Synergy of electrolyte manipulation and separator functionalization enables ultralong-life nonaqueous magnesium-organic batteries

Abstract

Organic molecules with redox centers have emerged as promising cathode materials for rechargeable magnesium batteries (RMBs), owing to their rich natural resources, high capacity, and sustainability. However, their application has been severely plagued by their high solubility and poor conductivity. Herein, we propose a dual-pronged strategy to mitigate these issues faced by phenazine (PZ) electrodes by employing the ionic liquid (IL) N-butyl-N-methyl-piperidinium bis((trifluoromethyl)sulfonyl)imide (PP14TFSI) as an electrolyte additive and coating a graphene/polyvinyl pyrrolidone (graphene@PVP) composite layer onto a commercial glass fiber (GF) separator. The addition of highly polar PP14TFSI with high ion conductivity and high viscosity into the electrolyte can mitigate the dissolution of the organic electrode, and catalyze the dissociation of Mg–Cl in large Mg_xCl_y^2x−y clusters to expedite reaction kinetics. Furthermore, the graphene@PVP layer which served as a barrier against soluble species and an upper current collector, can further retard the shuttle phenomenon and promote the reutilization of PZ molecules. Besides, the presence of graphene@PVP can build an internal electric field, thus facilitating charge transfer. As anticipated, the assembled Mg//PZ cells exhibited a high discharge capacity of 230 mA h g⁻¹ at 0.1 A g⁻¹ and a commendable rate capability of 97.5 mA h g⁻¹ at 5.0 A g⁻¹ with an exceptionally low capacity decay rate of 0.00164% per cycle for 17 700 cycles. This work has provided a new route for the advancement of high-performance metal–organic batteries through the synergistic implementation of electrolyte engineering and separator modification.