Calcium-ion batteries have been considered attractive candidates for large-scale energy storage applications due to their natural abundance and low redox potential of Ca²⁺/Ca. However, current calcium ion technology is still hampered by the lack of high-capacity and long-life electrode materials to accommodate the large Ca²⁺ (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 VS₄ 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 Ca²⁺ 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.

Organosulfur materials containing sulfur–sulfur bonds are an emerging class of high-capacity cathodes for lithium storage. However, it remains a great challenge to achieve rapid conversion reaction kinetics at practical testing conditions of high cathode mass loading and low electrolyte utilization. In this study, a Li-rich pyrolyzed polyacrylonitrile/selenium disulfide (pPAN/Se₂S₃) composite cathode is synthesized by deep lithiation to address the above challenges. The Li-rich molecular structure significantly boosts the lithium storage kinetics by accelerating lithium diffusivity and improving electronic conductivity. Even under practical test conditions requiring a lean electrolyte (Electrolyte/sulfur ratio of 4.1 μL mg⁻¹) and high loading (7 mg cm⁻² of pPAN/Se₂S₃), DL-pPAN/Se₂S₃ exhibits a specific capacity of 558 mAh g⁻¹, maintaining 484 mAh g⁻¹ at the 100th cycle with an average Coulombic efficiency of near 100%. Moreover, it provides (electro)chemically stable Li resources to offset Li consumption over charge–discharge cycles. As a result the as-fabricated anode-free cell shows a superior cycling stability with 90% retention of the initial capacity over 45 cycles. This study provides a novel approach for fabricating high-energy and stable Li–SPAN cells.