Stable functional electrode–electrolyte interface formed by multivalent cation additives in lithium-metal anode batteries†

Li-metal anodes face challenges in terms of cyclability due to non-uniform deposition morphology and progressive electrolyte decomposition. Here, we discover the effects of multivalent cation salts (Ca²⁺, Ba²⁺, La³⁺, Ce³⁺) as electrolyte additives for Li-metal anodes in exemplary [TFSI]⁻/EC–PC electrolytes. These additives induce strong Coulomb interactions that alter the solvation environment in the electrolyte, promoting the direct coordination of cations with [TFSI]⁻. This modification of the solvation structure increases the desolvation energy, effectively slowing down the Li⁺ depletion at the electrode surface and flattening the deposition morphology. Besides, the coordinated [TFSI]⁻ tends to participate in the formation of the solid-electrolyte interphase (SEI), increasing the fluoride concentration ratio. Furthermore, these multivalent cations are also incorporated into the SEI and play an important role in its formation. In particular, the lanthanide additives form La–O and La–F bonds instead of Li-related bonds, which would effectively improve the uniformity and stability of the SEI, enabling the reversible formation of a flat and dense Li metal layer on the Cu foil current collector. In addition, full-cell tests with LiFePO₄ cathodes show that the lanthanide additives mitigate the internal resistance increase on Li metal anodes during cycling and drastically improve capacity retention in either “anode-free” or excess Li configurations.