In the post-lithium-ion battery era, calcium-ion batteries (CIBs) are considered a desirable candidate due to their great physicochemical and economic properties. Unfortunately, the lack of high-performance cathode materials has limited the development of CIBs to a large extent. Metal oxides are the most studied CIB cathodes by virtue of their superior electrochemical performance, cost advantages, and scalable synthesis. Among numerous metal oxides, layered vanadium oxides are a popular option because of their unique structural properties and high Ca²⁺ storage capability. Herein, VO₂(B) nanofibers, a typical layered vanadium oxide, are synthesized by a simple one-step synthesis method using a commercial precursor. Employing as a CIB cathode, it could deliver high reversible capacities of 97.5 mAh·g^–1 at 5 A·g^–1 after 1000 cycles and 74.6 mAh·g^–1 at 10 A·g^–1 after 2000 cycles. Moreover, a CIB full battery assembled by perylene-3,4,9,10-tetracarboxylic diimide as an anode and the nanofiber as a cathode achieved a specific capacity of 38.8 mAh·g^–1 at a current density of 0.5 A·g^–1 even over 30,000 cycles. This work may provide CIBs with a promising cathode material that can be produced on a large scale and at a low cost.

Heteroatom doping is a universal approach to improve rate capability for various carbon anodes of sodium-ion batteries (SIBs) owing to the interlayer spacing expansion and pseudocapacitive enhancement. However, there is still a limitation for ion adsorption of internal voids and dopants in the bulk phase of carbon materials due to the sluggish intercalation kinetics of large-size sodium ions. In this work, the highly sulfur-doped carbon nanosheets are synthesized and investigated as the anode of SIBs. It shows that the electrochemical performance in ether-based electrolytes significantly outperforms that in ester-based electrolytes. The carbon anodes exhibit a specific capacity of 617 mAh·g⁻¹ at 100 mA·g⁻¹ after 300 cycles, especially an outstanding rate performance of delivering specific capacities of 305 and 191 mAh·g⁻¹ at current densities of 10 and 50 A·g⁻¹, respectively. It is speculated that the ion-storage kinetics was greatly enhanced in ether-based electrolytes owing to the better accessibility of sodium-ion diffusion from electrode interfaces to internal hosts. As a result, the carbon nanovoids and sulfur dopants in the bulk phase are efficiently activated for ion storage. This work provides a new insight into the ion-storage mechanism optimization of carbon materials for SIBs.