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

Abstract Magnesium 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 Mg_xTiS₂, 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 Mg_xTiS₂) 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.