Copper Tetraselenophosphate Cathode for Rechargeable Magnesium Batteries: A Redox-Active Polyatomic Anion Strategy to Design the Cathode Material

Rechargeablemagnesium batteries attract interest asadvantageousenergy-storage devices, but the application is being hampered by thedeficiency of suitable cathodes. The traditional method to weakenthe interaction between bivalent Mg2+ cations and the cathodematerial is to increase the anion radius, but excessive expansionof the anion would lead to a decrease of the theoretical capacityand offset the performance improvement. Herein, a new strategy usinga redox-active polyatomic anion is developed in terms of copper tetraselenophosphate(Cu3PSe4) fabricated by the PSe4 (3-) anion. The covalent P-Se bond facilitatesthe negative charge delocalization of the PSe4 (3-) anion and weakens the interaction with Mg2+ cations,which result in rapid solid-phase Mg2+ diffusion kinetics.The PSe4 (3-) anion also provides extracapacities by reversible valence state change of the P element. Cu3PSe4 delivers a high Mg-storage capacity of 225mAh g(-1) at 50 mA g(-1) and a superiorrate performance of 62 mAh g(-1) at 5000 mA g(-1), as well as a stable cyclability of 500 cycles. Theredox-active polyatomic anion strategy herein opens a new avenue forthe exploration of magnesium battery cathodes with a comprehensiveconsideration of kinetic performance and theoretical capacity.

Automated summary

Rechargeable magnesium batteries are limited by the lack of suitable cathodes. A new strategy using a redox-active polyatomic anion, copper tetraselenophosphate (Cu3PSe4), effectively weakens the interaction between magnesium ions and the cathode material, improving the battery's performance.