Intercalation pseudocapacitance in flexible and self-standing V₂O₃ porous nanofibers for high-rate and ultra-stable K ion storage

Transition metal oxides possess eminently high capacity based on the conversion reaction by delivering multiple electrons. However, they usually demonstrate limited cycle life and inferior rate capability due to the pulverization and aggregation of active materials. V₂O₃ is considered to be an attractive electrode material due to its intrinsic tunnel structure provided by 3D V-V framework. Herein, a flexible and self-standing electrode of V₂O₃ nanoparticles embedded in porous N-doped carbon nanofibers (V₂O₃@PNCNFs) has been fabricated through a facile electrospinning method and subsequent thermal treatment. Electrochemical kinetic analysis, in situ XRD, ab initio molecular dynamics (AIMD) and density functional theory (DFT) calculation suggest that the potassium storage of V₂O₃ is dominated by intercalation pseudocapacitance and only up to 1 mol K⁺ can insert into V₂O₃ crystal. Different from the conversion reaction in conventional transition metal oxides, in the mechanism of intercalation pseudocapacitance, K⁺ intercalate into the tunnels of V₂O₃ accompanied by a faradaic charge-transfer with no crystallographic phase change. This mechanism combines short charging/discharging times with long cycle life, which is reported in PIBs for the first time. This work may open up a new avenue for further development of pseudocapacitive nanomaterials for high-rate and ultra-stable energy storage.