Duncan H. Gregory

All‐solid‐state batteries have gained considerable attention due to their high safety and energy density. However, solid state electrolytes which contribute to the ionic conductivity component of a composite electrode, are not utilized during the electrode reaction and cannot directly contribute to capacity. This study focuses on decreasing the amount of electrolyte in the electrode by utilizing Ca(BH 4 ) 2 as an active electrode material. In this work, the charge‐discharge properties of Ca(BH 4 ) 2 as an electrode material were determined for the first time. The lithiation of the Ca(BH 4 ) 2 anode creates LiBH 4 within the electrode mixture, providing new Li‐ion conduction pathways within the composite electrode in situ . An electrode fabricated only from Ca(BH 4 ) 2 and acetylene black (AB) showed an initial capacity of 473 mAh g −1 at 120 °C, which is comparable to the performance obtained from a composite electrode additionally containing electrolyte. Evidently, Ca(BH 4 ) 2 is a promising candidate negative electrode for increased energy density all‐solid‐state Li‐ion batteries.