570 Wh kg⁻¹‐Grade Lithium Metal Pouch Cell with 4.9V Highly Li⁺ Conductive Armor‐Like Cathode Electrolyte Interphase via Partially Fluorinated Electrolyte Engineering

Abstract Lithium‐rich manganese‐based layered oxides (LRMOs) are promisingly used in high‐energy lithium metal pouch cells due to high specific capacity/working voltage. However, the interfacial stability of LRMOs remains challenging. To address this question, a novel armor‐like cathode electrolyte interphase (CEI) model is proposed for stabilizing LRMO cathode at 4.9 V by exploring partially fluorinated electrolyte formulation. The fluoroethylene carbonate (FEC) and tris (trimethylsilyl) borate (TMSB) in formulated electrolyte largely contribute to the formation of 4.9 V armor‐like CEI with LiB_xO_y and Li_xPO_yF_z outer layer and LiF‐ and Li₃PO₄‐rich inner part. Such CEI effectively inhibits lattice oxygen loss and facilitates the Li⁺ migration smoothly for guaranteeing LRMO cathode to deliver superior cycling and rate performance. As expected, Li||LRMO batteries with such electrolyte achieve capacity retention of 85.7% with high average Coulomb efficiency (CE) of 99.64% after 300 cycles at 4.8 V/0.5 C, and even obtain capacity retention of 87.4% after 100 cycles at higher cut‐off voltage of 4.9 V. Meanwhile, the 9 Ah‐class Li||LRMO pouch cells with formulated electrolyte show over thirty‐eight stable cycling life with high energy density of 576 Wh kg⁻¹ at 4.8 V.