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

Abstract

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 Mg 2+ cations in solid lattices. Here, we propose a co-insertion strategy to facilitate cation diffusions and present a polyanion cathode of Li 3 V 2 (PO 4 ) 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 Mg 2+ from the 0.5 m Mg(ClO 4 ) 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 Li 3 V 2 (PO 4 ) 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 Li 3 V 2 (PO 4 ) 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. • A high potential polyanion cathode of Li 3 V 2 (PO 4 ) 3 is proposed for Mg-ion batteries. • A co-insertion strategy is revealed to enhance cation diffusion in solid lattices. • The Li 3 V 2 (PO 4 ) 3 electrode delivers 124 mAh g −1 capacity at 100 mA g −1 . • High discharge potentials of 0.46 V and −0.44 V vs. Ag/Ag + are achieved. • A capacity retention of 80% is realized over 300 cycles with 99.3% CE.