity of the battery is high. The density of the positive electrode active material layer after drying and pressing is generally 3.0g/cm3Or larger.
This can be done: molding an active material to which a binder, a conductive material, and the like are added in situ by rolling to form a sheet-like electrode; or forming the sheet-like electrode by pressing; or a thin film of an electrode material is formed on the current collector by a method such as vapor deposition, sputtering, or plating.
Various current collectors can be used, and metals or alloys are generally used. Examples of the negative electrode collector include copper, nickel and stainless steel, and copper is preferably used. Examples of the positive electrode collector include metals such as aluminum, titanium, and tantalum and alloys thereof, and aluminum and alloys thereof are preferably used.
A porous film is generally interposed between the positive electrode and the negative electrode to prevent short-circuiting. In this case, the electrolyte solution is used in the form of being impregnated in a porous membrane. The material and shape of the porous film are not particularly limited as long as it is stable to an electrolyte solution and excellent in the ability to fix a liquid, and porous sheets, nonwoven fabrics, and the like formed from polyolefins such as polyethylene and polypropylene as raw materials are preferred.
The material of the case used in the battery of the present invention can be arbitrarily selected, and nickel-plated iron, stainless steel, aluminum or an alloy thereof, nickel, titanium, or the like can be used.
Examples
The present invention will now be more specifically explained with reference to the following examples and comparative examples, to which the present invention is not limited without departing from the spirit thereof.
[ production of negative electrode (1)]
94 parts by weight of graphite having a lattice plane(002 plane) having a d value of 0.336nm, a crystallite size (Lc) of 652nm, an ash content of 0.07% by weight, a median diameter of 12 μm as measured by a laser diffraction and scattering method, and a BET specific surface area of 7.5m was mixed with 6 parts by weight of polyvinylidene fluoride (trade name KF-1000, manufactured by Kureha chemical Industry Co., Ltd.)2The Raman spectrum obtained by adopting an argon laser is 1570-1620 cm-1. Peak of the range PAPeak intensity of (1)AAnd the center of the spectrum is 1300-1400 cm-1Peak of the range PBPeak intensity of (1)BIntensity ratio of (R) is IB/IAIs 0.12 and is located at 1570-1620 cm in spectrum-1The half-value width of the peak of the range was 19.9cm-1And N-methyl-2-pyrrolidone was added thereto to thereby form a slurry. The slurry was uniformly coated on one surface of a copper foil having a thickness of 18 μm and dried, followed by pressing to give a density of 1.5g/cm3Thereby producing the negative electrode (1).
[ production of negative electrode (2)]
A negative electrode (2) was produced in the same manner as the negative electrode (1) except that a copper foil having a thickness of 12 μm was used, the slurry was uniformly coated on both surfaces of a copper foil having a thickness of 18 μm and dried, and then pressed to give a density of 1.55g/cm3The negative electrode active material layer of (3).
[ preparation of Positive electrode (1)]
85 parts by weight of LiCoO26 parts by weight of carbon black and 9 parts by weight of polyvinylidene fluoride were mixed, N-methyl-2-pyrrolidone was added thereto to form a slurry, and the slurry was uniformly coated on both surfaces of an aluminum foil having a thickness of 20 μm and dried, and then pressed to make a density of 3.0g/cm3Thereby producing a positive electrode (1).
[ preparation of Positive electrode (2)]
The positive electrode (2) was prepared in the same manner as the positive electrode (1), except that an aluminum foil having a thickness of 14 μm was used.
[ production of cylindrical lithium Secondary Battery]
The positive electrode (2) and the negative electrode (2) were wound together with a polyethylene separator to prevent the positive electrode and the negative electrode from contacting each other, and the outermost annular faces were fixed with an adhesive tape to obtain a spiral-shaped electrode assembly. Next, as shown in fig. 1, insulating rings 7 were placed on the top and bottom of the spiral electrode assembly 4, and inserted into a stainless steel battery case, which was formed in a cylindrical shape, serving as a negative electrode terminal. Thereafter, a negative electrode terminal 6 connected to the negative electrode of the spiral electrode assembly 4 is welded to the inside of the battery can 1, and a positive electrode terminal 5 connected to the positive electrode of the electrode assembly is welded to the bottom of a current breaker 8, the current breaker 8 functioning when the gas pressure in the battery reaches a predetermined pressure. A current breaker and an explosion-proof valve are attached to the bottom of the sealing plate 2. After the electrolyte solution described below was added to the battery can 1, the open end of the battery can 1 was sealed with a sealing plate and a polypropylene insulating gasket 3 to produce a cylindrical battery having a volumetric capacity density of 133 mAh/cc.
[ evaluation of the Capacity of cylindrical Battery]
The cylindrical battery was charged at 25 ℃ to 4.2V at a constant current equivalent to 0.2C, and then discharged to 3V at a constant current equivalent to 0.2C. This operation was repeated for 3 cycles to stabilize the battery, and in the 4 th cycle, the battery was charged to 4.2V at a constant current of 0.5C and further charged at a constant voltage of 4.2V until the current value reached 0.05C, followed by discharging to 3V at a constant current of 0.2C, resulting in an initial discharge capacity.
As used herein, the term 1C refers to the current value at which the rated capacity of the battery is discharged within 1 hour, and 0.2C refers to 1/5 of the current value.
[ evaluation of continuous Charge characteristics of cylindrical Battery]
After the capacity evaluation was completed, the cylindrical battery was charged to 4.2V at 60 ℃ at a constant current of 0.5C, and then further continuously charged at a constant voltage for 2 weeks.
After the battery was cooled, the battery was discharged to 3V at 25 ℃ at a constant current of 0.2C, and then the retention capacity was measured after the continuous charge test, thereby obtaining the retention capacity after the continuous charge, assuming that the discharge capacity before the continuous charge test was 100.
[ evaluation of the cycle characteristics of cylindrical batteries]
After the capacity evaluation was completed, the cylindrical battery was subjected to a cycle test in which the battery was charged at 25 ℃ to 4.2V at a constant current of 1C and further charged at a constant voltage of 4.2V until the current value reached 0.05C, and then the battery was discharged to 3V at a constant current of 1C. The discharge capacity after 100 cycles was obtained, assuming that the discharge capacity before the cycle test was 100.
Example 1
2 parts by weight of vinylene carbonate was added to a mixture of 98 parts by weight of ethylene carbonate, ethylmethyl carbonate, dimethyl carbonate and diethyl carbonate (volume ratio: 2/4/2/2) under a dry argon atmosphere, and LiPF which had been sufficiently dried was added6LiBF of4Dissolved therein in respective proportions of 1.0 mol/L and 0.05 mol/L to prepare electrolyte solutions.
A cylindrical lithium secondary battery was prepared using the electrolyte solution thus prepared, and characteristics after continuous charging and cycle characteristics were evaluated. The results are shown in Table 1.
Example 2
2 parts by weight of vinylene carbonate was added to a mixture of 98 parts by weight of ethylene carbonate and ethyl methyl carbonate (volume ratio: 2/8), and the LiPF which had been sufficiently dried was added6LiB of (2)F4Dissolved therein in respective proportions of 1.0 mol/L and 0.05 mol/L to prepare electrolyte solutions.
A cylindrical lithium secondary battery was prepared using the electrolyte solution thus prepared, and characteristics after continuous charging and cycle characteristics were evaluated. The results are shown in Table 1.
Example 3
2 parts by weight of vinylene carbonate was added to 98 parts by weight of a mixture of ethylene carbonate and diethyl carbonate (volume ratio: 2/8), and the LiPF which had been sufficiently dried was added6LiBF of4Dissolved therein in respective proportions of 1.0 mol/L and 0.05 mol/L to prepare electrolyte solutions.
A cylindrical lithium secondary battery was prepared using the electrolyte solution thus prepared, and characteristics after continuous charging and cycle characteristics were evaluated. The results are shown in Table 1.
Comparative example 1
The LiPF which is fully dried6Was dissolved in a mixture of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and diethyl carbonate (volume ratio: 2/4/2/2) to make the ratio 1.0 mol/L, thereby preparing an electrolyte solution.
A cylindrical lithium secondary battery was prepared using the electrolyte solution thus prepared, and characteristics after continuous charging and cycle characteristics were evaluated. The results are shown in Table 1.
Comparative example 2
2 parts by weight of vinylene carbonate was added to a mixture of 98 parts by weight of ethylene carbonate, ethylmethyl carbonate, dimethyl carbonate and diethyl carbonate (volume ratio: 2/4/2/2), and the LiPF which had been sufficiently dried was added6Dissolved therein at a ratio of 1.0 mol/L to prepare an electrolyte solution.
A cylindrical lithium secondary battery was prepared using the electrolyte solution thus prepared, and characteristics after continuous charging and cycle characteristics were evaluated. The results are shown in Table 1.
The cylindrical battery was subjected to the operation of the current breaker due to the increase of the internal pressure during the continuous charge test, and thus could not be discharged.
Example 4
2 parts by weight of vinylene carbonate and 1 part by weight of cyclohexylbenzene were added to a mixture of 97 parts by weight of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and diethyl carbonate (volume ratio: 2/4/2/2), and LiPF which had been sufficiently dried was added6And LiBF4Dissolved therein in respective proportions of 1.0 mol/L and 0.05 mol/L to prepare electrolyte solutions.
A cylindrical lithium secondary battery was prepared using the electrolyte solution thus prepared, and characteristics after continuous charging and cycle characteristics were evaluated. The results are shown in Table 1.
Comparative example 3
2 parts by weight of vinylene carbonate and 1 part by weight of cyclohexylbenzene were added to a mixture of 97 parts by weight of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and diethyl carbonate (volume ratio: 2/4/2/2), and LiPF which had been sufficiently dried was added6Dissolved therein at a ratio of 1.0 mol/L to prepare an electrolyte solution.
A cylindrical lithium secondary battery was prepared using the electrolyte solution thus prepared, and characteristics after continuous charging and cycle characteristics were evaluated. The results are shown in Table 1.
The cylindrical battery was subjected to the operation of the current breaker due to the increase of the internal pressure during the continuous charge test, and thus could not be discharged.
Example 5
1 part by weight of vinylene carbonate was added to 99 parts by weight of a mixture of ethylene carbonate, ethylmethyl carbonate, dimethyl carbonate and diethyl carbonate (volume ratio: 2/4/2/2), and the LiPF which had been sufficiently dried was added6And LiBF4Dissolved therein in respective proportions of 1.0 mol/L and 0.05 mol/L to prepare electrolyte solutions.
A cylindrical lithium secondary battery was prepared using the electrolyte solution thus prepared, and characteristics after continuous charging and cycle characteristics were evaluated. The results are shown in Table 1.
Example 6
0.5 part by weight of carbonateEthylene ester was added to 99.5 parts by weight of a mixture of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and diethyl carbonate (volume ratio: 2/4/2/2), and the LiPF which had been sufficiently dried was added6And LiBF4Dissolved therein in respective proportions of 1.0 mol/L and 0.05 mol/L to prepare electrolyte solutions.
A cylindrical lithium secondary battery was prepared using the electrolyte solution thus prepared, and characteristics after continuous charging and cycle characteristics were evaluated. The results are shown in Table 1.
Comparative example 4
1 part by weight of vinylene carbonate was added to 99 parts by weight of a mixture of ethylene carbonate, ethylmethyl carbonate, dimethyl carbonate and diethyl carbonate (volume ratio: 2/4/2/2), and the LiPF which had been sufficiently dried was added6Dissolved therein at a ratio of 1.0 mol/L to prepare an electrolyte solution.
A cylindrical lithium secondary battery was prepared using the electrolyte solution thus prepared, and characteristics after continuous charging and cycle characteristics were evaluated. The results are shown in Table 1.
The cylindrical battery was subjected to the operation of the current breaker due to the increase of the internal pressure during the continuous charge test, and thus could not be discharged.
Comparative example 5
0.5 part by weight of vinylene carbonate was added to 99.5 parts by weight of a mixture of ethylene carbonate, ethylmethyl carbonate, dimethyl carbonate and diethyl carbonate (volume ratio: 2/4/2/2), and the LiPF which had been sufficiently dried was added6Dissolved therein at a ratio of 1.0 mol/L to prepare an electrolyte solution.
A cylindrical lithium secondary battery was prepared using the electrolyte solution thus prepared, and characteristics after continuous charging and cycle characteristics were evaluated. The results are shown in Table 1.
The cylindrical battery was subjected to the operation of the current breaker due to the increase of the internal pressure during the continuous charge test, and thus could not be discharged.
Comparative example 6
Adding 0.1 part by weight of vinylene carbonate to 99.9 parts by weightIn a mixture of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and diethyl carbonate (volume ratio: 2/4/2/2), LiPF which has been sufficiently dried is added6Dissolved therein at a ratio of 1.0 mol/L to prepare an electrolyte solution.
A cylindrical lithium secondary battery was prepared using the electrolyte solution thus prepared, and characteristics after continuous charging and cycle characteristics were evaluated. The results are shown in Table 1.
In Table 1, comparison between examples 1 to 3 and comparative examples 1 and 2 shows that LiBF was added thereto4Examples 1 to 3 of (1) have excellent continuous charging characteristics and cycle characteristics. In comparative example 2, since LiBF was not added4And thus cannot suppress gas generation, and thus has deteriorated continuous charging characteristics although the cycle characteristics are improved by the addition of vinylene carbonate.
Comparison between example 1 and examples 2 and 3 shows that example 1 having a symmetrical chain carbonate and an asymmetrical chain carbonate has superior continuous charging characteristics and cycle characteristics than examples 2 and 3.
Comparison between example 4 and comparative example 3 shows that even in the case where cyclohexylbenzene is contained as an overcharge inhibitor, LiBF was added thereto4Example 4 of (a) also had excellent sustained charging characteristics and cycle characteristics.
Comparison between examples 5 and 6 and comparative examples 4 to 6 shows that LiBF was added even in the case of changing the concentration of vinylene carbonate4Examples 5 and 6 of (a) still had excellent continuous charging characteristics and cycle characteristics.
TABLE 1
| Concentration of lithium salt (mol/L) | Kind of solvent | ||
| Has been dried sufficiently LiPF of6 | LiBF4 | ||
| Example 1 | 1.0 | 0.05 | EC/EMC，DMC，DEC/VC |
| Example 2 | 1.0 | 0.05 | EC/EMC/VC |
| Example 3 | 1.0 | 0.05 | EC/DEC/VC |
| Comparative example 1 | 1.0 | - | EC/EMC，DMC，DEC |
| Comparative example 2 | 1.0 | - | EC/EMC，DMC，DEC/VC |
| Example 4 | 1.0 | 0.05 | EC/EMC，DMC，DEC/VC |
| Comparative example 3 | 1.0 | - | EC/EMC，DMC，DEC/VC |
| Example 5 | 1.0 | 0.05 | EC/EMC，DMC，DEC/VC |
| Example 6 | 1.0 | 0.05 | EC/EMC，DMC，DEC/VC |
| Comparative example 4 | 1.0 | - | EC/EMC，DMC，DEC/VC |
| Comparative example 5 | 1.0 | - | EC/EMC，DMC，DEC/VC |
| Comparative example 6 | 1.0 | - | EC/EMC，DMC，DEC/VC |
In the above table, EC represents ethylene carbonate, EMC represents ethyl methyl carbonate, DMC represents dimethyl carbonate, DEC represents diethyl carbonate, and VC represents vinylene carbonate.
TABLE 1 (continuation)
| Retention capacity after continuous charging test (%) | Discharge capacity after 100 cycles (%) | |
| Example 1 | 97 | 85 |
| Example 2 | 95 | 83 |
| Example 3 | 91 | 81 |
| Comparative example 1 | 82 | 77 |
| Comparative example 2 | Circuit breaker operation | 82 |
| Example 4 | 93 | 85 |
| Comparative example 3 | Circuit breaker operation | 81 |
| Example 5 | 97 | 84 |
| Example 6 | 95 | 81 |
| Comparative example 4 | Circuit breaker operation | 81 |
| Comparative example 5 | Circuit breaker operation | 80 |
| Comparative example 6 | 83 | 78 |
[ production of sheet-shaped lithium Secondary Battery]
A positive electrode (1), a negative electrode (1) and a polyethylene separator were stacked in this order as a negative electrode, a separator, a positive electrode, a separator and a negative electrode to prepare a unit cell, and the unit cell was packed in a pouch formed of an aluminum laminated film (thickness: 40 μm) coated on both sides with resin layers in such a manner that terminals of the positive electrode and the negative electrode were exposed to the outside. Subsequently, an electrolyte solution described below was added thereto, followed by vacuum sealing, to prepare a sheet-shaped battery.
[ evaluation of capacity of sheet Battery]
The sheet-shaped battery was fixed between glass plates to improve the contact between the electrodes, and the battery was charged to 4.2V at a constant current equivalent to 0.2C and then discharged to 3V at a constant current equivalent to 0.2C. This operation was repeated for 3 cycles to stabilize the battery, and in the 4 th cycle, the battery was charged to 4.2V at a constant current of 0.5C and further charged at a constant voltage of 4.2V until the current reached 0.05C, followed by discharging to 3V at a constant current of 0.2C, resulting in an initial discharge capacity.
[ evaluation of continuous Charge characteristics]
(1) Gas production rate
After the completion of the capacity evaluation, the battery was charged at 60 ℃ to 4.25V at a constant current of 0.5C, and then further constant-voltage charging was continued for 1 week.
After the cell was cooled, the cell was immersed in an ethanol bath to measure its volume, and the gas production was obtained from the volume change before and after continuous charging.
(2) Reserve capacity after continuous charging
After measuring the gas production amount, the battery was discharged to 3V at 25 ℃ at a constant current of 0.2C to measure the retention capacity after the continuous charge test and obtain the retention capacity of the continuous charge assuming that the discharge capacity before the continuous charge test was 100.
Example 7 and comparative examples 7 to 10
1 part by weight of vinylene carbonate was added to a mixture of 99 partsby weight of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate (volume ratio: 3/5/2), and the LiPF which had been sufficiently dried was added6And cyclic lithium 1, 3-perfluoropropanedisulfonimide were dissolved in the above-mentioned solvent in the respective proportions shown in Table 2 below to prepare electrolyte solutions.
A sheet-shaped battery was prepared using the thus prepared electrolyte solution, and the continuous charging characteristics were evaluated. The results are shown in table 2 below.
As can be seen from table 2, the battery including the lithium salt represented by the following formula (1) in a specific ratio is excellent in gas generation and sustained charge characteristics.
TABLE 2
| Concentration of lithium salt | Gas production (mL) | Retention capacity (%) | ||
| Has been dried sufficiently Dried LiPF6 | Formula (1) | |||
| Example 7 | 0.8 | 0.2 | 0.24 | 75 |
| Comparative example 7 | 1 | - | 0.57 | 75 |
| Comparative example 8 | 0.5 | 0.5 | 0.44 | 74 |
| Comparative example 9 | 0.2 | 0.8 | 0.58 | 68 |
| Comparative example 10 | - | 1 | 1.01 | 0 |
In the table, formula (1) represents a cyclic lithium 1, 3-perfluoropropanedisulfonimide.
The present invention has been described in detail with reference to specific embodiments thereof, but it will be apparent to one of ordinary skill in the art that various substitutions and modifications can be made thereto without departing from the spirit and scope thereof.
The basis of this application is: japanese patent applications (patent application No. 2003-51684) filed on 27/2/2003, Japanese patent application (patent application No. 2003-134694) filed on 13/5/2003, and Japanese patent application (patent application No. 2003-174756) filed on 19/6/2003, the entire disclosures of which are incorporated herein by reference.
Industrial applicability
According to the present invention, a battery can be prepared: which has a high capacity, excellent storage characteristics, cycle characteristics and continuous charging characteristics, and a small gas production amount, thereby making it possible to obtain a lithium secondary battery having a reduced size and improved performance.
Claims (16)
1. A non-aqueous electrolyte solution comprising a lithium salt and a non-aqueous solvent dissolving the lithium salt, wherein the electrolyte solution comprises LiPF at a concentration of 0.2 to 2 mol/L6And relative to LiPF6In a molar ratio of 0.005 to 0.4, and a LiBF4And/or a compound represented by the following formula (1) as a lithium salt; the nonaqueous solvent mainly contains:
(1) ethylene carbonate and/or propylene carbonate,
(2-1) a symmetrical chain carbonate,
(2-2) an asymmetric chain carbonate, and
(3) vinylene carbonate:
(wherein R represents a linear or branched alkylene group having 1 to 20 carbon atoms, which may be substituted with a fluorine atom, provided that the alkylene chain has not more than 12 carbon atoms except for the side chain).
2. The non-aqueous electrolyte solution according to claim 1, wherein the electrolyte solution comprises LiBF at a concentration of 0.001 to 0.3 mol/L4And/or a compound represented by the following formula (1).
3. A non-aqueous electrolyte solution comprises a lithium salt and a non-aqueous solvent for dissolving the lithium salt, wherein the electrolyte solution comprises LiPF at a concentration of 0.2-2 mol/L6And LiBF at a concentration of 0.001 to 0.3 mol/L4As a lithium salt; and the nonaqueous solvent mainly comprises:
(1) ethylene carbonate and/or propylene carbonate,
(2-1) a symmetrical chain carbonate,
(2-2) an asymmetric chain carbonate, and
(3) vinylene carbonate.
4. The nonaqueous electrolyte solution according to claim 3, wherein the electrolyte solution contains LiPF6In a molar ratio of 0.005 to 0.4, and a LiBF4。
5. A nonaqueous electrolyte solution comprising a lithium salt and a nonaqueous solvent dissolving the lithium salt, wherein the electrolyte solutionThe electrolyte solution contains LiPF with the concentration of 0.5-2.5 mol/L6And a lithium salt represented by the following formula (1) at a concentration of 0.001 to 0.3 mol/L, as the lithium salt:
(wherein R represents a linear or branched alkylene group having 1 to 20 carbon atoms, which may be substituted with a fluorine atom, provided that the alkylene chain has not more than 12 carbon atoms except for the side chain).
6. The nonaqueous electrolyte solution according to claim 5, wherein the nonaqueous solvent mainly contains:
(1) ethylene carbonate and/or propylene carbonate,
(2-1) a symmetrical chain carbonate,
(2-2) a symmetrical chain carbonate, and
(3) vinylene carbonate.
7. The nonaqueous electrolyte solution according to any one of claims 1 to 6, wherein a total amount of ethylene carbonate, propylene carbonate, symmetrical chain carbonate, asymmetrical chain carbonate, and vinylene carbonate other than the lithium salt in the nonaqueous electrolyte solution is 80% by weight or more.
8. The nonaqueous electrolyte solution according to any one of claims 1 to 7, wherein the proportion of the vinylene carbonate in the nonaqueous electrolyte solution other than the lithium salt is 0.01 to 8% by weight.
9. The non-aqueous electrolyte solution of any one of claims 1 to 8, wherein the symmetrical carbonate is selected from dimethyl carbonate and diethyl carbonate and the asymmetrical carbonate is selected from ethyl methyl carbonate.
10. The nonaqueous electrolyte solution according to any one of claims 1 to 9, wherein a volume ratio of the total amount of the ethylene carbonate (1) to the total amount of the symmetrical chain carbonate (2-1) and the asymmetrical chain carbonate (2-2) is 10/90 to 70/30.
11. The nonaqueous electrolyte solution according to any one of claims 1 to 10, wherein the nonaqueous solvent further contains an aromatic compound selected from the group consisting of: biphenyl, alkylbiphenyl, terphenyl, partial hydrogenation products of terphenyl, cyclohexylbenzene, tert-butylbenzene, tert-amylbenzene, diphenyl ether and dibenzofuran.
12. According to one of claims 1 to 11The nonaqueous electrolyte solution of (1), wherein the electrolyte solutionAnd a lithium salt having a concentration of 0.001 to 0.2 mol/L and selected from the group consisting of: LiN (CF)3SO2)2，LiN(C2F5SO2)2And LiCF3SO3。
13. A lithium secondary battery characterized in that it comprises a negative electrode and a positive electrode capable of inserting and extracting lithium, and the nonaqueous electrolyte solution according to one of claims 1 to 12.
14. The lithium secondary battery according to claim 13, wherein the positive electrode comprises, as a positive electrode active material, a lithium-transition metal composite oxide selected from the group consisting of a lithium-cobalt oxide, a lithium-nickel oxide and a lithium-manganese oxide, or a composite oxide obtained by substituting a part of transition metals in the composite oxide with another metal.
15. A lithium secondary battery comprising a negative electrode and a positive electrode capable of intercalating and deintercalating lithium, and a nonaqueous electrolyte solution, wherein
The negative electrode contains a carbonaceous material as an active material; the nonaqueous electrolyte solution mainly contains a lithium salt and a nonaqueous solvent dissolving the lithium salt, and the nonaqueous electrolyte solution contains LiPF as the lithium salt at a concentration of 0.2 to 2 mol/L6And relative to LiPF6In a molar ratio of 0.005 to 0.4, and a LiBF4And/or a lithium salt represented by the following formula (1); the nonaqueous solvent mainly contains:
(1) ethylene carbonate and/or propylene carbonate,
(2) chain carbonate, and
(3) vinylene carbonate:
(wherein R represents a linear or branched alkylene group having 1 to 20 carbon atoms, which may be substituted with a fluorine atom, provided that the alkylene chain has not more than 12 carbon atoms except for the side chain).
16.A nonaqueous electrolyte solution for a lithium secondary battery, comprising: a negative electrode containing a carbonaceous material as an active material capable of inserting and extracting lithium; a positive electrode containing an active material capable of inserting and extracting lithium; and a nonaqueous electrolyte solution mainly comprising a lithium salt and a nonaqueous solvent dissolving the lithium salt, wherein
The non-aqueous electrolyte solution contains LiPF at a concentration of 0.2 to 2 mol/L as a lithium salt6To do so byAnd relative to LiPF6In a molar ratio of 0.005 to 0.4, and a LiBF4And/or a lithium salt represented by the following formula (1); and the nonaqueous solvent mainly comprises:
(1) ethylene carbonate and/or propylene carbonate,
(2) chain carbonate, and
(3) vinylene carbonate:
(wherein R represents a linear or branched alkylene group having 1 to 20 carbon atoms, which may be substituted with a fluorine atom, provided that the alkylene chain has not more than 12 carbon atoms except for the side chain).
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP51684/2003 | 2003-02-27 | ||
| JP2003051684 | 2003-02-27 | ||
| JP134694/2003 | 2003-05-13 | ||
| JP174756/2003 | 2003-06-19 |
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| CN1698232A true CN1698232A (en) | 2005-11-16 |
| CN100347903C CN100347903C (en) | 2007-11-07 |
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| CN (1) | CN100347903C (en) |
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