Tuning vacancy and size of metallic VC_x quantum dots for capacitive potassium-ion batteries

Potassium-ion batteries (KIBs) are an emerging, promising and low-cost energy storage technology, but the study on KIBs is in the early stage. In this work, we design a unique 3D foam-like composite by encapsulating carbon vacancies assisted VC_x quantum dots within ultralarge highly N-doped macroporous carbon microsheets. The composite is synthesized by an ultrafast solution combustion synthesis method (completed within two minutes) and a subsequent carbothermal reduction process, easily amenable to large-scale processing. By tuning the vacancy and size of VC_x quantum dots, improved electronic conductivity and highly reversible K⁺ adsorption are achieved. As an effective support, the foam-like high-level N-doped macroporous carbon microsheets offer significant advantages by enhancing the electronic conductivity and K⁺ mobility. The optimized sample presents a promising anode for capacitive potassium-ion batteries, which delivers a high capacity and a high cycling stability (345 mAh g⁻¹ at 0.05 A g⁻¹ in 100 cycles tests, and 130 mAh g⁻¹ at 1 A g⁻¹ even after 1500 cycles), among the best anode materials reported for KIBs. Equally importantly, the effective strategy can be easily mass produced and also potentially used for producing other carbides/carbon composites in energy storage.