Deciphering the Degradation Mechanisms and Realize High-Voltage Stability of AV(PO) (A = Li, Na) in Aqueous Dual-Ion Batteries.

Polyanionic AV(PO) (A = Li, Na) with open channels have been extensively utilized as cathode materials for aqueous zinc-metal batteries (AZMBs), whereas suffering from severe capacity fading and rapid operation voltage decay during cycling. when used as In this work, it is disclosed that the rapid degradation is induced by an irreversible phase change from electrochemical active LiV(PO) to nonactive monoclinic LiZnPO, as well as active NaV(PO) to nonactive rhombic Zn(PO)(HO). Subsequently, a rational dual-cation (Al-Fe) doping strategy is proposed to suppress these detrimental transformations. Such dual-cation doping entails stronger P-O and V-O bonds, thus stabilizing the initial polyanionic structures. Consequently, the optimized member of LiVAlFe(PO) (LVAFP) exhibits desirable cycling stability (1000 cycles, 68.5% capacity retention) and notable rate capability (92.1% of the initial capacity at 10 C). Moreover, the dual-cation doping methodology is successfully extended to improve the stability of NaV(PO) cathode in aqueous dual-ion batteries, signifying the versatility and feasibility of this strategy. The comprehensive identification of local structural evolution in these polyanions will broaden the scope of designing high-performance alkali-vanadyl-phosphates for multivalent aqueous batteries.