Designing Advanced Electrolytes for Lithium Secondary Batteries Based on the Coordination Number Rule

Advanced electrolytes play a key role in the development of next-generation lithium secondary batteries. However, many strong polar solvents, as a major component of the electrolyte, are incompatible with the commercialized graphite anode in Li-ion batteries. In this work, we propose a new concept of the coordination number (CN) rule to tune electrochemical compatibility of electrolytes by regulating the ion–solvent-coordinated (ISC) structure. Based on this rule, we introduced the low-coordination-number solvents (LCNSs) into the high-coordination-number solvent (HCNS) electrolytes to induce anions into the first solvation shell of Li+, forming the anion-induced ISC (AI-ISC) structure. The HCNS-LCNS electrolytes with the AI-ISC structure show enhanced reduction stability, enabling reversible lithiation/delithiation of the graphite anode. Infrared analysis and theoretical calculations confirm the working mechanism of the electrochemical compatibility in the HCNS-LCNS electrolytes based on the CN rule. Therefore, the CN rule provides guidance for the design of highly stable and multifunctional electrolytes to develop next-generation lithium secondary batteries.