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

Abstract

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 Hδ- 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.