低温电解液的构筑及Li+迁移强化新方法

低温锂离子电池被誉为电化学储能领域“皇冠上的明珠”，低温下Li+在电解液和电极/电解液界面的传输是其发展的主要瓶颈。与电解液常用的羧酸酯、碳酸酯类相比，CH3O(CH2CH2O)nCH3（Gn）结构多元醚具有熔点低、蒸汽压低、介电常数高等特点，但由于与石墨相容性差而很少被用于锂离子电池电解液。本项目拟引入“solvent in salt”的概念，将多元醚与特殊结构的锂盐复合，从而制备出具有[Li(Gn)][X]结构的离子液体，提高多元醚的电化学稳定性、解决相容性差的问题，同时将具有不同长度醚链的离子液体复配，引入具有较低熔点的有机溶剂如DEC、EMC，以降低电解液粘度和熔点、提升电导率，加入具有特定功能的添加剂，从而得到具有液程范围宽、电化学稳定性好、饱和蒸汽压低、可在-60~60℃的温度范围内工作的安全型低温离子液体电解液，建立低温下强化Li+迁移新方法，破除低温锂离子电池研究的瓶颈。

Low temperature operated lithium ion battery (LIB) was call “the pearl on the crown” in electrochemical energy storage area. The low transport speed of lithium ions in both electrolyte and electrode/electrolyte interface under low temperature is the main bottleneck which hindering the research of low temperature operated LIB. Polyether with the structure of CH3O(CH2CH2O)nCH3 (short as Gn) often shows lower melting point, lower vapour pressure as well as higher dielectric constant compared to common esters or carbonates which usually be used in electrolytes for LIB, while it was rarely used for its poor compatibility with graphite. We intend to introduce the concept of “solvent in salt”, which means to mix polyether with equal molar of lithium salt with proper ionize capability to form a special ionic liquid with the structure of [Li(Gn)][X], moreover, we will try to combine theoretical calculation and experimental research to improve the electrochemical stability of polyether and settle the compatibility issue. Meantime, we will try to mix [Li(Gn)][X] with different n, which means the length of ether chain, to reduce the viscosity and melting point, as well as to improve the conductivity. And by introduce organic solvents with low melting point, such as DEC or EMC, to further improve the low temperature performances of the electrolyte. Functional additives will also be used to enhance the control of solid state interface between electrode and electrolyte. The final goal is to obtain electrolyte with wide liquid range, good electrochemical stability, low vapour pressure, and capable of work between the temperature range of -60~60℃. On which we will try to issue a new method to reinforce the low temperature Li+ transportation, and breakthrough the bottle neck in low temperature lithium ion battery development.