Fully Lithiated Li_<i>x</i>TiO_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 (Li⁰), 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_<i>x</i>TiO_2-δ coated polypropylene (PP) separator with oxygen vacancies, preventing the depletion of limited Li⁰ resources while promoting uniform Li⁰ plating. Moreover, the dense closest packing structure of Li_<i>x</i>TiO_2-δ can reduce the contact area and side reaction between Li⁰ and ester-based electrolytes, stabilizing the solid electrolyte interface (SEI) on Li⁰. 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.