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

Ca(BH₄)₂ can operate successfully in an all-solid-state Li-ion cell in electrode compositions without solid electrolyte. LiBH₄ electrolyte is formed in situ in the electrode, enabling the active material to be maximised and improving the energy density of the battery.

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.

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