Over 500 Wh kg ^–1 Solid-State Lithium Metal Batteries with Long Cycling Stability Using <i>In Situ</i> Polymerized Electrolyte

Lithium metal batteries (LMBs) are regarded as the "holy grail" of next-generation energy storage systems due to their potential for high energy density. However, uncontrolled lithium dendrite growth on lithium metal anodes leads to poor cycling stability and serious safety risks, hindering their practical deployment. Herein, we design an <i>in situ</i> polymerized POSS-based gel polymer electrolyte (POSS-GPE) that exhibits high ionic conductivity (3.04 mS cm^-1 at room temperature), excellent oxidative stability (>4.9 V vs Li⁺/Li), broad compatibility with diverse electrode materials, and intrinsic flame retardancy. The POSS-GPE establishes an anion-rich solvation environment that promotes the formation of robust, anion-derived electrode-electrolyte interphase on both the cathode and anode, thus mitigating interfacial degradation. As a result, LiNi_0.8Co_0.1Mn_0.1O₂|POSS-GPE|Li (50 μm) full cell delivers long-term cycling stability of 500 cycles with 87.3% capacity retention. Furthermore, a 6.08 Ah pouch cell with lean electrolyte (1.40 g Ah^-1) achieves a remarkable energy density of 511.2 Wh kg^-1 and cycles stably for 70 cycles at 4.6 V, representing the best balance between cycling performance and energy density for polymer-electrolyte-based LMBs. The high-energy-density pouch cells also demonstrate superior safety in nail-penetration tests. This work presents a promising strategy for developing practical high-energy-density and high-safety LMBs.