Rational Lithium Salt Selection Principle for Designing High-Entropy Electrolytes toward High-Performance Lithium Metal Batteries
Yingchun Xia, Da Zhu, Wenhui Hou, Pan Zhou, Yu Ou, Haiyu Zhou, Xuan Song, Weili Zhang, Shuaishuai Yan, Yang Lu, Xiao Ma, Yunxiong Zeng, Hong Xu, Kai Liu
Abstract
High-entropy electrolytes (HEEs), typically formed by mixing over four types of salts or solvents, have attracted considerable attention due to their diverse solvation microenvironments that improve the cyclability of high-energy lithium metal batteries (LMBs). However, knowledge of salt screening is limited beyond merely increasing the number of salts in electrolyte formulations to increase the solvation configurations. Here, we present a new design principle for constructing an HEE (LTFA-LDFN) by selecting lithium salts containing amphiphilic anions with asymmetric Li + -chelating capabilities (i.e., trifluoroacetate) together with anions featuring multiple Li + coordination sites (i.e., difluorophosphate and nitrate). The amphiphilic trifluoroacetate, containing both a high donor number and a noncoordinating moiety, competitively coordinates with Li + from poorly soluble lithium difluorophosphate and lithium nitrate, disrupting their inherent three-dimensional cation–anion network and enhancing solubility in carbonate solvents. Molecular dynamics calculations further reveal that LTFA-LDFN supports 64 distinct Li + solvation configurations within the top 80% of all configurations, with 71.2% being anion-dominated─unlike the fully solvent-coordinated configurations in conventional carbonate electrolytes. As quantified using the Boltzmann equation, LTFA-LDFN reached a solvation configurational entropy of up to 6.5 × 10 –23 J K –1 . Such high-entropy solvation characteristics enhance the compatibility of Li||NCM811 cells with carbonate electrolytes, achieving stable cycling for over 1000 cycles with 80.2% capacity retention at room temperature under 1 C and more than 300 cycles with over 80% retention at 60 °C under 2 C. Our findings underscore the significant potential of delicate anion engineering to achieve high-entropy-like configuration diversity, paving a new way for advancements in LMBs and beyond.