High Entropy Electrolytes for Practical Lithium Metal Batteries

Abstract

Electrolyte engineering is crucial for improving battery performance, particularly for lithium metal batteries. Recent advances in electrolytes have greatly improved cyclability by enhancing electrochemical stability at the electrode interfaces, but concurrently achieving high ionic conductivity has remained challenging. Here we report an electrolyte design strategy for enhanced lithium metal batteries by increasing the molecular diversity in electrolytes, which essentially leads to high entropy electrolytes (HEEs). We find that in weakly solvating electrolytes, the entropy effect reduces ion clustering while preserving the characteristic anion-rich solvation structures, which is characterized by synchrotron-based X-ray scattering and molecular dynamics simulations. Electrolytes with smaller-sized clusters exhibit a 2-fold improvement in ionic conductivity compared to conventional weakly-solvating electrolytes, enabling stable cycling at high current densities up to 2C (6.2 mA cm-2) in anode-free LiNi0.6Mn0.2Co0.2 (NMC622) || Cu pouch cells. The efficacy of the design strategy is verified by performance improvements in three disparate weakly solvating electrolyte systems.