Hydrogen‐Deficient Chain‐Like Molecular Structure Confined Hydride Electrolyte for High‐Voltage All‐Solid‐State Lithium Metal Batteries

The practical application of LiBH₄ in all-solid-state Li metal batteries (ASSLMBs) is hindered by low Li-ion conductivity at room temperature, poor oxidative stability, and severe dendrite growth. Herein, porous [LiNBH]_n with a hydrogen-deficient chain-like molecular structure are designed for in situ space-confining LiBH₄, which enables strong attraction of negatively charged H^δ- atoms of [BH₄]^- anions by Li⁺ of [LiNBH]_n chains that weakens Coulombic interaction between Li⁺ and [BH₄]^- anions and hence promotes Li ion diffusion. Additionally, the electron-withdrawing effect of [LiNBH]_n chains induces the local electron localization of LiBH₄ that enhances oxidative stability of LiBH₄. Therefore, the Li ion conductivity of LiBH₄ reaches 2.2 × 10^-4 S cm^-1 at 30 °C, nearly 4 orders of magnitude higher than that of LiBH₄, with a voltage window of 5 V. Moreover, the interaction between Li metal and [LiNBH]_n chains results in in situ formation of ultrathin layer composed of Li₃N and LiB alloys that hinders Li dendrites growth, leading to a critical current density value of 7.5 mA cm^-2 and a cycling life of 100 h at 4 mA cm^-2 with an overpotential of 125 mV. Hence, LiCoO₂|LiBH₄-70LiNBH|Li cell at 0.5 C deliver a high capacity of 89.5 mA h g^-1 after 400 cycles.