Facilitating Mg2+ diffusion in high potential LixV2(PO4)3 cathode material with a co-insertion strategy for rechargeable Mg-ion batteries

Rechargeable Mg-ion batteries offer high energy density and good safety. However, the lack of cathode materials with high operating potential and considerable capacity is a great challenge for their practical applications. This is limited by the sluggish diffusion of multivalent Mg2+ cations in solid lattices. Here, we propose a co-insertion strategy to facilitate cation diffusions and present a polyanion cathode of Li3V2(PO4)(3) to provide high redox potential. The initial charge of the material is associated with the extraction of two Li+ cations, which are co inserted with Mg2+ from the 0.5 m Mg(ClO4)(2)/PC electrolyte during the following electrochemical processes. The cation diffusion coefficients are largely enhanced in comparison to the electrode without Li+ co-insertion, and higher capacity is obtained. At room temperature, the Li3V2(PO4)(3) electrode delivers 124 mAh g(-1) capacity at 100 mA g(-1) with discharge plateaus at 0.46 V and-0.44 V vs. Ag/Ag+. A capacity retention of 80% is realized after 300 cycles at 500 mA g(-1). A rocking-chair Mg-ion full cell coupling the Li3V2(PO4)(3) cathode with an anthraquinone anode achieves 41 mAh g(-1) capacity (based on the mass of both electrodes). The work demonstrates a promising pathway for the design of high performance cathode materials for Mg-ion batteries.

Automated summary

Rechargeable Mg-ion batteries face the challenge of lacking cathode materials with high operating potential and considerable capacity. This study proposes a co-insertion strategy and designs a polyanion cathode, Li3V2(PO4)(3), with high redox potential. The co-insertion of Li+ cations enhances the cation diffusion coefficients and improves the capacity. The Li3V2(PO4)(3) cathode exhibits high capacity and good capacity retention at room temperature.