WO2018099091A1 - 一种电解液及二次电池 - Google Patents

一种电解液及二次电池 Download PDF

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WO2018099091A1
WO2018099091A1 PCT/CN2017/093005 CN2017093005W WO2018099091A1 WO 2018099091 A1 WO2018099091 A1 WO 2018099091A1 CN 2017093005 W CN2017093005 W CN 2017093005W WO 2018099091 A1 WO2018099091 A1 WO 2018099091A1
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substituted
unsubstituted
group
electrolyte
compound
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PCT/CN2017/093005
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English (en)
French (fr)
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张昌明
付成华
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宁德时代新能源科技股份有限公司
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Publication of WO2018099091A1 publication Critical patent/WO2018099091A1/zh

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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
    • H01M10/0567—Liquid materials characterised by the additives
    • 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
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • 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
    • 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 application relates to the field of battery technologies, and in particular, to an electrolyte and a secondary battery.
  • Lithium-ion batteries are widely used in consumer electronics and energy storage and power batteries because of their high specific energy, long cycle life and low self-discharge.
  • the use environment has long been versatile, and the requirements for battery life and high temperature performance are getting higher and higher.
  • the battery still has a long life in the case of rapid charging and discharging at a large rate, and there is no safety risk when working at a high temperature for a long time.
  • the life and high temperature performance of lithium-ion batteries are affected by many factors. Among them, non-aqueous electrolytes have an important impact on lithium-ion batteries.
  • the non-aqueous electrolyte can improve the dynamic performance of the battery, reduce the polarization of large-magnification, and the stability of the interface between the positive and negative electrodes during the cycle and high-temperature storage to achieve the purpose of improving life and safety.
  • the first object of the present application is to propose an electrolytic solution.
  • a second object of the present invention is to provide a secondary battery.
  • the present application relates to an electrolyte comprising a solvent, an electrolyte and an additive, the additive comprising a barbituric acid compound and an SEI film-forming additive.
  • the barbituric acid compound is selected from at least one of the compounds of the formula I,
  • R 11 and R 12 are each independently selected from substituted or unsubstituted C 1 -C 12 alkyl, substituted or unsubstituted C 2 -C 12 alkenyl, substituted or unsubstituted C 6 -C 26 aromatic base;
  • R 13 and R 14 are each independently selected from hydrogen, amino, substituted or unsubstituted C 1 -C 12 alkyl, substituted or unsubstituted C 2 -C 12 alkenyl, substituted or unsubstituted C 6 -C 26 aryl, -NH-R ', wherein R' is a substituted or unsubstituted C 1 ⁇ C 12 alkyl; and
  • X is selected from an O atom or an S atom
  • the substituent is selected from halogen.
  • R 11 and R 12 are each independently selected from a substituted or unsubstituted C 1 -C 6 alkyl group, a substituted or unsubstituted phenyl group; and R 13 and R 14 are each independently selected from hydrogen, substituted or unsubstituted. C 1 -C 6 alkyl, substituted or unsubstituted phenyl, amino.
  • the barbituric acid compound is selected from at least one of the following compounds,
  • the SEI film-forming additive is at least one selected from the group consisting of a cyclic carbonate compound, a cyclic sulfate compound, a sultone compound, a methylene disulfonate compound, a sulfone compound, and a dinitrile compound.
  • the structural formula of the cyclic carbonate compound is as shown in Formula IIA
  • the structural formula of the cyclic sulfate compound is as shown in Formula IIB
  • the structural formula of the sultone compound is as in Formula IIC.
  • the structural formula of the dinitrile compound is as shown in formula IID
  • the methylene disulfonate compound is selected from methylene methane disulfonate;
  • R 21 , R 22 and R 23 are each independently selected from a substituted or unsubstituted C 1 -C 6 alkylene group, a substituted or unsubstituted C 2 -C 6 alkenylene group;
  • R 24 is selected from substituted or unsubstituted C 1 -C 12 alkylene, substituted or unsubstituted C 2 -C 12 alkenylene, C 6 -C 12 arylene;
  • the substituent is selected from the group consisting of halogen, C 1 -C 6 alkyl, and C 2 -C 6 alkenyl.
  • R 21 , R 22 and R 23 are each independently selected from a substituted or unsubstituted C 1 -C 4 alkylene group, a substituted or unsubstituted C 2 -C 4 alkenylene group; the substituent is selected from halogen C 1 -C 3 alkyl, C 2 -C 4 alkenyl; R 24 is selected from C 1 -C 6 alkylene, C 2 -C 6 alkenylene, C 6 -C 12 arylene.
  • the SEI film-forming additive is selected from the group consisting of vinylene carbonate, fluoroethylene carbonate, 1,3-propane sultone, vinyl vinylene carbonate, 1,3-propene sultone, sulfuric acid At least one of vinyl ester, methylene methane disulfonate, polyether sulfone, adiponitrile, and the like.
  • the barbituric acid compound is contained in the electrolyte in an amount of 0.01% to 3% by mass; preferably 0.05% to 2%.
  • the SEI film-forming additive is contained in the electrolyte in an amount of 0.01% to 30% by mass; preferably 0.1% to 10%.
  • the present application relates to a secondary battery including a positive electrode sheet, a negative electrode sheet, a separator disposed between the positive electrode sheet and the negative electrode sheet, and the foregoing electrolytic solution.
  • the application of the barbituric acid compound and the SEI film-forming additive as a functional additive can significantly improve the low-temperature discharge performance, cycle performance, and high-temperature storage performance of the battery. Box performance and overcharge performance.
  • the present application relates to an electrolyte comprising a solvent, an electrolyte and an additive, the additive comprising a barbituric acid compound and an SEI film-forming additive.
  • CEI dense solid electrolyte phase interface film
  • the negative electrode film forming (SEI) additive is mainly reduced in the negative electrode during the first charging of the battery, and the product adheres to the surface of the negative electrode to form a stable solid electrolyte membrane, thereby preventing the solvent of the ion conducting ion from being further reduced during charging and discharging.
  • SEI films have a great influence on the internal resistance of the negative electrode interface.
  • the present application has found through research that when a barbituric acid compound is used together with an SEI film-forming additive, a stable passivation film can be formed on both the positive and negative electrodes of the secondary battery, and the battery can be significantly improved by the presence of effective and stable CEI and SEI. Low temperature discharge performance, cycle performance, high temperature storage performance, hot box performance and overcharge performance after cycling.
  • the barbituric acid compound of the present application is selected from at least one of the compounds of the formula I,
  • R 11 and R 12 are each independently selected from substituted or unsubstituted C 1 -C 12 alkyl, substituted or unsubstituted C 2 -C 12 alkenyl, substituted or unsubstituted C 6 -C 26 aromatic base;
  • R 13 and R 14 are each independently selected from hydrogen, amino, substituted or unsubstituted C 1 -C 12 alkyl, substituted or unsubstituted C 2 -C 12 alkenyl, substituted or unsubstituted C 6 -C 26 aryl, -NH-R ', wherein, R' is a substituted or unsubstituted C 1 ⁇ C 12 alkyl; and
  • X is selected from an O atom or an S atom
  • the substituent is selected from halogens such as F and Cl.
  • an alkyl group having 1 to 12 carbon atoms an alkyl group may be a chain alkyl group or a cycloalkyl group, and a hydrogen group at a ring of a cycloalkyl group may be substituted with an alkyl group.
  • the lower limit of the number of carbon atoms in the alkyl group is preferably 2, 3, 4, 5, and the preferred upper limit is 3, 4, 5, 6, 8, 10, 12.
  • an alkyl group having 1 to 10 carbon atoms is selected, and more preferably, a chain alkyl group having 1 to 6 carbon atoms and a cycloalkyl group having 3 to 8 carbon atoms are selected, and still more preferably, A chain alkyl group having 1 to 4 carbon atoms and a cycloalkyl group having 5 to 7 carbon atoms are selected.
  • Specific examples of the alkyl group include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, and new.
  • the alkenyl group having 2 to 12 carbon atoms may be a cyclic alkenyl group or a chain alkenyl group. Further, the number of double bonds in the alkenyl group is preferably one.
  • the lower limit of the number of carbon atoms in the alkenyl group is preferably 3, 4, 5, and the preferred upper limit is 3, 4, 5, 6, 8, 10, 12, 14, 16, 18.
  • a chain alkenyl group having 2 to 10 carbon atoms is selected, and more preferably, a chain alkenyl group having 2 to 6 carbon atoms is selected, and more preferably, an alkene having 2 to 5 carbon atoms is selected. base.
  • alkenyl group examples include a vinyl group, an allyl group, an isopropenyl group, a pentenyl group, and a cyclohexenyl group. Cycloheptenyl, cyclooctenyl.
  • An aryl group having 6 to 26 carbon atoms such as a phenyl group, a phenylalkyl group, an aryl group containing at least one phenyl group such as a biphenyl group, a fused ring aromatic hydrocarbon group such as naphthalene, anthracene or phenanthrene, a biphenyl group and a thick group.
  • the cycloaromatic hydrocarbon group may also be substituted by an alkyl group or an alkenyl group.
  • an aryl group having 6 to 16 carbon atoms is selected, and more preferably, an aryl group having 6 to 14 carbon atoms is selected, and even more preferably an aryl group having 6 to 9 carbon atoms is selected.
  • Specific examples of the aryl group include a phenyl group, a benzyl group, a biphenyl group, a p-tolyl group, an o-tolyl group, and an m-tolyl group.
  • the halogenated alkyl group is a halogenated alkyl group having 1 to 20 carbon atoms, a halogenated alkenyl group having 2 to 20 carbon atoms or a halogenated aryl group having 6 to 26 carbon atoms, wherein the halogen atom is F, Cl or Br, and preferably F or Cl.
  • the halogen atom may be substituted for a part of hydrogen atoms or all hydrogen atoms, and the number of halogen atoms may be 1, 2, 3 or 4.
  • a halogenated alkyl group having 1 to 10 carbon atoms, a halogenated alkenyl group having 2 to 10 carbon atoms, or a halogenated aryl group having 6 to 16 carbon atoms is selected, and more preferably, the number of carbon atoms is selected.
  • a halogenated chain alkyl group having 1 to 4 carbon atoms, a halogenated cycloalkyl group having 5 to 7 carbon atoms, a halogenated alkenyl group having 2 to 5 carbon atoms, and carbon are selected.
  • the atom is a halogenated aryl group of 6 to 10.
  • halogenated group examples include trifluoromethyl (-CF 3 ), 2-fluoroethyl, 3-fluoro-n-propyl, 2-fluoroisopropyl, 4-fluoro-n-butyl, 3-fluorosec-butyl, 5-fluoro-n-pentyl, 4-fluoroisopentyl, 1-fluorovinyl, 3-fluoroallyl, 6-fluoro-4-hexenyl, o-fluorophenyl, p- Fluorophenyl, m-fluorophenyl, 4-fluoromethylphenyl, 2,6-difluoromethylphenyl, 2-fluoro-1-naphthyl, fluoromethoxy.
  • F may be substituted by Cl and/or Br.
  • R 11 and R 12 are each independently selected from a substituted or unsubstituted C 1 -C 6 alkyl group, a substituted or unsubstituted C 2 -C 6 alkenyl group, a substituted or not Substituted phenyl;
  • R 13 and R 14 are each independently selected from hydrogen, amino, substituted or unsubstituted C 1 -C 6 alkyl, substituted or unsubstituted C 2 -C 6 alkenyl, substituted or unsubstituted Phenyl.
  • R 11 and R 12 are each independently selected from a substituted or unsubstituted C 1 -C 6 alkyl group, a substituted or unsubstituted phenyl group; and R 13 and R 14 are each independently selected. From hydrogen, amino, substituted or unsubstituted C 1 -C 6 alkyl, substituted or unsubstituted phenyl.
  • R 11 and R 12 are each independently selected from a substituted or unsubstituted C 1 -C 6 alkyl group, a phenyl group; and R 13 and R 14 are each independently selected from hydrogen and an amino group.
  • R 11 and R 12 are the same substituents.
  • R 13 and R 14 are simultaneously hydrogen, or at least one of R 13 and R 14 is hydrogen, and the other substituent is selected from amino, substituted or unsubstituted C 1 -C 6 alkyl, substituted or unsubstituted phenyl.
  • the barbituric acid compound of the present application is selected from at least one of the following compounds:
  • the barbituric acid compound of the present application may also be selected from at least one of the following compounds:
  • the mass percentage of the barbituric acid compound of the present application in the electrolyte is from 0.01% to 3%.
  • the content of the barbituric acid compound is less than 0.01%, a complete and effective CEI film cannot be formed on the surface of the positive electrode, thereby failing to effectively prevent the electrolyte and the electrode.
  • Positive electrode interface stability is provided.
  • the upper limit of the mass percentage range of the barbituric acid compound in the electrolytic solution of the present application is selected from 3%, 2.8%, 2.5%, 2.0%, 1.5%, 1.0%, and the lower limit is selected from 0.01%. , 0.03%, 0.05%, 0.1%, 0.3%, 0.5%, 0.6%. Still more preferably, the percentage of the barbituric acid compound in the electrolyte is from 0.05% to 2%.
  • the SEI film-forming additive is selected from the group consisting of a cyclic carbonate compound, a cyclic sulfate compound, a sultone compound, a methylene disulfonate compound, a sulfone compound, and a nitrile compound. At least one.
  • the structural formula of the cyclic carbonate compound is as shown in Formula IIA, and R 21 is selected from a substituted or unsubstituted C 1 -C 6 alkylene group, a substituted or unsubstituted C 2 -C. a 6 alkenylene group; the substituent is selected from the group consisting of halogen, C 1 -C 6 alkyl, C 2 -C 6 alkenyl;
  • R 21 is selected from a substituted or unsubstituted C 1 -C 4 alkylene group, a substituted or unsubstituted C 2 -C 4 alkenylene group; the substituent is selected from halogen, C 1 -C 3 alkyl group, C 2 -C 4 alkenyl group.
  • the cyclic carbonate compound is at least one selected from the group consisting of fluoroethylene carbonate, vinylene carbonate, and vinyl ethylene carbonate; the specific structural formula is as follows:
  • the cyclic carbonate compound may also be selected from:
  • the structural formula of the cyclic sulfate compound is as shown in Formula IIB, and R 22 is selected from a substituted or unsubstituted C 1 -C 6 alkylene group, a substituted or unsubstituted C 2 -C. a 6 alkenylene group; the substituent is selected from the group consisting of halogen, C 1 -C 6 alkyl, C 2 -C 6 alkenyl;
  • R 22 is selected from a substituted or unsubstituted C 1 -C 4 alkylene group, a substituted or unsubstituted C 2 -C 4 alkenylene group; the substituent is selected from halogen, C 1 -C 3 alkyl group, C 2 -C 4 alkenyl group.
  • the cyclic sulfate compound is at least one selected from the group consisting of ethylene sulfate, 4-methyl ethylene sulfate, and propylene sulfate, and the specific structural formula is as follows;
  • the cyclic sulfate compound is selected from the group consisting of ethylene sulfate.
  • the cyclic sulfate compound may also be selected from:
  • the structural formula of the sultone compound is as shown in formula IIC, and R 23 is selected from a substituted or unsubstituted C 1 -C 6 alkylene group, a substituted or unsubstituted C 2 -C. a 6 alkenylene group; the substituent is selected from the group consisting of halogen, C 1 -C 6 alkyl, C 2 -C 6 alkenyl;
  • R 23 is selected from a substituted or unsubstituted C 1 -C 4 alkylene group, a substituted or unsubstituted C 2 -C 4 alkenylene group; the substituent is selected from halogen, C 1 -C 3 alkyl group, C 2 -C 4 alkenyl group.
  • the sultone compound is at least one selected from the group consisting of 1,3-propane sultone, 1,4-butane sultone, and 1,3-propene sultone.
  • the specific structural formula is as follows;
  • the sultone compound is at least one selected from the group consisting of 1,3-propane sultone and 1,3-propene sultone.
  • the sultone compound can also be selected from:
  • the structural formula of the dinitrile compound is as shown by IID;
  • R 24 is selected from a substituted or unsubstituted C 1 -C 12 alkylene group, a substituted or unsubstituted C 2 -C 12 alkenylene group, and a C 6 -C 12 arylene group, wherein the substituent is selected From halogen, C 1 -C 6 alkyl, C 2 -C 6 alkenyl.
  • R 24 is selected from the group consisting of C 1 -C 6 alkylene, C 2 -C 6 alkenylene, C 6 -C 12 arylene.
  • the dinitrile compound is selected from at least one of dinitrile, malononitrile and glutaronitrile.
  • the dinitrile compound is selected from the group consisting of dinitrile.
  • the dinitrile compound may also be selected from at least one of the dinitrile compounds shown by the following structures;
  • the methylene disulfonate compound is selected from methane methane disulfonate, as shown in Formula IIE;
  • the sulfone compound is selected from polyethersulfone.
  • the SEI film-forming additive is selected from the group consisting of vinylene carbonate (VC), fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), and vinyl carbonate.
  • VEC vinyl ester
  • PST 1,3-propene sultone
  • DTD vinyl sulphate
  • MMDS methane methane disulfonate
  • PES polyether sulfone
  • ADN adiponitrile
  • the mass percentage of the SEI film-forming additive in the present application is from 0.01% to 30%, more preferably from 0.1% to 10%.
  • the upper limit of the mass percentage range of the SEI film-forming additive in the electrolyte is selected from the group consisting of 5%, 7%, 8%, 12%, 15%, 18%, 20%, 22%, 25 %, the lower limit is selected from 0.05%, 0.08%, 0.2%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 2%, 3%. Still more preferably, the SEI film-forming additive compound is present in the electrolyte in an amount of from 0.2% to 8%.
  • the organic solvent of the present application is selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, fluoroethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate. , diethyl carbonate (DEC), dipropyl carbonate, methyl propyl carbonate, carbonic acid At least one of ethyl propyl ester, 1,4-butyrolactone, methyl propionate, methyl butyrate, propyl propionate, ethyl acetate, ethyl propionate, and ethyl butyrate.
  • EC ethylene carbonate
  • PC propylene carbonate
  • DEC diethyl carbonate
  • dipropyl carbonate methyl propyl carbonate
  • carbonic acid At least one of ethyl propyl ester, 1,4-butyrolactone, methyl propionate, methyl butyrate, propyl propionate, ethyl
  • the lithium salt of the present application is selected from at least one of an organic lithium salt or an inorganic lithium salt.
  • the lithium salt of the present application contains at least one of a fluorine element, a boron element, and a phosphorus element.
  • the lithium salt of the present application is selected from lithium hexafluorophosphate LiPF 6 , lithium bistrifluoromethanesulfonimide LiN(CF 3 SO 2 ) 2 (abbreviated as LiTFSI), bis(fluorosulfonyl) Lithium lithium Li(N(SO 2 F) 2 ) (abbreviated as LiFSI), lithium bis(oxalate) borate LiB(C 2 O 4 ) 2 (abbreviated as LiBOB), lithium difluorooxalate borate LiBF 2 (C 2 O 4 ) ( At least one of LiDFOB).
  • LiTFSI lithium bistrifluoromethanesulfonimide LiN(CF 3 SO 2 ) 2
  • LiFSI bis(fluorosulfonyl) Lithium lithium Li(N(SO 2 F) 2 )
  • LiBOB lithium bis(oxalate) borate LiB(C 2 O 4 ) 2
  • LiBOB lithium difluoroox
  • the present application also relates to a secondary battery comprising a positive electrode sheet, a negative electrode sheet, a separator disposed between the positive electrode sheet and the negative electrode sheet, and an electrolyte;
  • the positive electrode sheet includes a cathode current collector and is coated on the cathode current collector.
  • the positive electrode film, the negative electrode sheet includes a negative electrode current collector and an negative electrode film coated on the negative electrode current collector; and the electrolytic solution is the electrolytic solution described in any of the above paragraphs.
  • the positive electrode film of the present application includes a positive electrode active material, a binder, and a conductive agent.
  • the positive electrode active material of the present application is at least one selected from the group consisting of lithium cobaltate LiCoO 2 , lithium nickel manganese cobalt ternary material, lithium iron phosphate, and lithium manganate.
  • a mixture of a lithium cobaltate and a lithium nickel manganese cobalt ternary material of the positive electrode active material of the present application is provided.
  • the negative electrode membrane of the present application includes a negative electrode active material, a binder, and a conductive agent.
  • the anode active material of the present application is graphite and/or silicon.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • PC propylene carbonate
  • propionic acid B in an argon atmosphere glove box with a water content of ⁇ 10 ppm
  • the ester is uniformly mixed at a mass ratio of 20:30:20:30 to obtain a nonaqueous solvent, and the sufficiently dried lithium salt LiPF 6 is dissolved in the above nonaqueous solvent to prepare a basic electrolysis having a LiPF 6 concentration of 1 mol/L. liquid.
  • barbituric acid compounds are: 1,3-dimethylbarbituric acid (B1), 1,3-dibutylbarbituric acid (B2), and 1,3-diphenylbarbital Acid (B3), 1,3-dimethyl-2-thiobarbituric acid (B4), 5-amino-2-thiobarbituric acid (B5), the specific chemical structural formula is as follows:
  • SEI film-forming additives examples include vinylene carbonate (VC), fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), vinyl sulphate (DTD), adiponitrile (ADN).
  • Positive electrode sheet The positive electrode active material lithium cobaltate (LiCoO 2 molecular formula), conductive agent acetylene black, binder polyvinylidene fluoride (abbreviated as PVDF) in a weight ratio of 96:2:2 in an appropriate amount
  • the N-methylpyrrolidone (abbreviated as NMP) solvent was thoroughly stirred and mixed to form a uniform positive electrode slurry; the slurry was coated on a positive electrode current collector Al foil, dried, and cold pressed to obtain a positive electrode sheet.
  • NMP N-methylpyrrolidone
  • negative electrode sheet The negative electrode active material graphite, conductive agent acetylene black, binder styrene-butadiene rubber (abbreviated as SBR), thickener sodium carboxymethyl cellulose (abbreviated as CMC) according to the weight The ratio of 95:2:2:1 is thoroughly stirred and mixed in an appropriate amount of deionized water solvent to form a uniform negative electrode slurry; the slurry is coated on the negative current collector Cu foil, dried, and cold pressed to obtain Negative electrode sheet.
  • SBR binder styrene-butadiene rubber
  • CMC thickener sodium carboxymethyl cellulose
  • Isolation film A PE porous polymer film is used as a separator.
  • the positive electrode sheet, the separator film and the negative electrode sheet are stacked in order, so that the separator is in the role of isolation between the positive electrode sheet and the negative electrode sheet, and then wound to obtain a bare cell;
  • the core is placed in the outer packaging foil, and the prepared electrolyte is injected into the dried battery, and after vacuum encapsulation, standing, formation, shaping, and the like, the preparation of the lithium ion battery is completed.
  • the electrolytic solutions and lithium ion batteries of Examples 1 to 14 and Comparative Examples 1 to 5 were prepared according to the above preparation methods; the additives in the electrolytic solution and the respective addition amounts thereof are shown in Table 1.
  • the prepared lithium ion batteries were each subjected to the following tests:
  • Lithium-ion battery is charged to 4.4V at 0.5C rate at 25°C, 10°C, 0°C, -10°C, -20°C, and constant voltage charging is performed at 4.4V, until the charging current is equal to 0.05.
  • C after discharging with a current of 0.5 C to 3.0 V, the discharge capacities at different temperatures were recorded, and the discharge capacity at different temperatures was calculated using a discharge capacity of 25 ° C and 0.5 C as a reference (100%). See Table 2 for the electrolytes selected for each lithium-ion battery and the relevant test data obtained.
  • the prepared lithium ion batteries were each subjected to the following tests:
  • the lithium-ion battery is charged to 4.4V with a constant current of 1C, then charged at a constant voltage of 4.4V to a current of 0.05C, and then discharged with a constant current of 1C to 3.0V, which is the first In the secondary cycle, the charging/discharging was performed for so many times according to the above conditions, and the capacity retention ratios of the lithium ion battery after 50, 100, 200, 300, and 500 cycles were calculated. There were 5 batteries in each group, and the capacity retention rate after the cycle was calculated according to the following formula.
  • the electrolytes selected for each of the lithium ion batteries and the relevant test data obtained are shown in Table 3.
  • the cycle performance of the battery is less improved.
  • the content of the barbituric acid compound in the electrolyte exceeds 3%, the cycle performance of the battery is not improved or even deteriorated.
  • the cycle retention rate of the battery is lower than that of the other groups.
  • the prepared lithium ion batteries were each subjected to the following tests:
  • Example 12h thickness test Group 12h thickness test Example 1 6.3% Example 11 5.7% Example 2 7.4% Example 12 18.9 Example 3 7.6% Example 13 9.1% Example 4 6.7% Example 14 7.9% Example 5 7.7% Comparative example 1 29% Example 6 5.9% Comparative example 2 5.2% Example 7 10.3% Comparative example 3 19.5% Example 8 8.9% Comparative example 4 20.3% Example 9 5.8% Comparative example 5 11.5% Example 10 7.7%
  • the addition of barbituric acid compounds can reduce high temperature storage.
  • the battery is produced during the process.
  • a thicker CEI film is formed during high-temperature storage, and the positive electrode interface is protected from the contact reaction between the positive electrode material and the electrolyte, thereby reducing gas generation and preventing cell expansion from deteriorating high-temperature storage performance.
  • the present application can significantly improve the high temperature storage performance of a lithium ion battery by simultaneously adding a barbituric acid compound having a mass fraction of less than 3% to the electrolyte.
  • the battery that has been subjected to 500 cycles of 25 ° C is charged to 4.4 V at a constant current of 0.5 C at 25 ° C, and is charged at a constant voltage of 0.25 V to a current of 0.025 C, so that it is at a full charge state of 4.4 V. Then, the battery was placed in a high temperature furnace at 150 ° C for 1 hour, while the voltage change of the battery in the high temperature furnace and the surface temperature of the battery were tested, and the state of the battery after the test was observed.
  • the results of the post-cycle hot box test are shown in Table 5.
  • the semi-charged battery was discharged at a constant current of 0.5 C to 3.0 V at 25 ° C, then charged at a constant current of 0.4 C to 10 V, and then charged at a constant voltage of 2 V for 2 h while the battery was being charged.
  • the results of the anti-overcharge test are shown in Table 6.
  • Example 13 5/5OK
  • Example 14 5/5OK Comparative example 1 5/5fire Comparative example 2 1/5OK, 4/5fire Comparative example 3 1/5OK, 4/5fire Comparative example 4 0/5OK, 5/5fire Comparative example 5 2/5OK, 3/5fire
  • the lithium batteries of Examples 15 to 28 were prepared according to the method of the foregoing examples, except that the components and the addition ratios in the electrolyte were as shown in Table 7:
  • Table 7 Components and addition ratios in battery electrolytes of Examples 15 to 36

Abstract

一种电解液及二次电池，所述电解液包括溶剂、电解质和添加剂，添加剂中含有巴比妥酸化合物和SEI成膜添加剂。通过将巴比妥酸化合物和SEI成膜添加剂作为功能性混合添加剂，可显著改善电池的低温放电性能、循环性能、高温存储性能、循环后热箱性能和过充性能。

Description

一种电解液及二次电池 技术领域
本申请涉及电池技术领域，具体涉及一种电解液及二次电池。
背景技术
锂离子电池因具有比能量高、循环寿命长、自放电小等优点，被广泛应用于消费类电子产品以及储能与动力电池中。随着锂离子电池的广泛应用，其使用环境也早已趋于多种多样，对电池的寿命、高温性能要求越来越高。例如，电池在大倍率快速充放电的情况下仍具有较长的寿命，在高温长时间工作仍无安全风险等。
锂离子电池的寿命、高温性能受到诸多因素的影响，其中，非水电解液作为锂离子电池的重要组成部分，对其有着重大的影响。通过非水电解液能够改善电池的动力学性能，减小大倍率极化，循环及高温存储过程中正负极界面稳定性从而达到改善寿命、安全的目的。
鉴于此，特提出本申请。
发明内容
本申请的第一发明目的在于提出一种电解液。
本申请的第二目发明目的在于提出一种二次电池。
本申请的具体技术方案为：
本申请涉及一种电解液，包括溶剂、电解质和添加剂，所述添加剂中含有巴比妥酸化合物和SEI成膜添加剂。
优选的，所述巴比妥酸化合物选自结构式为式Ⅰ所示的化合物中的至少一种，
Figure PCTCN2017093005-appb-000001
其中，R11、R12各自独立地分别选自取代或未取代的C1～C12烷基、取代或未取代的C2～C12烯基、取代或未取代的C6～C26芳基；
R13、R14各自独立地分别选自氢、氨基、取代或未取代的C1～C12烷基、取代或未取代的C2～C12烯基、取代或未取代的C6～C26芳基、-NH-R’，其中R’为取代或未取代的C1～C12的烷基；
X选自O原子或S原子；
取代基选自卤素。
优选的，R11、R12各自独立地选自取代或未取代的C1～C6烷基、取代或未取代的苯基；R13、R14各自独立地选自氢、取代或未取代的C1～C6烷基、取代或未取代的苯基、氨基。
优选的，所述巴比妥酸化合物选自以下化合物中的至少一种，
Figure PCTCN2017093005-appb-000002
优选的，所述SEI成膜添加剂选自环状碳酸酯化合物、环状硫酸酯化合物、磺酸内酯化合物、二磺酸亚甲酯化合物、砜化合物、二腈化合物中的至少一种。
优选的，所述环状碳酸酯化合物的结构式如式ⅡA所示，所述环状硫酸酯化合物的结构式如式ⅡB所示，所述磺酸内酯化合物的结构式如式ⅡC 所示，所述二腈化合物的结构式如式ⅡD所示，所述二磺酸亚甲酯化合物选自甲烷二磺酸亚甲酯；
Figure PCTCN2017093005-appb-000003
其中，
R21、R22、R23各自独立地分别选自取代或未取代的C1～C6亚烷基、取代或未取代的C2～C6亚烯基；
R24选自取代或未取代的C1～C12的亚烷基、取代或未取代的C2～C12亚烯基、C6～C12的亚芳基；
取代基选自卤素、C1～C6烷基、C2～C6烯基。
优选的，R21、R22、R23各自独立地分别选自取代或未取代的C1～C4亚烷基、取代或未取代的C2～C4亚烯基；取代基选自卤素、C1～C3烷基、C2～C4烯基；R24选自C1～C6的亚烷基、C2～C6亚烯基、C6～C12亚芳基。
优选的，所述SEI成膜添加剂选自碳酸亚乙烯酯、氟代碳酸乙烯酯、1,3-丙磺酸内酯、乙烯基碳酸亚乙烯酯、1,3-丙烯磺酸内酯、硫酸乙烯酯、甲烷二磺酸亚甲酯、聚醚砜、己二腈等中的至少一种。
优选的，所述巴比妥酸化合物在所述电解液中的质量百分含量为0.01％～3％；优选为0.05％～2％。
优选的，所述SEI成膜添加剂在所述电解液中的质量百分含量为0.01％～30％；优选为0.1％～10％。
本申请涉及一种二次电池，包括正极片、负极片、间隔设置于正极片和负极片之间的隔离膜、以及前述电解液。
本申请提供的技术方案可以达到以下有益效果：
本申请通过将巴比妥酸化合物和SEI成膜添加剂作为功能性混合添加剂，可显著改善电池的低温放电性能、循环性能、高温存储性能循环后热 箱性能和过充性能。
具体实施方式
为使本申请的目的、技术方案和优点更加清楚，下面将结合本申请实施例，对本申请的技术方案进行清楚、完整地描述，显然，所描述的实施例是本申请一部分实施例，而不是全部的实施例。基于本申请提供的技术方案及所给出的实施例，本领域技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本申请保护的范围。
本申请涉及一种电解液，包括溶剂、电解质和添加剂，添加剂中含有巴比妥酸化合物和SEI成膜添加剂。
研究表明，巴比妥酸化合物的氧化电位比溶剂低，可以在电芯正极表面氧化聚合形成致密的固体电解质相界面膜(CEI)，有效减少溶剂在正极的分解，对电池的性能非常有益；这是因为巴比妥酸化合物与锂形成的聚合物覆盖在正极表面相对于烷基锂更难被溶剂溶解，CEI更加稳定。CEI能有效阻止正极材料与电解液在正极表面发生副反应，并且能够有效的减少循环过程中正极界面阻抗的增加。巴比妥酸化合物聚合成膜后，可防止正极材料中如Mn元素、Co元素的溶出，抑制电解液发生氧化产气使电池膨胀。负极成膜(SEI)添加剂主要在电池首次充电过程中在负极还原，产物附着在负极表面形成稳定的固态电解质膜，从而阻止导离子的溶剂在充放电过程中被进一步还原。不同的SEI膜对负极界面的内阻有很大的影响。本申请通过研究发现，巴比妥酸化合物与SEI成膜添加剂配合使用时，可在二次电池的正负极均生成稳定的钝化膜，有效及稳定的CEI和SEI的存在而显著改善电池的低温放电性能、循环性能、高温存储性能循环后热箱性能和过充性能。
作为本申请电解液的一种改进，本申请巴比妥酸化合物选自结构式为式Ⅰ所示的化合物中的至少一种，
Figure PCTCN2017093005-appb-000004
其中，R11、R12各自独立地分别选自取代或未取代的C1～C12烷基、取代或未取代的C2～C12烯基、取代或未取代的C6～C26芳基；
R13、R14各自独立地分别选自氢、氨基、取代或未取代的C1～C12烷基、取代或未取代的C2～C12烯基、取代或未取代的C6～C26芳基、-NH-R’，其中，R’为取代或未取代的C1～C12的烷基；
X选自O原子或S原子；
取代基选自卤素，如F、Cl。
在本申请中：碳原子数为1～12的烷基，烷基可为链状烷基，也可为环烷基，位于环烷基的环上的氢可被烷基取代。烷基中碳原子数优选的下限值为2，3，4，5，优选的上限值为3，4，5，6，8，10，12。优选地，选择碳原子数为1～10的烷基，进一步优选地，选择碳原子数为1～6的链状烷基，碳原子数为3～8的环烷基，更进一步优选地，选择碳原子数为1～4的链状烷基，碳原子数为5～7的环烷基。作为烷基的实例，具体可以举出：甲基、乙基、正丙基、异丙基、正丁基、异丁基、仲丁基、叔丁基、正戊基、异戊基、新戊基、己基、2-甲基-戊基、3-甲基-戊基、1,1,2-三甲基-丙基、3,3,-二甲基-丁基、庚基、2-庚基、3-庚基、2-甲基己基、3-甲基己基、异庚基、辛基、壬基、癸基。
碳原子数为2～12的烯基可为环状烯基，也可为链状烯基。另外，烯基中双键的个数优选为1个。所述烯基中碳原子数优选的下限值为3，4，5，优选的上限值为3，4，5，6，8，10，12，14，16，18。优选地，选择碳原子数为2～10的链状烯基，进一步优选地，选择碳原子数为2～6的链状烯基，更进一步优选地，选择碳原子数为2～5的烯基。作为烯基的实例，具体可以举出：乙烯基、烯丙基、异丙烯基、戊烯基、环己烯基、 环庚烯基、环辛烯基。
碳原子数为6～26的芳基，例如苯基、苯烷基、至少含有一个苯基的芳基如联苯基、稠环芳烃基如萘、蒽、菲均可，联苯基和稠环芳烃基还可被烷基或是烯基所取代。优选地，选择碳原子数为6～16的芳基，进一步优选地，选择碳原子数为6～14的芳基，更进一步优选地，选择碳原子数为6～9的芳基。作为芳基的实例，具体可以举出：苯基、苄基、联苯基、对甲苯基、邻甲苯基、间甲苯基。
当前述提到的碳原子数为1～12的烷基、碳原子数为2～12的烯基、碳原子数为6～26的芳基被卤原子取代后，依次相应的形成碳原子数为1～20的卤代烷基、碳原子数为2～20的卤代烯基、碳原子数为6～26的卤代芳基，其中卤原子为F、Cl、Br，优选为F、Cl。在所形成的卤代基团中，卤原子对部分氢原子或者全部氢原子进行取代，卤原子的个数可为1个、2个、3个或4个。
优选地，选择碳原子数为1～10的卤代烷基、碳原子数为2～10的卤代烯基、碳原子数为6～16的卤代芳基，进一步优选地，选择碳原子数为1～6的卤代链状烷基、碳原子数为3～8的卤代环烷基、碳原子数为2～6的卤代烯基、碳原子数为6～14的卤代芳基，更进一步优选地，选择碳原子数为1～4的卤代链状烷基、碳原子数为5～7的卤代环烷基、碳原子数为2～5的卤代烯基、碳原子为6～10的卤代芳基。
作为卤代基团的实例，具体可以举出：三氟甲基(-CF3)、2-氟乙基、3-氟正丙基、2-氟异丙基、4-氟正丁基、3-氟仲丁基、5-氟正戊基、4-氟异戊基、1-氟乙烯基、3-氟烯丙基、6-氟-4-己烯基、邻氟苯基、对氟苯基、间氟苯基、4-氟甲基苯基、2,6-二氟甲基苯基、2-氟-1-萘基、氟代甲氧基。在上述具体的实例中，F可被Cl和/或Br取代。
作为本申请电解液的一种改进，R11、R12各自独立地分别选自取代或未取代的C1～C6烷基、取代或未取代的C2～C6烯基、取代或未取代的苯基；R13、R14各自独立地分别选自氢、氨基、取代或未取代的C1～C6烷基、取代或未取代的C2～C6烯基、取代或未取代的苯基。
作为本申请电解液的一种改进，R11、R12各自独立地选自取代或未取代的C1～C6烷基、取代或未取代的苯基；R13、R14各自独立地选自氢、氨基、取代或未取代的C1～C6烷基、取代或未取代的苯基。
作为本申请电解液的一种改进，R11、R12各自独立地选自取代或未取代的C1～C6烷基、苯基；R13、R14各自独立地选自氢、氨基。
作为本申请电解液的一种改进，R11与R12为相同的取代基。
作为本申请电解液的一种改进，R13与R14同时为氢，或R13与R14中至少一个取代基为氢，另一个取代基选自氨基、取代或未取代的C1～C6烷基、取代或未取代的苯基。
作为本申请电解液的一种改进，本申请巴比妥酸化合物选自以下化合物中的至少一种：
Figure PCTCN2017093005-appb-000005
作为本申请电解液的一种改进，本申请巴比妥酸化合物还可选自以下化合物中的至少一种：
Figure PCTCN2017093005-appb-000006
Figure PCTCN2017093005-appb-000007
作为本申请电解液的一种改进，本申请巴比妥酸化合物在电解液中的质量百分含量为0.01％～3％。当巴比妥酸化合物的含量低于0.01％时，不能在正极表面形成完整而有效的CEI膜，从而不能有效阻止电解液与电极 之间的电子转移所引起的副反应；而当巴比妥酸化合物含量大于3％时，会在正极表面形成较厚的CEI膜，导致锂离子迁移阻力增大，不利于循环过程中电池的正极界面稳定性。
进一步优选地，本申请巴比妥酸化合物在电解液中的质量百分含量范围的上限任选自3％、2.8％、2.5％、2.0％、1.5％、1.0％，下限任选自0.01％、0.03％、0.05％、0.1％、0.3％、0.5％、0.6％。更进一步优选地，巴比妥酸化合物在电解液中的百分含量为0.05％～2％。
作为本申请电解液的一种改进，SEI成膜添加剂选自环状碳酸酯化合物、环状硫酸酯化合物、磺酸内酯化合物、二磺酸亚甲酯化合物、砜化合物、腈类化合物中的至少一种。
作为本申请电解液的一种改进，环状碳酸酯化合物的结构式如式ⅡA所示，R21选自取代或未取代的C1～C6亚烷基、取代或未取代的C2～C6亚烯基；取代基选自卤素、C1～C6烷基、C2～C6烯基；
Figure PCTCN2017093005-appb-000008
作为本申请电解液的一种改进，R21选自取代或未取代的C1～C4亚烷基、取代或未取代的C2～C4亚烯基；取代基选自卤素、C1～C3烷基、C2～C4烯基。
作为本申请电解液的一种改进，环状碳酸酯化合物选自氟代碳酸乙烯酯、碳酸亚乙烯酯、乙烯基碳酸亚乙酯的至少一种；具体结构式如下：
Figure PCTCN2017093005-appb-000009
作为本申请电解液的一种改进，环状碳酸酯化合物还可以选自：
Figure PCTCN2017093005-appb-000010
作为本申请电解液的一种改进，环状硫酸酯化合物的结构式如式ⅡB所示，R22选自取代或未取代的C1～C6亚烷基、取代或未取代的C2～C6亚烯基；取代基选自卤素、C1～C6烷基、C2～C6烯基；
Figure PCTCN2017093005-appb-000011
作为本申请电解液的一种改进，R22选自取代或未取代的C1～C4亚烷基、取代或未取代的C2～C4亚烯基；取代基选自卤素、C1～C3烷基、C2～C4烯基。
作为本申请电解液的一种改进，环状硫酸酯化合物选自硫酸亚乙酯、4-甲基硫酸亚乙酯、硫酸亚丙酯中的至少一种，具体结构式如下；
Figure PCTCN2017093005-appb-000012
作为本申请电解液的一种改进，环状硫酸酯化合物选自硫酸亚乙酯。
作为本申请电解液的一种改进，环状硫酸酯化合物还可以选自：
Figure PCTCN2017093005-appb-000013
作为本申请电解液的一种改进，磺酸内酯化合物的结构式如式ⅡC所示，R23选自取代或未取代的C1～C6亚烷基、取代或未取代的C2～C6亚烯基；取代基选自卤素、C1～C6烷基、C2～C6烯基；
Figure PCTCN2017093005-appb-000014
作为本申请电解液的一种改进，R23选自取代或未取代的C1～C4亚烷基、取代或未取代的C2～C4亚烯基；取代基选自卤素、C1～C3烷基、C2～C4烯基。
作为本申请电解液的一种改进，磺酸内酯化合物选自1,3-丙磺酸内酯、1,4-丁磺酸内酯、1,3-丙烯磺酸内酯中的至少一种，具体结构式如下；
Figure PCTCN2017093005-appb-000015
作为本申请电解液的一种改进，磺酸内酯化合物选自1,3-丙磺酸内酯、1,3-丙烯磺酸内酯中的至少一种。
作为本申请电解液的一种改进，磺酸内酯化合物还可以选自：
Figure PCTCN2017093005-appb-000016
作为本申请电解液的一种改进，二腈化合物的结构式如ⅡD所示；
Figure PCTCN2017093005-appb-000017
其中，R24选自取代或未取代的C1～C12的亚烷基、取代或未取代的C2～C12亚烯基、C6～C12的亚芳基，其中，取代基选自卤素、C1～C6烷基、C2～C6烯基。
作为本申请电解液的一种改进，R24选自C1～C6的亚烷基、C2～C6亚烯基、C6～C12亚芳基。
作为本申请电解液的一种改进，二腈化合物选自己二腈、丙二腈、戊二腈中的至少一种。
作为本申请电解液的一种改进，二腈化合物选自己二腈。
作为本申请电解液的一种改进，二腈化合物还可以选自以下结构所示二腈化合物中的至少一种；
Figure PCTCN2017093005-appb-000018
作为本申请电解液的一种改进，二磺酸亚甲酯化合物选自甲烷二磺酸亚甲酯，如式ⅡE所示；
Figure PCTCN2017093005-appb-000019
作为本申请电解液的一种改进，砜化合物选自聚醚砜。
作为本申请电解液的一种改进，SEI成膜添加剂选自碳酸亚乙烯酯(VC)、氟代碳酸乙烯酯(FEC)、1,3-丙磺酸内酯(PS)、乙烯基碳酸亚乙烯酯(VEC)、1,3-丙烯磺酸内酯(PST)、硫酸乙烯酯(DTD)、甲烷二磺酸亚甲酯(MMDS)、聚醚砜(PES)、己二腈(ADN)等中的至少一种。
作为本申请电解液的一种改进，本申请SEI成膜添加剂在电解液中的质量百分含量为0.01％～30％，进一步优选为0.1％～10％。
进一步优选地，本申请SEI成膜添加剂在电解液中的质量百分含量范围的上限任选自5％、7％、8％、12％、15％、18％、20％、22％、25％，下限任选自0.05％、0.08％、0.2％、0.5％、0.8％、1％、1.2％、1.5％、2％、3％。更进一步优选地，SEI成膜添加剂化合物在电解液中的百分含量为0.2％～8％。
作为本申请电解液的一种改进，本申请有机溶剂选自碳酸乙烯酯(EC)、碳酸丙烯脂(PC)、碳酸丁烯酯、氟代碳酸乙烯酯、碳酸甲乙酯、碳酸二甲酯、碳酸二乙酯(DEC)、碳酸二丙酯、碳酸甲丙酯、碳酸 乙丙酯、1,4-丁内酯、丙酸甲酯、丁酸甲酯、丙酸丙酯、乙酸乙酯、丙酸乙酯、丁酸乙酯中的至少一种。
作为本申请电解液的一种改进，本申请锂盐选自有机锂盐或无机锂盐中的至少一种。
作为本申请电解液的一种改进，本申请锂盐中含有氟元素、硼元素、磷元素中的至少一种。
作为本申请电解液的一种改进，本申请锂盐选自六氟磷酸锂LiPF6、双三氟甲烷磺酰亚胺锂LiN(CF3SO2)2(简写为LiTFSI)、双(氟磺酰)亚胺锂Li(N(SO2F)2)(简写为LiFSI)、双草酸硼酸锂LiB(C2O4)2(简写为LiBOB)、二氟草酸硼酸锂LiBF2(C2O4)(简写为LiDFOB)中的至少一种。
本申请还涉及一种二次电池，包括正极片、负极片、间隔设置于正极片和负极片之间的隔离膜、以及电解液；正极片包括正极集流体及涂布在正极集流体上的正极膜片，负极片包括负极集流体及涂布在负极集流体上的负极膜片；电解液为前述任一段落所述的电解液。
作为本申请二次电池的一种改进，本申请正极膜片包括正极活性材料、粘结剂和导电剂。
作为本申请二次电池的一种改进，本申请正极活性材料任选自钴酸锂LiCoO2、锂镍锰钴三元材料、磷酸亚铁锂、锰酸锂中的至少一种。
作为本申请二次电池的一种改进，本申请正极活性材料钴酸锂与锂镍锰钴三元材料的混合物。
作为本申请二次电池的一种改进，本申请负极膜片包括负极活性材料、粘结剂和导电剂。
作为本申请二次电池的一种改进，本申请负极活性材料为石墨和/或硅。
以下通过具体实施例对本申请的技术方案做示例性描述：
电解液的制备：在含水量<10ppm的氩气气氛手套箱中，将碳酸乙烯酯(简写为EC)、碳酸二乙酯(简写为DEC)、碳酸丙烯酯(简写为PC)、丙酸乙酯、按照20:30:20:30的质量比混合均匀后，得到非水溶剂，再将充分干燥的锂盐LiPF6溶解于上述非水溶剂，配成LiPF6浓度为1mol/L的基 础电解液。
按照表1所示，在基础电解液中加入巴比妥酸化合物及SEI成膜添加剂。
作为巴比妥酸化合物的实例为：1,3-二甲基巴比妥酸(B1)、1,3-二丁基巴比妥酸(B2)、1,3-二苯基巴比妥酸(B3)，1,3-二甲基-2-硫代巴比妥酸(B4)，5-氨基-2-硫代巴比妥酸(B5)，其具体化学结构式如下：
Figure PCTCN2017093005-appb-000020
作为SEI成膜添加剂的实例为：自碳酸亚乙烯酯(VC)、氟代碳酸乙烯酯(FEC)、1,3-丙磺酸内酯(PS)、硫酸乙烯酯(DTD)、己二腈(ADN)。
锂离子电池的制备：
1)正极片的制备：将正极活性物质钴酸锂(分子式为LiCoO2)、导电剂乙炔黑、粘结剂聚偏二氟乙烯(简写为PVDF)按重量比96:2:2在适量的N-甲基吡咯烷酮(简写为NMP)溶剂中充分搅拌混合，使其形成均匀的正极浆料；将此浆料涂覆于正极集流体Al箔上，烘干、冷压，得到正极片。
2)负极片的制备：将负极活性物质石墨、导电剂乙炔黑、粘结剂丁苯橡胶(简写为SBR)、增稠剂羧甲基纤维素钠(简写为CMC)按照重量 比95:2:2:1在适量的去离子水溶剂中充分搅拌混合，使其形成均匀的负极浆料；将此浆料涂覆于负极集流体Cu箔上，烘干、冷压，得到负极片。
3)隔离膜：以PE多孔聚合物薄膜作为隔离膜。
4)锂离子电池的制备：将正极片、隔离膜、负极片按顺序叠好，使隔离膜处于正极片和负极片之间起到隔离的作用，然后卷绕得到裸电芯；将裸电芯置于外包装箔中，将上述制备好的电解液注入到干燥后的电池中，经过真空封装、静置、化成、整形等工序，即完成锂离子电池的制备。
按照上述制备方法制备实施例1～14以及对比例1～5的电解液及锂离子电池；电解液中添加剂及各自的添加量如表1所示。
表1：实施例1～14以及对比例1～5的电解液添加剂及添加量
Figure PCTCN2017093005-appb-000021
Figure PCTCN2017093005-appb-000022
其中，“－”表示未添加该物质。
以下将通过实验对本申请各对比例和实施例制得的锂离子电池进行性能测试。
测试一、低温放电倍率测试
将制备得到的锂离子电池均分别进行下述测试：
分别在25℃、10℃、0℃、-10℃、-20℃条件下，将锂离子电池以0.5C倍率充电至4.4V，在4.4V的电压下进行恒压充电，至充电电流等于0.05C，后用0.5C的电流放电至3.0V，分别记录不同温度的放电容量，以25℃、0.5C的放电容量作为基准(100％)，计算不同温度放电的容量。各个锂离子电池中所选用的电解液以及得到的相关测试数据参见表2。
表2：实施例1～14以及对比例1～5的锂离子电池低温放电倍率测试结果
Figure PCTCN2017093005-appb-000023
Figure PCTCN2017093005-appb-000024
结合表1和表2中可以看出，与对比例1相比，对比例3的电解液中单独加入0.01％巴比妥酸化合物时，锂离子电池的低温放电倍率略有改善。在实施例1～11中，电解液中同时加入质量分数为1％的巴比妥酸化合物和质量分数为4％的SEI成膜添加剂时，电池的低温放电容量显著提升。特别是实施例10，DTD成膜后具有更低的阻抗，所以低温放电速度快，低温放电倍率高。然而，当电解液中巴比妥酸化合物的含量超过3％时，电池的低温放电容量非但没有改善，甚至会恶化，原因是巴比妥酸化合物过多时会导致成膜厚且电解液粘度高，锂离子传导变得困难特别是电解液中添加4％巴比妥酸化合物的对比例2，其电池的低温放电容量远低于其他组别。
测试二、循环测试
将制备得到的锂离子电池均分别进行下述测试：
在45℃下，将锂离子电池，以1C恒流充电至4.4V，然后在4.4V的条件下恒压充电至电流为0.05C，再用1C的电流恒流放电至3.0V，此时为首次循环，按照上述条件进行如此多次循环充电/放电，分别计算得出锂离子电池循环50次、100次、200次、300次和500次后的容量保持率。每组各5只电池，其中，循环后的容量保持率按照下式进行计算。各个锂离子电池中所选用的电解液以及得到的相关测试数据参见表3。
循环后的容量保持率＝(对应循环的放电容量/首次循环的放电容量)×100％，循环测试的结果如表3所示。
表3：实施例1～14以及对比例1～5的锂离子电池循环后的容量保持率
Figure PCTCN2017093005-appb-000025
Figure PCTCN2017093005-appb-000026
结合表1和表3中可以看出，与对比例1相比，对比例3的电解液中单独加入0.01％的1，3-二甲基巴比妥酸时，锂离子电池的循环性能略有改善。在实施例1～5中，电解液中加入质量分数为1％的1,3-二甲基巴比妥酸，1,3-二丁基巴比妥酸，1,3-二苯基巴比妥酸，1,3-二甲基-2-硫代巴比妥酸和5-氨基-2-硫代巴比妥酸时，电池的循环性能显著提升。然而，当电解液中巴比妥酸化合物的含量小于0.05％时，电池的循环性能改善幅度较小。当电解液中巴比妥酸化合物的含量超过3％时，电池的循环性能非但没有改善，甚至会恶化，如对比例2，其电池的循环保持率低于其他组别。
测试三、高温存储测试
将制备得到的锂离子电池均分别进行下述测试：
在25℃下以0.5C电流恒流充电至4.4V，在4.4V的条件下恒压充电至电流为0.025C，使其处于4.4V满充状态，然后将电池放在85℃的高温炉中保持24小时，同时每4h热测一次；以100％SOC电芯厚度作为基准(0％)，记录电芯的厚度数据。高温存储测试的结果如表4所示，所列数据为测试电池相对于基准厚度变化百分比例。
表4：实施例1～14以及对比例1～5锂离子电池在热箱测试后结果
组别 12h厚度测试 组别 12h厚度测试
实施例1 6.3％ 实施例11 5.7％
实施例2 7.4％ 实施例12 18.9
实施例3 7.6％ 实施例13 9.1％
实施例4 6.7％ 实施例14 7.9％
实施例5 7.7％ 对比例1 29％
实施例6 5.9％ 对比例2 5.2％
实施例7 10.3％ 对比例3 19.5％
实施例8 8.9％ 对比例4 20.3％
实施例9 5.8％ 对比例5 11.5％
实施例10 7.7％    
结合表1和表4中可以看出，加入巴比妥酸化合物均能减少高温存储 过程中电池产气。随着巴比妥酸化合物的含量增加，高温存储过程中会形成较厚的CEI膜，保护正极界面阻止正极材料与电解液的接触反应，从而减少气体产生，防止电芯膨胀恶化高温存储性能。
通过以上所有描述可知，本申请通过在电解液中同时加入质量分数低于3％的巴比妥酸化合物，可以显著地改善锂离子电池的高温存储性能。
测试四、循环后的热箱测试
将进行过500次25℃循环后的电池，在25℃下以0.5C电流恒流充电至4.4V，在4.4V的条件下恒压充电至电流为0.025C，使其处于4.4V满充状态，然后将电池放在150℃的高温炉中保持1小时，同时测试电池在高温炉中电压变化以及电芯表面温度，并观察测试后电池的状态。循环后热箱测试的结果如表5所示。
表5：实施例1～14以及对比例1～5锂电池在25℃循环后在热箱测试后结果
组别 热箱测试
实施例1 5/5OK
实施例2 5/5OK
实施例3 5/5OK
实施例4 5/5OK
实施例5 5/5OK
实施例6 5/5OK
实施例7 5/5OK
实施例8 5/5OK
实施例9 5/5OK
实施例10 5/5OK
实施例11 5/5OK
实施例12 5/5OK
实施例13 5/5OK
实施例14 5/5OK
对比例1 5/5fire
对比例2 1/5OK,4/5fire
对比例3 1/5OK,4/5fire
对比例4 0/5OK,5/5fire
对比例5 2/5OK,3/5fire
结合表1和表5中可以看出，巴比妥酸化合物作为电解液添加剂同时搭配SEI负极成膜添加剂使用时，可以显著提高电池在循环后的热箱性能。当巴比妥酸化合物的含量高于3％时，将会导致循环后电池热箱测试着火，其原因可以考虑是因为过多的巴比妥酸化合物在循环过程中膜阻抗增加，导致电池在循环过程中金属锂析出，恶化电池负极的热稳定性，恶化电池循环后的热箱性能。
测试五、抗过充测试
将半充态的电池在25℃下以0.5C的电流恒流放电至3.0V，再以0.4C的电流恒流充电至10V，再在10V的电压下恒压充电2h，同时测试电池在充电过程中的温度变化并观察测试后电池的状态。抗过充测试的结果如表6所示。
表6实施例1～14以及对比例1～5锂电池在25℃循环后热箱测试结果
组别 抗过充测试
实施例1 5/5OK
实施例2 5/5OK
实施例3 5/5OK
实施例4 5/5OK
实施例5 5/5OK
实施例6 5/5OK
实施例7 5/5OK
实施例8 5/5OK
实施例9 5/5OK
实施例10 5/5OK
实施例11 5/5OK
实施例12 5/5OK
实施例13 5/5OK
实施例14 5/5OK
对比例1 5/5fire
对比例2 1/5OK,4/5fire
对比例3 1/5OK,4/5fire
对比例4 0/5OK,5/5fire
对比例5 2/5OK,3/5fire
结合表1和表6中可以看出，当巴比妥酸化合物的含量高于3％时，将会导致电池在抗过充过程中着火，其原因可以考虑是因为过多的巴比妥酸在持续充电循环过程中膜阻抗增加，导致电池在循环过程中金属锂析出，持续的锂在负极表面沉积易导致电池短路，电池燃烧。相比之下，电解液中加入巴比妥酸与ADN可以形成稳定的复合钝化膜，该钝化膜在持续充电过程中不易被破坏，有效降低充电过程中金属锂的析出，因此不易形成微短路，从而改善电池抗过充性能。因此，巴比妥酸化合物和SEI成膜添加剂特别是ADN作为电解液添加剂同时搭配使用时，可以显著提高电池的抗过充性能。
本申请其它实施例：
按照前述实施例的方法制备实施例15～28的锂电池，区别在于：电解液中各组分及添加比例如表7所示：
表7：实施例15～36电池电解液中的组分及添加比例
Figure PCTCN2017093005-appb-000027
Figure PCTCN2017093005-appb-000028
按照前述实施例的方法对制备得到的电池的性能进行检测，检测得到实施例电池15～28的性能与以上实施例相似，限于篇幅不再赘述。
本申请虽然以较佳实施例公开如上，但并不是用来限定权利要求，任何本领域技术人员在不脱离本申请构思的前提下，都可以做出若干可能的变动和修改，因此本申请的保护范围应当以本申请权利要求所界定的范围为准。

Claims (10)

  1. 一种电解液，包括溶剂、电解质和添加剂，其特征在于，所述添加剂中含有巴比妥酸化合物和SEI成膜添加剂。
  2. 根据权利要求1所述的电解液，其特征在于，所述巴比妥酸化合物选自结构式为式Ⅰ所示的化合物中的至少一种，
    Figure PCTCN2017093005-appb-100001
    其中，R11、R12各自独立地分别选自取代或未取代的C1～C12烷基、取代或未取代的C2～C12烯基、取代或未取代的C6～C26芳基；
    R13、R14各自独立地分别选自氢、氨基、取代或未取代的C1～C12烷基、取代或未取代的C2～C12烯基、取代或未取代的C6～C26芳基、-NH-R’，其中，R’为取代或未取代的C1～C12的烷基；
    X选自O原子或S原子；
    取代基选自卤素。
  3. 根据权利要求2所述的电解液，其特征在于，R11、R12各自独立地选自取代或未取代的C1～C6烷基、取代或未取代的苯基；R13、R14各自独立地选自氢、取代或未取代的C1～C6烷基、取代或未取代的苯基、氨基。
  4. 根据权利要求3所述的电解液，其特征在于，所述巴比妥酸化合物选自以下化合物中的至少一种，
    Figure PCTCN2017093005-appb-100002
    Figure PCTCN2017093005-appb-100003
  5. 根据权利要求1所述的电解液，其特征在于，所述SEI成膜添加剂选自环状碳酸酯化合物、环状硫酸酯化合物、磺酸内酯化合物、二磺酸亚甲酯化合物、砜化合物、二腈化合物中的至少一种。
  6. 根据权利要求5所述的电解液，其特征在于，所述环状碳酸酯化合物的结构式如式ⅡA所示，所述环状硫酸酯化合物的结构式如式ⅡB所示，所述磺酸内酯化合物的结构式如式ⅡC所示，所述二腈化合物的结构式如式ⅡD所示，所述二磺酸亚甲酯化合物选自甲烷二磺酸亚甲酯；
    Figure PCTCN2017093005-appb-100004
    其中，
    R21、R22、R23各自独立地分别选自取代或未取代的C1～C6亚烷基、取代或未取代的C2～C6亚烯基；
    R24选自取代或未取代的C1～C12的亚烷基、取代或未取代的C2～C12亚烯基、C6～C12的亚芳基；
    取代基选自卤素、C1～C6烷基、C2～C6烯基。
  7. 根据权利要求5所述的电解液，其特征在于，所述SEI成膜添加剂选自碳酸亚乙烯酯、氟代碳酸乙烯酯、1,3-丙磺酸内酯、乙烯基碳酸亚乙烯酯、1,3-丙烯磺酸内酯、硫酸乙烯酯、甲烷二磺酸亚甲酯、聚醚砜、己二腈等中的至少一种。
  8. 根据权利要求1所述的电解液，其特征在于，所述巴比妥酸化合物在所述电解液中的质量百分含量为0.01％～3％，优选为0.05％～2％。
  9. 根据权利要求1所述的电解液，其特征在于，所述SEI成膜添加剂 在所述电解液中的质量百分含量为0.01％～30％；优选为0.1％～10％。
  10. 一种二次电池，包括正极片、负极片、间隔设置于正极片和负极片之间的隔离膜、以及电解液，其特征在于，所述电解液为权利要求1～9任一所述的电解液。
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