Carbon Quantum Dot-Coated VSe₂ Nanosheets as Anodes for High-Performance Potassium-Ion Batteries

Potassium-ion batteries (PIBs) are of great importance in energy storage due to their natural abundance, low cost, and high operating potential compared to lithium and sodium. Herein, we first propose carbon quantum dot coating on VSe2 nanosheets (VSe2@CQDs) as anodes for PIBs with the solvothermal and annealing methods. In the composite, carbon quantum dots are embedded in VSe2 nanosheets, which inhibit the aggregation and volume expansion of the VSe2 nanosheets during cycling, resulting in stabilizing the structure and long cycling stability. Besides, with abundant edge positions and surface oxygen-containing functional groups, small-sized carbon quantum dots have strong absorption of K+, enhancing the capacity of the composite. As a result, for PIBs, the composite exhibits a superior reversible capacity of 362 mA h g–1 after 200 cycles at 100 mA g–1 with a high capacity retention of 76.7%, high rate capacity (255 mA h g–1 at 1000 mA g–1), and a long-term cycling life of 162 mA h g–1 after 3000 cycles at 500 mA g–1 with a high coulombic efficiency (above 99%). The VSe2@CQD composite shows the best performances reported to date for long-term cycling stability, excellent reversible capacity, and rate capacity in TMD-based PIB anodic materials. The excellent performance and simple synthesis indicate the promising VSe2@CQD composite as a potential anode material for PIBs.