WO2020238302A1 - 锂二次电池电解液及其制备方法和锂二次电池 - Google Patents

锂二次电池电解液及其制备方法和锂二次电池 Download PDF

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WO2020238302A1
WO2020238302A1 PCT/CN2020/076844 CN2020076844W WO2020238302A1 WO 2020238302 A1 WO2020238302 A1 WO 2020238302A1 CN 2020076844 W CN2020076844 W CN 2020076844W WO 2020238302 A1 WO2020238302 A1 WO 2020238302A1
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pentafluoro
cyclotriphosphazene
secondary battery
lithium secondary
electrolyte
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PCT/CN2020/076844
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English (en)
French (fr)
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马强
秦德君
邓耀明
李阳兴
徐凡
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华为技术有限公司
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Priority to EP20812799.3A priority Critical patent/EP3972029A4/en
Publication of WO2020238302A1 publication Critical patent/WO2020238302A1/zh
Priority to US17/536,697 priority patent/US20220085413A1/en

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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
    • 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
    • H01M10/0568—Liquid materials characterised by the solutes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0569—Liquid materials characterised by the solvents
    • 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
    • H01M10/058—Construction or manufacture
    • 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
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H01M2300/0028—Organic electrolyte characterised by the solvent
    • H01M2300/0037—Mixture of solvents
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H01M2300/0045—Room temperature molten salts comprising at least one organic ion
    • 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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Definitions

  • the embodiments of the present invention relate to the technical field of lithium secondary batteries, in particular to lithium secondary battery electrolytes and preparation methods thereof, and lithium secondary batteries.
  • the electrolyte of lithium-ion batteries is mainly non-aqueous organic electrolyte (normally carbonate electrolyte).
  • the electrolyte is easy to exist. Potential hazards such as volatilization and flammability can easily cause safety problems caused by battery thermal runaway.
  • the current mainstream solution is to add flame retardant additives to conventional electrolytes, although there are many reported flame retardant additives, such as phosphorus compounds, halogenated compounds, and nitrogen-containing compounds. Compounds, silicon compounds, etc., but most of them have poor compatibility with positive and negative materials. Even if the phosphazene flame retardant with good compatibility with the positive and negative materials is used, in order to ensure the safety of high energy density batteries, it still needs to be added at a relatively high amount (10-20wt.%) to achieve good flame retardancy. effect.
  • an embodiment of the present invention provides an electrolyte for a lithium secondary battery by adding a (pentafluoro) ring triphosphazene substituted with an electron donating group and a (pentafluoro) ring substituted with an electron withdrawing group to the electrolyte at the same time
  • the two flame retardants of triphosphazene enable the battery to have both high safety performance and good electrochemical performance, so as to solve to a certain extent that the addition of a large number of phosphazene flame retardants will cause electrolyte delamination or lithium salt precipitation. Eventually lead to the problem of poor electrochemical performance of the battery.
  • the first aspect of the embodiments of the present invention provides an electrolyte for a lithium secondary battery, which includes a lithium salt, an organic solvent, and a flame retardant, and the flame retardant includes (pentafluoro)cyclotriphosphorus substituted with electron-donating groups. Nitrile and electron withdrawing group substituted (pentafluoro) cyclotriphosphazene.
  • the electron-donating group-substituted (pentafluoro) cyclotriphosphazene includes one of alkoxy (pentafluoro) cyclotriphosphazene and phenoxy (pentafluoro) cyclotriphosphazene Or multiple.
  • the number of carbon atoms of the alkoxy group is 1-20.
  • the alkoxy (pentafluoro) cyclotriphosphazene includes one or more of methoxy (pentafluoro) cyclotriphosphazene and ethoxy (pentafluoro) cyclotriphosphazene .
  • the (pentafluoro) cyclotriphosphazene substituted by the electron withdrawing group includes fluoroalkoxy (pentafluoro) cyclotriphosphazene and alkylsulfonic acid group (pentafluoro) cyclotriphosphazene One or more of.
  • the number of carbon atoms of the fluoroalkoxy is 1-20.
  • the fluoroalkoxy (pentafluoro) cyclotriphosphazene includes trifluoroethoxy (pentafluoro) cyclotriphosphazene and perfluorobutoxy (pentafluoro) cyclotriphosphazene.
  • trifluoroethoxy (pentafluoro) cyclotriphosphazene and perfluorobutoxy (pentafluoro) cyclotriphosphazene One or more of.
  • the alkylsulfonic acid group in the alkylsulfonic acid group (pentafluoro) cyclotriphosphazene, the alkylsulfonic acid group has 1-20 carbon atoms.
  • the alkylsulfonic acid (pentafluoro) cyclotriphosphazene includes methylsulfonic acid (pentafluoro) cyclotriphosphazene and ethylsulfonic acid (pentafluoro) cyclotriphosphazene.
  • methylsulfonic acid (pentafluoro) cyclotriphosphazene and ethylsulfonic acid (pentafluoro) cyclotriphosphazene One or more of.
  • the mass percentage of the (pentafluoro)cyclotriphosphazene substituted by the electron donating group in the electrolyte is 10%-30%.
  • the mass percentage of the (pentafluoro)cyclotriphosphazene substituted with the electron withdrawing group in the electrolyte is 1% to 5%.
  • the total mass percentage of the (pentafluoro) cyclotriphosphazene substituted by the electron donating group and the (pentafluoro) cyclotriphosphazene substituted by the electron withdrawing group in the electrolyte The content is 16%-30%.
  • the electrolyte further includes other additives, and the other additives include biphenyl, fluorobenzene, vinylene carbonate, trifluoromethyl ethylene carbonate, vinyl ethylene carbonate, 1,3-propane Sultone, 1,4-butane sultone, vinyl sulfate, vinyl sulfite, succinonitrile, adiponitrile, 1,2-bis(2-cyanoethoxy)ethane and 1, One or more of 3,6-hexane trinitrile.
  • the other additives include biphenyl, fluorobenzene, vinylene carbonate, trifluoromethyl ethylene carbonate, vinyl ethylene carbonate, 1,3-propane Sultone, 1,4-butane sultone, vinyl sulfate, vinyl sulfite, succinonitrile, adiponitrile, 1,2-bis(2-cyanoethoxy)ethane and 1, One or more of 3,6-hexane trinitrile.
  • the mass percentage of the other additives in the electrolyte is 0.1%-20%.
  • the lithium salt includes LiClO 4 , LiBF 4 , LiPF 6 , LiAsF 6 , LiPF 2 O 2 , LiCF 3 SO 3 , LiTDI, LiB(C 2 O 4 ) 2 (LiBOB), LiBF 2 C 2 O 4 (LiDFOB), Li[(CF 3 SO 2 ) 2 N], Li[(FSO 2 ) 2 N] and Li[(C m F 2m+1 SO 2 )(C n F 2n+1 SO 2 ) One or more of N], where m and n are natural numbers.
  • the molar concentration of the lithium salt in the electrolyte is 0.01 mol/L-2.0 mol/L.
  • the organic solvent includes a carbonate-based solvent and/or a carboxylate-based solvent.
  • the carbonate-based solvent is a mixed solvent composed of cyclic carbonate and linear carbonate.
  • the cyclic carbonate includes ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), gamma-butyrolactone (GBL), butylene carbonate (BC) );
  • the chain carbonate includes one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC)kind or more.
  • the mass percentage of the cyclic carbonate in the electrolyte is 5%-70%, and the mass percentage of the chain carbonate in the electrolyte is 5% -70%.
  • the carboxylic acid ester solvent includes methyl acetate (MA), ethyl acetate (EA), propyl acetate, butyl acetate, propyl propionate (PP), and butyl propionate.
  • MA methyl acetate
  • EA ethyl acetate
  • PP propyl propionate
  • butyl propionate PP
  • butyl propionate PP
  • the (pentafluoro) cyclotriphosphazene substituted by the electron donating group and the (pentafluoro) cyclotriphosphazene substituted with the electron withdrawing group are simultaneously added to the electrolyte.
  • the two flame retardants of phosphazene, under the synergistic effect of the two flame retardants, further improve the solubility of the phosphazene flame retardant in the electrolyte, and better overcome the problems of electrolyte delamination or lithium salt precipitation. Ensure the electrochemical performance and safety performance of the battery.
  • an embodiment of the present invention also provides a method for preparing an electrolyte for a lithium secondary battery, including the following steps:
  • the preparation method provided in the second aspect of the embodiment of the present invention has a simple process and is suitable for industrial production.
  • an embodiment of the present invention also provides a lithium secondary battery, including a positive electrode, a negative electrode, a separator, and an electrolyte.
  • the electrolyte adopts the lithium secondary battery electrolyte described in the first aspect of the present invention.
  • Fig. 1 is a photograph of the electrolyte of a lithium secondary battery prepared in Example 1 of the present invention
  • Figure 3 is a photo of the electrolyte of the lithium secondary battery prepared in Comparative Example 2 of the present invention.
  • Example 4 is a graph of the cycle performance at room temperature of lithium secondary batteries of Example 1-2 and Comparative Example 1-2 of the present invention.
  • the industry has added flame retardants to conventional electrolytes.
  • the phosphazene flame retardant has good compatibility with the positive and negative materials, and the flame retardant performance is better.
  • a relatively high addition amount (10-20wt.%) is required to achieve a good flame retardant effect.
  • the addition of a large amount of single phosphazene flame retardant will cause electrolyte layering or lithium salt precipitation, which will affect the electrochemical performance of the battery.
  • phosphazene flame retardants and other non-phosphazene flame retardants to add in combination to reduce the use of phosphazene flame retardants, but non-phosphazene flame retardants not only have poor flame retardant effects, Moreover, the compatibility with the positive and negative materials is poor, which affects the safety performance and electrochemical performance of the battery.
  • an embodiment of the present invention provides an electrolyte for a lithium secondary battery, in which a (pentafluoro) ring triphosphazene substituted with an electron donating group and a (pentafluoro) ring substituted with an electron withdrawing group are added to the electrolyte at the same time
  • the two flame retardants of triphosphazene can make the battery have both high safety performance and good electrochemical performance.
  • an embodiment of the present invention provides an electrolyte for a lithium secondary battery, including a lithium salt, an organic solvent, and a flame retardant, wherein the flame retardant includes (pentafluoro) cyclotriphosphazene substituted with electron-donating groups and absorption Electron group substituted (pentafluoro) cyclotriphosphazene.
  • the synergistic effect of the two types of phosphazene flame retardants has the following beneficial effects: 1) Due to the different polarity and solubility of the two types of flame retardants, the existence of (pentafluoro) cyclotriphosphazene substituted with electron withdrawing groups can break the (pentafluoro) cyclotriphosphazene substituted with electron donating groups in the electrolyte The saturated solubility limit of phosphazene, increase the total usage of phosphazene flame retardant, avoid electrolyte delamination or lithium salt precipitation, improve the flame resistance of electrolyte, and effectively guarantee the safety of the battery; 2) Two different polar phosphorus The mixed use of nitrile flame retardants can well control the amount of (pentafluoro) cyclotriphosphazene substitute
  • Film formation causes the battery impedance to be too large; it can also improve the high-voltage capability of the electrolyte, effectively inhibit the oxidative decomposition caused by the electrolyte contact with the positive electrode material under high voltage, and improve the high-voltage cycle performance of the battery; 3) Two types of flame retardants The structure is similar, which can effectively avoid the problem of poor compatibility between different flame retardants and ensure that the battery has good electrochemical performance.
  • R When R is an electron donating group, it is a (pentafluoro) cyclotriphosphazene substituted with an electron donating group; when R is an electron withdrawing group, it is a (pentafluoro) cyclotriphosphazene substituted with an electron withdrawing group Nitrile.
  • the electron-donating group may be an alkoxy group or a phenoxy group, that is, the (pentafluoro) cyclotriphosphazene substituted by the electron-donating group includes an alkoxy (pentafluoro) cyclotriphosphazene and One or more of phenoxy (pentafluoro) cyclotriphosphazene.
  • the electron-donating group may also be another electron-donating group that can form a bond with the phosphorus atom of cyclotriphosphazene.
  • the number of carbon atoms of the alkoxy group can be 1-20, further, the number of carbon atoms of the alkoxy group can be 1-10, and further, the number of carbon atoms of the alkoxy group can be 2-6.
  • the alkoxy group may be linear or branched.
  • the alkoxy (pentafluoro) cyclotriphosphazene may include one or more of methoxy (pentafluoro) cyclotriphosphazene and ethoxy (pentafluoro) cyclotriphosphazene .
  • the electron withdrawing group may be a fluoroalkoxy group or an alkylsulfonic acid group, that is, the electron withdrawing group substituted (pentafluoro) cyclotriphosphazene includes fluoroalkoxy (pentafluoro ) One or more of cyclotriphosphazene and alkylsulfonic acid (pentafluoro) cyclotriphosphazene.
  • the electron withdrawing group may also be another electron withdrawing group that can form a bond with the phosphorus atom of cyclotriphosphazene.
  • the number of carbon atoms of the fluoroalkoxy group is 1-20. Further, the number of carbon atoms of the fluoroalkoxy group can be 1-10. Furthermore, the number of carbon atoms of the fluoroalkoxy group is 1-10. The number of carbon atoms can be 2-6.
  • the fluoroalkoxy group may be a perfluoroalkoxy group or a partially fluoroalkoxy group. The fluoroalkoxy group may be straight or branched.
  • the fluoroalkoxy (pentafluoro) cyclotriphosphazene includes trifluoroethoxy (pentafluoro) cyclotriphosphazene and perfluorobutoxy (pentafluoro) cyclotriphosphazene One or more.
  • the number of carbon atoms of the alkyl sulfonate group is 1-20. Further, the number of carbon atoms of the alkyl sulfonate group can be 1-10. The number of carbon atoms can be 2-6.
  • the alkylsulfonic acid group may be linear or branched. In some specific embodiments, the alkylsulfonic acid group (pentafluoro) cyclotriphosphazene includes methylsulfonic acid group (pentafluoro) cyclotriphosphazene and ethylsulfonic acid group (pentafluoro) cyclotriphosphazene One or more.
  • the mass percentage of the (pentafluoro)cyclotriphosphazene substituted with the electron-donating group in the electrolyte may be 10%-30%. Further, the mass percentage of (pentafluoro)cyclotriphosphazene substituted with electron-donating groups in the electrolyte may be 15%-25%.
  • the mass percentage of (pentafluoro)cyclotriphosphazene substituted with electron withdrawing groups in the electrolyte is 1% to 5%.
  • the addition of (pentafluoro) cyclotriphosphazene substituted by electron withdrawing group can effectively increase the total usage of phosphazene flame retardant and improve the flame retardancy of electrolyte.
  • controlling it to a relatively small amount can not only prevent a large number of electron-withdrawing groups substituted (pentafluoro) cyclotriphosphazene from being reduced to a film on the negative electrode, resulting in a large battery impedance; but also can increase the high voltage of the electrolyte Ability to effectively inhibit the oxidation and decomposition of the electrolyte caused by contact with the positive electrode material under high voltage, and improve the high voltage cycle performance of the battery.
  • the total mass percentage of the electron-donating group-substituted (pentafluoro)cyclotriphosphazene and the electron-withdrawing group-substituted (pentafluoro)cyclotriphosphazene in the electrolyte is 11% -35%, further may be 16%-30%, and still further, may be 20%-25%.
  • the other additives may include one or more of film-forming additives, high-voltage additives, anti-overcharge additives, and interface wetting agents ,
  • film-forming additives can be but not limited to vinylene carbonate, trifluoromethyl ethylene carbonate, vinyl ethylene carbonate, 1,3-propane sultone, 1,4-butane sultone, sulfuric acid Vinyl ester, vinyl sulfite, high voltage additives can be but not limited to succinonitrile, adiponitrile, 1,2-bis(2-cyanoethoxy)ethane and 1,3,6-hexane trinitrile One or more of.
  • the anti-overcharge additive may be biphenyl, for example, and the interfacial wetting agent may be fluorobenzene, for example.
  • the mass percentage content of other additives in the electrolyte may be 0.1%-20%, and further may be 0.5-10%.
  • the lithium salt may be a commonly used conductive lithium salt, and specifically may include LiClO 4 , LiBF 4 , LiPF 6 , LiAsF 6 , LiPF 2 O 2 , LiCF 3 SO 3 , LiTDI, LiB(C 2 O 4 ) 2 (LiBOB), LiBF 2 C 2 O 4 (LiDFOB), Li[(CF 3 SO 2 ) 2 N], Li[(FSO 2 ) 2 N] and Li[(C m F 2m+1 SO 2 ) One or more of (C n F 2n+1 SO 2 )N], where m and n are natural numbers.
  • the molar concentration of the lithium salt in the electrolyte may be 0.01 mol/L-2.0 mol/L.
  • the organic solvent in order to coordinate the dissolution of the flame retardant with a high added amount, can be a carbonate-based solvent and/or a carboxylate-based solvent.
  • the carbonate-based solvent may be a mixed solvent composed of a cyclic carbonate and a chain carbonate.
  • the cyclic carbonate may include one of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), gamma-butyrolactone (GBL), and butylene carbonate (BC).
  • the chain carbonate may include one or more of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC).
  • the mass percentage of the cyclic carbonate in the electrolyte may be 5%-70%, and the mass percentage of the chain carbonate in the electrolyte may be 5%-70%.
  • the carboxylic acid ester solvent may include one of methyl acetate (MA), ethyl acetate (EA), propyl acetate, butyl acetate, propyl propionate (PP), and butyl propionate.
  • MA methyl acetate
  • EA ethyl acetate
  • PP propyl propionate
  • One or more; the mass percentage of the carboxylic acid ester solvent in the electrolyte can be 5%-30%.
  • the lithium secondary battery electrolyte provided by the embodiments of the present invention, by adding two types of phosphazene flame retardants with different polarities and similar structures to the electrolyte at the same time, the total usage of the phosphazene flame retardants is increased, and the battery is While having high safety performance, it effectively guarantees the electrochemical performance of the battery, and the two types of phosphazene flame retardants have good compatibility with the positive and negative materials, without deteriorating other aspects of the battery performance (such as low temperature and rate performance), and has a broader Application prospects.
  • the embodiment of the present invention also provides a preparation method of the above-mentioned lithium secondary battery electrolyte, which includes the following steps:
  • the preparation method provided by the embodiment of the present invention has a simple process and is suitable for industrial production.
  • An embodiment of the present invention also provides a lithium secondary battery, including a positive electrode, a negative electrode, a separator, and an electrolyte, and the electrolyte adopts the lithium secondary battery electrolyte of the foregoing embodiment of the present invention.
  • the lithium secondary battery provided by the embodiment of the present invention has a relatively large amount of phosphazene flame retardant added to its electrolyte, and the phosphazene flame retardant has good compatibility with the positive and negative electrode materials and has good flame retardancy, so that the battery It has both excellent safety performance and electrochemical performance.
  • An electrolyte for lithium secondary batteries including lithium salts (LiPF 6 and LiDFOB), a non-aqueous organic solvent formed by mixing EC, DEC, PC, FEC and PP in a weight ratio of 25:20:25:5:15, and Including the flame retardants ethoxy (pentafluoro) cyclotriphosphazene and trifluoroethoxy (pentafluoro) cyclotriphosphazene, the concentration of LiPF 6 is 1.0 mol/L, and the concentration of LiDFOB is 0.05 mol/L
  • the mass percentages of ethoxy (pentafluoro) cyclotriphosphazene and trifluoroethoxy (pentafluoro) cyclotriphosphazene are 15% and 2%, respectively.
  • PVDF polyvinylidene fluoride
  • NMP N-methylpyrrolidone
  • the positive pole piece, the negative pole piece and the commercial PP/PE/PP three-layer separator prepared above were made into batteries, and polymer packaging was used to infuse the lithium secondary battery electrolyte prepared in Example 1 of the present invention. After the process, a 3.8 Ah soft-packed lithium secondary battery was produced.
  • An electrolyte for lithium secondary batteries including lithium salts (LiPF 6 and LiDFOB), a non-aqueous organic solvent formed by mixing EC, DEC, PC, FEC and PP in a weight ratio of 25:20:25:5:15, and Including flame retardants ethoxy (pentafluoro) cyclotriphosphazene and methylsulfonic acid group (pentafluoro) cyclotriphosphazene, the concentration of LiPF 6 is 1.0 mol/L, and the concentration of LiDFOB is 0.05 mol/L
  • the mass percentages of ethoxy (pentafluoro) cyclotriphosphazene and methylsulfonic acid (pentafluoro) cyclotriphosphazene are 15% and 2%, respectively.
  • the production of the lithium secondary battery was the same as in Example 1.
  • An electrolyte for lithium secondary batteries including lithium salts (LiPF 6 and LiDFOB), a non-aqueous organic solvent formed by mixing EC, DEC, PC, FEC and PP in a weight ratio of 25:20:25:5:15, and Including flame retardants ethoxy (pentafluoro) cyclotriphosphazene, trifluoroethoxy (pentafluoro) cyclotriphosphazene and methylsulfonic acid group (pentafluoro) cyclotriphosphazene, among which the concentration of LiPF 6 1.0mol/L, the concentration of LiDFOB is 0.05mol/L, ethoxy (pentafluoro) cyclotriphosphazene, trifluoroethoxy (pentafluoro) cyclotriphosphazene and methanesulfonate (pentafluoro)
  • the mass percentages of cyclotriphosphazene are 15%, 1% and 1% respectively.
  • EC, DEC, PC, FEC and PP are mixed to form an organic solvent, then fully dried LiPF 6 and LiDFOB are dissolved in the above solvent, stirred and mixed into a uniform solution, and then ethoxylated (Pentafluoro) cyclotriphosphazene, trifluoroethoxy (pentafluoro) cyclotriphosphazene and methylsulfonic acid group (pentafluoro) cyclotriphosphazene are added to the above solution and mixed uniformly to prepare the embodiment 3 of the present invention Lithium secondary battery electrolyte.
  • the production of the lithium secondary battery was the same as in Example 1.
  • EC, DEC, PC, FEC, and PP are mixed to form an organic solvent, and then fully dried LiPF 6 and LiDFOB are dissolved in the above solvent, and stirred and mixed to uniformly prepare the comparative example 1 of the present invention.
  • the concentration of LiPF 6 is 1.0 mol/L
  • the concentration of LiDFOB is 0.05 mol/L
  • the mass percentages of EC, DEC, PC, FEC and PP are 25:20:25:5:15, respectively.
  • the production of the lithium secondary battery was the same as in Example 1.
  • the concentration of LiPF 6 is 1.0mol/L
  • the concentration of LiDFOB is 0.05mol/L
  • the mass percentages of EC, DEC, PC, FEC and PP are 25:20:25:5:15
  • the mass percentage of cyclotriphosphazene is 17%.
  • the production of the lithium secondary battery was the same as in Example 1.
  • Use a rotary viscometer to test the viscosity of the electrolyte Take a 0.5mL-1mL electrolyte sample and place it in the sample table of the viscometer. The test condition is 25°C, the measurement range of the rotor is 1-100mPa/s, and the measurement speed is 50rpm. The viscosity of the electrolyte sample was tested 3 times and the average value was taken.
  • the battery was subjected to a charge-discharge cycle test at a charge-discharge rate of 0.7/0.7C.
  • the voltage range of the graphite/LiCoO 2 battery was 3.0-4.5V, and the capacity retention rate was recorded for 200 weeks.
  • Figure 1, Figure 2, and Figure 3 are photos of the electrolyte of Example 1, Comparative Document 1 and Comparative Example 2, respectively. It can be seen from Table 1 and Figures 1, 2 and 3 that in Examples 1-3 The prepared electrolyte is in a clear, transparent and uniform state, while the electrolyte prepared in Comparative Example 2 is turbid and a little lithium salt is precipitated at the bottom. This is mainly due to the amount of ethoxy (pentafluoro) cyclotriphosphazene used in the electrolysis The liquid reaches the upper limit.
  • Example 1 of the present invention ethoxy (pentafluoro) cyclotriphosphazene and trifluoroethoxy (pentafluoro) cyclotriphosphazene are simultaneously introduced, effectively avoiding a single ethoxy (pentafluoro) cyclotriphosphazene. (Fluorine) the limit on the amount of cyclotriphosphazene used.
  • Figure 4 we can see from Figure 4 that compared to Comparative Example 1-2, the battery in Example 1-2 has better high-voltage cycling performance, and the battery exhibits a higher capacity retention rate after 200 cycles of cycling.
  • the lithium secondary battery electrolyte provided by the embodiments of the present invention not only solves the limitation of the use of a single phosphazene flame retardant and avoids the problem of poor compatibility with the electrolyte, but also effectively ensures the electrochemical performance of the battery. Performance and safety performance.

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Abstract

本发明实施例提供一种锂二次电池电解液，包括锂盐、有机溶剂和阻燃剂，所述阻燃剂包括给电子基团取代的(五氟)环三磷腈和吸电子基团取代的(五氟)环三磷腈。该锂二次电池电解液中同时添加了给电子基团取代的(五氟)环三磷腈和吸电子基团取代的(五氟)环三磷腈两种阻燃剂，使电池兼具高安全性能和良好电化学性能。本发明实施例还提供了该锂二次电池电解液的制备方法和包含该锂二次电池电解液的锂二次电池。

Description

锂二次电池电解液及其制备方法和锂二次电池 技术领域
本发明实施例涉及锂二次电池技术领域，特别是涉及锂二次电池电解液及其制备方法和锂二次电池。
背景技术
随着手机、数码相机、笔记本电脑等电子消费品使用功能的不断扩增，对锂离子电池的能量密度提出了越来越高的要求，而电池能量密度提升的同时会带来电池的安全问题。目前，锂离子电池的电解质主要为非水有机电解液(常规为碳酸酯类电解液)，当电池在滥用(热冲击、过充、针刺和外部短路等)状态下因其电解液存在易挥发、易燃烧等隐患，极易引起电池热失控而导致的安全性问题。
针对以上碳酸酯类电解液存在的易燃问题，目前主流的解决方案是向常规电解液中添加阻燃添加剂，虽然报道的阻燃添加剂有很多种，如磷系化合物、卤代化合物、含氮化合物、硅系化合物等，但是它们大多数与正负极材料的兼容性较差。而即使采用与正负极材料兼容性良好的磷腈阻燃剂，为了保证高能量密度电池的安全性，仍然需要在相当高的添加量(10-20wt.％)下才能实现良好的阻燃效果。然而大量单一磷腈阻燃剂的添加(>15wt.％)，会引起电解液分层或锂盐析出，影响电池电化学性能。为了解决这一问题，业界采用磷腈阻燃剂和其它非磷腈阻燃剂进行组合添加，以降低磷腈阻燃剂的使用量，但是非磷腈阻燃剂不仅阻燃效果不佳，而且与正负极材料的兼容性较差，影响了电池的安全性能和电化学性能。
发明内容
鉴于此，本发明实施例提供一种锂二次电池电解液，通过向电解液中同时添加给电子基团取代的(五氟)环三磷腈和吸电子基团取代的(五氟)环三磷腈两种阻燃剂，使电池能兼具高安全性能和良好电化学性能，以在一定程度上解决现有大量磷腈阻燃剂的添加会引起电解液分层或锂盐析出，最终导致电池电化学性能较差的问题。
具体地，本发明实施例第一方面提供一种锂二次电池电解液，包括锂盐、有机溶剂和阻燃剂，所述阻燃剂包括给电子基团取代的(五氟)环三磷腈和吸电子基团取代的(五氟)环三磷腈。
本发明实施方式中，所述给电子基团取代的(五氟)环三磷腈包括烷氧基(五氟)环三磷腈和苯氧基(五氟)环三磷腈中的一种或多种。
本发明实施方式中，所述烷氧基(五氟)环三磷腈中，所述烷氧基的碳原子数为1-20。
本发明实施方式中，所述烷氧基(五氟)环三磷腈包括甲氧基(五氟)环三磷腈和乙氧基(五氟)环三磷腈中的一种或多种。
本发明实施方式中，所述吸电子基团取代的(五氟)环三磷腈包括氟代烷氧基(五氟)环三磷腈和烷基磺酸基(五氟)环三磷腈中的一种或多种。
本发明实施方式中，所述氟代烷氧基(五氟)环三磷腈中，所述氟代烷氧基的碳原子 数为1-20。
本发明实施方式中，所述氟代烷氧基(五氟)环三磷腈包括三氟乙氧基(五氟)环三磷腈和全氟丁氧基(五氟)环三磷腈中的一种或多种。
本发明实施方式中，所述烷基磺酸基(五氟)环三磷腈中，所述烷基磺酸基的碳原子数为1-20。
本发明实施方式中，所述烷基磺酸基(五氟)环三磷腈包括甲基磺酸基(五氟)环三磷腈和乙基磺酸基(五氟)环三磷腈中的一种或多种。
本发明实施方式中，所述给电子基团取代的(五氟)环三磷腈在所述电解液中的质量百分含量为10％-30％。
本发明实施方式中，所述吸电子基团取代的(五氟)环三磷腈在所述电解液中的质量百分含量为1％-5％。
本发明实施方式中，所述给电子基团取代的(五氟)环三磷腈和所述吸电子基团取代的(五氟)环三磷腈在所述电解液中的总质量百分含量为16％-30％。
本发明实施方式中，所述电解液还包括其它添加剂，所述其它添加剂包括联苯、氟苯、碳酸亚乙烯酯、三氟甲基碳酸乙烯酯、碳酸乙烯亚乙酯、1,3-丙磺酸内酯、1,4-丁磺酸内酯、硫酸乙烯酯、亚硫酸乙烯酯、丁二腈、己二腈、1,2-二(2-氰乙氧基)乙烷和1,3,6-己烷三腈中的一种或多种。
本发明实施方式中，所述其它添加剂在所述电解液中的质量百分含量为0.1％-20％。
本发明实施方式中，所述锂盐包括LiClO 4、LiBF 4、LiPF 6、LiAsF 6、LiPF 2O 2、LiCF 3SO 3、LiTDI、LiB(C 2O 4) 2(LiBOB)、LiBF 2C 2O 4(LiDFOB)、Li[(CF 3SO 2) 2N]、Li[(FSO 2) 2N]和Li[(C mF 2m+1SO 2)(C nF 2n+1SO 2)N]中的一种或多种，其中，m和n为自然数。
本发明实施方式中，所述锂盐在所述电解液中的摩尔浓度为0.01mol/L-2.0mol/L。
本发明实施方式中，所述有机溶剂包括碳酸酯类溶剂和/或羧酸酯类溶剂。
本发明实施方式中，所述碳酸酯类溶剂为环状碳酸酯和链状碳酸酯组成的混合溶剂。
本发明实施方式中，所述环状碳酸酯包括碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、氟代碳酸乙烯酯(FEC)、γ-丁内酯(GBL)、碳酸亚丁酯(BC)中的一种或多种；所述链状碳酸酯包括碳酸二甲酯(DMC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二丙酯(DPC)中的一种或多种。
本发明实施方式中，所述环状碳酸酯在所述电解液中的质量百分含量为5％-70％，所述链状碳酸酯在所述电解液中的质量百分含量为5％-70％。
本发明实施方式中，所述羧酸酯类溶剂包括乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯、乙酸丁酯、丙酸丙酯(PP)、丙酸丁酯中的一种或多种；所述羧酸酯类溶剂在所述电解液中的质量百分含量为5％-30％。
本发明实施例第一方面提供的锂二次电池电解液，通过向电解液中同时添加给电子基团取代的(五氟)环三磷腈和吸电子基团取代的(五氟)环三磷腈两种阻燃剂，在两种阻燃剂的协同作用下进一步提高了磷腈阻燃剂在电解液中的溶解度，较好地克服了电解液分层或锂盐析出的问题，同时保证了电池的电化学性能及安全性能。
第二方面，本发明实施例还提供了一种锂二次电池电解液的制备方法，包括以下步骤：
在填充氩气的手套箱中，将充分干燥的锂盐溶解于有机溶剂中，搅拌混合成均匀溶液，然后将给电子基团取代的(五氟)环三磷腈和吸电子基团取代的(五氟)环三磷腈加入到所述均匀溶液中，混合均匀后，得到锂二次电池电解液。
本发明实施例第二方面提供的制备方法，工艺简单，适于工业化生产。
第三方面，本发明实施例还提供了一种锂二次电池，包括正极、负极、隔膜和电解液，所述电解液采用本发明第一方面所述的锂二次电池电解液。
附图说明
图1为本发明实施例1制备的锂二次电池电解液的照片；
图2为本发明对比例1制备的锂二次电池电解液的照片；
图3为本发明对比例2制备的锂二次电池电解液的照片；
图4为本发明实施例1-2及对比例1-2的锂二次电池室温下的循环性能图。
具体实施方式
下面将结合本发明实施例中的附图，对本发明实施例进行说明。
为提高锂离子电池安全性能，业界向常规电解液中添加阻燃剂，其中磷腈阻燃剂与正负极材料兼容性良好，阻燃性能较好而被关注。但为了保证高能量密度电池的安全性，需要在相当高的添加量(10-20wt.％)下才能实现良好的阻燃效果。然而大量单一磷腈阻燃剂的添加，会引起电解液分层或锂盐析出，影响电池电化学性能。为解决这一问题，业界采用磷腈阻燃剂和其它非磷腈阻燃剂进行组合添加，以降低磷腈阻燃剂的使用量，但是非磷腈阻燃剂不仅阻燃效果不佳，而且与正负极材料的兼容性较差，影响了电池的安全性能和电化学性能。鉴于此，本发明实施例提供一种锂二次电池电解液，该电解液中同时添加有给电子基团取代的(五氟)环三磷腈和吸电子基团取代的(五氟)环三磷腈两种阻燃剂，能够使电池兼具高安全性能和良好电化学性能。
具体地，本发明实施例提供一种锂二次电池电解液，包括锂盐、有机溶剂和阻燃剂，其中，阻燃剂包括给电子基团取代的(五氟)环三磷腈和吸电子基团取代的(五氟)环三磷腈。
本发明实施例的锂二次电池电解液，通过向常规电解液中同时添加两类结构类似的磷腈阻燃剂，在两类磷腈阻燃剂的协同作用下具有如下有益效果：1)由于两类阻燃剂的极性不同，溶解度不同，吸电子基团取代的(五氟)环三磷腈的存在，可打破电解液中给电子基团取代的(五氟)环三磷腈的饱和溶解度限制，增加磷腈阻燃剂的总使用量，避免电解液分层或锂盐析出，提高电解液的耐燃性，使电池的安全性得到有效保证；2)两种不同极性磷腈阻燃剂混合使用，可以很好地控制吸电子基团取代的(五氟)环三磷腈使用量，既可避免大量吸电子基团取代的(五氟)环三磷腈在负极还原成膜，造成电池阻抗偏大；又可提高电解液的高电压能力，有效抑制电解液在高电压下与正极材料接触引起的氧化分解，提高电池高电压循环性能；3)两类阻燃剂的结构类似，可以有效避免不同阻燃剂之间相容性差的问题，保证电池具有良好的电化学性能。
本发明实施方式中，给电子基团取代的(五氟)环三磷腈和吸电子基团取代的(五氟) 环三磷腈的结构式均可以采用式(Ⅰ)所示的结构式表示：
Figure PCTCN2020076844-appb-000001
当R为给电子基团时，即为给电子基团取代的(五氟)环三磷腈；当R为吸电子基团时，即为吸电子基团取代的(五氟)环三磷腈。
在本发明一些实施例中，给电子基团可以是烷氧基或苯氧基，即给电子基团取代的(五氟)环三磷腈包括烷氧基(五氟)环三磷腈和苯氧基(五氟)环三磷腈中的一种或多种。在其他一些实施例中，给电子基团也可以是其他的可与环三磷腈的磷原子形成键合的给电子基团。在本发明一些实施例中，烷氧基的碳原子数可为1-20，进一步地，烷氧基的碳原子数可为1-10，更进一步地，烷氧基的碳原子数可为2-6。烷氧基可以是直链，也可以是支链。在一些具体实施例中，烷氧基(五氟)环三磷腈可包括甲氧基(五氟)环三磷腈和乙氧基(五氟)环三磷腈中的一种或多种。
在本发明一些实施例中，吸电子基团可以是氟代烷氧基或烷基磺酸基，即吸电子基团取代的(五氟)环三磷腈包括氟代烷氧基(五氟)环三磷腈和烷基磺酸基(五氟)环三磷腈中的一种或多种。在其他一些实施例中，吸电子基团也可以是其他的可与环三磷腈的磷原子形成键合的吸电子基团。
在本发明一些实施例中，氟代烷氧基的碳原子数为1-20，进一步地，氟代烷氧基的碳原子数可为1-10，更进一步地，氟代烷氧基的碳原子数可为2-6。本发明实施方式中，氟代烷氧基可以是全氟代烷氧基，也可以是部分氟代烷氧基。氟代烷氧基可以是直链，也可以是支链。在一些具体实施例中，氟代烷氧基(五氟)环三磷腈包括三氟乙氧基(五氟)环三磷腈和全氟丁氧基(五氟)环三磷腈中的一种或多种。
在本发明一些实施例中，烷基磺酸基的碳原子数为1-20，进一步地，烷基磺酸基的碳原子数可为1-10，更进一步地，烷基磺酸基的碳原子数可为2-6。烷基磺酸基可以是直链，也可以是支链。在一些具体实施例中，烷基磺酸基(五氟)环三磷腈包括甲基磺酸基(五氟)环三磷腈和乙基磺酸基(五氟)环三磷腈中的一种或多种。
本发明实施方式中，给电子基团取代的(五氟)环三磷腈在电解液中的质量百分含量可为10％-30％。进一步地，给电子基团取代的(五氟)环三磷腈在电解液中的质量百分含量可为15％-25％。
本发明实施方式中，吸电子基团取代的(五氟)环三磷腈在所述电解液中的质量百分含量为1％-5％。吸电子基团取代的(五氟)环三磷腈的加入，可有效提高磷腈阻燃剂的总使用量，提高电解液阻燃性。且将其控制在相对较少的加入量，既可避免大量吸电子基团取代的(五氟)环三磷腈在负极还原成膜，造成电池阻抗偏大；又可提高电解液的高电压能力，有效抑制电解液在高电压下与正极材料接触引起的氧化分解，提高电池高电压循环性能。
本发明实施方式中，给电子基团取代的(五氟)环三磷腈和所述吸电子基团取代的(五氟)环三磷腈在电解液中的总质量百分含量为11％-35％，进一步地可为16％-30％，更进一步地，可为20％-25％。
本发明实施方式中，根据实际需要，电解液中还可包括其它添加剂，具体地，其它添加剂可包括成膜添加剂、高电压添加剂、防过充添加剂、界面润湿剂中的一种或多种，其中成膜添加剂可以但不限于是碳酸亚乙烯酯、三氟甲基碳酸乙烯酯、碳酸乙烯亚乙酯、1,3-丙磺酸内酯、1,4-丁磺酸内酯、硫酸乙烯酯、亚硫酸乙烯酯，高电压添加剂可以但不限于是丁二腈、己二腈、1,2-二(2-氰乙氧基)乙烷和1,3,6-己烷三腈中的一种或多种。防过充添加剂例如可以是联苯，界面润湿剂例如可以是氟苯。其它添加剂在电解液中的质量百分含量可为0.1％-20％，进一步地可为0.5-10％。
本发明实施方式中，锂盐可以是现有常用的导电锂盐，具体可包括LiClO 4、LiBF 4、LiPF 6、LiAsF 6、LiPF 2O 2、LiCF 3SO 3、LiTDI、LiB(C 2O 4) 2(LiBOB)、LiBF 2C 2O 4(LiDFOB)、Li[(CF 3SO 2) 2N]、Li[(FSO 2) 2N]和Li[(C mF 2m+1SO 2)(C nF 2n+1SO 2)N]中的一种或多种，其中，m和n为自然数。在本发明一些实施例中，锂盐在电解液中的摩尔浓度可以为0.01mol/L-2.0mol/L。
本发明实施方式中，为配合高添加量阻燃剂的溶解，有机溶剂可选择碳酸酯类溶剂和/或羧酸酯类溶剂。其中，碳酸酯类溶剂可以是环状碳酸酯和链状碳酸酯组成的混合溶剂。具体地，环状碳酸酯可包括碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、氟代碳酸乙烯酯(FEC)、γ-丁内酯(GBL)、碳酸亚丁酯(BC)中的一种或多种；链状碳酸酯可包括碳酸二甲酯(DMC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二丙酯(DPC)中的一种或多种。
本发明一些实施例中，环状碳酸酯在电解液中的质量百分含量可为5％-70％，链状碳酸酯在电解液中的质量百分含量可为5％-70％。
本发明实施方式中，羧酸酯类溶剂可包括乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯、乙酸丁酯、丙酸丙酯(PP)、丙酸丁酯中的一种或多种；羧酸酯类溶剂在电解液中的质量百分含量可为5％-30％。
本发明实施例提供的锂二次电池电解液，通过向电解液中同时加入两类极性不同、结构类似的磷腈阻燃剂，提高了磷腈阻燃剂的总使用量，使电池在具有高安全性能的同时，有效保证了电池的电化学性能，且两类磷腈阻燃剂与正负极材料兼容性良好，没有恶化电池其它方面性能(如低温和倍率性能)，具有更广阔的应用前景。
相应地，本发明实施例还提供了上述锂二次电池电解液的制备方法，包括以下步骤：
在填充氩气的手套箱中，将充分干燥的锂盐溶解于有机溶剂中，搅拌混合成均匀溶液，然后将给电子基团取代的(五氟)环三磷腈和吸电子基团取代的(五氟)环三磷腈加入到上述均匀溶液中，再混合均匀后，得到锂二次电池电解液。
本发明实施例提供的制备方法，工艺简单，适于工业化生产。
本发明实施例还提供了一种锂二次电池，包括正极、负极、隔膜和电解液，所述电解液采用本发明上述实施例的锂二次电池电解液。本发明实施例提供的锂二次电池，由于其电解液中加入了较大量的磷腈阻燃剂，且磷腈阻燃剂与正负极材料兼容性好、阻燃性好，因此使得电池兼具优异的安全性能和电化学性能。
下面分多个实施例对本发明实施例进行进一步的说明。
实施例1
一种锂二次电池电解液，包括锂盐(LiPF 6和LiDFOB)，由EC、DEC、PC、FEC和PP按重量比25:20:25:5:15混合形成的非水有机溶剂，以及包括阻燃剂乙氧基(五氟)环三磷腈和三氟乙氧基(五氟)环三磷腈，其中，LiPF 6的浓度为1.0mol/L，LiDFOB的浓度为0.05mol/L，乙氧基(五氟)环三磷腈和三氟乙氧基(五氟)环三磷腈的质量百分数分别为15％和2％。
本实施例上述锂二次电池电解液的制备：
在填充氩气的手套箱中，将EC、DEC、PC、FEC和PP混合形成有机溶剂，再将充分干燥的LiPF 6和LiDFOB溶解于上述溶剂中，搅拌混合成均匀溶液，然后将乙氧基(五氟)环三磷腈和三氟乙氧基(五氟)环三磷腈加入到上述均匀溶液中，再混合均匀制得本发明实施例1的锂二次电池电解液。
锂二次电池的制作：
称取质量百分含量为2％聚偏氟乙烯(PVDF)、2％导电剂super P和96％钴酸锂(LiCoO 2)，依次加入到N-甲基吡咯烷酮(NMP)中，充分搅拌混合均匀得到浆料，将所得浆料涂布在铝箔集流体上，烘干、冷压、分切制得正极极片；
称取质量百分含量为1.5％CMC、2.5％SBR、1％乙炔黑和95％石墨，依次加入到去离子水中，充分搅拌混合均匀得到浆料，将所得浆料涂布在铜箔集流体上，烘干、冷压、分切制得负极极片；
将上述制备的正极极片、负极极片和商用PP/PE/PP三层隔膜制成电芯，采用聚合物包装，灌注本发明实施例1制备得到的锂二次电池电解液，经化成等工艺后制成3.8Ah的软包锂二次电池。
实施例2
一种锂二次电池电解液，包括锂盐(LiPF 6和LiDFOB)，由EC、DEC、PC、FEC和PP按重量比25:20:25:5:15混合形成的非水有机溶剂，以及包括阻燃剂乙氧基(五氟)环三磷腈和甲基磺酸基(五氟)环三磷腈，其中，LiPF 6的浓度为1.0mol/L，LiDFOB的浓度为0.05mol/L，乙氧基(五氟)环三磷腈和甲基磺酸基(五氟)环三磷腈的质量百分数分别为15％和2％。
本实施例上述锂二次电池电解液的制备：
在填充氩气的手套箱中，将EC、DEC、PC、FEC和PP混合形成有机溶剂，再将充分干燥的LiPF 6和LiDFOB溶解于上述溶剂中，搅拌混合成均匀溶液，然后将乙氧基(五氟)环三磷腈和甲基磺酸基(五氟)环三磷腈加入到上述均匀溶液中，再混合均匀制得本发明实施例2的锂二次电池电解液。
锂二次电池的制作同实施例1。
实施例3
一种锂二次电池电解液，包括锂盐(LiPF 6和LiDFOB)，由EC、DEC、PC、FEC和PP按重量比25:20:25:5:15混合形成的非水有机溶剂，以及包括阻燃剂乙氧基(五氟)环三磷腈、三氟乙氧基(五氟)环三磷腈和甲基磺酸基(五氟)环三磷腈，其中，LiPF 6 的浓度为1.0mol/L，LiDFOB的浓度为0.05mol/L，乙氧基(五氟)环三磷腈、三氟乙氧基(五氟)环三磷腈和甲基磺酸基(五氟)环三磷腈的质量百分数分别为15％、1％和1％。
本实施例上述锂二次电池电解液的制备：
在填充氩气的手套箱中，将EC、DEC、PC、FEC和PP混合形成有机溶剂，再将充分干燥的LiPF 6和LiDFOB溶解于上述溶剂中，搅拌混合成均匀溶液，然后将乙氧基(五氟)环三磷腈、三氟乙氧基(五氟)环三磷腈和甲基磺酸基(五氟)环三磷腈加入上述溶液，混合均匀制得本发明实施例3的锂二次电池电解液。
锂二次电池的制作同实施例1。
对比例1
在填充氩气的手套箱中，将EC、DEC、PC、FEC和PP混合形成有机溶剂，再将充分干燥的LiPF 6和LiDFOB溶解于上述溶剂中，搅拌混合成均匀制得本发明对比例1的电解液。其中LiPF 6的浓度为1.0mol/L，LiDFOB的浓度为0.05mol/L，EC、DEC、PC、FEC和PP的质量百分数分别为25:20:25:5:15。锂二次电池制作同实施例1。
对比例2
在填充氩气的手套箱中，将EC、DEC、PC、FEC和PP混合形成有机溶剂，再将充分干燥的LiPF 6和LiDFOB溶解于上述溶剂中，搅拌混合成均匀溶液，然后将乙氧基(五氟)环三磷腈加入上述溶液，充分混合制得本发明对比例2的电解液。其中LiPF 6的浓度为1.0mol/L，LiDFOB的浓度为0.05mol/L，EC、DEC、PC、FEC和PP的质量百分数分别为25:20:25:5:15，乙氧基(五氟)环三磷腈的质量百分数为17％。锂二次电池制作同实施例1。
将本发明实施例1-3和对比例1-2中的电解液和锂二次电池进行以下测试：
(1)电解液粘度和电导率的测试
采用旋转粘度计测试电解液的粘度，取0.5mL-1mL的电解液样品置于粘度计的样品台中，测试条件为25℃，转子测量范围为1-100mPa/s，测量转速为50rpm，每种电解液样品的粘度测试3次并取其平均值。采用电导率仪测试电解液的电导率，取1mL-5mL的电解液样品置于电导率仪的测试管中，测试温度为25℃，每种电解液样品的电导率测试3次并取其平均值。
(2)电解液自熄性能的测试
取1.0g电解液置于5.0mL的坩埚中，点燃测试其自熄时间。用点火装置迅速点燃，记录点火装置移开后至火焰自动熄灭的时间，即为自熄时间(SET)。每种电解液样品的SET测试5次并取其平均值。以单位质量电解液的自熄时间为标准，比较不同电解液的阻燃性能。
(3)锂二次电池性能的测试
以0.7/0.7C充放电倍率对电池进行充放电循环测试，石墨/LiCoO 2电池的电压范围为3.0-4.5V，记录200周的容量保持率。
实施例1-3和对比例1-2的上述测试的结果列于表1、图1、图2、图3和图4。
表1实施例1-3和对比例1-2的测试结果
Figure PCTCN2020076844-appb-000002
从表1可以看出，与对比例1比较可知，实施例1-3和对比例2中的电解液具有优异的耐燃性，这主要归因于实施例1-3和对比例2中的电解液含有磷腈阻燃剂发挥高效的阻燃特性所致，在电解液受热情况下，其中的磷腈基团会分解产生P系自由基捕获电解液受热分解产生的H或OH自由基，切断链式反应，从而提高电解液的耐燃性；同时我们也可以看出，虽然在实施例1-3中引入磷腈阻燃剂，会增加电解液的粘度和降低电解液的电导率，但是与对比例2比较可知，采用两类磷腈阻燃剂组合使用，对电解液粘度和电导率的影响程度更小，这得益于两类阻燃剂都是结构类似的磷腈化合物，可以有效避免不同添加剂之间相容性差的问题，且给电子基团取代的(五氟)环三磷腈和吸电子基团取代的(五氟)环三磷腈协同作用可以进一步提高磷腈阻燃剂的总使用量，不至于引起电解液出现分层或锂盐析出的现象。
另外，图1、图2、图3分别为实施例1、对比文件1和对比例2的电解液照片，从表1和图1、图2、图3可以看出，实施例1-3中配制的电解液呈现澄清透明均匀状态，而对比例2中配制的电解液呈现浑浊且底部有少许锂盐析出，这主要是由于乙氧基(五氟)环三磷腈的使用量在该电解液中达到上限所致，本发明实施例1通过乙氧基(五氟)环三磷腈和三氟乙氧基(五氟)环三磷腈同时引入，有效避免了单一乙氧基(五氟)环三磷腈使用量的限制。同时从图4我们也可以看出，相比对比例1-2，实施例1-2中的电池具有更好的高电压循环性能，电池在200周循环后展现出更高的容量保持率，这主要是归因于适量吸电子基团取代的(五氟)环三磷腈的引入，不仅提高了电解液的高电压能力，而且其中的吸电子基团(如三氟乙氧基或甲基磺酸基)在高电压条件下，能够在电池的正极材料表面形成致密的界面膜，有效地抑制电解液在高电压下与正极材料直接接触引起的氧化分解，避免严重副反应的发生，提高电池的高电压循环性能。因此，本发明实施例提供的锂二次电池电解液，不仅解决了单一磷腈阻燃剂使用量的限制和避免与电解液之间的相容性差的问题，而且有效保证了电池的电化学性能和安全性能。

Claims (23)

  1. 一种锂二次电池电解液，其特征在于，包括锂盐、有机溶剂和阻燃剂，所述阻燃剂包括给电子基团取代的(五氟)环三磷腈和吸电子基团取代的(五氟)环三磷腈。
  2. 如权利要求1所述的锂二次电池电解液，其特征在于，所述给电子基团取代的(五氟)环三磷腈包括烷氧基(五氟)环三磷腈和苯氧基(五氟)环三磷腈中的一种或多种。
  3. 如权利要求2所述的锂二次电池电解液，其特征在于，所述烷氧基(五氟)环三磷腈中，所述烷氧基的碳原子数为1-20。
  4. 如权利要求3所述的锂二次电池电解液，其特征在于，所述烷氧基(五氟)环三磷腈包括甲氧基(五氟)环三磷腈和乙氧基(五氟)环三磷腈中的一种或多种。
  5. 如权利要求1所述的锂二次电池电解液，其特征在于，所述吸电子基团取代的(五氟)环三磷腈包括氟代烷氧基(五氟)环三磷腈和烷基磺酸基(五氟)环三磷腈中的一种或多种。
  6. 如权利要求5所述的锂二次电池电解液，其特征在于，所述氟代烷氧基(五氟)环三磷腈中，所述氟代烷氧基的碳原子数为1-20。
  7. 如权利要求6所述的锂二次电池电解液，其特征在于，所述氟代烷氧基(五氟)环三磷腈包括三氟乙氧基(五氟)环三磷腈和全氟丁氧基(五氟)环三磷腈中的一种或多种。
  8. 如权利要求5所述的锂二次电池电解液，其特征在于，所述烷基磺酸基(五氟)环三磷腈中，所述烷基磺酸基的碳原子数为1-20。
  9. 如权利要求8所述的锂二次电池电解液，其特征在于，所述烷基磺酸基(五氟)环三磷腈包括甲基磺酸基(五氟)环三磷腈和乙基磺酸基(五氟)环三磷腈中的一种或多种。
  10. 如权利要求1所述的锂二次电池电解液，其特征在于，所述给电子基团取代的(五氟)环三磷腈在所述电解液中的质量百分含量为10％-30％。
  11. 如权利要求1所述的锂二次电池电解液，其特征在于，所述吸电子基团取代的(五氟)环三磷腈在所述电解液中的质量百分含量为1％-5％。
  12. 如权利要求1所述的锂二次电池电解液，其特征在于，所述给电子基团取代的(五氟)环三磷腈和所述吸电子基团取代的(五氟)环三磷腈在所述电解液中的总质量百分含量为16％-30％。
  13. 如权利要求1所述的锂二次电池电解液，其特征在于，所述电解液还包括其它添加剂，所述其它添加剂包括联苯、氟苯、碳酸亚乙烯酯、三氟甲基碳酸乙烯酯、碳酸乙烯亚乙酯、1,3-丙磺酸内酯、1,4-丁磺酸内酯、硫酸乙烯酯、亚硫酸乙烯酯、丁二腈、己二腈、1,2-二(2-氰乙氧基)乙烷和1,3,6-己烷三腈中的一种或多种。
  14. 如权利要求13所述的锂二次电池电解液，其特征在于，所述其它添加剂在所述电解液中的质量百分含量为0.1％-20％。
  15. 如权利要求1所述的锂二次电池电解液，其特征在于，所述锂盐包括LiClO 4、LiBF 4、LiPF 6、LiAsF 6、LiPF 2O 2、LiCF 3SO 3、LiTDI、LiB(C 2O 4) 2(LiBOB)、LiBF 2C 2O 4(LiDFOB)、Li[(CF 3SO 2) 2N]、Li[(FSO 2) 2N]和Li[(C mF 2m+1SO 2)(C nF 2n+1SO 2)N]中的一种或多种，其中，m 和n为自然数。
  16. 如权利要求1所述的锂二次电池电解液，其特征在于，所述锂盐在所述电解液中的摩尔浓度为0.01mol/L-2.0mol/L。
  17. 如权利要求1所述的锂二次电池电解液，其特征在于，所述有机溶剂包括碳酸酯类溶剂和/或羧酸酯类溶剂。
  18. 如权利要求17所述的锂二次电池电解液，其特征在于，所述碳酸酯类溶剂为环状碳酸酯和链状碳酸酯组成的混合溶剂。
  19. 如权利要求18所述的锂二次电池电解液，其特征在于，所述环状碳酸酯包括碳酸乙烯酯、碳酸丙烯酯、氟代碳酸乙烯酯、γ-丁内酯、碳酸亚丁酯中的一种或多种；所述链状碳酸酯包括碳酸二甲酯、碳酸甲乙酯、碳酸二乙酯、碳酸二丙酯中的一种或多种。
  20. 如权利要求18所述的锂二次电池电解液，其特征在于，所述环状碳酸酯在所述电解液中的质量百分含量为5％-70％，所述链状碳酸酯在所述电解液中的质量百分含量为5％-70％。
  21. 如权利要求17所述的锂二次电池电解液，其特征在于，所述羧酸酯类溶剂包括乙酸甲酯、乙酸乙酯、乙酸丙酯、乙酸丁酯、丙酸丙酯、丙酸丁酯中的一种或多种；所述羧酸酯类溶剂在所述电解液中的质量百分含量为5％-30％。
  22. 一种锂二次电池电解液的制备方法，其特征在于，包括以下步骤：
    在填充氩气的手套箱中，将充分干燥的锂盐溶解于有机溶剂中，搅拌混合成均匀溶液，然后将给电子基团取代的(五氟)环三磷腈和吸电子基团取代的(五氟)环三磷腈加入到所述均匀溶液中，混合均匀后，得到锂二次电池电解液。
  23. 一种锂二次电池，其特征在于，包括正极、负极、隔膜和电解液，所述电解液采用如权利要求1-21任一项所述的锂二次电池电解液。
PCT/CN2020/076844 2019-05-29 2020-02-26 锂二次电池电解液及其制备方法和锂二次电池 WO2020238302A1 (zh)

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