Zou Yuxi, Cheng Fangyuan, Lu Yu, Xu Yue, Fang Chun, Han Jiantao
State Key Laboratory of Material Processing and Die & Mould Technology, School of Materials Science and Engineering, Huazhong University of Science and Technology, Wuhan, 430074, P. R. China.
Small. 2023 Apr;19(14):e2203394. doi: 10.1002/smll.202203394. Epub 2023 Feb 2.
The electrochemical performances of lithium metal batteries are determined by the kinetics of interfacial de-solvation and ion transport, especially at low-temperature environments. Here, a novel electrolyte that easily de-solvated and conducive to interfacial film formation is designed for low-temperature lithium metal batteries. A fluorinated carboxylic ester, diethyl fluoromalonate (DEFM), and a fluorinated carbonate, fluoroethylene carbonate (FEC) are used as solvents, while high concentrated lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is served as the solute. Through tailoring the electrolyte formulation, the lithium ions in the high concentrated fluorinated carboxylic ester electrolyte are mainly combined with anions, which weakens the bonding strength of lithium ions and solvent molecules in the solvation structure, beneficial to the de-solvation process at low temperature. The fluorinated carboxylic ester (FCE) electrolyte enables the LiFePO (LFP) | Li half-cell achieves a high capacity of 91.9 mAh g at -30 °C, with high F content in the interface. With optimized de-solvation kinetics, the LFP | Li full cell remains over 100 mAh g at 0 °C after cycling 100 cycles. Building new solvents with outstanding low-temperature properties and weaker solvation to match with Li metal anode, this work brings new possibilities of realizing high energy density and low temperature energy storage batteries.
锂金属电池的电化学性能由界面去溶剂化和离子传输的动力学决定，尤其是在低温环境下。在此，为低温锂金属电池设计了一种易于去溶剂化且有利于界面膜形成的新型电解质。一种氟化羧酸酯，即氟代丙二酸二乙酯（DEFM），和一种氟化碳酸酯，即氟代碳酸乙烯酯（FEC）用作溶剂，而高浓度的双（三氟甲烷磺酰）亚胺锂（LiTFSI）用作溶质。通过调整电解质配方，高浓度氟化羧酸酯电解质中的锂离子主要与阴离子结合，这削弱了溶剂化结构中锂离子与溶剂分子的键合强度，有利于低温下的去溶剂化过程。氟化羧酸酯（FCE）电解质使LiFePO（LFP）|Li半电池在-30°C下实现了91.9 mAh g的高容量，界面中氟含量高。通过优化去溶剂化动力学，LFP|Li全电池在0°C下循环100次后仍保持超过100 mAh g的容量。构建具有优异低温性能和较弱溶剂化作用的新型溶剂以匹配锂金属负极，这项工作为实现高能量密度和低温储能电池带来了新的可能性。
