High area-capacity Mg batteries enabled by sulfur/copper integrated cathode design

Rechargeable Mg batteries potentially display lower cost and competitive energy density compared with their Li-ion counterparts. However, the practical implementation of high area-capacity cathodes still remains a formidably challenging task. This work presents the sulfur/copper integrated cathodes fabricated by the conventional blade-coating process and slurry-dipping method. The sulfur/copper foil integrated cathodes deliver a high area-capacity of 2.6 mAh cm⁻² after 40 cycles, while the sulfur/copper-foam integrated cathode exhibits an ultrahigh area-capacity of 35.4 mAh cm⁻², corresponding to 743.1 Wh L⁻¹ at the electrode level (1.5 times higher than the LiCoO₂-graphite system). The in-situ formed copper sulfide intermediates with sufficient cation defects can act as functional intermediates to regulate the sulfur electrochemistry during the first discharge process. The subsequent cycles are operated by the reversible displacement reaction between Mg-ions and copper sulfide active substances. In particular, the copper ions prefer to extrude along the [001] direction in copper sulfides lattice and simultaneously the rock-salt MgS crystals are generated. Besides, the nonuniform surface topography of the cycled Mg-metal anode, caused by the spatial inhomogeneity in current distribution, is demonstrated to lead to the battery performance degradation for high area-capacity Mg batteries.