WO2022032802A1 - 一种低温电解液和锂离子电池 - Google Patents

一种低温电解液和锂离子电池 Download PDF

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WO2022032802A1
WO2022032802A1 PCT/CN2020/116259 CN2020116259W WO2022032802A1 WO 2022032802 A1 WO2022032802 A1 WO 2022032802A1 CN 2020116259 W CN2020116259 W CN 2020116259W WO 2022032802 A1 WO2022032802 A1 WO 2022032802A1
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lithium
low
electrolyte
temperature
carbonate
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PCT/CN2020/116259
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English (en)
French (fr)
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孙晓玉
李炳江
王立群
郑浪
易祖良
刘奕凯
叶鑫
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常州赛得能源科技有限公司
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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
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0569—Liquid materials characterised by the solvents
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • H01M2300/0028—Organic electrolyte characterised by the solvent
    • H01M2300/0037—Mixture of solvents
    • H01M2300/004—Three solvents
    • 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 invention relates to the technical field of chemical power sources, in particular to a low-temperature electrolyte and a lithium ion battery.
  • Low-temperature lithium battery is a special battery specially developed for the inherent low-temperature defect of chemical power supply performance.
  • the important feature of low-temperature battery is that it can be charged and discharged normally at lower temperature.
  • the application field of ion batteries is of strategic significance to the development of lithium ion batteries.
  • the first object of the present invention is to provide a low-temperature electrolyte, which has good electrical conductivity at low temperature and is beneficial to the formation of the SEI film.
  • the technical scheme of the present invention is: a low-temperature electrolyte, including a solvent, an additive and a lithium salt;
  • the solvent is a mixture of ethylene carbonate, carbonate and chain carboxylate
  • the additive is a sulfur-containing additive.
  • the chain carboxylate is one or more of methyl acetate, ethyl acetate, methyl formate, methyl propionate, ethyl propionate, methyl butyrate, and ethyl butyrate.
  • the carbonate is one or more of ethyl methyl carbonate, propylene carbonate, dimethyl carbonate and diethyl carbonate.
  • the mass ratio of EC:carbonate solvent:chain carboxylate in the solvent is 1:1:1 or 5:2:3 or 5:3:2 or 4:3:3.
  • the sulfur-containing additive is one or more of ethyl sulfite, propyl sulfite, dimethyl sulfite, and diethyl sulfite.
  • the sulfur-containing additive accounts for 1%-5% of the total mass of the electrolyte.
  • the lithium salt is one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis-oxalateborate, lithium perchlorate, lithium hexafluoroarsenate, and lithium trifluoromethanesulfonate.
  • the lithium salt is a mixture of lithium hexafluorophosphate and lithium tetrafluoroborate; the lithium salt accounts for 1%-3% of the mass of the electrolyte.
  • lithium hexafluorophosphate is preferably used in combination with lithium tetrafluoroborate, wherein lithium tetrafluoroborate has low sensitivity to moisture and high low-temperature conductivity, but its own conductivity is lower than that of lithium hexafluorophosphate. The combination of the two can significantly improve the low-temperature performance of the electrolyte.
  • the second object of the present invention is to provide a lithium ion battery, which improves the low temperature performance without sacrificing the normal temperature electrochemical performance.
  • a lithium ion battery comprising a positive electrode, a negative electrode, an electrolyte and a separator; the electrolyte is the electrolyte described in any one of claims 1 to 8.
  • the thickness of the membrane is between 10-14 ⁇ m.
  • Wet-coated ceramic and PVDF diaphragms are used for the diaphragm; ceramics can increase the liquid retention capacity, and PVDF can increase the adhesion between the pole pieces, reduce the internal resistance of the gap, improve the ion-conducting performance of the system, and help the rapid conduction of ions at low temperatures; among them , the thickness of the diaphragm is between 10-14 ⁇ m; the film is too thick, which is not conducive to the rapid passage of lithium ions, and the diaphragm is too thin, which is easy to short-circuit, preferably 12 ⁇ m.
  • the negative electrode is composed of graphite, conductive agent, dispersant, and binder; according to the mass fraction, graphite is 92%-97%, conductive agent 1-3%, dispersant 1-2%, and binder 1-3%.
  • the principle of graphite selection the particles are appropriately small; the OI value of the powder and the pole piece is controlled; the soft carbon coating reduces the Rct of the material; the degree of graphitization increases the diffusion rate of Li + at low temperature.
  • Further preferred graphite is artificial graphite, its D50 is between 5-10um, the surface is covered with soft carbon, and the powder OI value is between 1-3;
  • the positive electrode is composed of a main material, a conductive agent, a dispersant, and a binder; according to the mass fraction: the main material is a mixed ternary material of lithium manganate, 10-30% of lithium manganate, and 63%-87% of ternary material. , Conductive agent 1-2%, dispersant 1-2%, binder 1-3%;
  • the positive electrode selects lithium manganate with ternary material; lithium manganate has a spinel structure, and its structure is stable and has good low temperature performance, but its capacity is not high, and it needs to be matched with a high-capacity ternary material to improve the overall positive electrode. capacity;
  • lithium manganate adopts small particle structure, D50 is between 5-12um, and the proportion of lithium manganate in the positive electrode is 10%-30%;
  • the ternary material is one or more of NCM523, NCM622, NCM811, and NCA, and it is required to be a small particle material, and the D50 is between 5-15um;
  • the conductive agent is one or more of SP, KS-6, conductive graphite, carbon nanotubes, graphene, carbon fiber VGCF, wherein preferably SP mixed VGCF, SP mixed VGCF can form a stable conductive network inside the negative electrode, It can still conduct electrons quickly at low temperature;
  • the dispersant is sodium carboxymethyl cellulose CMC
  • the binder is one or more substances that can improve the adhesion force of the pole piece, such as polyvinyl alcohol PVA, polytetrafluoroethylene PTFE, styrene butadiene rubber SBR, polyvinylidene fluoride PVDF, etc.
  • the electrolyte is selected from a solvent with a lower melting point, and at the same time, a lithium salt and an additive with better conductivity at low temperature are selected to configure an electrolyte with relatively low viscosity and relatively high conductivity at low temperature;
  • ethylene carbonate has Good film-forming effect, but the melting point of ethylene carbonate is relatively high, so it needs to be matched with low-melting point additives and substances with lower melting point in carbonate, which has good fluidity at low temperature, and can be used as a co-solvent to improve the low-temperature performance of the system;
  • the electrolyte additive is selected from sulfur-containing additives.
  • the sulfur-containing additives have good low-temperature performance, and can still form a dense SEI film on the graphite surface at low temperature, and has good anti-oxidation performance. SEI film can improve the low temperature cycle performance of the battery;
  • the combination of solvent and additive in the present invention does not cause any burden on the environment, and has no impact on the production rhythm of the battery; at the same time, the parameters of the solvent and additive are within a reasonable range, and the battery is safe;
  • the battery of the present invention has a cycle life of more than 550 weeks at room temperature. When the temperature is lowered to -20°C, the cycle performance is maintained at about 400 weeks. Compared with the cycle life level at room temperature, it is less affected by low temperature attenuation. The invention effectively improves the electrochemical performance of the battery at low temperature, and the battery can still maintain a good cycle life at low temperature.
  • Fig. 1 is the low-temperature discharge curve of the lithium-ion battery obtained from Example 1 to Example 6;
  • Fig. 2 is the low temperature cycle curve of the lithium ion battery prepared in Example 1 to Example 6;
  • FIG. 3 is the normal temperature cycle curve of the lithium ion batteries prepared in Examples 1 to 6.
  • FIG. 3 is the normal temperature cycle curve of the lithium ion batteries prepared in Examples 1 to 6.
  • the invention discloses a low-temperature electrolyte and a lithium ion battery using the low-temperature electrolyte.
  • the specific composition and mass fraction of the positive electrode, negative electrode, electrolyte and diaphragm of the lithium ion battery are as follows:
  • Negative electrode graphite 93%, of which the graphite D50 is 7.7 ⁇ m, the surface is coated with soft carbon, the powder OI value is 2.8; graphene 1.5%; carbon nanotubes 1.5%; CMC 2%; PTEF 2%;
  • Positive electrode lithium manganate 20%, NCA 74%, carbon nanotubes 2%, CMC 2%, PVDF 2%; the D50 of lithium manganate is 6.7 ⁇ m, and the D50 of NCA is 6.9 ⁇ m;
  • the diaphragm is made of wet-coated ceramic and PVDF diaphragm with a thickness of 12 ⁇ m.
  • the positive electrode is subjected to stirring the main material, coating, cold pressing, slitting, and filming to obtain a negative electrode pole piece;
  • the negative electrode is subjected to graphite stirring, coating, cold pressing, slitting, and filming to obtain a negative electrode pole piece;
  • the positive and negative pole pieces together with the separator are subjected to a lamination process to obtain a bare cell, and the bare cell is encapsulated, liquid-injected, allowed to stand, formed, and volume-distributed to obtain a finished battery.
  • Negative electrode graphite 95%; SP1%; VGCF1%; CMC 1%; PVA 2%; among them, the D50 of graphite is 5.5um, and the OI value is 1.7;
  • D50 of lithium manganate is 5.5um
  • D50 of NCA is 5.8um
  • the diaphragm is made of wet-coated ceramic and PVDF diaphragm with a thickness of 12 ⁇ m.
  • Negative electrode graphite 94%; KS-6 1.5%; VGCF 1%; CMC 1.5%; SBR 2%; D50 of graphite is 6.3um, OI value is 2.2;
  • Positive electrode lithium manganate 30%; NCA 63%; graphene 2%; CMC 2%; PVDF 3%; wherein, the D50 of lithium manganate is 7.4um, and the D50 of NCA is 8.1um.
  • Negative electrode graphite 96%; SP1%; VGCF 1%; CMC 1%; SBR 1%; D50 of graphite is 9.3um, OI value is 2.5;
  • Positive electrode lithium manganate 30%; NCA 67%; VGCF 1%; CMC 1%; PVDF 1%; D50 of lithium manganate is 9.4um, and D50 of NCA is 13.9um.
  • Negative electrode graphite 97%; SP1%; CMC 1%; SBR 1%; among them, the D50 of graphite is 5.9um, and the OI value is 2.5;
  • Positive electrode lithium manganate 30%; NCA 66%; KS-6 1%; CMC 1%; PVDF 2%; among them, the D50 of lithium manganate is 8.4um, and the D50 of NCA is 10.3um.
  • Negative electrode graphite 93%; graphene 1.5%; carbon nanotubes 1.5%; CMC 2%;
  • Positive electrode NCA 94%; carbon nanotubes 2%; CMC 2%; PVDF 2%.
  • the lithium-ion batteries prepared in Examples 1 to 6 were subjected to a low-temperature discharge test, a low-temperature cycle and a normal-temperature cycle test, and the specific test methods were as follows:
  • the batteries of Examples 1 to 5 have a 1C discharge capacity greater than 1400mAh and a capacity retention rate greater than 70% at -40°C; at -20°C, the 0.5C/0.5C cycle life is greater than 370 weeks, which is far greater than that of the battery in Example 6. For 220 weeks, the cycle performance is improved by 68%, which shows that the low-temperature battery proposed by the present invention has good low-temperature electrical performance.
  • the low-temperature battery proposed by the present invention has good electrical performance under low temperature test, and can not only discharge at -40°C, but also has a discharge capacity of more than 70%. It can be charged and discharged in a cycle at -20 °C, and the cycle life is more than 370 weeks, which is far superior to existing batteries.
  • the present invention successfully solves the limitation of low temperature on the application of lithium ion batteries from four aspects: negative electrode, positive electrode, electrolyte and separator.
  • the negative electrode is optimized for its particle size, preferably artificial graphite-coated soft carbon;
  • the positive electrode is made of small particle materials;
  • the electrolyte is selected from a solvent with a lower melting point, and at the same time, a lithium salt and additives with better conductivity at low temperature are used to configure a low temperature
  • the diaphragm is selected to be coated with PVDF on both sides, which can narrow the gap between the pole pieces and reduce the internal resistance of the gap.
  • a lithium-ion battery that can be discharged at a high rate and has a long cycle life.

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Abstract

本发明公开一种低温电解液包括溶剂、添加剂和锂盐；溶剂为乙烯碳酸脂、碳酸脂和链状羧酸酯的混合物；添加剂为含硫添加剂；本发明还公开使用该低温电解液的锂离子电池；本发明的低温电解液低温下导电性好，利于SEI膜的形成；本发明的锂离子电池提升低温性能的同时，不牺牲常温电化学性能。

Description

一种低温电解液和锂离子电池 技术领域
本发明涉及化学电源技术领域，特别是涉及一种低温电解液和锂离子电池。
背景技术
低温锂电池是针对化学电源的性能所固有的低温缺陷而专门研发的一种特种电池，低温电池重要的特点在于可以在较低的温度下正常的进行充放电，此电池的开发，可拓宽锂离子电池的应用领域，对锂离子电池的发展具有战略意义。
现今市场上的电池多数在低温下放不出电，尤其在-40℃下放电更是锂离子电池面对的一项极大的挑战，常规的锂离子电池在-40℃下，存在严重的浓差极化，电池无法工作，且在-20℃下循环充放电使用寿命低，严重阻碍了锂离子电池的应用。
发明内容
本发明的第一个目的在于提供一种低温电解液，该发明低温下导电性好，利于SEI膜的形成。
为解决此技术问题，本发明的技术方案是：一种低温电解液，包括溶剂、添加剂和锂盐；
溶剂为乙烯碳酸脂、碳酸脂和链状羧酸酯的混合物；
添加剂为含硫添加剂。
优选所述链状羧酸酯为乙酸甲酯、乙酸乙酯、甲酸甲酯、丙酸甲酯、丙酸乙酯、丁酸甲酯、丁酸乙酯中的一种或几种。
优选碳酸脂为碳酸甲乙酯，丙烯碳酸脂，二甲基碳酸脂，二乙基碳酸中的 一种或几种。
优选溶剂中EC:碳酸脂溶剂:链状羧酸酯的质量比为1:1:1或者5:2:3或者5：3：2或4：3：3。
优选所述含硫添加剂为亚硫酸乙酯、亚硫酸丙酯、亚硫酸二甲酯、亚硫酸二乙酯中的一种或几种。
优选含硫添加剂占所述电解液总质量的1％-5％。
优选所述锂盐为六氟磷酸锂、四氟硼酸锂、双草酸硼酸锂、高氯酸锂、六氟砷酸锂、三氟甲磺酸锂中的一种或几种。
进一步优选所述锂盐为六氟磷酸锂和四氟硼酸锂的混合物；所述锂盐占所述电解液质量的1％-3％。本发明中优选六氟磷酸锂搭配四氟硼酸锂使用，其中四氟硼酸锂对水分敏感度低，低温导电率高，但自身导电率不及六氟磷酸锂，二者搭配，电解液低温性能显著提升。
本发明的第二个目的在于提供一种锂离子电池，该发明提升低温性能的同时，不牺牲常温电化学性能。
为解决此技术问题，本发明的技术方案是：一种锂离子电池，包括正极、负极、电解液和隔离膜；所述电解液为权1至权8任一项所述的电解液。
优选所述隔膜厚度在10-14μm之间。隔膜选用湿法涂覆陶瓷和PVDF隔膜；陶瓷可以增加保液量，PVDF可以增加极片间粘结性，减小间隙内阻，提升体系导离子性能，有助于低温下离子快速传导；其中，隔膜厚度在10-14μm之间；膜太厚，不利于锂离子快速通过，隔膜太薄，容易短路，优选12μm。
优选，负极由石墨、导电剂、分散剂、粘结剂组成；按照质量分数，石墨92％-97％、导电剂1-3％、分散剂1-2％、粘结剂1-3％。
石墨选择原则：颗粒适当的小；控制粉体和极片OI值；软碳包覆降低材料的Rct；降低石墨化度提升材料低温时Li +的扩散速度。进一步优选石墨优选人造石墨，其D50在5～10um之间，表面软碳包覆，粉体OI值在1-3之间；
本发明中正极由主材、导电剂、分散剂、粘结剂组成；按照质量分数：主材为锰酸锂混合三元材料，锰酸锂10-30％，三元材料63％-87％、导电剂1-2％、分散剂1-2％、粘结剂1-3％；
本发明中正极选用锰酸锂搭配三元材料；锰酸锂为尖晶石结构，其结构稳定，具有良好的低温性能，但是其容量不高，需要搭配高容量的三元材料提升正极的整体容量；
其中，锰酸锂选用小颗粒结构，D50在5-12um之间，正极中锰酸锂占比在10％-30％；
其中，三元材料为NCM523、NCM622、NCM811、NCA中的一种或几种，要求为小颗粒材料，D50在5-15um之间；
其中，导电剂为SP、KS-6、导电石墨、碳纳米管、石墨烯、碳纤维VGCF中的一种或几种，其中优选SP混合VGCF，SP混合VGCF可在负极内部形成稳定的导电网络，低温下仍可以快速的传导电子；
其中，分散剂为羧甲基纤维素钠CMC；
其中，粘结剂为聚乙烯醇PVA，聚四氟乙烯PTFE，丁苯橡胶SBR，聚偏氟乙烯PVDF等可提升极片粘结力物质的一种或几种。
通过采用上述技术方案，本发明的有益效果是：
1、本发明中电解液选用熔点较低的溶剂，同时选用低温下导电性较好的锂盐和添加剂，配置出低温下具有比较低的粘度和比较高电导率的电解液；乙烯 碳酸脂具有良好的成膜效果，但乙烯碳酸脂的熔点较高，需搭配低熔点添加剂，配合碳酸脂中熔点较低的物质，低温下流动性好，作为共溶剂改善体系的低温性能；
2、本发明中电解液添加剂选用含硫添加剂，含硫添加剂具有良好的低温性能，在低温下仍然可以在石墨表面形成一层致密的SEI膜，并且具有良好的抗氧化性能，低温下致密的SEI膜可提升电池的低温循环性能；
3、本发明中通过溶剂和添加剂的配合，不对环境造成任何负担，对电池的生产节拍并无影响；同时，溶剂与添加剂参数都在合理范围内，电池安全；
4、本发明的电池在常温下，循环寿命在550周以上，当温度降低至-20℃后，循环性能则保持在400周左右，与常温循环寿命水平相比，受低温影响衰减较小，本发明有效改善电池低温下的电化学性能，电池在低温下，依旧可以保持良好的循环寿命。
从而实现本发明的上述目的。
附图说明
图1是实施例1至实施例6制得锂离子电池的低温放电曲线；
图2是实施例1至实施例6制得锂离子电池的低温循环曲线；
图3是实施例1至实施例6制得锂离子电池的常温循环曲线。
具体实施方式
为了进一步解释本发明的技术方案，下面通过具体实施例来对本发明进行详细阐述。
实施例1
本发明公开一种低温电解液和使用该低温电解液的锂离子电池，锂离子电 池的正极、负极、电解液和隔膜的具体组成和质量分数如下：
电解液：溶剂96％，其中EC(乙烯碳酸脂):EMC(碳酸甲乙酯):MF(甲酸甲酯)＝1:1:1；PS(亚硫酸丙酯)2％；LiPF 61％，LiBF 41％；
负极：石墨93％，其中石墨D50为7.7μm，表面软碳包覆，粉体OI值2.8；石墨烯1.5％；碳纳米管1.5％；CMC 2％；PTEF 2％；
正极：锰酸锂20％，NCA74％、碳纳米管2％、CMC 2％、PVDF 2％；其中锰酸锂的D50为6.7μm，NCA的D50为6.9μm；
隔膜选用湿法涂覆陶瓷和PVDF隔膜，厚度12μm。
本实施例锂离子电池的具体制备方式如下：
正极经过搅拌主材、涂布、冷压、分条，制片得到负极极片；
负极经过搅拌石墨、涂布、冷压、分条，制片得到负极极片；
将正负极极片与隔膜一起经过叠片工艺得到裸电芯，裸电芯经过封装、注液、静置、化成、分容后，得到成品电池。
实施例2
本实施例与实施例1的主要区别在于：锂离子电池的正极、负极、电解液和隔膜的具体组成和质量分数如下：
电解液：溶剂98％，其中，EC:EMC:MA(乙酸甲酯)＝1:1:1；ES(亚硫酸乙酯)1％；LiPF 61％；
负极：石墨95％；SP1％；VGCF1％；CMC 1％；PVA 2％；其中，石墨的D50为5.5um，OI值为1.7；
正极：锰酸锂的D50为5.5um，NCA的D50为5.8um；
锰酸锂10％；NCA85％；SP 1％；CMC 2％；PVDF 2％；
隔膜选用湿法涂覆陶瓷和PVDF隔膜，厚度12μm。
实施例3
本实施例与实施例1的主要区别在于：锂离子电池的正极、负极、电解液和隔膜的具体组成和质量分数如下：
电解液：溶剂96％，其中，EC:PC(丙烯碳酸脂):MB(丁酸甲酯)＝4:3:3,DMS(亚硫酸二甲酯)3％，LiPF 62％LiBOB 1％；
负极：石墨94％；KS-6 1.5％；VGCF 1％；CMC 1.5％；SBR 2％；其中石墨的D50为6.3um，OI值为2.2；
正极：锰酸锂30％；NCA63％；石墨烯2％；CMC 2％；PVDF 3％；其中，锰酸锂的D50为7.4um，NCA的D50为8.1um。
实施例4
本实施例与实施例1的主要区别在于：锂离子电池的正极、负极、电解液和隔膜的具体组成和质量分数如下：
电解液：溶剂94％，其中EC:DEC(二乙基碳酸脂):EP(丙酸乙酯)＝5:3:2；DES(亚硫酸二乙酯)4％；LiPF 61％，LiClO 41％；
负极：石墨96％；SP1％；VGCF 1％；CMC 1％；SBR 1％；其中石墨的D50为9.3um，OI值为2.5；
正极：锰酸锂30％；NCA67％；VGCF 1％；CMC 1％；PVDF 1％；其中锰酸锂的D50为9.4um，NCA的D50为13.9um。
实施例5
本实施例与实施例1的主要区别在于：锂离子电池的正极、负极、电解液和隔膜的具体组成和质量分数如下：
电解液：溶剂93％，其中EC:DMC(二甲基碳酸脂):EA(乙酸乙酯)＝5:2:3；DMS(亚硫酸二甲酯)5％；LiBF 41％，LiAsF 61％；
负极：石墨97％；SP1％；CMC 1％；SBR 1％；其中，石墨的D50为5.9um，OI值为2.5；
正极：锰酸锂30％；NCA66％；KS-6 1％；CMC 1％；PVDF 2％；其中，锰酸锂的D50为8.4um，NCA的D50为10.3um。
实施例6
本例与实施例1的主要区别如下，其中百分数为质量的分数：
电解液：溶剂96.5％，其中EC:EMC:MF＝1:1:1；PS 2％；LiPF 61.5％；
负极：石墨93％；石墨烯1.5％；碳纳米管1.5％；CMC 2％；PTEF 2％；其中，石墨的D50为10.3um，OI值为2.8；
正极：NCA94％；碳纳米管2％；CMC 2％；PVDF 2％。
将实施例1至6制得的锂离子电池进行低温放电测试、低温循环和常温循环测试，具体的测试方法如下：
低温放电测试：
常温下给电池满充，然后放入-40℃环境下，静置5h，进行1C放电测试；
低温循环测试：
将电池放入-20℃环境中，静置5h，然后进行0.5C/0.5C循环测试，容量衰减至80％结束；
常温循环测试：
将电池放入25℃环境中，静置5h，然后进行0.5C/0.5C循环测试，容量衰减至80％结束。
结合图1至图3可知，实施例1至实施例6，在常温下，循环寿命在550周以上，实施例间差别较小，当温度降低至-20℃后，循环性能明显下降，而实施例的循环性能则保持在400周左右，与常温循环寿命水平相比，受低温影响衰减较小，由此说明本发明提出的方案，可有效改善电池低温下的电化学性能，电池在低温下，依旧可以保持良好的循环寿命。
实施例1至5的电池在-40℃下，1C放电容量大于1400mAh，容量保持率大于70％；在-20℃下，0.5C/0.5C循环寿命大于370周，远远大于实施例6电池的220周，循环性能提升68％，从而说明本发明提出的低温电池具有良好的低温电性能。
现今市场上的电池多数在低温下放不出电，尤其在-40℃下放电更是锂离子电池面对的一项极大的挑战，常规的锂离子电池在-40℃下，存在严重的浓差极化，电池无法工作，且在-20℃下循环充放电使用寿命低，严重阻碍了锂离子电池的应用。本发明提出的低温电池，低温下测试电性能良好，不仅可以在-40℃下放电，且放电容量在70％以上，说明本发明提出的低温电池可以支持-40℃严峻环境使用，同时，可以在-20℃的环境下循环进行充放电，循环寿命大于370周，远远优于现有电池。
结合实施例1至5的电池数据可知，本发明从负极、正极、电解液及隔离膜四个方面成功解决了低温对锂离子电池应用的限制。其中，负极优化其颗粒粒径，优选人造石墨包覆软碳；正极选用小颗粒材料；电解液选用熔点较低的溶剂，同时选用低温下导电性较好的锂盐和添加剂，配置出低温下具有比较低的粘度和比较高电导率的电解液；隔膜选择双面涂PVDF隔膜，可缩小极片间隙，降低间隙内阻，在低温下，帮助离子快速传导，四个方面结合，制备出低温下可大倍率放电、具有长循环寿命的锂离子电池。

Claims (10)

  1. 一种低温电解液，其特征在于：包括溶剂、添加剂和锂盐；
    溶剂为乙烯碳酸脂、碳酸脂溶剂和链状羧酸酯的混合物；
    添加剂为含硫添加剂。
  2. 如权利要求1所述的一种低温电解液，其特征在于：所述链状羧酸酯为乙酸甲酯、乙酸乙酯、甲酸甲酯、丙酸甲酯、丙酸乙酯、丁酸甲酯、丁酸乙酯中的一种或几种。
  3. 如权利要求1所述的一种低温电解液，其特征在于：碳酸脂为碳酸甲乙酯，丙烯碳酸脂，二甲基碳酸脂，二乙基碳酸中的一种或几种。
  4. 如权利要求1所述的一种低温电解液，其特征在于：溶剂中乙烯碳酸脂:碳酸脂溶剂:链状羧酸酯的质量比为1:1:1或者5:2:3或者5：3：2或4：3：3。
  5. 如权利要求1所述的一种低温电解液，其特征在于：所述含硫添加剂为亚硫酸乙酯、亚硫酸丙酯、亚硫酸二甲酯、亚硫酸二乙酯中的一种或几种。
  6. 如权利要求1所述的一种低温电解液，其特征在于：含硫添加剂占所述电解液总质量的1％-5％。
  7. 如权利要求1所述的一种低温电解液，其特征在于：所述锂盐为六氟磷酸锂、四氟硼酸锂、双草酸硼酸锂、高氯酸锂、六氟砷酸锂、三氟甲磺酸锂中的一种或几种。
  8. 如权利要求1所述的一种低温电解液，其特征在于：所述锂盐为六氟磷酸锂和四氟硼酸锂的混合物；所述锂盐占所述电解液质量的1％-3％。
  9. 一种锂离子电池，其特征在于：包括正极、负极、电解液和隔离膜；所述电解液为权1至权8任一项所述的电解液。
  10. 如权利要求9所述的一种锂离子电池，其特征在于：所述隔膜厚度在 10-14μm之间。
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