Fully Lithiated Li_xTiO_2−δ Layer Coated Separator for Securing a Lithium-less Anode in an Ester-Based Electrolyte

Ester-based electrolytes, known for their cost-effectiveness and wide voltage windows, face compatibility challenges with lithium metal (Li 0 ), leading to irreversible decomposition and dendrite growth, which impede their application in high-energy-density lithium metal batteries (LMBs). This work develops an electrochemical prelithiation strategy to obtain a fully lithiated Li x TiO 2−δ coated polypropylene (PP) separator with oxygen vacancies, preventing the depletion of limited Li 0 resources while promoting uniform Li 0 plating. Moreover, the dense closest packing structure of Li x TiO 2−δ can reduce the contact area and side reaction between Li 0 and ester-based electrolytes, stabilizing the solid electrolyte interface (SEI) on Li 0 . Symmetric Li cells operating under 1.0 mA cm –2 and 1.0 mA h cm –2 demonstrate a long cycle life exceeding 5000 h. Full cells with NMC811 cathodes (4.3 mA h cm –2 areal capacity) and Li anodes (40 μm, N/P ratio ≈ 1.9) maintain 90% capacity retention after 100 cycles with an average Coulombic efficiency (CE avg ) exceeding 99.85%. The anode-free Cu|NMC811 cells also show a CE avg of 98.36% after 60 cycles. This work provides a cost-effective strategy to enhance the safety, cycling stability, and energy density of next-generation LMBs.