WO2020015346A1 - 一种电池非水电解液及含有该电解液的二次电池 - Google Patents

一种电池非水电解液及含有该电解液的二次电池 Download PDF

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WO2020015346A1
WO2020015346A1 PCT/CN2019/072454 CN2019072454W WO2020015346A1 WO 2020015346 A1 WO2020015346 A1 WO 2020015346A1 CN 2019072454 W CN2019072454 W CN 2019072454W WO 2020015346 A1 WO2020015346 A1 WO 2020015346A1
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battery
formula
aqueous electrolyte
secondary battery
ionic liquid
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PCT/CN2019/072454
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English (en)
French (fr)
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王群峰
梅骜
唐道平
李进
李扬
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广州汽车集团股份有限公司
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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
    • H01M10/058—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
    • 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
    • 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 invention relates to a battery non-aqueous electrolyte and a secondary battery containing the electrolyte, and belongs to the technical field of battery materials.
  • lithium-ion batteries have been widely used in the field of new energy vehicles.
  • a silicon system as the negative electrode active material can greatly increase the energy density of a lithium ion battery.
  • adding about 10% of a silicon carbon material to a graphite negative electrode can increase the discharge gram capacity of the negative electrode active material from 350mAh / g to about 500mAh / g.
  • the most important role of the electrolyte in the lithium ion battery is to form a solid electrolyte layer (SEI) on the surface of the negative electrode during the formation process, and to repair the cracks generated by the SEI during the cycle in a timely manner.
  • SEI solid electrolyte layer
  • a very important reason for the poor cycling performance of silicon-based lithium-ion batteries is the SEI rupture caused by the expansion and contraction of silicon particles during cycling. Therefore, the selection of appropriate electrolyte additives is of great significance for improving the cycle performance of silicon-based lithium-ion batteries.
  • FEC or additives containing siloxane functional groups such as TMVS in the electrolyte can effectively improve the cycling performance of silicon-based lithium ion batteries, but the improvement effect brought by a single additive is limited, especially when the content of silicon material in the negative electrode active material is After the upgrade, the addition of a single additive does not improve the cycle performance of the battery to meet practical needs.
  • the purpose of the present invention is to overcome the shortcomings of the above secondary battery with a silicon-based active material added to the negative electrode, but the cycle performance is not good, and to provide a new battery non-aqueous electrolyte.
  • the secondary battery adopts the battery non-aqueous electrolyte, and its cycle performance is significantly improved.
  • the present invention also provides a secondary battery containing the above-mentioned electrolytic solution.
  • the technical solution adopted by the present invention is: a battery non-aqueous electrolyte, which includes an organic solvent, an electrolyte salt, and an additive, the additive is composed of a siloxane functionalized ionic liquid and a fluoroethylene carbonate ;
  • the siloxane functionalized ionic liquid is composed of a monovalent cation and a monovalent anion, and the structural formula of the monovalent cation is shown by the following formula (I) or formula (VII);
  • R1, R2, and R3 represent an alkoxy group having 1 to 8 carbon atoms or an alkyl group having 1 to 8 carbon atoms, and Z1 and Z2 represent a carbon number of A linear alkyl group of 1 to 5; and at least one of R1, R2, and R3 is an alkoxy group;
  • the structural formula of the siloxane functionalized ionic liquid is as shown in the following formula (III), formula (IV), formula (V) or formula (VI);
  • the mass fraction of the siloxane-functionalized ionic liquid in the electrolytic solution is 0.5% to 15%.
  • the organic solvent comprises ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ⁇ -butyrolactone, methyl acetate, ethyl acetate, propyl acetate, acetic acid It is composed of at least two of butyl ester, ethyl propionate, propyl propionate, and butyl propionate.
  • the electrolyte salt is at least one of LiPF 6 , LiBF 4 , LiFSI, LiTFSI, LiBOB, LiODFB, and LiPO 2 F 2 .
  • the concentration of the electrolyte salt in the electrolytic solution is 0.5 to 2 mol / L.
  • the mass fraction of the fluoroethylene carbonate in the electrolytic solution is 2% to 20%;
  • the present invention also provides a secondary battery including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and the battery non-aqueous electrolyte; wherein the active material of the negative electrode contains a silicon-based Active material.
  • the secondary battery is a lithium ion secondary battery.
  • the present invention also provides an application of the battery non-aqueous electrolyte in the preparation of a secondary battery, wherein the negative electrode active material of the secondary battery contains a silicon-based active material.
  • the present invention has the beneficial effects that the battery non-aqueous electrolyte of the present invention contains both a siloxane functionalized ionic liquid and a fluoroethylene carbonate.
  • the combination of these two substances can produce a synergistic effect and is effective Improve the cycling performance of secondary batteries with silicon-based active materials added to the negative electrode.
  • the present invention provides a battery non-aqueous electrolyte, which includes an organic solvent, an electrolyte salt, and an additive, the additive is a siloxane functionalized ionic liquid and a fluoroethylene carbonate Composition; wherein the siloxane functionalized ionic liquid is composed of a monovalent cation and a monovalent anion, and the structural formula of the monovalent cation is as shown in the following formula (I) or formula (VII);
  • R1, R2, and R3 represent an alkoxy group having 1 to 8 carbon atoms or an alkyl group having 1 to 8 carbon atoms, and Z1 and Z2 represent a carbon number of A linear alkyl group of 1 to 5; and at least one of R1, R2, and R3 is an alkoxy group;
  • siloxane-functionalized ionic liquids in combination with fluoroethylene carbonate in battery electrolytes can play a synergistic role to achieve a higher ratio than using siloxane-functionalized ionic liquids or fluorocarbonates alone.
  • Vinyl ester has more excellent improvement effect.
  • the possible synergistic mechanism of the siloxane functionalized ionic liquid and fluoroethylene carbonate of the present invention is as follows: First, during the electrolyte infiltration process, the siloxane functional group in the ionic liquid reacts with the hydroxyl group on the surface of the silicon negative electrode to form Si- O-Si bond, so that the ionic liquid adheres to the surface of the negative electrode of the silicon electrode.
  • the excellent electrochemical stability of the ionic liquid can play a good role in protecting the silicon material.
  • the addition of fluoroethylene carbonate can obtain a more uniform and stable solid electrolyte layer (SEI), and slow the SEI cracking caused by the expansion and contraction of silicon particles during the cycle.
  • SEI solid electrolyte layer
  • the reduction potential of the fluoroethylene carbonate on the surface of the silicon negative electrode is sufficiently high. Repair the SEI crack for a while.
  • the siloxane functionalized ionic liquid is used in combination with fluoroethylene carbonate, the cycle performance of the secondary battery of the silicon system can be significantly improved.
  • the battery non-aqueous electrolyte of the present invention can be obtained by mixing the components therein uniformly.
  • the structural formula of the siloxane functionalized ionic liquid is as shown in the following formula (III), formula (IV), formula (V) or formula (VI);
  • the battery electrolyte containing the siloxane functionalized ionic liquid represented by formula (III) has a more significant effect on improving the cycle performance of the silicon system secondary battery; Therefore, preferably, the structural formula of the siloxane functionalized ionic liquid is as shown in the above formula (III).
  • the viscosity of the siloxane-functionalized ionic liquid is large, and its content in the electrolyte has a significant effect on the cycle improvement effect.
  • the mass fraction of the siloxane-functionalized ionic liquid in the electrolyte is 0.5 % To 15%; more preferably, the mass fraction of the siloxane-functionalized ionic liquid in the electrolyte is 2% to 10%; more preferably, the siloxane-functionalized ionic liquid is in the electrolyte The mass fraction in is 5%.
  • the amount of the siloxane functionalized ionic liquid is too high, the viscosity of the electrolyte is significantly increased, the kinetic performance of the secondary battery is deteriorated, and the cycle performance of the secondary battery 1C / 1C is further deteriorated.
  • the amount of silicone-functionalized ionic liquid is higher than 15%, the cycle improvement effect is significantly deteriorated.
  • the organic solvent is composed of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). ), ⁇ -butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, and butyl propionate.
  • the organic solvent may be composed of ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC).
  • the electrolyte salt is at least one of LiPF 6 , LiBF 4 , LiFSI, LiTFSI, LiBOB, LiODFB, and LiPO 2 F 2 .
  • the electrolyte salt is LiPF 6 .
  • the concentration of the electrolyte salt in the electrolytic solution is 0.5 to 2 mol / L.
  • the concentration of the electrolyte salt in the electrolytic solution is 1 mol / L.
  • the content of the fluoroethylene carbonate has a certain effect on the cycle performance improvement effect of the secondary battery.
  • the mass fraction of the fluoroethylene carbonate in the electrolyte is 2% to 20%; more preferably, the fluoroethylene carbonate
  • the mass fraction of the substituted vinyl carbonate in the electrolytic solution is 15% to 20%; more preferably, the mass fraction of the fluoroethylene carbonate in the electrolytic solution is 15%.
  • the present invention also provides a secondary battery including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and the battery non-aqueous electrolyte; wherein the active material of the negative electrode contains a silicon-based Active material.
  • a secondary battery generally refers to a power storage device that can be repeatedly charged and discharged.
  • Secondary batteries include “nickel metal hydride”, “nickel cadmium”, “lead acid (lead battery)”, “lithium ion (including lithium batteries and lithium ion polymer batteries)", and the like.
  • the secondary battery is a lithium ion secondary battery.
  • the active material of the positive electrode of the secondary battery is LiNi 0.5 Co 0.2 Mn 0.3 O 2
  • the active material of the negative electrode is artificial graphite or Si / C composite material.
  • the present invention also provides an application of the battery non-aqueous electrolyte in the preparation of a secondary battery, wherein the negative electrode active material of the secondary battery contains a silicon-based active material.
  • the siloxane functionalized ionic liquid represented by the following formula (III) is referred to as ionic liquid L1; the siloxane functionalized ionic liquid represented by the formula (IV) is referred to as ionic liquid L2; V)
  • the siloxane functionalized ionic liquid shown in the formula is referred to as ionic liquid L3; the siloxane functionalized ionic liquid shown in formula (VI) is referred to as the ionic liquid L4.
  • the battery non-aqueous electrolyte according to this embodiment is composed of an organic solvent, an electrolyte salt, and an additive.
  • the additive is a siloxane functionalized ionic liquid and fluoroethylene carbonate. Ester (FEC) composition.
  • FEC Ester
  • the method for preparing the battery non-aqueous electrolyte in this embodiment is as follows: In a glove box or a drying room, each organic solvent subjected to rectification and dehydration treatment is mixed uniformly in proportion, and then the electrolyte salt is slowly added, and finally silicon oxide is added in proportion. The alkane-functionalized ionic liquid and fluoroethylene carbonate are stirred and mixed uniformly to obtain the final battery non-aqueous electrolyte.
  • the secondary battery of this embodiment is a lithium ion secondary battery, which includes a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and the battery non-aqueous electrolyte solution of this embodiment.
  • the method for preparing the secondary battery in this embodiment is as follows: an isolation film (thickness: 15 ⁇ m) is placed between the positive electrode sheet and the negative electrode sheet, a square bare cell is prepared by winding, and an aluminum plastic film composite material is used for packaging Bag, put the bare cell into a packaging bag and package it to obtain a dry cell.
  • the dry cell is subjected to baking and dewatering, liquid injection, sealing, standing, chemical formation, degassing packaging, and volume separation to obtain lithium ion II. Secondary battery.
  • the preparation method of the positive electrode sheet is: mixing the positive electrode active material lithium nickel cobalt manganese LiNi 0.5 Co 0.2 Mn 0.3 O 2 with a conductive agent super-P, CNT, and a binder PVDF in a mass ratio of 96.8: 1.5: 0.5: 1.2 Evenly, add N-methylpyrrolidone (NMP), and stir and mix with a vacuum mixer to obtain a positive electrode active material slurry.
  • NMP N-methylpyrrolidone
  • the above slurry was uniformly coated on both sides of a current collector of an aluminum foil (thickness: 12 ⁇ m), and dried, cold-pressed, and cut to obtain a positive electrode sheet.
  • the preparation method of the negative electrode sheet is: the negative electrode active material artificial graphite, Si / C composite material and conductive agent super-P, CNT, adhesive styrene-butadiene rubber (SBR), carboxymethyl cellulose sodium (CMC), polymer Acrylic acid (PAA) was mixed uniformly at a mass ratio of 85: 9: 1.5: 0.5: 2.2: 1.4: 0.4, deionized water was added, and the mixture was stirred and mixed by a vacuum mixer to obtain a negative electrode active material slurry.
  • the above slurry was uniformly coated on both sides of a current collector of a copper foil (thickness: 8 ⁇ m), and dried, cold pressed, and cut to obtain a negative electrode sheet.
  • Example 2 to 4 The battery non-aqueous electrolytes described in Examples 2 to 4 are the same as Example 1 except that the specific substances of the components and the amounts of each component are different from those of Example 1.
  • Example 1 Except for the battery non-aqueous electrolyte, the secondary batteries described in Examples 2 to 4 are all in Example 1.
  • the secondary batteries described in Examples 2 to 4 respectively contain the battery non-aqueous electrolyte described in Examples 2 to 4.
  • the methods for preparing the battery non-aqueous electrolyte and the secondary battery described in Examples 2 to 4 are the same as those in Example 1.
  • the test method is: in a 25 ° C incubator, charge the lithium ion batteries obtained in Examples 1 to 4 above to a constant current of 1C to 4.25V, and then charge to a current of 0.05C at a constant voltage, and then discharge at a constant current of 1C To 2.75V, the charging / discharging cycle is performed in this way, and the capacity retention rate of the battery is recorded after 200 cycles.
  • Lithium-ion secondary battery 200-week cycle capacity retention rate (%) 200-week cycle discharge capacity / 1-week cycle discharge capacity * 100%
  • the battery non-aqueous electrolyte of the present invention can significantly improve the cycle performance of the secondary battery.
  • this effect example A series of non-aqueous electrolytes and lithium-ion secondary batteries for the test group and the control group were prepared, and the lithium-ion secondary batteries of the test group and the control group were measured in accordance with the test methods for the performance of the lithium-ion secondary batteries in Examples 1 to 4. performance.
  • the battery non-aqueous electrolyte and lithium ion secondary battery of test group 1 are the same as those in Example 1.
  • the battery non-aqueous electrolyte and lithium ion secondary battery of test group 2 to 12 and control group 1 to 11 are in addition to additives. All are the same as in Example 1; each group of lithium ion secondary batteries contains the corresponding battery non-aqueous electrolyte.
  • the methods for preparing the non-aqueous electrolyte solution and the lithium ion secondary battery of each test group and the control group are the same as those in Example 1.
  • composition of the additives of each test group and the performance of the lithium ion secondary battery are shown in Table 2.
  • the percentages of FEC and siloxane functionalized ionic liquids in Table 2 represent their weight percentages in the electrolyte.
  • test group 1 and control group 2 Compare (a) test group 1, control group 1 and control group 2, (b) test group 10, control group 6, and control group 7, (c) test group 11, control group 8, and control group 9, (d) In the test group 12, the control group 10, and the control group 11, it can be found that within the scope of the present invention, the use of a siloxane-functionalized ionic liquid and FEC as an additive can obtain a ionic liquid or FEC has a better cycle improvement effect, and the degree of improvement is larger, which is difficult for those skilled in the art to predict.

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Abstract

一种电池非水电解液及含有该电解液的二次电池，属于电池材料技术领域。所述电池非水电解液包含有机溶剂、电解质盐和添加剂，添加剂由硅氧烷官能团化的离子液体和氟代碳酸乙烯酯组成；硅氧烷官能团化的离子液体由一价阳离子和一价阴离子组成，一价阳离子的结构式如下述式(Ⅰ)或式(∏)所示；式(Ⅰ)和式(∏)中，R1、R2、R3表示碳原子数为1～8的烷氧基或碳原子数为1～8的烷基，Z1、Z2表示碳原子数为1～5的直链烷基；且R1、R2、R3中，至少有一个为烷氧基；一价阴离子为PF 6 -、BF 4 -、FSI -或TFSI -。所述电解液同时含有硅氧烷官能团化的离子液体和氟代碳酸乙烯酯，这两种物质组合有效改善负极添加硅系活性材料的二次电池的循环性能。

Description

一种电池非水电解液及含有该电解液的二次电池 技术领域
本发明涉及一种电池非水电解液及含有该电解液的二次电池，属于电池材料技术领域。
背景技术
近年来，锂离子电池已经广泛应用于新能源汽车领域，随着新能源汽车产业的发展，对锂离子电池的各项性能，尤其是能量密度，也提出了越来越高的要求。
当前，各种提升锂离子电池能量密度的技术手段中，负极使用硅系材料正成为产业界研究最为广泛的方法。使用硅体系作为负极活性材料可以大幅提升锂离子电池的能量密度，例如，在石墨负极中添加大约10％左右的硅碳材料，即可将负极活性材料的放电克容量由350mAh/g提升至约500mAh/g。
然而，高克容量的硅系负极材料大规模产业化应用仍需克服许多技术难点，主要是该类锂离子电池的循环寿命较短，尤其是当负极添加的硅系活性材料较多时，通常经过200次充放电循环，放电容量即衰减至初始放电容量的70％以下。如此低的循环寿命，阻碍了硅系高容量负极材料的应用。
锂离子电池中电解液除了起锂离子传输介质的作用外，其最重要作用便是化成过程中在负极表面生成固态电解质层(SEI)，并对SEI在循环过程中产生的裂纹进行及时修复。硅体系锂离子电池循环性能差的一个很重要的原因便是循环过程中硅颗粒的膨胀收缩引起的SEI破裂。因此，选择合适的电解液添加剂对于改善硅体系锂离子电池的循环性能具有十分重要的意义。
Choi N S,Yew K H,和Lee K Y等人(Effect of fluoroethylene carbonate additive on interfacial properties of silicon thin-film electrode[J].Journal of Power Sources,2006,161(2):1254-1259.)在EC/DEC(3/7，v/v)1.3M LiPF6中添加3％FEC，使用硅薄膜电极制作的Si/Li半电池研究发现，未含添加剂的电池经过80 周循环后容量保持率为67.9％，含3％FEC的电池80周循环后容量保持率为88.5％。分析认为FEC的加入可使得电解液在负极表面生成更为均匀稳定的SEI。Song S W.(Roles of Oxygen and Interfacial Stabilization in Enhancing the Cycling Ability of Silicon Oxide Anodes for Rechargeable Lithium Batteries[J].Journal of the Electrochemical Society,2013,160(6).)研究发现TMVS可以改善硅体系电池的循环性能。分析认为，TMVS中的硅氧烷官能团与硅负极表面的羟基反应生成Si-O-Si键，进而提高硅负极表面SEI稳定性，改善电池循环性能。
当前，学术界及产业界研究了大量添加剂，但仍未发现一款单一添加该添加剂即可完全满足硅体系锂离子电池对循环性能改善的要求。
在电解液中添加FEC或含有硅氧烷官能团的添加剂如TMVS均可以有效改善硅体系锂离子电池的循环性能，但单一添加剂带来的改善效果有限，尤其是当负极活性物质中硅材料的含量提升后，加入单一添加剂，对电池的循环性能改善不能满足实用需求。
发明内容
本发明的目的在于克服上述负极添加硅系活性材料的二次电池虽然能量密度较高，但循环性能不佳的缺点，而提供一种新的电池非水电解液，负极添加硅系活性材料的二次电池采用该电池非水电解液后，其循环性能得到显著改善。
同时，本发明还提供了含有上述电解液的二次电池。
为实现上述目的，本发明采取的技术方案为：一种电池非水电解液，其包含有机溶剂、电解质盐和添加剂，所述添加剂由硅氧烷官能团化的离子液体和氟代碳酸乙烯酯组成；其中，所述硅氧烷官能团化的离子液体由一价阳离子和一价阴离子组成，所述一价阳离子的结构式如下述式(Ⅰ)或式(∏)所示；
Figure PCTCN2019072454-appb-000001
所述式(Ⅰ)和式(∏)中，R1、R2、R3表示碳原子数为1～8的烷氧基或 碳原子数为1～8的烷基，Z1、Z2表示碳原子数为1～5的直链烷基；且R1、R2、R3中，至少有一个为烷氧基；
所述一价阴离子为PF 6 -、BF 4 -、FSI -或TFSI -。
优选地，所述硅氧烷官能团化的离子液体的结构式如下述式(Ⅲ)、式(Ⅳ)、式(Ⅴ)或式(Ⅵ)所示；
Figure PCTCN2019072454-appb-000002
优选地，所述硅氧烷官能团化的离子液体在电解液中的质量分数为0.5％～15％。
优选地，所述有机溶剂由碳酸乙烯酯、碳酸丙烯酯、碳酸二甲酯、碳酸二乙酯、碳酸甲乙酯、γ-丁内酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、乙酸丁酯、丙酸乙酯、丙酸丙酯、丙酸丁酯中的至少两种组成。
优选地，所述电解质盐为LiPF 6、LiBF 4、LiFSI、LiTFSI、LiBOB、LiODFB、LiPO 2F 2中的至少一种。
优选地，所述电解质盐在电解液中的浓度为0.5～2mol/L。
优选地，所述氟代碳酸乙烯酯在电解液中的质量分数为2％～20％；
另外，本发明还提供了一种二次电池，其包括正极、负极、置于所述正极与负极之间的隔离膜和上述电池非水电解液；其中，所述负极的活性物质含有硅系活性材料。
优选地，所述二次电池为锂离子二次电池。
最后，本发明还提供了上述电池非水电解液在制备二次电池中的应用；其中，所述二次电池的负极活性物质含有硅系活性材料。
与现有技术相比，本发明的有益效果为：本发明的电池非水电解液同时含有硅氧烷官能团化的离子液体和氟代碳酸乙烯酯，这两种物质组合可产生协同作用，有效改善负极添加硅系活性材料的二次电池的循环性能。
具体实施方式
现有技术为改善硅体系二次电池的循环性能，在电解液中添加氟代碳酸乙烯酯(FEC)或含有硅氧烷官能团，但单一添加剂带来的改善效果有限，尤其是当负极活性物质中硅系活性材料的含量提升后，加入单一添加剂，对电池的循环性能改善不能满足实用需求。为了克服现有技术的这一缺陷，本发明提供了一种电池非水电解液，其包含有机溶剂、电解质盐和添加剂，所述添加剂由硅氧烷官能团化的离子液体和氟代碳酸乙烯酯组成；其中，所述硅氧烷官能团化的离子液体由一价阳离子和一价阴离子组成，所述一价阳离子的结构式如下述式(Ⅰ)或式(∏)所示；
Figure PCTCN2019072454-appb-000003
所述式(Ⅰ)和式(∏)中，R1、R2、R3表示碳原子数为1～8的烷氧基或碳原子数为1～8的烷基，Z1、Z2表示碳原子数为1～5的直链烷基；且R1、R2、R3中，至少有一个为烷氧基；
所述一价阴离子为PF 6 -、BF 4 -、FSI -或TFSI -。
研究表明，在电池电解液中将硅氧烷官能团化的离子液体与氟代碳酸乙烯酯组合使用，发挥二者的协同作用，可以取得比单独使用硅氧烷官能团化的离子液体或氟代碳酸乙烯酯更优异的改善效果。本发明硅氧烷官能团化的离子液体与氟代碳酸乙烯酯可能的协同作用机制如下：首先，在电解液浸润过程中，离子液体中的硅氧烷官能团与硅负极表面的羟基反应生成Si-O-Si键，从而使得 离子液体附着在负极硅电极表面，由于离子液体优异的电化学稳定性可以起到对硅材料很好的保护作用。在二次电池化成过程中，氟代碳酸乙烯酯的加入可以得到更均匀稳定的固态电解质层(SEI)，减缓由于循环过程中硅颗粒的膨胀收缩引起的SEI破裂。其次，在循环过程中，当SEI产生裂纹时，由于离子液体在硅表面的附着没有反应电位的条件限制，同时氟代碳酸乙烯酯在硅负极表面的还原电位足够高，二者均可以在第一时间对SEI裂纹进行修复。以上，当硅氧烷官能团化的离子液体与氟代碳酸乙烯酯组合使用，可以明显改善硅体系二次电池循环性能。
本发明的电池非水电解液可通过将其中的各组分混合均匀得到。
在本发明的一个实施例中，所述硅氧烷官能团化的离子液体的结构式如下述式(Ⅲ)、式(Ⅳ)、式(Ⅴ)或式(Ⅵ)所示；
Figure PCTCN2019072454-appb-000004
申请人进一步的研究发现，在其他条件都相同的情况下，含有式(Ⅲ)所示硅氧烷官能团化的离子液体的电池电解液对硅体系二次电池循环性能改善的效果更为明显；因此，优选地，所述硅氧烷官能团化的离子液体的结构式如上述式(Ⅲ)所示。
硅氧烷官能团化的离子液体的黏度较大，其在电解液中的含量对循环改善效果有明显影响，优选地，所述硅氧烷官能团化的离子液体在电解液中的质量分数为0.5％～15％；更优选地，所述硅氧烷官能团化的离子液体在电解液中的质 量分数为2％～10％；更优选地，所述硅氧烷官能团化的离子液体在电解液中的质量分数为5％。当硅氧烷官能团化的离子液体添加量过高时会明显增大电解液的黏度，恶化二次电池的动力学性能，进而恶化二次电池1C/1C的循环性能。例如，当硅氧烷官能团化的离子液体添加量高于15％时，会明显恶化循环改善效果。
在本发明的一个实施例中，所述有机溶剂由碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、碳酸二甲酯(DMC)、碳酸二乙酯(DEC)、碳酸甲乙酯(EMC)、γ-丁内酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、乙酸丁酯、丙酸乙酯、丙酸丙酯和丙酸丁酯中的至少两种组成。例如，有机溶剂可由碳酸乙烯酯(EC)、碳酸丙烯酯(PC)和碳酸二乙酯(DEC)组成，优选地，碳酸乙烯酯(EC)、碳酸丙烯酯(PC)和碳酸二乙酯(DEC)的质量比为碳酸乙烯酯(EC)：碳酸丙烯酯(PC)：碳酸二乙酯(DEC)＝2：3：5。
在本发明的一个实施例中，所述电解质盐为LiPF 6、LiBF 4、LiFSI、LiTFSI、LiBOB、LiODFB、LiPO 2F 2中的至少一种。优选地，所述电解质盐为LiPF 6。
在本发明的一个实施例中，所述电解质盐在电解液中的浓度为0.5～2mol/L。优选地，所述电解质盐在电解液中的浓度为1mol/L。
氟代碳酸乙烯酯的含量对二次电池循环性能改善效果有一定影响，优选地，所述氟代碳酸乙烯酯在电解液中的质量分数为2％～20％；更优选地，所述氟代碳酸乙烯酯在电解液中的质量分数为15％～20％；更优选地，所述氟代碳酸乙烯酯在电解液中的质量分数为15％。且研究表明，氟代碳酸乙烯酯的含量达到25％时，会一定程度恶化循环改善效果。
另外，本发明还提供了一种二次电池，其包括正极、负极、置于所述正极与负极之间的隔离膜和上述电池非水电解液；其中，所述负极的活性物质含有硅系活性材料。
在本发明中，二次电池一般是指能够反复进行充放电的蓄电装置。二次电池有“镍氢”、“镍镉”、“铅酸(铅蓄电池)”、“锂离子(包括锂电池和锂离子聚合物电池)”等。优选地，所述二次电池为锂离子二次电池。优选地，所述二次 电池正极的活性物质为LiNi 0.5Co 0.2Mn 0.3O 2，负极的活性物质为人造石墨、Si/C复合材料。
最后，本发明还提供了上述电池非水电解液在制备二次电池中的应用；其中，所述二次电池的负极活性物质含有硅系活性材料。
为更好地说明本发明的目的、技术方案和优点，下面将结合具体实施例对本发明作进一步说明。在具体实施例中，下述式(Ⅲ)所示硅氧烷官能团化的离子液体简称为离子液体L1；式(Ⅳ)所示硅氧烷官能团化的离子液体简称为离子液体L2；式(Ⅴ)所示硅氧烷官能团化的离子液体简称为离子液体L3；式(Ⅵ)所示硅氧烷官能团化的离子液体简称为离子液体L4。
Figure PCTCN2019072454-appb-000005
实施例1
本发明电池非水电解液的一种实施例，本实施例所述电池非水电解液由有机溶剂、电解质盐和添加剂组成，所述添加剂由硅氧烷官能团化的离子液体和氟代碳酸乙烯酯(FEC)组成。本实施例所述电池非水电解液中各组分的具体物质以及各组分的用量如表1所示。
本实施例所述电池非水电解液的制备方法为：在手套箱或干燥房中，将经过精馏脱水处理的各有机溶剂按比例混合均匀，然后缓慢加入电解质盐，最后按比例加入硅氧烷官能团化的离子液体和氟代碳酸乙烯酯，搅拌混合均匀得最终电池非水电解液。
本实施例的二次电池为锂离子二次电池，其包括正极、负极、置于所述正极与负极之间的隔离膜和本实施例的电池非水电解液。
本实施例的二次电池的制备方法为：将隔离膜(厚度15μm)置于正极极片与负极极片之间，通过卷绕的方式制备方形裸电芯，用铝塑膜复合材料制作包装袋，将裸电芯置入包装袋中封装后得干电芯，干电芯经过烘烤除水、注液、封口、静置、化成、除气封装、分容等工序后得到锂离子二次电池。其中，正极极片的制备方法为：将正极活性材料锂镍钴锰LiNi 0.5Co 0.2Mn 0.3O 2与导电剂super-P、CNT、粘接剂PVDF按质量比96.8:1.5:0.5:1.2混合均匀，加入N-甲基吡咯烷酮(NMP)，经真空搅拌机搅拌混合均匀得正极活性材料浆料。将上述浆料均匀涂覆在铝箔(厚度12μm)集流体两面上，经过烘干、冷压、分切后得正极极片。负极极片的制备方法为：将负极活性材料人造石墨、Si/C复合材料与导电剂super-P、CNT、粘接剂丁苯橡胶(SBR)、羧甲基纤维素钠(CMC)、聚丙烯酸(PAA)按质量比85：9:1.5:0.5:2.2:1.4:0.4混合均匀，加入去离子水，经真空搅拌机搅拌混合均匀得负极活性材料浆料。将上述浆料均匀涂覆在铜箔(厚度8μm)集流体两面上，经过烘干、冷压、分切后得负极极片。
实施例2～4
实施例2～4所述电池非水电解液除组分的具体物质以及各组分的用量与实施例1不同之外，其他均同实施例1。
实施例2～4所述二次电池除电池非水电解液外，其他均实施例1；实施例2～4所述二次电池分别对应含有实施例2～4所述电池非水电解液。实施例2～4所述电池非水电解液与二次电池的制备方法均同实施例1。
实施例2～4所述电池非水电解液中各组分的具体物质以及各组分的用量如表1所示。
同时，测试实施例1～4锂离子二次电池的性能，结果如表1所示。测试的方法为：在25℃的恒温箱中，将上述实施例1～4所得锂离子电池，以1C恒流充电至4.25V，然后恒压充电至电流为0.05C，然后用1C恒流放电至2.75V，如此进行充电/放电循环，记录电池经过200周循环后得容量保持率。
锂离子二次电池200周循环容量保持率(％)＝第200周循环放电容量/第1周循环放电容量*100％
表1
Figure PCTCN2019072454-appb-000006
由表1可见，本发明的电池非水电解液可使二次电池的循环性能得到显著改善。
效果例
为了考察电池非水电解液中添加剂—硅氧烷官能团化的离子液体和氟代碳酸乙烯酯(FEC)(包括具体的物质选择、组分含量)对二次电池循环性能的影 响，本效果例制备了一系列试验组与对照组电池非水电解液和锂离子二次电池，并按照实施例1～4锂离子二次电池性能的测试方法测定了试验组与对照组锂离子二次电池的性能。其中，试验组1的电池非水电解液和锂离子二次电池同实施例1；试验组2～12与对照组1～11的电池非水电解液和锂离子二次电池除添加剂外，其他均同实施例1；各组锂离子二次电池含有相应的电池非水电解液。各试验组与对照组电池非水电解液和锂离子二次电池的制备方法均同实施例1。
各试验组添加剂的组成以及锂离子二次电池的性能如表2所示，表2中FEC和硅氧烷官能团化的离子液体的百分数表示的是它们在电解液中的重量百分比。
表2
Figure PCTCN2019072454-appb-000007
Figure PCTCN2019072454-appb-000008
根据表2，比较试验组1～4可知，含有离子液体L1的电池非水电解液对硅体系二次电池循环性能改善的效果较含有离子液体L2～L4的电池非水电解液更为明显。比较试验组1、5、6、7和对照组5可知，硅氧烷官能团化的离子液体含量对二次电池循环性能改善效果有明显影响，当其含量为2％～10％时，二次电池循环性能改善效果更为明显，尤其是其含量为5％时，改善效果最为明显；而当其添加量达到20％时，会明显恶化循环改善效果。比较试验组1、8、9和对照组3、4可知，氟代碳酸乙烯酯的含量对二次电池循环性能改善效果有一定影响，其含量为15％～20％时，二次电池循环性能改善效果更为明显，尤其是其含量为15％时，改善效果最为明显。分别比较(a)试验组1、对照组1和对照组2，(b)试验组10、对照组6和对照组7，(c)试验组11、对照组8和对照组9，(d)试验组12、对照组10和对照组11，可以发现在本发明范围内，将硅氧烷官能团化的离子液体与FEC作为添加剂组合使用，可取得比单一添加硅氧烷官能团化的离子液体或FEC更好的循环改善效果，且改善程度较大，这是本领域的技术人员难以预料到的。
最后所应当说明的是，以上实施例仅用以说明本发明的技术方案而非对本 发明保护范围的限制，尽管参照较佳实施例对本发明作了详细说明，本领域的普通技术人员应当理解，可以对本发明的技术方案进行修改或者等同替换，而不脱离本发明技术方案的实质和范围。

Claims (10)

  1. 一种电池非水电解液，其特征在于，包含有机溶剂、电解质盐和添加剂，所述添加剂由硅氧烷官能团化的离子液体和氟代碳酸乙烯酯组成；其中，所述硅氧烷官能团化的离子液体由一价阳离子和一价阴离子组成，所述一价阳离子的结构式如下述式(Ⅰ)或式(∏)所示；
    Figure PCTCN2019072454-appb-100001
    所述式(Ⅰ)和式(∏)中，R1、R2、R3表示碳原子数为1～8的烷氧基或碳原子数为1～8的烷基，Z1、Z2表示碳原子数为1～5的直链烷基；且R1、R2、R3中，至少有一个为烷氧基；
    所述一价阴离子为PF 6 -、BF 4 -、FSI -或TFSI -。
  2. 如权利要求1所述的电池非水电解液，其特征在于，所述硅氧烷官能团化的离子液体的结构式如下述式(Ⅲ)、式(Ⅳ)、式(Ⅴ)或式(Ⅵ)所示；
    Figure PCTCN2019072454-appb-100002
  3. 如权利要求1或2所述的电池非水电解液，其特征在于，所述硅氧烷官能团化的离子液体在电解液中的质量分数为0.5％～15％。
  4. 如权利要求1所述的电池非水电解液，其特征在于，所述有机溶剂由碳酸乙烯酯、碳酸丙烯酯、碳酸二甲酯、碳酸二乙酯、碳酸甲乙酯、γ-丁内酯、乙酸甲酯、乙酸乙酯、乙酸丙酯、乙酸丁酯、丙酸乙酯、丙酸丙酯、丙酸丁酯中的至少两种组成。
  5. 如权利要求1所述的电池非水电解液，其特征在于，所述电解质盐为LiPF 6、LiBF 4、LiFSI、LiTFSI、LiBOB、LiODFB、LiPO 2F 2中的至少一种。
  6. 如权利要求1或5所述的电池非水电解液，其特征在于，所述电解质盐在电解液中的浓度为0.5～2mol/L。
  7. 如权利要求1所述的电池非水电解液，其特征在于，所述氟代碳酸乙烯酯在电解液中的质量分数为2％～20％。
  8. 一种二次电池，其特征在于，包括正极、负极、置于所述正极与负极之间的隔离膜和权利要求1～7任一项所述的电池非水电解液；其中，所述负极的活性物质含有硅系活性材料。
  9. 如权利要求8所述的二次电池，其特征在于，所述二次电池为锂离子二次电池。
  10. 权利要求1～7任一项所述的电池非水电解液在制备二次电池中的应用；其中，所述二次电池的负极活性物质含有硅系活性材料。
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