WO2018024095A1 - 锂离子电池添加剂，含有该添加剂的电池及制备方法 - Google Patents

锂离子电池添加剂，含有该添加剂的电池及制备方法 Download PDF

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WO2018024095A1
WO2018024095A1 PCT/CN2017/093169 CN2017093169W WO2018024095A1 WO 2018024095 A1 WO2018024095 A1 WO 2018024095A1 CN 2017093169 W CN2017093169 W CN 2017093169W WO 2018024095 A1 WO2018024095 A1 WO 2018024095A1
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ion battery
lithium ion
additive
lithium
solution
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French (fr)
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王珂
史松君
谢岚
王耀辉
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Contemporary Amperex Technology Co Ltd
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Contemporary Amperex Technology Co Ltd
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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
    • 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
    • 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 lithium ion batteries, and in particular to a lithium ion battery additive, a battery containing the additive, and a preparation method.
  • Lithium-ion batteries are widely used in portable 3C electronic devices such as mobile phones and notebook computers because of their high volumetric specific energy, weight-to-weight ratio, and good environmental friendliness. With the demand for electronic products tending to be smaller, lighter, and thinner in recent years, in pursuit of lower prices, the pursuit of higher energy density has become a powerful driving force for improving electronic products. In addition, in recent years, countries have increased their investment in high-power lithium-ion batteries, such as the development of power tools, electric bicycles and automobiles. If the development of this field is successful, it can alleviate the increasingly tense oil resources, so it has a high international economic strategic significance.
  • Electrolyte is an important part of lithium-ion battery, and its composition directly affects the cycle capacity and life of the battery.
  • the composition of the electrolyte (involving the choice and amount of salt, solvent and additives) can effectively play and improve the electrochemical performance of the positive and negative materials of lithium ion batteries, such as cycle life, capacity retention, high temperature storage, safety performance, rate discharge Characteristics, platform time of discharge, and capacity of positive and negative electrodes.
  • some components (solvents or additives) in the electrolyte are reductively decomposed and the product is deposited on the surface of the anode material graphite to form a solid electrolyte interface film (SEI), or occurs.
  • SEI solid electrolyte interface film
  • the oxidative decomposition and product deposition on the surface of the positive electrode material form a positive electrode interface protective film.
  • a good and dense interface protective film can alleviate the decomposition of the electrolyte, thereby reducing the irreversible capacity of the battery and improving its cycle performance.
  • Optimization of electrolyte composition, selection of suitable solvents, lithium salts and additives is an effective way to improve the interface film.
  • the primary object of the present application is to propose a lithium ion battery additive.
  • a second object of the present application is to propose a lithium ion battery containing the additive.
  • a third object of the present application is to propose a method of producing the lithium ion battery.
  • the present application relates to a lithium ion battery additive selected from at least one of the compounds of formula I:
  • the additive is polyvinylpyrrolidone having the formula as shown in Formula II:
  • the polyvinylpyrrolidone has a relative molecular mass of from 10,000 to 360,000 g/mol.
  • the present application also relates to a lithium ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, the electrolyte containing a lithium salt, an organic solvent, and an additive described herein.
  • the additive and the lithium salt are separately dissolved in an organic solvent and sequentially injected into the lithium ion battery.
  • the organic solvent is selected from the group consisting of ethylene carbonate, propylene carbonate, ⁇ -butyrolactone, sulfolane, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, At least one of ethyl propyl carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and propyl propionate.
  • the organic solvent further contains at least one of a carboxylic acid ester, a sulfone, a sulfite, a ketone, an amine, a nitrile, an ether, and a furan.
  • the carboxylic acid ester is selected from methyl butyrate and methyl acrylate;
  • the sulfone is selected from the group consisting of sulfolane and dimethyl sulfoxide; and the sulfite is selected from the group consisting of dimethyl sulfite and diethyl sulfite;
  • the ketone is selected from N-methylpyrrolidone;
  • the amine is selected from the group consisting of N-methylformamide, N-methylacetamide, N,N-dimethylformamide;
  • the nitrile is selected from the group consisting of acetonitrile, propionitrile, and propylene.
  • the ether is selected from the group consisting of diethyl ether and methyl sulfide; and the furan is selected from the group consisting of tetrahydrofuran.
  • the lithium salt is selected from the group consisting of LiPF 6 , LiBF 4 , LiBOB, LiDFOB, LiAsF 6 , LiClO 4 , LiFAP, LiCF 3 SO 3 , Li(FSO 2 ) 2 N, Li(CF 3 SO 2 ) 2 N, At least one of Li(C 2 F 5 SO 2 ) 2 N is more preferably at least one selected from the group consisting of LiPF 6 , LiBF 4 , and Li(FSO 2 ) 2 N.
  • the application also relates to a method of preparing the lithium ion battery, comprising adding the additive in the following manner:
  • Step 1 the additive described in the application is dissolved in the first organic solvent to obtain a solution A, the lithium salt is dissolved in the second organic solvent to obtain a solution B;
  • Step two injecting solution A into a lithium ion battery
  • Step 3 Inject solution B into the lithium ion battery.
  • the lithium ion battery is allowed to stand for 6 to 24 hours, and then the third step is performed. More preferably, after the end of the second step, the lithium ion battery is allowed to stand at normal temperature for 6 to 24 hours, then allowed to stand at 50 to 70 ° C for 6 to 24 hours, and then the third step is performed.
  • the first organic solvent and the second organic solvent are the same or different, preferably the same.
  • the content of the additive is 0.1% to 5% of the total mass of the solution A, and the rest is The first organic solvent.
  • the concentration of the lithium salt in solution B is from 1.5 M to 3 M.
  • the mass ratio of the solution A to the solution B is from 0.5 to 2:1, more preferably from 1:1.
  • the first organic solvent and solution B in the solution A constitute an electrolyte of a lithium ion battery.
  • the electrolytic solution contains a lithium salt, a chain carbonate, and a cyclic carbonate.
  • the content of the cyclic carbonate is 10% to 40% of the total mass of the electrolyte
  • the content of the chain carbonate is 40% to 70% of the total mass of the electrolyte
  • the lithium salt is in the electrolyte
  • concentration in the range is 0.3M to 1.8M.
  • the present application provides a lithium ion battery additive, which is a polyvinylpyrrolidone compound, which is added to an electrolyte to effectively wet the electrode material and enhance the reversible capacity of the battery.
  • a lithium ion battery additive which is a polyvinylpyrrolidone compound, which is added to an electrolyte to effectively wet the electrode material and enhance the reversible capacity of the battery.
  • the nitrogen element contained in the polyvinylpyrrolidone compound can effectively capture the transition metal ion eluted from the positive electrode and the acid generated by the decomposition of the electrolyte to prevent it from damaging the SEI.
  • the electrode sheet and the separator are infiltrated by the solution A containing the polyvinylpyrrolidone compound, and then the solution B is added, and the polyvinylpyrrolidone compound is precipitated into a film under the action of the lithium salt. It is coated on the surface of the electrode sheet and the separator to provide a skeleton for the solid electrolyte membrane (SEI).
  • SEI solid electrolyte membrane
  • the present application relates to a lithium ion battery additive which is a polyvinylpyrrolidone compound selected from at least one of the compounds of formula I:
  • R 1 , R 2 and R 3 are each independently selected from the group consisting of hydrogen and C 1 -C 8 alkyl.
  • R 1 , R 2 and R 3 are the same substituents.
  • the alkyl group may be a chain alkyl group or a cycloalkyl group, and a hydrogen group on the ring of the cycloalkyl group may be substituted with an alkyl group.
  • the preferred lower limit of the number of carbon atoms is 1, 2, 3, 4, and the preferred upper limit is 3, 4, 5, 6, 8, 10, 12.
  • an alkyl group having 1 to 8 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 3 carbon atoms is selected.
  • alkyl group examples include methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, isopentyl, and new.
  • aryl group having 6 to 26 carbon atoms it is preferred to select an aryl group having 6 to 16 carbon atoms, more preferably an aryl group having 6 to 14 carbon atoms, and still more preferably, carbon 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.
  • An aryl group having 5 to 22 carbon atoms which may be selected from the group consisting of furyl, thienyl, pyrrolyl, thiazolyl, imidazolyl, pyridyl, pyrazinyl, pyrimidinyl, pyridazinyl, fluorenyl and quinolinyl. Orolinic group and the like.
  • the additive is polyvinylpyrrolidone, and the structural formula is as shown in formula II:
  • the relative molecular mass of polyvinylpyrrolidone is 10,000 to 360,000 g/mol.
  • the additive of the present application may also be selected from at least one of the following compounds:
  • the present application also relates to a lithium ion battery comprising a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, the electrolyte containing a lithium salt, an organic solvent, and an additive described herein.
  • the positive electrode sheet includes a positive electrode current collector and a positive electrode active material coated on the positive electrode current collector;
  • the negative electrode sheet includes a negative electrode current collector and a negative electrode active material coated on the negative electrode current collector;
  • the separator is located adjacent to the positive and negative electrodes Between the pieces.
  • the upper limit cutoff voltage of the lithium ion battery of the present application is 3.5V to 4.4V.
  • the negative active material is selected from one or more of natural graphite, artificial graphite, soft carbon, hard carbon, lithium titanate, and silicon.
  • the lithium salt is selected from lithium hexafluorophosphate LiPF 6 , lithium tetrafluoroborate LiBF 4 , lithium bis(oxalate) borate LiB(C 2 O 4 ) 2 (abbreviated as LiBOB), lithium difluorooxalate borate LiBF 2 (C 2 O 4 ) (abbreviated as LiDFOB), lithium hexafluoroarsenate (LiAsF 6 ), lithium perchlorate (LiClO 4 ), lithium tris(perfluoroethyl) lithium trifluorophosphate, trifluoromethylsulfonate Lithium acid LiCF 3 SO 3 , bis(trifluoromethylsulfonate)methyllithium Li(FSO 2 ) 2 N, bis(trifluoromethanesulfonic acid) lithium imide LiN(CF 3 SO 2 ) 2 , two ( Perfluoroethylsulf
  • the additive and the lithium salt are respectively dissolved in an organic solvent and sequentially injected into the lithium ion battery.
  • the application also relates to a method of preparing the lithium ion battery, comprising adding the additive in the following manner:
  • Step 1 the additive described in the application is dissolved in the first organic solvent to obtain a solution A, the lithium salt is dissolved in the second organic solvent to obtain a solution B;
  • Step two injecting solution A into a lithium ion battery
  • Step 3 Inject solution B into the lithium ion battery.
  • the present application has found that directly adding a polyvinylpyrrolidone compound to an organic solvent containing a lithium salt leads to precipitation of a polyvinylpyrrolidone compound, so that it is necessary to complete the infiltration of the electrode sheet and the separator after the solution A is completed.
  • Solution B containing lithium salt Under the action of lithium salt, polyvinylpyrrolidone compound precipitates into a film and coats the surface of the electrode sheet and the separator to provide a skeleton for the solid electrolyte membrane (SEI).
  • SEI solid electrolyte membrane
  • the nitrogen element contained in the polyvinylpyrrolidone compound can effectively capture the transition metal ion eluted from the positive electrode and the acid generated by the decomposition of the electrolyte, preventing it from damaging the SEI and prolonging the cycle life of the battery.
  • the lithium ion battery is allowed to stand for 6 to 24 hours, and then the third step is performed to further precipitate the polyvinylpyrrolidone compound.
  • the lithium ion battery is first allowed to stand at room temperature for 6 to 24 hours, so that the electrolyte can fully wet the electrode material (mainly physical infiltration), and then allowed to stand at 50 to 70 ° C for 6 to 24 hours, which can accelerate The interaction of the additive with the electrode material (mainly by chemical action) facilitates the formation of a uniformly stable film on the surface of the electrode after the addition of solution B in step 3.
  • the first organic solvent and the second organic solvent are the same or different, preferably the same.
  • the first organic solvent and the second one have The solvent of the machine contains a cyclic carbonate and a chain carbonate.
  • the cyclic carbonate is preferably at least one selected from the group consisting of ethylene carbonate (EC) and propylene carbonate (PC);
  • the chain carbonate is preferably selected from the group consisting of dimethyl carbonate, diethyl carbonate (DEC), and dipropylene carbonate.
  • EMC ethyl methyl carbonate
  • methylpropyl carbonate methylpropyl carbonate
  • ethyl propyl carbonate ethyl propyl carbonate.
  • the first organic solvent and/or the second organic solvent further contains at least one of a carboxylate, a sulfone, a sulfite, a ketone, an amine, a nitrile, an ether, and a furan.
  • the carboxylic acid ester is selected from methyl butyrate and methyl acrylate
  • the sulfone is selected from the group consisting of sulfolane and dimethyl sulfoxide
  • the sulfite is selected from the group consisting of dimethyl sulfite and diethyl sulfite
  • the ketone is selected from the group consisting of N-A.
  • a pyrrolidone the amine is selected from the group consisting of N-methylformamide, N-methylacetamide, N,N-dimethylformamide; the nitrile is selected from the group consisting of acetonitrile, propionitrile, and acrylonitrile; and the ether is selected from the group consisting of diethyl ether and methyl sulfide; The furan is selected from the group consisting of tetrahydrofuran.
  • the additive is added in an amount of 0.1% to 5% of the total mass of the solution A, and the balance is the first organic solvent.
  • the research has found that when the content is more than 5%, the proportion of the polyvinylpyrrolidone compound in the organic solvent is too large, resulting in the viscosity of the electrolyte system becoming large, and the interface film formed on the surface of the positive and negative electrodes is too thick, which affects Cycle performance of lithium-ion batteries.
  • the storage performance is further improved because the high content of polyvinylpyrrolidone can form a good interface film on the positive and negative electrodes, which reduces the reactivity of the surface of the positive electrode.
  • the polyvinylpyrrolidone compound contains Lewis base. It can neutralize acid gases generated during storage, such as PF 5 , HF, CO 2 , etc.
  • the mass percentage of the polyvinylpyrrolidone compound in the electrolyte is ⁇ 0.05%, a sufficient protective film cannot be formed on the surface of the electrode sheet and the separator, and the improvement of the performance of the lithium ion battery is not remarkable.
  • the content of the second organic solvent is 60% to 85% of the total mass of the solution B, and the balance is a lithium salt.
  • Solution B may also contain other additives than the additives described herein, such as vinylene carbonate, fluoroethylene carbonate, vinylene sulfate, 1,3-propane sultone, and the like.
  • the mass ratio of the solution A to the solution B is 0.5 to 2:1, so as to ensure that the lithium salt concentration and the additive concentration in the prepared lithium ion battery are adjusted within a certain range.
  • the mass ratio of the two is 1:1.
  • the concentration of the lithium salt in the solution B is 1.5 M to 3 M.
  • the polyvinylpyrrolidone compound added as an additive forms a film on the surface of the electrode sheet and the separator, and the first organic solvent and the solution B in the solution A constitute an electrolyte of the lithium ion battery.
  • the electrolyte contains a lithium salt, a chain carbonate, and a cyclic carbonate, and may also contain other organic solvents and other additives.
  • the content of the cyclic carbonate is 10% to 40% of the total mass of the electrolyte
  • the content of the chain carbonate is 40% to 70% of the total mass of the electrolyte
  • the concentration of the lithium salt in the electrolyte is 0.3M. ⁇ 1.8M.
  • the positive electrode active material lithium nickel cobalt manganese oxide (LiNi 0.6 Co 0.2 Mn 0.2 O 2 ), the conductive agent Super-P, and the binder polyvinylidene fluoride (PVDF) were dissolved in the solvent N-A at a mass ratio of 97.2:1.3:1.5.
  • the base pyrrolidone was uniformly mixed to prepare a positive electrode slurry, and then the positive electrode slurry was uniformly coated on the front and back sides of the current collector aluminum foil, and the coating amount was 0.0102 g/cm 2 , followed by drying at 85 ° C and then cold pressing. , trimming, cutting, and slitting, and then drying under vacuum at 85 ° C for 4 h, welding the tabs to form a positive electrode of a lithium ion battery.
  • the negative active material artificial graphite, conductive agent Super-P, thickener carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) were dissolved in solvent deionized water at a mass ratio of 95.4:1.2:1.2:2.2.
  • the mixture was uniformly mixed to prepare a negative electrode slurry, and then the negative electrode slurry was uniformly coated on both sides of the current collector copper foil, and the coating amount was 0.0071 g/cm 2 , followed by drying at 85 ° C, followed by cold pressing and cutting. Edge, cut piece, and strip, then dried under vacuum at 110 ° C for 4 h, and soldered the ear to make a negative electrode of a lithium ion battery.
  • the electrolyte of the lithium ion battery uses 1 mol/L of LiPF 6 as a lithium salt, and a mixture of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) as a non-aqueous organic solvent, wherein the electrolyte solvent portion EC: EMC quality
  • the ratio is 30:70.
  • the electrolyte of the lithium ion battery also contains an additive, and the name of the additive and the content in the electrolyte are as shown in Table 1.
  • the polyvinylpyrrolidone used in the examples had a K value of 30 and was purchased from Sinopharm Chemical Reagent Co., Ltd. (China).
  • the positive electrode sheet, the negative electrode sheet and the separator (PE film containing ceramic coating) of the lithium ion battery prepared according to the foregoing process are subjected to a winding process to form a battery core having a thickness of 5.7 mm, a width of 16 mm, and a length of 33 mm, wherein The battery has a long air bag to observe its gas production.
  • the injection step is divided into the following three steps:
  • Step 1 The additive represented by Formula II is dissolved in the first organic solvent to obtain Solution A, and the lithium salt LiPF 6 is dissolved in the second organic solvent to obtain Solution B.
  • the first organic solvent and the second organic solvent are mixed solvents of EC and EMC, and the mass ratio of the two is 30:70.
  • the weight content of the additive in the solution A is 0.1% to 5%, and the specific names and contents are shown in Table 1.
  • the content of LiPF 6 in the solution B was 2 mol/L.
  • Step 2 the solution A is injected into the lithium ion battery, and then allowed to stand at normal temperature for 12 h, and then allowed to stand at 50 to 70 ° C for 12 h;
  • Step 3 Inject the solution B into the lithium ion battery to complete the encapsulation.
  • the packaged lithium ion battery was allowed to stand for 24 h, then charged to 3.4 V with a constant current of 0.05 C (11 mA), and the battery was removed and then vacuum prepackaged for degassing; then a constant current of 0.05 C (11 mA) was used.
  • Comparative Example 1 a lithium ion battery was prepared according to the method of Example 1, except that no additive was used in the electrolyte; in Comparative Examples 2 to 3, the name of the additive and the content in the electrolyte were as shown in Table 1. The remaining steps are the same as in the first embodiment.
  • the high temperature cycle performance and high temperature storage performance of the lithium ion battery were prepared by testing the examples and comparative examples.
  • the detection methods are as follows:
  • the discharge capacity of this time is the discharge capacity of the first cycle.
  • the lithium ion battery was subjected to a cyclic charge and discharge test in the above manner, and the discharge capacity at the 1000th cycle was taken.
  • Capacity retention ratio (%) after 1000 cycles of the lithium ion battery (discharge capacity at the 100th cycle / discharge capacity at the first cycle) ⁇ 100%.
  • Volume change rate (%) of lithium ion battery after high temperature storage (volume after high temperature storage of lithium ion battery / volume before high temperature storage of lithium ion battery) ⁇ 100%.
  • Examples 1-6 are lithium ion batteries in which polyvinylpyrrolidone is added to the electrolyte, and lithium ion battery of Comparative Example 1 without adding any additives. Compared with better high temperature cycle performance and high temperature storage performance.
  • Comparative Example 3 shows that when the content of polyvinylpyrrolidone in the electrolyte is more than 5%, the cycle performance deteriorates. The reason may be that the interfacial film formed on the surface of the positive and negative electrodes of polyvinylpyrrolidone is too thick, which affects the lithium ion battery. Cyclic performance, however, the storage performance is still further improved, because the high content of polyvinylpyrrolidone complex can form a good interface film on the positive and negative electrodes on the one hand, reducing the reactivity of the positive electrode surface, while polyvinylpyrrolidone contains a large amount of Lewis. base, acid gas can be stored and generated in the process, such as PF 5, HF, CO 2 and the like. Comparative Example 2 shows that when the mass percentage of polyvinylpyrrolidone in the electrolyte of the lithium ion battery is ⁇ 0.1%, the improvement in the performance of the lithium ion battery is not significant.
  • the lithium ion battery additive provided by the present application can form a good interface film on the surface of the positive and negative electrodes, reduce the reactivity of the surface of the positive electrode, inhibit the oxidative decomposition of the electrolyte on the surface of the positive electrode, and utilize the Lewis contained in the compound.
  • the characteristics of the base capture the acidic components and transition metal ions produced in the electrolyte to improve the high temperature storage performance and cycle performance of the battery at high voltages.
  • An electrolytic solution and a lithium ion battery containing the same were prepared according to the method of Example 1, except that the compound structural formula and the addition ratio of the additive in the electrolytic solution are as shown in Table 2, and the ratio of the additive is in the electrolytic solution. Content calculation.
  • the performance of the prepared battery was tested according to the method in Example 1.
  • the performance of the batteries 7 to 11 was similar to that of the above embodiment, and the details are not described herein.

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Abstract

一种锂离子电池添加剂、含有该添加剂的电池及制备方法，涉及锂离子电池领域。所述添加剂为聚乙烯吡咯烷酮类化合物，选自如式I所示化合物中的至少一种。将其加入电解液中可以有效地浸润电极材料，提升电池的可逆容量。同时聚乙烯吡咯烷酮类化合物中的氮元素可以有效捕获正极溶出的过渡金属离子和电解液分解产生的酸，防止其破坏SEI膜。

Description

锂离子电池添加剂，含有该添加剂的电池及制备方法 技术领域
本申请涉及锂离子电池领域，具体讲，涉及一种锂离子电池添加剂，含有该添加剂的电池及制备方法。
背景技术
锂离子电池具有高的体积比能量、重量比能量和良好的环保性，被广泛使用于手机、笔记本电脑等便携式3C电子设备中。随着近年来对电子产品要求趋向于更小、更轻、更薄，除追求更低的价格之外，追求更高的能量密度成为改进电子产品的强有力的驱动力。此外，近年来各国加大对大功率锂离子电池的投资力度，如电动工具、电动自行车以及汽车的开发。如该领域开发成功，可以缓解日益紧张的石油资源，因此有着很高的国际经济战略意义。
电解液是锂离子电池的一个重要组成部分，其组成直接影响电池的循环容量和寿命。组成合适(涉及到盐，溶剂及添加剂的选择和用量)的电解液能够有效发挥和提升锂离子电池正负极材料的电化学性能，如循环寿命、容量保持、高温存储、安全性能、倍率放电特性、放电的平台时间以及正负极的容量发挥等。通常在锂离子电池首次充放电的过程中，电解液中的某些组分(溶剂或是添加剂)发生还原分解并且产物沉积在负极材料石墨的表面形成固体电解质界面膜(SEI)，或是发生氧化分解并且产物沉积在正极材料的表面形成正极界面保护膜。良好而致密的界面保护膜能够缓解电解液的分解，从而减少电池的不可逆容量并改善其循环性能。电解液组分优化，选择合适的溶剂、锂盐以及添加剂是改善界面膜的有效途径。
开发改善负极成膜性能的添加剂，并研究其作用机理和成膜成分已经得到广泛研究。开发比较成功的有机添加剂主要有1,2-亚乙烯碳酸酯(VC)，卤化碳酸乙烯酯(简写为X-EC，X＝F、Cl.etc),亚硫酸乙烯酯和 1,3-丙磺酸内酯(PS)等。这些添加剂的作用主要是优先于电解液溶剂发生还原分解，从而抑制电解液的分解，并在石墨负极形成良好的SEI，提高电极的可逆容量和稳定性。然而电化学成膜会消耗活性锂离子，导致首次库伦效率低。
鉴于此，特提出本申请。
发明内容
本申请的首要发明目的在于提出一种锂离子电池添加剂。
本申请的第二发明目的在于提出含有该添加剂的锂离子电池。
本申请的第三发明目的在于提出所述锂离子电池的制备方法。
为了完成本申请的目的，采用的技术方案为：
本申请涉及一种锂离子电池添加剂，其选自如式I所示化合物中的至少一种：
Figure PCTCN2017093169-appb-000001
其中，所述R1、R2和R3各自独立地选自氢、取代或未取代的C1～C12烷基、取代或未取代的C6～C26芳基，取代或未取代的C5～C22芳杂基，取代基为卤素，n＝90～3200；优选所述R1、R2和R3为氢或C1～C8烷基。
优选地，当R1、R2和R3为氢时，所述添加剂为聚乙烯吡咯烷酮，其结构式如式II所示：
Figure PCTCN2017093169-appb-000002
优选地，所述聚乙烯吡咯烷酮的相对分子质量为10000-360000g/mol。
本申请还涉及一种锂离子电池，其含有正极片、负极片、隔离膜以及电解液，所述电解液中含有锂盐、有机溶剂和本申请所述的添加剂。
优选地，所述添加剂和锂盐是分别溶于有机溶剂后，依次注入锂离子电池内的。
优选的，所述有机溶剂选自碳酸乙烯酯、碳酸丙烯酯、γ-丁内酯、环丁砜、碳酸二甲酯、碳酸二乙酯、碳酸二丙酯、碳酸甲乙酯、碳酸甲丙酯、碳酸乙丙酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯、丙酸丙酯中的至少一种。
优选的，所述有机溶剂还含有羧酸酯、砜、亚硫酸酯、酮、胺、腈、醚、呋喃中的至少一种。所述羧酸酯选自丁酸甲酯、丙烯酸甲酯；所述砜选自环丁砜、二甲亚砜；所述亚硫酸酯选自二甲基亚硫酸酯、二乙基亚硫酸酯；所述酮选自N-甲基吡咯烷酮；所述胺选自N-甲基甲酰胺、N-甲基乙酰胺、N,N-二甲基甲酰胺；所述腈选自乙腈、丙腈、丙烯腈；所述醚选自乙醚、甲硫醚；所述呋喃选自四氢呋喃。
优选的，所述锂盐选自LiPF6、LiBF4、LiBOB、LiDFOB、LiAsF6、LiClO4、LiFAP、LiCF3SO3、Li(FSO2)2N、Li(CF3SO2)2N、Li(C2F5SO2)2N中的至少一种，更优选选自LiPF6、LiBF4、Li(FSO2)2N中的至少一种。
本申请还涉及所述锂离子电池的制备方法，包括将所述添加剂按以下方式加入：
步骤一、将本申请所述添加剂溶于第一有机溶剂得到溶液A，将锂盐溶于第二有机溶剂得到溶液B；
步骤二、将溶液A注入锂离子电池中；以及
步骤三、将溶液B注入锂离子电池中。
优选的，步骤二结束后，将锂离子电池静置6～24h，然后进行步骤三。更优选步骤二结束后，将锂离子电池在常温下静置6～24h，接着在50～70℃下静置6～24h，然后进行步骤三。
优选地，所述第一有机溶剂和第二有机溶剂相同或不同，优选相同。
优选地，所述添加剂的含量为溶液A的总质量的0.1％～5％，其余为 第一有机溶剂。
优选地，所述锂盐在溶液B中的浓度为1.5M～3M。
优选地，所述溶液A与溶液B的质量比为0.5～2：1，更优选为1：1。
所述溶液A中的第一有机溶剂和溶液B构成了锂离子电池的电解液。该电解液含有锂盐、链状碳酸酯和环状碳酸酯。优选所述环状碳酸酯的含量为电解液的总质量的10％～40％，所述链状碳酸酯的含量为电解液的总质量的40％～70％，所述锂盐在电解液中的浓度为0.3M～1.8M。
本申请的技术方案所能达到的有益效果为：
本申请提供了一种锂离子电池添加剂，其为聚乙烯吡咯烷酮类化合物，将其加入电解液中可以有效的浸润电极材料，提升电池的可逆容量。同时，聚乙烯吡咯烷酮类化合物含有的氮元素可以有效捕获正极溶出的过渡金属离子和电解液分解产生的酸，防止其破坏SEI。
在本申请优选的技术方案中，先通过含有聚乙烯吡咯烷酮类化合物的溶液A完成对电极片和隔离膜的浸润，再加入溶液B，在锂盐的作用下聚乙烯吡咯烷酮类化合物析出成膜，包覆在电极片和隔离膜表面，为固体电解质膜(SEI)提供骨架。聚合物特有的柔韧性可以提升SEI的稳定性，改善锂离子电池的高温循环性能。
具体实施方式
下面结合具体实施例，进一步阐述本申请。应理解，这些实施例仅用于说明本申请而不用于限制本申请的范围。
本申请涉及一种锂离子电池添加剂，其为聚乙烯吡咯烷酮类化合物，选自如式I所示化合物中的至少一种：
Figure PCTCN2017093169-appb-000003
其中，R1、R2和R3各自独立地选自氢、取代或未取代的C1～C12烷基、取代或未取代的C6～C26芳基，取代或未取代的C5～C22芳杂基，取代基为卤素，n＝90～3200；优选R1、R2和R3为氢或C1～C8烷基。
作为本申请锂离子电池添加剂的一种改进，R1、R2和R3各自独立地选自氢和C1～C8烷基。
作为本申请锂离子电池添加剂的一种改进，R1、R2和R3为相同的取代基。
在本申请的上述结构式中：
对于取代或未取代的C1～C12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，所述烷基中碳原子数优选的下限值为1，2，3，4，优选的上限值为3，4，5，6，8，10，12。优选地，选择碳原子数为1～8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1～3的链状烷基。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。
对于碳原子数为6～26的芳基，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。
碳原子数为5～22的芳杂基，可选自：呋喃基、噻吩基、吡咯基、噻唑基、咪唑基、吡啶基、吡嗪基、嘧啶基、哒嗪基、吲哚基、喹啉基等。
作为本申请锂离子电池添加剂的一种改进，当R1、R2和R3为氢时，所述添加剂为聚乙烯吡咯烷酮，其结构式如式II所示：
Figure PCTCN2017093169-appb-000004
作为本申请锂离子电池添加剂的一种改进，聚乙烯吡咯烷酮的相对分子质量为10000-360000g/mol。
作为本申请锂离子电池添加剂的一种改进，本申请的添加剂还可选自以下化合物中的至少一种：
Figure PCTCN2017093169-appb-000005
其中n＝90～3200，优选n＝100～3000。
本申请还涉及一种锂离子电池，其含有正极片、负极片、隔离膜以及电解液，所述电解液中含有锂盐、有机溶剂和本申请所述的添加剂。进一步地，正极片包括正极集流体以及涂覆于正极集流体上的正极活性材料；负极片包括负极集流体以及涂覆于负极集流体上的负极活性材料；隔离膜位于相邻的正负极片之间。本申请的锂离子电池的上限截止电压为3.5V～4.4V。
作为本申请锂离子电池的一种改进，正极活性材料选自钴酸锂、锰酸锂、镍钴锰酸锂Li(NixMnyCoz)O2(0<x,y,z<1；x+y+z＝1)中的一种或几种；负极活性材料选自天然石墨、人造石墨、软碳、硬碳、钛酸锂、硅中的一种或几种。
作为本申请锂离子电池的一种改进，锂盐选自六氟磷酸锂LiPF6、四氟硼酸锂LiBF4、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)、六氟砷酸锂(LiAsF6)、高氯酸锂(LiClO4)、三(全氟乙基)三氟磷酸锂LiFAP、三氟甲基磺酸锂LiCF3SO3、 二(三氟甲基磺酸)甲基锂Li(FSO2)2N、二(三氟甲基磺酸)亚氨锂LiN(CF3SO2)2、二(全氟乙基磺酸)亚氨锂Li(C2F5SO2)2N、Li(C4F9SO2)2N、Li(SO2(CF2)3SO2)2N中的至少一种，锂盐优选LiPF6、LiBF4、Li(FSO2)2N中的至少一种。
作为本申请锂离子电池的一种改进，所述添加剂和锂盐是分别溶于有机溶剂后，依次注入锂离子电池内的。
本申请还涉及所述锂离子电池的制备方法，包括将所述添加剂按以下方式加入：
步骤一、将本申请所述添加剂溶于第一有机溶剂得到溶液A，将锂盐溶于第二有机溶剂得到溶液B；
步骤二、将溶液A注入锂离子电池中；以及
步骤三、将溶液B注入锂离子电池中。
本申请经研究发现：直接将聚乙烯吡咯烷酮类化合物加入到含锂盐的有机溶剂中会导致聚乙烯吡咯烷酮类化合物的析出，因此需要待溶液A完成对电极片和隔离膜的浸润后，再加入含锂盐的溶液B。在锂盐的作用下，聚乙烯吡咯烷酮类化合物析出成膜，包覆在电极片和隔离膜表面，为固体电解质膜(SEI)提供骨架，聚合物具有的柔韧性可以提升SEI的稳定性。同时，聚乙烯吡咯烷酮类化合物含有的氮元素可以有效捕获正极溶出的过渡金属离子和电解液分解产生的酸，防止其破坏SEI，延长电池的循环寿命。
本申请经研究发现：步骤二结束后，将锂离子电池静置6～24h，然后进行步骤三，能够使聚乙烯吡咯烷酮类化合物析出更为充分。作为更优选的方案，先将锂离子电池在常温下静置6～24h，使电解液能够充分浸润电极材料(主要是物理浸润)，接着在50～70℃下静置6～24h，能够加速添加剂与电极材料的相互作用(以化学作用为主)，有利于步骤三加入溶液B后聚乙烯吡咯烷酮类化合物在电极表面形成均一稳定的膜。
作为本申请锂离子电池制备方法的一种改进，第一有机溶剂和第二有机溶剂相同或不同，优选相同。
作为本申请锂离子电池制备方法的一种改进，第一有机溶剂和第二有 机溶剂中均含有环状碳酸酯和链状碳酸酯。其中环状碳酸酯优选选自碳酸乙烯酯(EC)、碳酸丙烯酯(PC)中的至少一种；链状碳酸酯优选选自碳酸二甲酯、碳酸二乙酯(DEC)、碳酸二丙酯、碳酸甲乙酯(EMC)、碳酸甲丙酯、碳酸乙丙酯中的至少一种。
作为本申请锂离子电池制备方法的一种改进，第一有机溶剂和/或第二有机溶剂中还含有羧酸酯、砜、亚硫酸酯、酮、胺、腈、醚、呋喃中的至少一种。其中羧酸酯选自丁酸甲酯、丙烯酸甲酯；砜选自环丁砜、二甲亚砜；亚硫酸酯选自二甲基亚硫酸酯、二乙基亚硫酸酯；酮选自N-甲基吡咯烷酮；胺选自N-甲基甲酰胺、N-甲基乙酰胺、N,N-二甲基甲酰胺；腈选自乙腈、丙腈、丙烯腈；醚选自乙醚、甲硫醚；呋喃选自四氢呋喃。
作为本申请锂离子电池制备方法的一种改进，加入的添加剂含量为溶液A的总质量的0.1％～5％，其余为第一有机溶剂。本申请经研究发现：当含量大于5％时，聚乙烯吡咯烷酮类化合物在有机溶剂中的比例过大，导致电解液体系粘度变大，同时在正负极表面形成的界面膜过厚，影响了锂离子电池的循环性能。然而存储性能仍进一步改善，这是因为高含量的聚乙烯吡咯烷酮类化合物一方面可以在正负极表面形成良好的界面膜，降低了正极表面的反应活性，同时，聚乙烯吡咯烷酮类化合物含有路易斯碱，可以中和存储过程中产生的酸性气体，如PF5、HF、CO2等。当聚乙烯吡咯烷酮类化合物在电解液中的质量百分含量<0.05％时，无法在电极片和隔离膜表面形成充足的保护膜，对锂离子电池的性能的改善不明显。
作为本申请锂离子电池制备方法的一种改进，第二有机溶剂的含量为溶液B的总质量的60％～85％，其余为锂盐。除此以外，溶液B中也可含有除本申请所述添加剂以外的其它添加剂，如碳酸亚乙烯酯，氟代碳酸乙烯酯，硫酸亚乙烯酯，1，3-丙烷磺酸内酯等。
作为本申请锂离子电池制备方法的一种改进，溶液A与溶液B的质量比为0.5～2：1，以保证在制备的锂离子电池中的锂盐浓度与添加剂浓度在一定范围内进行调整，优选两者的质量比为1：1。
作为本申请锂离子电池制备方法的一种改进，锂盐在溶液B中的浓度为1.5M～3M。
在本申请中，作为添加剂加入的聚乙烯吡咯烷酮类化合物几乎全部在电极片和隔离膜表面成膜，溶液A中的第一有机溶剂和溶液B构成了锂离子电池的电解液。该电解液含有锂盐、链状碳酸酯和环状碳酸酯，还可以含有其它有机溶剂和其它添加剂。优选环状碳酸酯的含量为电解液的总质量的10％～40％，链状碳酸酯的含量为电解液的总质量的40％～70％，锂盐在电解液中的浓度为0.3M～1.8M。
实施例1～6
(1)锂离子电池的正极片的制备
将正极活性材料镍钴锰酸锂(LiNi0.6Co0.2Mn0.2O2)、导电剂Super-P、粘接剂聚偏氟乙烯(PVDF)按质量比97.2:1.3:1.5溶于溶剂N-甲基吡咯烷酮中混合均匀制成正极浆料，之后将正极浆料均匀涂布在集流体铝箔的正反两面上，涂布量为0.0102g/cm2，随后在85℃下烘干后进行冷压、切边、裁片、分条，之后在85℃真空条件下干燥4h，焊接极耳，制成锂离子电池的正极片。
(2)锂离子电池的负极片的制备
将负极活性材料人造石墨、导电剂Super-P、增稠剂羧甲基纤维素(CMC)、粘接剂丁苯橡胶(SBR)按质量比95.4：1.2：1.2：2.2溶于溶剂去离子水中混合均匀制成负极浆料，之后将负极浆料均匀涂布在集流体铜箔的正反两面上，涂布量为0.0071g/cm2，随后在85℃下烘干后进行冷压、切边、裁片、分条，之后在110℃真空条件下干燥4h，焊接极耳，制成锂离子电池的负极片。
(3)锂离子电池的电解液的制备
锂离子电池的电解液以1mol/L的LiPF6为锂盐，以碳酸乙烯酯(EC)、碳酸甲乙酯(EMC)的混合物为非水有机溶剂，其中电解液溶剂部分EC:EMC的质量比为30:70。此外，锂离子电池的电解液中还含有添加剂，添加剂的名称和在电解液中的含量如表1所示。实施例中使用的聚乙烯吡咯烷酮的K值为30，购自国药集团化学试剂有限公司(中国)。
(4)锂离子电池的制备
将根据前述工艺制备的锂离子电池的正极片、负极片以及隔离膜(PE膜，含有陶瓷涂层)经过卷绕工艺制作成厚度为5.7mm、宽度为16mm、长度为33mm的电芯，其中该电芯留有长气袋，以便观察其产气。注液步骤分为以下三步：
步骤一、将式II所示的添加剂溶于第一有机溶剂得到溶液A，将锂盐LiPF6溶于第二有机溶剂得到溶液B。其中第一有机溶剂和第二有机溶剂均为EC和EMC的混合溶剂，两者质量比为30:70。溶液A中添加剂的重量含量为0.1％～5％，具体名称和含量如表1所示。溶液B中LiPF6的含量为2mol/L。
步骤二、将溶液A注入锂离子电池中，然后在常温下静置12h，接着在50～70℃下静置12h；
步骤三、将溶液B注入锂离子电池中，完成封装。
将封装后的锂离子电池静置24h，之后用0.05C(11mA)的恒定电流充电至3.4V，取下电池然后先进行一次真空预封装以便除气；再以0.05C(11mA)的恒定电流充电至4.5V，而后再将电池取下进行第二次除气；然后以0.5C(110mA)的恒定电流放电至3V，重复2次充放电，最后以0.5C(110mA)的恒定电流充电至3.85V，完成锂离子电池的制备。
对比例1～3
在对比例1中，依照实施例1的方法制备锂离子电池，区别仅在于电解液中不使用任何添加剂；在对比例2～3中，添加剂的名称和在电解液中的含量如表1所示，其余步骤同实施例1。
测试实施例和对比例制备锂离子电池的高温循环性能和高温存储性能，检测方法如下：
(1)锂离子电池的高温循环性能测试
在45℃下，先以1C的恒定电流对锂离子电池充电至4.2V，进一步以4.2V恒定电压充电至电流为0.05C，然后以1C的恒定电流对锂离子电池放电至2.8V，此为一个充放电循环过程，此次的放电容量为第1次循环的放电容量。将锂离子电池按上述方式进行循环充放电测试，取第1000次循环的放电容量。
锂离子电池1000次循环后的容量保持率(％)＝(第100次循环的放电容量/第1次循环的放电容量)×100％。
(2)锂离子电池的高温存储性能测试
在25℃下，先以1C的恒定电流对锂离子电池充电至4.2V，进一步以4.2V恒定电压充电至电流为0.05C，然后将锂离子电池置于85℃下存储10天，观察电压降。
锂离子电池高温存储后的体积变化率(％)＝(锂离子电池高温存储后的体积/锂离子电池高温存储前的体积)×100％。
检测到的数据如表1所示。
表1
Figure PCTCN2017093169-appb-000006
其中，“/”表示未添加该物质。
锂离子电池的性能测试结果分析：
从实施例1-6与对比例1-3的对比中可以看出，实施例1-6为电解液中添加聚乙烯吡咯烷酮的锂离子电池，与不添加任何添加剂的对比例1的锂离子电池相比，具有较好的高温循环性能以及高温存储性能。
对比例3说明：当聚乙烯吡咯烷酮在电解液中的含量大于5％时，其循环性能出现恶化，原因可能是聚乙烯吡咯烷酮在正负极表面形成的界面膜过厚，影响了锂离子电池的循环性能，然而存储性能仍进一步改善，这是因为高含量聚乙烯吡咯烷酮配合物一方面可以在正负极表面形成良好 的界面膜，降低了正极表面的反应活性，同时聚乙烯吡咯烷酮含有大量的路易斯碱，可以中和存储过程中产生的酸性气体，如PF5、HF、CO2等。对比例2说明：当聚乙烯吡咯烷酮在锂离子电池的电解液中的质量百分含量<0.1％时，对锂离子电池的性能的改善不明显。
由此可见，本申请提供的锂离子电池添加剂可以在正负极表面形成良好的界面膜，降低正极表面的反应活性，抑制电解液在正极表面的氧化分解；同时利用该化合物中所含有的路易斯碱的特性捕获在电解液中产生的酸性组分和过渡金属离子，以改善电池在高电压下的高温存储性能以及循环性能。
实施例7～11
按照实施例1的方法制备电解液和含有该电解液的锂离子电池，区别在于：电解液中的添加剂的化合物结构式和添加比例如表2所示，添加剂的比例是以其在电解液中的含量计算。
表2
Figure PCTCN2017093169-appb-000007
Figure PCTCN2017093169-appb-000008
按照实施例1中的方法对制备得到的电池的性能进行检测，检测得到电池7～11的性能与以上实施例相似，限于篇幅不再赘述。
以上是本发明的较佳实施例的具体说明，但本发明并不限于所述实施例，某些变形或替换化合物均包含在本申请权利要求所限定的范围内。此外，本发明使用了某些特定的术语，但这些术语只是为了方便说明，并不对本发明构成任何限制。

Claims (10)

  1. 一种锂离子电池添加剂，其特征在于，其选自如式I所示化合物中的至少一种：
    Figure PCTCN2017093169-appb-100001
    其中，所述R1、R2和R3各自独立地选自氢、取代或未取代的C1～C12烷基、取代或未取代的C6～C26芳基，取代或未取代的C5～C22芳杂基，取代基为卤素，n＝90～3200；优选所述R1、R2和R3为氢或C1～C8烷基。
  2. 根据权利要求1所述的添加剂，其特征在于，所述添加剂的结构式如式II所示：
    Figure PCTCN2017093169-appb-100002
  3. 一种锂离子电池，其含有正极片、负极片、隔离膜以及电解液，其特征在于，所述电解液中含有锂盐、有机溶剂和权利要求1或2所述的添加剂。
  4. 根据权利要求3所述的锂离子电池，其特征在于，所述添加剂和锂盐是分别溶于有机溶剂后，依次注入锂离子电池内的。
  5. 根据权利要求4所述的锂离子电池，其特征在于，所述有机溶剂选自碳酸乙烯酯、碳酸丙烯酯、γ-丁内酯、环丁砜、碳酸二甲酯、碳酸二乙酯、碳酸二丙酯、碳酸甲乙酯、碳酸甲丙酯、碳酸乙丙酯、乙酸甲酯、 乙酸乙酯、乙酸丙酯、丙酸甲酯、丙酸乙酯、丙酸丙酯中的至少一种。
  6. 根据权利要求4所述的锂离子电池，其特征在于，所述锂盐选自LiPF6、LiBF4、LiBOB、LiDFOB、LiAsF6、LiClO4、LiFAP、LiCF3SO3、Li(FSO2)2N、Li(CF3SO2)2N、Li(C2F5SO2)2N中的至少一种，更优选选自LiPF6、LiBF4、Li(FSO2)2N中的至少一种。
  7. 一种根据权利要求3所述锂离子电池的制备方法，其特征在于，包括将所述添加剂按以下方式加入：
    步骤一、将所述添加剂溶于第一有机溶剂得到溶液A，将锂盐溶于第二有机溶剂得到溶液B；
    步骤二、将溶液A注入锂离子电池中；以及
    步骤三、将溶液B注入锂离子电池中。
  8. 根据权利要求7所述的方法，其特征在于，步骤二结束后，将锂离子电池静置6～24h，然后进行步骤三；优选步骤二结束后，将锂离子电池在常温下静置6～24h，接着在50～70℃下静置6～24h，然后进行步骤三。
  9. 根据权利要求7所述的方法，其特征在于，所述第一有机溶剂和第二有机溶剂相同或不同，优选相同。
  10. 根据权利要求7所述的方法，其特征在于，所述添加剂的含量为溶液A的总质量的0.1％～5％；所述锂盐在溶液B中的浓度为1.5M～3M；
    优选地，所述溶液A与溶液B的质量比为0.5～2：1，更优选为1：1。
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