Achieving a Stable 518 Wh kg⁻¹ Li Metal Pouch Cell via SEI Reconstruction Engineering for High Li⁺ Conductive Hetero-Grain Boundaries

Abstract

Carbonate electrolytes are highly corrosive to lithium (Li) metal, leading to side reactions, dendrite growth and dead Li, which pose critical challenges in achieving stable high-energy Li metal batteries under lean electrolyte. Here, we introduce a molecular surface reconstruction strategy to engineer a LiF/Li2O-rich solid electrolyte interphase (SEI) featuring high Li⁺-conductive hetero-grain boundaries. By spraying fluorinated ether-based carboxylic acid (PFOA) onto Li metal surface, we eliminate the native oxide layer and engineer a self-optimized inorganic interphase that integrates exceptional mechanical robustness with rapid Li⁺ transport along the hetero-grain boundaries. This dual functional interphase effectively suppresses Li dendrite growth and dead Li accumulation, as evidenced by microscopy visualization and isotope-labeled mass spectrometry titration (MST) techniques, with MST quantifying a significant reduction in dead Li and LiH within the modified SEI. Benefiting from the surface reconstruction strategy, a 5.8 Ah Li metal pouch cell achieves a high energy density of 518 Wh kg-1 (based on the total mass of the cell) with ultra-lean carbonate electrolyte (1.12 g Ah-1) and maintains stable cycling over 100 cycles. Our findings on surface reconstruction for high Li+ conductive hetero-grain boundary passivation layer points to a new pathway towards achieving stable cycling for energy dense Li metal batteries.