Suppressing the self-discharge of high-frequency supercapacitors using electrolytes containing BaTiO3 nanoparticles.

High-frequency supercapacitors (HF–SCs) are promising electric energy storage devices and alternating current line filters. However, severe self-discharge of HF–SCs causes significant energy loss and limits their applications. Current self-discharge suppression methods for supercapacitors typically lead to decreased rate performance and hence cannot be applied to HF–SCs directly. In this work, barium titanate (BTO) nanoparticles are employed as an electrolyte additive for HF–SCs to reduce self-discharge. By adding BTO nanoparticles into the electrolyte, both leakage current and decay of open circuit voltage of the devices are reduced without sacrificing the specific capacitance and high-frequency response. At a charging voltage of 2 V, the leakage current is reduced by 49 % (3.91 vs. 1.98 μA), while the time for the voltage to drop from 2.0 to 1.0 V is extended by 4.5 times (2300 vs. 10240 sec). When the HF–SCs with BTO electrolyte are employed to store the energy generated by a triboelectric nanogenerator, the time for charging the cells to 2.0 V is reduced by 82 %. Mechanistic analysis indicates that the reduced self-discharge can be attributed to the fluid electrorheological effect and the enhanced localized electric field within the gaps among BTO nanoparticles that lead to sluggish diffusion and migration of reactive species, so the diffusion-controlled faradaic reaction process is suppressed. [Display omitted] • Carbonized melamine foams were synthesized for high-frequency supercapacitors (HF–SCs). • BaTiO 3 nanoparticles were employed as electrolyte additive to reduce self-discharge. • Rate performances and high frequency responses of the HF–SCs were well retained. • Improved charging efficiency of the HF–SCs by a triboelectric nanogenerator was demonstrated. [ABSTRACT FROM AUTHOR]