Layered Titanium Sulfide Cathode for All‐Solid‐State Magnesium Batteries

Abstract

AbstractMagnesium solid‐state batteries attract significant attention as a future mean of energy storage. Here we present the first cathode study of an inorganic all‐solid‐state magnesium battery using a magnesium metal anode, a nanocomposite electrolyte Mg(BH4)2 ⋅ 1.6NH3‐MgO (75 wt %), and a layered titanium disulfide (TiS2) as cathode active material. The structural transformations of TiS2 particles with different sizes are investigated at different stages of battery life. Reversible Mg2+ intercalation occurs via three structurally distinct phases of MgxTiS2, identified by powder X‐ray diffraction. Magnesium intercalates initially on octahedral sites and at higher depth of discharge on tetrahedral sites in the interlayers of TiS2, which leads to an expansion initially mainly along the c‐axis and later along both the a‐ and c‐axes. A maximum discharge capacity of 172 mAh g−1 (Δx=0.36 in MgxTiS2) is observed for smaller TiS2 particles. Parasitic reactions could be reduced by decreasing the cut‐off voltage by a constant current constant voltage cycling procedure. The chemical diffusion coefficient of the entire cell is found from galvanostatic intermittent titration technique experiments to be in the order of 10−15 to 10−19 cm2 s−1.