A conductive selenized polyacrylonitrile cathode in nucleophilic Mg2+/Li+ hybrid electrolytes for magnesium–selenium batteries

Abstract

Rechargeable magnesium–selenium (Mg–Se) batteries are promising electrochemical systems with higher energy density than traditional magnesium batteries. It has been widely accepted that electrophilic selenium cathodes can only be chemically compatible with non-nucleophilic electrolytes. Herein, we report for the first time on Mg–Se batteries containing a selenized polyacrylonitrile (Se/PAN) cathode, Mg anode and nucleophilic electrolyte. The Se/PAN composite with a moderate Se content (45.37 wt%) exhibits high rate capacity and cycling stability in an easily prepared (PhMgCl)₂–AlCl₃ based electrolyte. It delivers an initial discharge capacity of 338.2 mA h g⁻¹ based on the mass of the whole composite at a rate of 100 mA g⁻¹, and the capacity can be maintained at around 188.4 mA h g⁻¹ after 100 cycles. Even at a high rate of 400 mA g⁻¹, a capacity of 118.3 mA h g⁻¹ can be obtained after 800 cycles with an inappreciable capacity decay of 0.021% per cycle, which is comparable to that of previously reported Mg–Se batteries using non-nucleophilic electrolytes. The excellent performance is attributed not only to the structural advantage of the material, but to the compatible electrolyte. Well trapped Se_n chains in the polymer backbone facilitate electron/ion transport and improve reaction kinetics, leading to high reactivity and utilization of Se with suppressed shuttle effect. In addition, the polymer backbone could buffer the volume changes during the electrochemical process and mitigate the structural degradation. Furthermore, the effective SEI film preserves the cathode and prevents it from irreversible reaction with the electrolyte. This work proposes combining a conductive Se/PAN cathode and a compatible electrolyte to promote the performance of Mg–Se batteries, with a view to sparking intense research interest in Mg–Se batteries with easily prepared nucleophilic electrolytes.