High Energy Density Solid State Lithium Metal Batteries Enabled by Sub‐5 µm Solid Polymer Electrolytes

Solid-state batteries (SSBs) are considered as the most promising next-generation high-energy-density energy storage devices due to their ability in addressing the safety concerns from organic electrolytes and enabling energy dense lithium anodes. To ensure the high energy density of SSBs, solid-state electrolytes (SSEs) are required to be thin and light-weight, and simultaneously offer a wide electrochemical window to pair with high-voltage cathodes. However, the decrease of SSE thickness and delicate structure may increase the cell safety risks, which is detrimental for the practical application of SSBs. Herein, to demonstrate a high-energy-density SSB with sufficient safety insurance, an ultrathin (4.2 µm) bilayer SSE with porous ceramic scaffold and double-layer Li⁺ -conducting polymer, is proposed. The fire-resistant and stiff ceramic scaffold improves the safety capability and mechanical strength of the composite SSE, and the bilayer polymer structure enhances the compatibility of Li metal anode and high-voltage cathodes. The 3D ceramic facilitates Li-ion conduction and regulates Li deposition. Thus, high energy density of 506 Wh kg^-1 and 1514 Wh L^-1 is achieved based on LiNi_0.8 Co_0.1 Mn_0.1 O₂ (NCM811) cathodes with a low N/P ratio and long lifespan over 3000 h. High-energy-density anode-free cells are further demonstrated.