Copper sulfides (Cu2-xS, where x denotes position defects) with different structures of the S2- sublattice, such as cubic digenite and hexagonal chalcocite, have been investigated as cathode materials for magnesium (Mg) batteries. Rechargeable performance is only achieved using a cubic digenite cathode; however, using hexagonal chalcocite cathode yields poor rechargeable performance. The face-centered cubic S2- sublattice in cubic digenite, which enables Cu+ and Mg2+ ions to be displaced from each other without causing the lattice to collapse, could play a key role in improving the performance of rechargeable cathodes.