High-power and high-energy asymmetric supercapacitors based on Li+-intercalation into a T-Nb2O5/graphene pseudocapacitive electrode

Abstract

T-Nb ₂O ₅/graphene nanocomposites were fabricated and then paired with mesoporous carbon electrodes to construct the asymmetrical supercapacitors with high energy and power densities.

Abstract

The intercalation pseudocapacitance which leads to the extraordinary charge storage properties has been confirmed as an intrinsic capacitive property of orthorhombic Nb ₂O ₅ (T-Nb ₂O ₅) nanocrystals. However, the poor electronic conductivity of T-Nb ₂O ₅ nanocrystals may limit their electrochemical utilization and high-rate performance especially for thick electrodes with high mass loadings. To address this issue, we herein reported a hydrothermal-heat treatment method to anchor T-Nb ₂O ₅ nanocrystals on conductive graphene sheets, which form a layer-by-layer integrated electrode with much shortened ion transport paths and results in excellent electrochemical capacitive properties, including high capacitance (626 C g ⁻¹), excellent rate handling and cyclic stability. Furthermore, asymmetric supercapacitors were constructed by using the high-rate response T-Nb ₂O ₅/graphene nanocomposite and mesoporous carbon as the negative and positive electrode, respectively. The asymmetric supercapacitor could deliver a high energy density of 16 W h kg ⁻¹ at an unprecedented power density of 45 kW kg ⁻¹ (discharge time of 1.2 s). The outstanding power properties of the supercapacitors are mainly attributed to the improved high-rate Li-insertion/extraction capability of the T-Nb ₂O ₅/graphene electrode and appropriate pairing of the mesoporous carbon electrode.