A conjugately configured supercapacitor based on pairs of pre-lithiated Nb2O5/TiO2 with optimized retained energy upon aging enabled by suppressed self-discharge

Abstract

Supercapacitors are advantageous in terms of power density and cycle life, but their wider application is limited by self-discharge. Previous attempts for improving the stability have mainly focused on the specific component (materials, separators or electrolytes) of the device, while the feasibility for mitigating self-discharge through a general device-scale configuration is largely unknown. Herein, we report a symmetric supercapacitor with a conjugated configuration, which consists of a pair of pre-lithiated niobium oxide decorated with evenly distributed titanium dioxide, forming a Lix[(Nb2O5):(TiO2)a] vs. Li2-x[(Nb2O5):(TiO2)a] conjugated configuration. The intercalation type pseudocapacitive Nb2O5 are unique due to their linearly sloped charge/discharge curve like electrochemical double layer capacitances (EDLCs) while the charged ions can be inserted/extracted reversibly from the bulk like batteries. As a result, such conjugated device can store energy like conventional EDLCs, while the self-discharge process is significantly supressed. When further added with suitable amount of titanium dioxide as the stabilizer, the conjugated supercapacitor retained 74% of its energy after aging for 48 h. These results are expected to provide a general guidance for designing materials specifically for constructing conjugated supercapacitors with high initial energy density and alleviated self-discharge.