Cascade Solvation Refinement for High-Voltage Lithium Metal Batteries.

Abstract

Unstable interfacial chemistry in Li metal batteries originates from the limited accessibility of anions at electrified interfaces, even in the electrolytes designed with anion-coordinated solvation structures. Here we report a cascade solvation refinement (CSR) strategy that enables molecular-level control over the size and dynamics of anion-coordinated Li⁺ clusters. This design principle is governed by the synergy between anion-anion repulsion and average polarizability, which together dictate cluster miniaturization and anion-exchange dynamics. By sequentially incorporating, bis(oxalate)borate (BOB^-) and bis(trifluoromethanesulphonyl)imide (TFSI^-) into a bis(fluorosulfonyl)imide (FSI^-) saturated electrolyte, the solvation environment evolves toward compact, highly dynamic Li⁺-anion clusters with accelerated anion-exchange kinetics. The BOB^- and TFSI^- co-refined electrolyte sustains continuous anion availability at electrode interfaces, facilitates the formation of robust inorganic-rich interphases, and suppresses solvent-dominated side reactions. Notably, the refined solvation structure also compresses the electric double layer, enabling anion-coordinated solvation structures to approach the electrode surface more closely and construct inorganic interphases. Consequently, 4.4 V Li-metal pouch cells with practical Ah-level capacities (>4 Ah), as well as the large-format 20 Ah cells, exhibit markedly extended cycling stability and high gravimetric energy density (>540 Wh kg^-1). These results highlight the CSR approach as a powerful platform for advancing practical, high-energy batteries.