Solvation Chemistry Reimagined: LiPF6-Enabled Suppression of Gas Evolution for Ultra-Stable 200 Ah Anode-Free Lithium-Metal Batteries.

Abstract

Anode-free lithium-metal batteries (AFBs) offer an attractive pathway to achieve cell-level energy densities >500 Wh kg^-1 but suffer from rapid degradation driven by parasitic electrolyte decomposition, gas evolution, and unstable interphases. Here, we report a solvation-structure engineering strategy using trace LiPF₆ additive in localized high-concentration electrolytes (LHCEs) to regulate homogeneous Li deposition and stabilize electrode-electrolyte interfacial chemistry. Molecular dynamics simulations and spectroscopic analyses reveal a synergistic PF₆ ^--FSI^- coordination that dramatically enriches aggregate (AGG) species in the Li⁺ solvation sheath, increasing AGG populations from 17% to 93% with only 1 wt.% LiPF₆. Owing to its persistent stability, this LiPF₆-derived AGG-dominated solvation suppresses ether-solvent reduction and CH₄ generation, forming an inorganic-rich solid-electrolyte interphase/cathode-electrolyte interphase. AFBs with optimized electrolyte achieve substantially improved performance, including a significant reduction in high-temperature gas evolution alongside increases in cycle life of 64% at 45°C and 28% at 25°C. When scaled to 240 Ah blade cells, this optimized electrolyte delivers stable cycling for nearly 100 cycles at 80% DOD and 45°C with negligible swelling and >1260 Wh L^-1 volumetric energy density. This study demonstrates a practical and scalable electrolyte design principle that overcomes the key barriers to commercial deployment of large-format AFBs.