In situ Electrolyte Design: Understanding the Prospects and Limitations of a High Capacity Ca(BH₄)₂ Anode for All Solid State Batteries

Abstract 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(BH₄)₂ as an active electrode material. In this work, the charge‐discharge properties of Ca(BH₄)₂ as an electrode material were determined for the first time. The lithiation of the Ca(BH₄)₂ anode creates LiBH₄ within the electrode mixture, providing new Li‐ion conduction pathways within the composite electrode in situ. An electrode fabricated only from Ca(BH₄)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(BH₄)₂ is a promising candidate negative electrode for increased energy density all‐solid‐state Li‐ion batteries.