CN106654370A - Non-aqueous electrolyte and lithium ion battery - Google Patents

Non-aqueous electrolyte and lithium ion battery Download PDF

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CN106654370A
CN106654370A CN201611079073.XA CN201611079073A CN106654370A CN 106654370 A CN106654370 A CN 106654370A CN 201611079073 A CN201611079073 A CN 201611079073A CN 106654370 A CN106654370 A CN 106654370A
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lithium
salt
electrolyte
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unsubstituted
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张昌明
付成华
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Contemporary Amperex Technology Co Ltd
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Contemporary Amperex Technology Co Ltd
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Priority to PCT/CN2017/093197 priority patent/WO2018099092A1/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
    • H01M10/42—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
    • 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

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  • Condensed Matter Physics & Semiconductors (AREA)
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Abstract

The application relates to a non-aqueous electrolyte, which comprises an organic solvent, an electrolyte salt and an additive, wherein the additive contains a barbituric acid compound and an additive lithium salt, and the additive lithium salt is different from the electrolyte salt. According to the application, the performance of the battery can be obviously improved by mixing the barbituric acid compound and the lithium salt as the additive.

Description

Non-aqueous electrolyte and lithium ion battery
Technical Field
The application relates to the technical field of lithium batteries, in particular to a non-aqueous electrolyte and a lithium ion battery.
Background
Lithium ion batteries have the advantages of high specific energy, long cycle life, low self-discharge, and the like, and are widely used in consumer electronics products and energy storage and power batteries. With the wide application of lithium ion batteries, the service environments of the lithium ion batteries tend to be various, and the requirements on the service life and the safety performance of the batteries are higher and higher. For example, the battery has a long service life even under the condition of high-rate rapid charge and discharge, and has no safety risk even when the battery works at high temperature for a long time.
The service life and safety performance of lithium ion batteries are influenced by many factors, and among them, the nonaqueous electrolytic solution is an important component of the lithium ion battery and has a great influence on the lithium ion battery. The nonaqueous electrolyte can improve the dynamic performance of the battery, and reduce the stability of the positive and negative electrode interfaces in the processes of polarization, circulation and high-temperature storage, thereby achieving the purposes of improving the service life and the safety performance.
Disclosure of Invention
An object of the present application is to provide a nonaqueous electrolytic solution.
It is another object of the present application to provide a lithium ion battery.
The specific technical scheme of the application is as follows:
the application relates to a non-aqueous electrolyte, which comprises an organic solvent, an electrolyte salt and an additive, wherein the additive contains a barbituric acid compound and an additive lithium salt, and the additive lithium salt is different from the electrolyte salt.
Preferably, the barbituric acid compound is at least one selected from the group consisting of compounds represented by the formula (I),
wherein,
R11、R12each independently selected from substituted or unsubstituted C1～12Alkyl, substituted or unsubstituted C2～12Alkenyl, substituted or unsubstituted C6～26An aryl group;
R13、R14each independently selected from hydrogen, amino, substituted or unsubstituted C1～12Alkyl, substituted or unsubstituted C2～12Alkenyl, substituted or unsubstituted C6～26Aryl, -NH-R ', wherein R' is substituted or unsubstituted C1～12Alkyl groups of (a);
x is selected from O or S;
the substituents are selected from halogens.
Preferably, R11、R12Each independently selected from substituted or unsubstituted C1～5Alkyl, substituted or unsubstituted phenyl;
R13、R14each independently selected from hydrogen, substituted or unsubstituted C1～5Alkyl, substituted or unsubstituted phenyl, amino.
Preferably, the barbituric acid compound is selected from at least one of the following compounds,
preferably, the barbituric acid compound accounts for 0.01 to 3 percent of the mass of the nonaqueous electrolyte; preferably 0.05% to 2%.
Preferably, the electrolyte salt is lithium hexafluorophosphate.
Preferably, the additive lithium salt is selected from at least one of lithium sulfimide, lithium boron-containing salt and lithium fluorine-containing phosphate; preferably, the lithium sulfonylimide salt is selected from lithium bis (trifluoromethane sulfonylimide) and/or lithium bis (fluorosulfonyl) imide, the boron-containing lithium salt is selected from at least one of lithium bis (oxalato) borate, lithium difluoro (oxalato) borate and lithium tetrafluoroborate, and the fluorine-containing lithium phosphate salt is lithium difluorophosphate.
Preferably, the mass percentage of the electrolyte salt in the non-aqueous electrolyte is 0.5-30%; preferably 10% to 20%.
Preferably, the mass percentage content of the additive lithium salt in the nonaqueous electrolyte is 0.01-5%; preferably 0.1% to 2%.
The application also relates to a lithium ion battery, which comprises a positive plate, a negative plate, an isolating membrane arranged between the positive plate and the negative plate at intervals, and the electrolyte.
The technical scheme provided by the application can achieve the following beneficial effects:
compared with the prior art, the method has the advantages that the barbituric acid compound and the lithium salt additive are jointly used as the additive, so that a stable passivation film is generated on the surface of the battery positive electrode, and inorganic salt substances are mixed on the passivation film. Therefore, the solvent can be isolated, the oxidation of the anode active substance by the electrolyte can be inhibited, the lithium ion migration rate can be enhanced, the polarization is reduced, and the cycle dynamics performance and the cycle hot box performance of the battery are obviously improved.
Detailed Description
In order to make the purpose, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below with reference to the embodiments of the present application, and it should be apparent that the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those skilled in the art without any creative effort based on the technical solutions and the given embodiments provided in the present application belong to the protection scope of the present application.
The application relates to a non-aqueous electrolyte, which comprises an organic solvent, an electrolyte salt and an additive. As an improvement of the non-aqueous electrolyte, the additive contains a barbituric acid compound and an additive lithium salt different from the electrolyte salt.
Research shows that the barbituric acid compound has lower oxidation potential than a solvent, can be oxidized and polymerized on the surface of the positive electrode of a battery cell to form a compact solid electrolyte phase interface film (CEI), effectively reduces the decomposition of the solvent on the positive electrode, and is very beneficial to the performance of the battery; this is because the polymer formed by the barbituric acid compound and lithium is more difficult to dissolve by the solvent on the surface of the positive electrode than the alkyllithium, and the CEI is more stable. Therefore, the side reaction of the anode material and the non-aqueous electrolyte on the surface of the anode can be effectively prevented, the increase of the interface impedance of the anode in the circulating process can be effectively reduced, and the capacity loss caused by the polarization of the anode in the circulating process can be reduced. After the barbituric acid compound is polymerized into a film, the dissolution of Mn and Co elements of a positive electrode material can be prevented, and the expansion of the battery caused by the oxidation gas generation of the nonaqueous electrolyte can be inhibited.
In the lithium ion battery, the electrolyte salt compound has good thermal stability, high conductivity and low viscosity in the electrolyte, and can reduce concentration polarization of the electrolyte and improve the dynamic performance. Certain electrolyte salts, such as the additive lithium salt in the application, are easy to react at a high potential to generate inorganic salt substances such as borate, phosphate or nitrogen fluoride, and the like, and are beneficial to the transmission of lithium ions. Therefore, when the barbituric acid compound is combined with the lithium salt additive, a stable passive film is formed on the positive electrode of the battery, and inorganic salt substances are also included in the passive film. The lithium ion battery can isolate a solvent, prevent the anode from being oxidized by electrolyte, enhance the migration rate of lithium ions and reduce polarization, thereby obviously improving the cycle performance and the rate performance of the battery and the performance of a hot box after the cycle.
As an improvement of the non-aqueous electrolyte, the barbituric acid compound is at least one compound selected from compounds represented by a structural formula (1),
wherein,
R11、R12each independently selected from substituted or unsubstituted C1～12Alkyl, substituted or unsubstituted C2～12Alkenyl, substituted or unsubstituted C6～26An aryl group;
R13、R14each independently selected from hydrogen, amino, substituted or unsubstituted C1～12Alkyl, substituted or unsubstituted C2～12Alkenyl, substituted or unsubstituted C6～26Aryl, -NH-R ', wherein R' is substituted or unsubstituted C1～12Alkyl groups of (a);
x is selected from O or S;
the substituents are selected from halogens, such as F, Cl.
As an improvement of the present application,
R11、R12each independently selected from substituted or unsubstituted C1～6Alkyl, substituted or unsubstituted C2～6Alkenyl, substituted or unsubstituted phenyl;
R13、R14each independently selected from hydrogen, substituted or unsubstituted C1～6Alkyl, substituted or unsubstituted C2～6Alkenyl group of (A), substituted or unsubstituted phenyl group, substituted or unsubstituted C1～6Aminoalkyl, amino, or C1～6An alkyl-substituted imino group.
As an improvement of the present application,
R11、R12each independently selected from substituted or unsubstituted C1～5Alkyl, substituted or unsubstituted phenyl;
R13、R14each independently selected from hydrogen, substituted or unsubstituted C1～5Alkyl, substituted or unsubstituted phenyl, amino.
In the above formula I, the substituents have the meanings as described below.
The alkyl group has 1 to 12 carbon atoms, the alkyl group can be a chain alkyl group or a cycloalkyl group, hydrogen on the ring of the cycloalkyl group can be replaced by the alkyl group, the number of the carbon atoms in the alkyl group has a preferable lower limit of 2, 3, 4, 5 and a preferable upper limit of 3, 4, 5, 6, 8, 10, 12. Preferably, an alkyl group having 1 to 10 carbon atoms is selected, more preferably, a chain alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 8 carbon atoms is selected, and still more preferably, a chain alkyl group having 1 to 5 carbon atoms is selected. Examples of alkyl groups include: methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, neopentyl, cyclopentyl, cyclohexyl.
The alkenyl group having 2 to 12 carbon atoms may be a cyclic alkenyl group or a chain alkenyl group. In addition, the number of double bonds in the alkenyl group is preferably 1. The number of carbon atoms in the alkenyl group preferably has a lower limit of 2, 3, 4 and a preferred upper limit of 3, 4, 5, 6, 8, 10, 12. Preferably, the alkenyl group having 2 to 10 carbon atoms is selected, more preferably, the alkenyl group having 2 to 6 carbon atoms is selected, and still more preferably, the alkenyl group having 2 to 5 carbon atoms is selected. Examples of alkenyl groups include: vinyl, allyl, isopropenyl, pentenyl, cyclohexenyl, cycloheptenyl, cyclooctenyl.
Aryl with 6-26 carbon atoms, such as phenyl, phenylalkyl, aryl with at least one phenyl group, such as biphenyl, condensed ring aromatic hydrocarbon group, such as naphthalene, anthracene, phenanthrene, biphenyl and condensed ring aromatic hydrocarbon group can be substituted by alkyl or alkenyl. Preferably, the aryl group having 6 to 16 carbon atoms is selected, more preferably, the aryl group having 6 to 14 carbon atoms is selected, and still more preferably, the aryl group having 6 to 9 carbon atoms is selected. Specific examples of aryl groups include: phenyl, benzyl, biphenyl, p-tolyl, o-tolyl, m-tolyl.
When the alkyl group with 1 to 12 carbon atoms, the alkenyl group with 2 to 12 carbon atoms and the aryl group with 6 to 26 carbon atoms are substituted by halogen atoms, a halogenated alkyl group with 1 to 12 carbon atoms, a halogenated alkenyl group with 2 to 12 carbon atoms and a halogenated aryl group with 6 to 26 carbon atoms are correspondingly formed in sequence, wherein the halogen atoms are F, Cl and Br, and F, Cl is preferred. In the halogenated group formed, the halogen atoms substitute part or all of the hydrogen atoms, and the number of the halogen atoms may be 1,2, 3 or 4.
Preferably, a halogenated alkyl group having 1 to 10 carbon atoms, a halogenated alkenyl group having 2 to 10 carbon atoms, and a halogenated aryl group having 6 to 16 carbon atoms are selected, more preferably, a halogenated chain alkyl group having 1 to 6 carbon atoms, a halogenated cycloalkyl group having 3 to 8 carbon atoms, a halogenated alkenyl group having 2 to 6 carbon atoms, and a halogenated aryl group having 6 to 14 carbon atoms are selected, and even more preferably, 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 a halogenated aryl group having 6 to 10 carbon atoms are selected.
Examples of the halogenated group include: trifluoromethyl (-CF)3) 2-fluoroethyl, 3-fluoro-n-propyl, 2-fluoroisopropyl, 4-fluoro-n-butyl, 3-fluoro-sec-butyl, 5-fluoro-n-pentyl, 4-fluoro-isopentyl, 1-fluorovinyl, 3-fluoroallyl, 6-fluoro-4-hexenyl, o-fluorophenyl, p-fluorophenyl, m-fluorophenyl, 4-fluoromethylphenyl, 2, 6-difluoromethylphenyl, 2-fluoro-1-naphthyl, fluoromethoxy, 1-fluoroethoxy, 2-fluoro-n-propoxy, 1-fluoro-isopropoxy, 3-fluoro-n-butoxy, 4-fluoro-n-pentyloxy, 2-difluoromethylpropoxy, 5-fluoro-n-hexyloxy, 1, 2-trifluoromethylpropoxy, 2-fluoro-n-hexyloxy, 6-fluoro-n-heptyloxy, 7-fluoro-n-octyloxy, 3-fluoro-cyclopentyloxy, 4-fluoro-2-methylcyclopentoxy, 3-fluoro-cyclohexyloxy, 3-fluorocycloheptyloxy, 4-fluoro-2-methylcycloheptyloxy, 3-fluorocyclooctyloxy. In the specific examples above, F may be substituted with Cl and/or Br.
The barbituric acid compound is selected from at least one of the following compounds:
as an improvement of the non-aqueous electrolyte of the present application, the barbituric acid compound of the present application is further selected from at least one of the following compounds, but is not limited thereto:
as an improvement of the non-aqueous electrolyte, the barbituric acid compound accounts for 0.01-3% of the non-aqueous electrolyte by mass. When 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, and thus side reactions caused by electron transfer between the nonaqueous electrolytic solution and the electrode cannot be effectively prevented; when the content of the barbituric acid compound is more than 3%, a thicker CEI film is formed on the surface of the positive electrode, so that the migration resistance of lithium ions is increased, and the stability of the positive electrode interface of the battery in the circulating process is not facilitated.
More preferably, the upper limit of the mass percentage content range of the barbituric acid compound in the nonaqueous electrolytic solution is selected from 3%, 2.8%, 2.5%, 2.0%, 1.5%, 1.0%, and the lower limit thereof is selected from 0.01%, 0.03%, 0.05%, 0.1%, 0.3%, 0.5%, and 0.6%. More preferably, the barbituric acid compound is contained in the non-aqueous electrolyte in an amount of 0.05% to 2%.
Due to the fact that lithium hexafluorophosphate (LiPF) is compared with other lithium additives6) Is the lithium salt most used by the commercial lithium battery at present. The lithium ion battery has wider electrochemical window, strong electrochemical stability, no corrosion to aluminum current collector, mature synthetic route and better comprehensive performance than other lithium salts, thereby being used as the batteryAn electrolyte salt in a nonaqueous electrolyte is claimed. However, since the decomposition temperature of lithium hexafluorophosphate is 80 ℃, thermal stability is poor and it can be decomposed even in a high purity state. The decomposition products are lithium fluoride (LiF) and phosphorus Pentafluoride (PF)5) Gaseous PF5Has stronger Lewis acidity, and can react with lone electron pair of oxygen atoms in solvent molecules to cause the solvent to generate decomposition reaction. Compared with lithium hexafluorophosphate, other lithium salts have better thermal stability and film forming property, so the lithium hexafluorophosphate lithium salt additive is further used in the additive to make up the defect that the lithium hexafluorophosphate is easy to decompose at 80-90 ℃.
As an improvement of the non-aqueous electrolyte, the additive lithium salt is selected from at least one of lithium sulfimide, lithium boron-containing salt and lithium fluorine-containing phosphate; lithium bistrifluoromethanesulfonylimide LiN (CF) is more preferable3SO2)2(abbreviated as LiTFSI), lithium bis (fluorosulfonyl) imide Li (N (SO)2F)2) (abbreviated as LiFSI) and lithium LiB (C) bis (oxalato-borate2O4)2(abbreviated as LiBOB), lithium difluorooxalate borate LiBF2(C2O4) (abbreviated as LiDFOB), lithium difluorophosphate (LiPO)2F2) Lithium tetrafluoroborate (LiBF)4) At least one of (1).
As an improvement of the non-aqueous electrolyte, the mass percentage of the electrolyte salt in the non-aqueous electrolyte is 0.5-30%. Generally, the conductivity of the electrolyte is proportional to the electrolyte salt concentration and inversely proportional to the viscosity of the solvent. Specifically, the concentration of the electrolyte salt is increased, and the electrolyzed free ions are also increased, so that the conductivity is increased; but at the same time the viscosity of the electrolyte and the degree of ionic association also increase with increasing electrolyte salt concentration, which in turn reduces conductivity.
More preferably, the upper limit of the mass percentage content range of the electrolyte salt in the nonaqueous electrolytic solution is selected from 5%, 10%, 15%, 20%, 25%, and 30%, and the lower limit is selected from 0.5%, 1%, 2%, 3%, 5%, and 10%. More preferably, the percentage content of the electrolyte salt in the nonaqueous electrolyte solution is 10% to 20%. For a common electrolyte system, the 15% mass percentage content has the advantages of higher conductivity and relatively lower cost.
As an improvement of the non-aqueous electrolyte, the additive lithium salt accounts for 0.01-5% of the non-aqueous electrolyte by mass. The content of the additive lithium salt in the non-aqueous electrolyte is too small, and the additive lithium salt is combined with a barbituric acid compound, so that the effect of generating a stable passivation film is not obvious; when the content of the additive lithium salt is too large, a large amount of lithium ions in the electrolyte leads to increase in the viscosity of the electrolyte and the internal resistance of the battery, which is not favorable for improvement of electrochemical properties.
More preferably, the upper limit of the mass percentage content range of the additive lithium salt in the nonaqueous electrolytic solution is selected from 1%, 2%, 3%, 4%, and 5%, and the lower limit thereof is selected from 0.01%, 0.1%, 0.5%, 0.3%, 0.5%, and 1%. Still more preferably, the percentage content of the additive lithium salt in the nonaqueous electrolytic solution is 0.1% to 2%, and still more preferably 1% to 2%.
As an improvement of the non-aqueous electrolyte solution of the present application, the organic solvent of the present application is at least one selected from the group consisting of Ethylene Carbonate (EC), Propylene Carbonate (PC), butylene carbonate, fluoroethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, diethyl carbonate (DEC), dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1, 4-butyrolactone, methyl propionate, methyl butyrate, propyl propionate, ethyl acetate, ethyl propionate, and ethyl butyrate.
The application also relates to a lithium ion battery, which comprises a positive plate, a negative plate, an isolating membrane arranged between the positive plate and the negative plate at intervals, and electrolyte; the electrolyte is the nonaqueous electrolyte solution described in any one of the preceding paragraphs.
The application also provides a lithium ion battery, which comprises a positive plate, a negative plate, an isolating membrane arranged between the positive plate and the negative plate at intervals, electrolyte and packaging foils; the positive plate comprises a positive current collector and a positive diaphragm coated on the positive current collector, and the negative plate comprises a negative current collector and a negative diaphragm coated on the negative current collector; the electrolyte is the nonaqueous electrolyte solution described in any one of the preceding paragraphs.
As an improvement of the lithium ion battery, the positive electrode diaphragm comprises a positive electrode active material, a binder and a conductive agent.
As an improvement of the lithium ion battery of the present application, the positive electrode active material of the present application is optionally selected from lithium cobaltate LiCoO2At least one of lithium nickel manganese cobalt ternary material, lithium iron (lithium) phosphate and lithium manganate.
As an improvement of the lithium ion battery, the positive active material is a mixture of lithium cobaltate and a lithium nickel manganese cobalt ternary material.
As an improvement of the lithium ion battery, the negative electrode diaphragm comprises a negative electrode active material, a binder and a conductive agent.
As an improvement of the lithium ion battery, the negative active material is graphite and/or silicon.
The technical solution of the present application is exemplarily described below by specific embodiments:
preparing an electrolyte: at water content<In a 10ppm argon atmosphere glove box, Ethylene Carbonate (EC), diethyl carbonate (DEC), Propylene Carbonate (PC) and ethyl propionate are uniformly mixed according to a mass ratio of 20:30:20:30 to obtain a non-aqueous solvent, and then a fully dried electrolyte salt LiPF is added6Dissolving in the non-aqueous solvent to obtain basic electrolyte.
As shown in table 1, a barbituric acid compound and an additive lithium salt were added to the base electrolyte as additives.
Examples of barbituric acid compounds are: 1, 3-dimethyl barbituric acid (B1, shown as formula I-1), 1, 3-dibutyl barbituric acid (B2, shown as formula I-2), 1, 3-diphenyl barbituric acid (B3, shown as formula I-3), 1, 3-dimethyl-2-thiobarbituric acid (B4, shown as formula I-4), and 5-amino-2-thiobarbituric acid (B5, shown as formula I-5).
Examples of lithium salts as additives are: LiBF4、LiFSI、LiTFSI、LiBOB、LiDFOB、LiPO2F2。
Preparing a lithium ion battery:
1) preparing a positive plate: mixing positive electrode active material lithium cobaltate (molecular formula is LiCoO)2) Fully stirring and mixing acetylene black serving as a conductive agent and polyvinylidene fluoride (PVDF) serving as a binder in a proper amount of N-methylpyrrolidone (NMP) solvent according to a weight ratio of 96:2:2 to form uniform positive electrode slurry; and coating the slurry on an Al foil of a positive current collector, drying and cold pressing to obtain the positive plate.
2) Preparing a negative plate: fully stirring and mixing a negative electrode active material graphite, a conductive agent acetylene black, a binder Styrene Butadiene Rubber (SBR), and a thickener sodium carboxymethyl cellulose (CMC) in a proper amount of deionized water solvent according to a weight ratio of 95:2:2:1 to form uniform negative electrode slurry; and coating the slurry on a Cu foil of a negative current collector, drying and cold pressing to obtain the negative plate.
3) And (3) isolation film: a PE porous polymer film is used as a separation film.
4) Preparing a lithium ion battery: stacking the positive plate, the isolating film and the negative plate in sequence to enable the isolating film to be positioned between the positive plate and the negative plate to play an isolating role, and then winding to obtain a bare cell; and placing the bare cell in an outer packaging foil, injecting the prepared electrolyte into the dried battery, and performing vacuum packaging, standing, formation, shaping and other processes to complete the preparation of the lithium ion battery.
Preparing the electrolyte and the lithium ion battery of the examples 1 to 20 and the comparative examples 1 to 6 according to the preparation method; the additives in the electrolyte and the respective amounts added are shown in table 1.
TABLE 1 electrolytes, electrolyte additives and addition amounts of examples 1 to 20 and comparative examples 1 to 6
The lithium ion batteries prepared in the comparative examples and comparative examples of the present application were tested for performance by the following experiments.
Test one, charge rate test
The lithium ion batteries obtained by the preparation were subjected to the following tests, respectively:
the lithium ion battery was charged to 4.4V at 25 ℃ at different rates of 0.5C, 1C, 2C, 3C, and 5C, and the charge capacity was recorded, and the charge capacity at different rates was calculated based on the 0.5C capacity (100%). The selected electrolytes for each lithium ion cell and the associated test data obtained are shown in table 2.
TABLE 2 test results of the charging rate of lithium ion batteries of examples 1 to 20 and comparative examples 1 to 6
As can be seen from table 1 and table 2, compared to comparative example 6, when 1% barbituric acid compound is added alone to the electrolyte of comparative example 1, the charge rate of the lithium ion battery is significantly improved. In examples 1 to 11, barbituric acid compound was added to the electrolyte in an amount of 1% by mass together with the mass fractionThe charging capacity of the battery is remarkably improved when the additive lithium salt accounts for 1 percent. In particular example 10, LiPO2F2The impedance is lower after the reaction of the positive electrode and the negative electrode, so the charging speed is high and the charging multiplying power is high. However, when the content of the barbituric acid compound in the electrolyte exceeds 3%, the charge capacity of the battery is not improved but not improved, or even deteriorated, because the film thickness is formed and the viscosity of the electrolyte is high when the amount of the barbituric acid compound is too large, and lithium ion conduction becomes difficult, particularly in comparative example 2 in which 4% barbituric acid compound is added to the electrolyte, the charge capacity of the battery is much lower than that of other groups. Also, as in examples 16 and 17, when the content of the additive lithium salt in the electrolyte is too small or too large, the battery performance starts to decrease. When a combination of two additive lithium salts is used in the electrolyte, the charge capacity at a large rate is improved, but the effect is not significant, as in examples 12-15. An increase in the content of the electrolyte salt is also not advantageous for improvement of the charge capacity as in examples 19 and 20 because the conductivity decreases as the viscosity of the electrolyte increases and the degree of ionic association increases.
Test two, cycle test
The lithium ion batteries obtained by the preparation were subjected to the following tests, respectively:
charging the lithium ion battery to 4.4V at a constant current of 1C at 45 ℃, then charging at a constant voltage until the current is 0.05C, then discharging at a constant current of 1C to 3.0V, and then performing cyclic charging/discharging for multiple times according to the conditions for the first cycle, thereby respectively calculating the capacity retention rate of the lithium ion battery after 50 cycles, 100 cycles, 200 cycles, 300 cycles and 500 cycles. Each group had 5 cells, wherein the capacity retention after cycling was calculated as follows. The electrolytes selected for use in each lithium ion cell and the associated test data obtained are shown in table 3.
The capacity retention after cycling (discharge capacity corresponding to cycling/discharge capacity of the first cycle) × 100%, and the results of the cycling test are shown in table 3.
TABLE 3 Capacity Retention ratio after cycling of lithium ion batteries of examples 1-20 and comparative examples 1-6
It can be seen from table 1 and table 3 that, compared with comparative example 1, when 1% of additive lithium salt is added to the electrolyte of examples 1 to 11, the cycle performance of the lithium ion battery is significantly improved. However, when the content of the additive lithium salt in the electrolyte is less than 0.01% and more than 5%, the cycle performance of the battery is less improved. When the content of the additive lithium salt in the electrolyte exceeds 10%, the cycle performance of the battery is not, but not improved, and even deteriorated, as in comparative example 4, the cycle retention of the battery is lower than that of other groups. When two additive lithium salts were used in the electrolyte additive, the cycle performance was hardly changed as in examples 12 to 15. Since the lithium hexafluorophosphate alone is used in the electrolyte solution to satisfy the charge transfer requirement inside the battery, in examples 1 to 18, when the amount of the electrolyte salt is controlled in the range of 10% to 20%, the cycle performance of the battery is mainly affected by the additive. However, when the amount of the electrolyte salt is more than 20%, the content of the organic solvent in the electrolyte is reduced, resulting in degradation of the cycle performance of the battery.
Hot box test after test three, cycle
The battery after 500 cycles of 25 ℃ is charged to 4.4V at a constant current of 0.5C and charged at a constant voltage of 4.4V to a current of 0.025C at 25 ℃ to be in a full charge state of 4.4V, then the battery is placed in a high-temperature furnace at 150 ℃ for 1 hour, and the voltage change of the battery in the high-temperature furnace and the surface temperature of a battery core are tested, and the state of the battery after the test is observed. The results of the hot box test after cycling are shown in table 4.
Table 4 examples 1-20 and comparative examples 1-6 lithium batteries were tested in a hot box after cycling at 25c
After result
It can be seen from table 1 and table 4 that when the barbituric acid compound is used as an electrolyte additive and is used in combination with an additive lithium salt additive, the hot box performance of the battery after cycling can be significantly improved. When the content of the barbituric acid compound is higher than 3% or the content of the additive lithium salt is higher than 10%, the heat box test of the battery after the cycle is ignited, and the reason for the ignition can be considered to be that the film impedance of the battery is increased during the cycle due to the excessive barbituric acid compound or additive lithium salt, so that metal lithium is separated out during the cycle of the battery, the thermal stability of the negative electrode of the battery is deteriorated, and the heat box performance of the battery after the cycle is deteriorated. An increase in the content of the electrolyte salt also leads to a decrease in the performance of the heat box.
Although the present application has been described with reference to preferred embodiments, it is not intended to limit the scope of the claims, and many possible variations and modifications may be made by one skilled in the art without departing from the spirit of the application.

Claims (10)

1. A non-aqueous electrolyte comprises an organic solvent, an electrolyte salt and an additive, and is characterized in that the additive contains a barbituric acid compound and an additive lithium salt, and the additive lithium salt is different from the electrolyte salt.
2. The nonaqueous electrolytic solution of claim 1, wherein the barbituric acid compound is at least one compound selected from the group consisting of compounds represented by the formula (I),
wherein,
R11、R12each independently selected from substituted or unsubstituted C1～12Alkyl, substituted or unsubstituted C2～12Alkenyl, substituted or unsubstituted C6～26An aryl group;
R13、R14each independently selected from hydrogen, amino, substituted or unsubstituted C1～12Alkyl, substituted or unsubstituted C2～12Alkenyl, substituted or unsubstituted C6～26Aryl, -NH-R ', wherein R' is substituted or unsubstituted C1～12Alkyl groups of (a);
x is selected from O or S;
the substituents are selected from halogens.
3. The nonaqueous electrolytic solution of claim 2, wherein,
R11、R12each independently selected from substituted or unsubstituted C1～5Alkyl, substituted or unsubstituted phenyl;
R13、R14each independently selected from hydrogen, substituted or unsubstituted C1～5Alkyl, substituted or unsubstituted phenyl, amino.
4. The nonaqueous electrolytic solution of claim 3, wherein the barbituric acid compound is at least one selected from the group consisting of,
5. the nonaqueous electrolytic solution of claim 1, wherein the barbituric acid compound is contained in the nonaqueous electrolytic solution in an amount of 0.01 to 3% by mass; preferably 0.05% to 2%.
6. The nonaqueous electrolytic solution of claim 1, wherein the electrolyte salt is lithium hexafluorophosphate.
7. The nonaqueous electrolytic solution of claim 1, wherein the additive lithium salt is at least one selected from a lithium sulfonimide salt, a lithium boron-containing salt, and a lithium fluorophosphate salt; preferably, the lithium sulfonylimide salt is selected from lithium bis (trifluoromethane sulfonylimide) and/or lithium bis (fluorosulfonyl) imide, the boron-containing lithium salt is selected from at least one of lithium bis (oxalato) borate, lithium difluoro (oxalato) borate and lithium tetrafluoroborate, and the fluorine-containing lithium phosphate salt is lithium difluorophosphate.
8. The nonaqueous electrolytic solution of claim 1, wherein the electrolyte salt is contained in the nonaqueous electrolytic solution in an amount of 0.5 to 30% by mass; preferably 10% to 20%.
9. The nonaqueous electrolyte solution of claim 1, wherein the additive lithium salt is present in the nonaqueous electrolyte solution in an amount of 0.01 to 5% by mass; preferably 0.1% to 2%.
10. A lithium ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator provided between the positive electrode sheet and the negative electrode sheet at an interval, and an electrolyte, wherein the electrolyte is the nonaqueous electrolyte according to any one of claims 1 to 9.
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