Mo Doping and Electrochemical Activation Co‐Induced Vanadium Composite as High‐Rate and Long‐Life Anode for Ca‐Ion Batteries

Calcium‐ion batteries have been considered attractive candidates for large‐scale energy storage applications due to their natural abundance and low redox potential of Ca 2+ /Ca. However, current calcium ion technology is still hampered by the lack of high‐capacity and long‐life electrode materials to accommodate the large Ca 2+ (1.00 Å). Herein, an amorphous vanadium structure induced by Mo doping and in‐situ electrochemical activation is reported as a high‐rate anode material for calcium ion batteries. The doping of Mo could destroy the lattice stability of VS 4 material, enhancing the flexibility of the structure. The following electrochemical activation further converted the material into sulfide and oxides co‐dominated composite (defined as MoVSO), which serves as an active material for the storage of Ca 2+ during cycling. Consequently, this amorphous vanadium structure exhibits excellent rate capability, achieving discharge capacities of 306.7 and 149.2 mAh g −1 at 5 and 50 A g −1 and an ultra‐long cycle life of 2000 cycles with 91.2% capacity retention. These values represent the highest level to date reported for calcium ion batteries. The mechanism studies show that the material undergoes a partial phase transition process to derive MoVSO. This work unveiled the calcium storage mechanism of vanadium sulfide in aqueous electrolytes and accelerated the development of high‐performance aqueous calcium ion batteries.