Highly conductive 3D dielectric skeleton for high voltage solid-state lithium metal batteries

High activation energy of Li⁺ transport caused by space charge layer in ceramic-polymer composite electrolytes results in low ion conductivity. Introducing dielectric materials is a promising approach to mitigate this issue. Here, we propose a three-dimensional coupling network for constructing a robust Li transporting pathway by fabricating a BaTiO₃-Li_0.3La_0.567TiO₃ dielectric skeleton membrane using ultrafast high-temperature sintering and tape casting. The dielectric skeleton is mechanically strong even with a thickness of ∼30 μm. Meanwhile, due to the short sintering time of ∼3 s, the grain sizes of the dielectric skeleton are constrained to ∼180 nm, increasing the polymer filling volume to achieve the “percolation point” in composite materials. The 3D dielectric coupling effects help to mitigate the space charge and acquire a homogeneous Li⁺ distribution across the interface, decreasing the activation energy of Li⁺transporting from 0.34 eV to 0.29 eV. After polarized at an electric field, the ion conductivity of the dielectric composite electrolytes improves from 0.19 mS·cm^-1 to 0.24 mS·cm^-1. The symmetric cell using the polarized dielectric electrolytes exhibits excellent cycling stability for ∼430 h at 0.2 mA·cm^-2, ∼130 h at 0.4 mA·cm^-2, and ∼70 h at 1 mA·cm^-2. The full cell LiFePO₄/polarized dielectric electrolytes/Li exhibits high-rate performance of nearly 1C (1C=170 mA·g^-1) and long-term cycling stability (>300 cycles at 50 mA·g^-1). Pairing with high-voltage cathode LiNi_0.8Co_0.1Mn_0.1O₂, the battery can cycle stably for ∼100 cycles at 20 mA·g^-1, with a Coulombic efficiency of 98 %. These results open a new avenue for the application of composite electrolytes in energy-storage devices.