Lithium-pre-intercalated T-Nb2O5/graphene composite promoting pseudocapacitive performance for ultralong lifespan capacitors

Orthorhombic niobium pentoxide (T-Nb2O5) has been deemed as the promising intercalation-type pseudocapacitive material due to its high theoretical capacitance and unique ion diffusion path. However, its intrinsic poor electronic conductivity limited its energy storage application severely. Herein, an integrated preintercalation strategy is developed to improve the electronic conductivity and accelerate charge transfer of T-Nb2O5. The LixNb2O5/G composite is fabricated for the first time via a chemical preintercalation of Li+ and utilized as the capacitor anode. The pre-intercalated Li+ into the tunnel of T-Nb2O5 can introduce more active sites, enhance electronic conductivity and beneficial to lithium ions diffusion in bulk electrode. Graphene further improves the electronic conductivity and reduces volume expansion significantly to maintain structure stability of the composite structure. Thereby, LixNb2O5/G exhibits a high specific capacitance (890 F g−1 at 1 mA cm−2), excellent rate capability (88% capacitance retention from 1 to 20 mA cm−2) and ultralong lifespan (90% capacitance retention after 130,000 cycles) in LiCl aqueous electrolyte. The assembled asymmetric capacitor (ASC) of LixNb2O5/G//MnO2 delivers high energy density of 115 Wh kg−1 at the power density of 5500 W kg−1. This structural engineering strategy can afford an in-depth insight of ion preintercalation and provide a useful guidance for the design of high performance capacitive materials.