Some facets of the Mg/Na_(3)VCr_(0.5)Fe_(0.5)(PO_(4))_(3) battery

Magnesium rechargeable batteries(MRBs)present opportunities for grid-scale energy storage applications as a complement to Li-ion batteries(LIBS).The major challenges are the low reversible capacity,inferior cycling stability and unsatisfactory energy densities.Na_(3)VCr_(0.5)Fe_(0.5)(PO_(4))_(3) with a well-defined NASIONtype structure is used as cathode in Mg cell.Two-electrons reaction(~116 m Ah/g),1.5 V average voltage and 65%of capacity retention over 100 cycles are accomplished.Mg is inserted by a biphasic reaction with the participation of V3+/V4+/V5+redox couples in the electrochemical reaction while the non-active redox couples such as Cr^(3+)/Cr^(4+)and Fe^(2+)/Fe^(3+)served as stabilizer to buffer the volume variation.A thermal stability up to~412℃ is also exhibited.Therefore,incorporating a mixture of three transition metal(V/Cr/Fe)in this type of structures will broaden new perspectives for realizing high performance cathodes for MRBs.