Room-Temperature Solid-State Lithium-Ion Battery Using a LiBH₄-MgO Composite Electrolyte

LiBH₄ has been widely studied as a solid-state electrolyte in Li-ion batteries working at 120 °C due to the low ionic conductivity at room temperature. In this work, by mixing with MgO, the Li-ion conductivity of LiBH₄ has been improved. The optimum composition of the mixture is 53 v/v % of MgO, showing a Li-ion conductivity of 2.86 × 10^-4 S cm^-1 at 20 °C. The formation of the composite does not affect the electrochemical stability window, which is similar to that of pure LiBH₄ (about 2.2 V vs Li⁺/Li). The mixture has been incorporated as the electrolyte in a TiS₂/Li all-solid-state Li-ion battery. A test at room temperature showed that only five cycles already resulted in cell failure. On the other hand, it was possible to form a stable solid electrolyte interphase by applying several charge/discharge cycles at 60 °C. Afterward, the battery worked at room temperature for up to 30 cycles with a capacity retention of about 80%.