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.