Electrochemically Induced Crystalline-to-Amorphous Transition of Dinuclear Polyoxovanadate for High-Rate Lithium-Ion Batteries

Polyoxometalates are intriguing high-capacity anode materials for alkali-metal-ion storage due to their multi-electron redox capabilities and flexible structure. However, their poor electrical conductivity and high working voltage severely restrict their practical application. Herein, the dinuclear polyoxovanadate Sr2V2O7 center dot H2O with unusually high electrical conductivity is reported as a promising anode material for lithium-ion batteries. During the initial lithiation process, the Sr2V2O7 center dot H2O anode experiences an electrochemically induced crystalline-to-amorphous transition. The resulting amorphous structure provides high redox activity and fast reaction kinetics via reversible V4.9+/V2.8+ redox couple through the intercalation mechanism. Furthermore, when coupled with the LiFePO4 cathode, the strong V-O bonds of the amorphous anode provide excellent structural stability, with the full-cell capable of performing >12 000 cycles with a capacity retention of 72%. Another advantage of Sr2xV2O7-delta center dot yH(2)O (0.5 <= x <= 1.0) is its composition adjustability, which enables delicately regulating the Sr vacancy content without destroying the structure. The defect Sr2xV2O7-delta center dot yH(2)O (x = 0.5) electrodes show significantly improved specific capacity and rate capability without sacrificing other key properties, delivering a high specific capacity of 479 mAh g(-1) at 0.1 mA cm(-2) and 41.9% of its capacity in 2 min. Overall, the preliminary study points the way forward for the facile preparation of high-quality polyoxometalates for advanced energy storage applications and beyond.