Double-Weak Coordination Electrolyte Enables 5 V and High Temperature Lithium Metal Batteries

Layered oxide cathodes offer high specific capacity and operating voltage, whereas constructing a stable interface to maintain the stable operation of high-voltage cathodes under high charge state and elevated temperature remains challenging. Herein, a double-weak coordination strategy which triggers by single solvent and dilute is designed. The solvent tris(2,2,2-trifluoroethyl) phosphate (TFEP) exhibits weak lithium coordination due to the partial fluorination of the alkyl chain, while the dilute ethoxy(pentafluoro)cyclo triphosphazene (PFPN) is involved in the inner solvation structure by weak lithium-TFEP coordination and its mild lithium affinity. This double-weak coordination increases the local anion concentration within the solvation structure, reduces the desolvation barrier of Li⁺, optimizes the desolvation and leads to a robust, hybrid organic-inorganic interface. Specifically, the DWCE electrolyte shows remarkable improvements in cycling stability under 60 °C for 4.7 V Li(50 µm)||NMC811 (1.84 mAh cm^-2) cell, 4.8  and 5.0 V Li(50 µm)||LRMO (1.75 mAh cm^-2) cells. Meanwhile, 5.2 Ah Li||LRMO pouch cell using DWCE achieves a high energy density of 495 Wh kg^-1 and DWCE-based Ah-level pouch cell also presents significantly enhanced safety under thermal runaway condition. This work provides a novel but universal double-weak coordination policy initiated by solvent and diluent for high energy density lithium metal batteries.