Room Temperature Operation and High Cycle Stability of an All-Solid-State Lithium Battery Fabricated by Cold Pressing Using Soft Li₂OHBr Solid Electrolyte

Lithium-rich antiperovskites (Li3-xOHxX (X = Cl, Br)) are considered as promising electrolyte candidates for all-solid-state lithium secondary batteries with Li metal as the negative electrode owing to their soft nature and similarity to sulfide-based solid electrolytes. However, it has been reported that all-solid-state batteries with Li3-xOHxX exhibit low cycling stability. Although the reasons for this are not fully understood, one possibility could be the electrochemical instability of Li3-xOHxX. In this work, the relationship between the decomposition of Li2OHBr and battery performance was investigated. First, the electrochemical potential window of Li2OHBr was experimentally determined to be 1.7-3.5 V vs Li/Li+. Next, all-solid-state batteries composed of Li/Li2OHBr/Fe2(MoO4)3 were fabricated by pressing at room temperature, and operated between 2.7 and 3.2 V at 25 °C. The battery exhibited high stability over 60 cycles while retaining near theoretical capacity. Finally, the charge-discharge characteristics were measured with the charging cutoff voltage changed stepwise from 3.2 to 3.9 V. Interestingly, high cycle stability was observed even when the Li2OHBr electrolyte decomposed, suggesting that the solid electrolyte decomposition is not the dominant factor in the degradation of all-solid-state batteries for this class of electrolyte materials, due to the formation of a protective interface layer.