Extended Electrochemical Window of Solid Electrolytes via Heterogeneous Multilayered Structure for High‐Voltage Lithium Metal Batteries

In response to the call for safer high-energy-density storage systems, high-voltage solid-state Li metal batteries have attracted extensive attention. Therefore, solid electrolytes are required to be stable against both Li anode and high-voltage cathodes; nevertheless, the requirements still cannot be completely satisfied. Herein, a heterogeneous multilayered solid electrolyte (HMSE) is proposed to broaden electrochemical window of solid electrolytes to 0-5 V, through different electrode/electrolyte interfaces to overcome the interfacial instability problems. Oxidation-resistance poly(acrylonitrile) (PAN) is in contact with the cathode, while reduction tolerant polyethylene glycol diacrylate contacts with Li metal anode. A Janus and flexible PAN@Li_1.4 Al_0.4 Ge_1.6 (PO₄ )₃ (80 wt%) composite electrolyte is designed as intermediate layer to inhibit dendrite penetration and ensure compact interface. Paired with LiNi_0.6 Co_0.2 Mn_0.2 O₂ and LiNi_0.8 Co_0.1 Mn_0.1 O₂ cathodes, which are rarely used in solid-state batteries, the solid-state Li metal batteries with HMSE exhibit excellent electrochemical performance including high capacity and long cycle life. Besides, the Li||Li symmetric batteries maintain a stable polarization less than 40 mV for more than 1000 h under 2 mA cm^-2 and effective inhibition of dendrite formation. This study offers a promising approach to extend the applications of solid electrolytes for high-voltage solid-state Li metal batteries.