Entropy-Driven Modulation of Ion Clustering and Polymer Crystallinity for Low-Temperature Lithium Metal Batteries.

Abstract

Solid-state Li metal batteries have garnered significant attention for their intrinsic safety and high energy density. Among various solid-state electrolytes, solid polymer electrolytes (SPEs) offer their excellent processability and interfacial compatibility but suffer from the formation of large ionic clusters and crystallization, which hinder Li+ transport and desolvation, particularly at low temperatures (e.g., deep-sea conditions). In this study, a multicomponent strategy is adopted to enhance the configurational entropy of SPEs, resulting in a 2-fold reduction in Li cluster size and suppression of polymer crystallization. These changes facilitate rapid desolvation and promote the formation of a high-entropy solid electrolyte interphase. Owing to these benefits, the resulting SPEs exhibit an 8.5-fold improvement in ionic conductivity at -20 °C (0.17 mS cm-1). The Li/Cu cells exhibit an impressive average Coulombic efficiency (CE) of 98.59% over 300 cycles at room temperature, and maintain nearly unchanged CE even after a temperature drop to -20 °C. Furthermore, the Li/LiFePO4 cells (N/P = 4) achieve a 13-fold capacity improvement and an average capacity retention of 91.49% after 500 cycles at -20°C (over 248 days). This strategy builds a new approach for high performance SPEs for practical low-temperature operation.