Layered Titanium Sulfide Cathode for All‐Solid‐State Magnesium Batteries
Lasse N. Skov, Jakob B. Grinderslev, Torben R. Jensen
Abstract
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(BH 4 ) 2 ⋅ 1.6NH 3 ‐MgO (75 wt %), and a layered titanium disulfide (TiS 2 ) as cathode active material. The structural transformations of TiS 2 particles with different sizes are investigated at different stages of battery life. Reversible Mg 2+ intercalation occurs via three structurally distinct phases of Mg x TiS 2 , 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 TiS 2 , 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 (Δ x =0.36 in Mg x TiS 2 ) is observed for smaller TiS 2 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 cm 2 s −1 .