High Entropy Electrolytes for Practical Lithium Metal Batteries

Electrolyte engineering is a critical approach to improve battery performance, particularly for lithium metal batteries. In this work, we introduce the concept of high entropy electrolytes (HEEs) that achieve improved ionic conductivity while maintaining excellent electrochemical stability. We find that increasing the molecular diversity and concomitantly the mixing entropy of weakly solvating electrolytes can reduce ion clustering while retaining anion-rich solvation structure, confirmed through synchrotron-based X-ray scattering and molecular dynamics simulations. Less clustered electrolytes exhibit higher diffusivity and ionic conductivity, enabling high current density cycling up to 2C (> 6 mA cm-2) for up to ~80 cycles in anode-free NMC-Cu pouch cells. We substantiate the generality of the concept by verifying performance improvement in three disparate electrolyte systems. This work highlights a large unexplored design space of HEEs that can improve electrolyte properties for lithium metal batteries.