Non-Faraday Electrolyte Additives for Capacitance Boosting by Compression of Dielectric Layer Thickness: Organic Ferroelectric Salts

Carbon-based supercapacitors are one of the most widely used commercial products. Organic electrolyte systems, such as tetraethylammonium tetrafluoroborate/acetonitrile (TEABF4/ACN), remain dominant after decades of development due to cost and performance advantages. However, improving the capacitance of existing carbon-electrolyte systems not by altering the pore structure and surface properties of activated carbon is full of challenges. Herein, a non-Faraday organic ferroelectric salt additive (diisopropylamine perchlorate, DIPAP) that can significantly increase capacitance from the standpoint of electrolyte dielectric modulation is proposed for the first time. Compared to counter ions, DIPA+ plays a vital role in capacity enhancement, in which electron-rich N-doped mesoporous carbon can greatly boost capacity by promoting local ion mobility. In situ Raman and theoretical studies show that small-size DIPA+ can enter the pore and be enriched closer to electrode surfaces than TEA+ and ACN, allowing it to regulate the distribution of electric double-layer species and dielectric properties (i.e., effective thickness of dielectric and/or relative dielectric constant), increasing capacity by up to 21.6-45.8% with only 1 wt% DIPAP while maintaining desired rate performances. The understanding of the mechanism of capacitance increase by such additives opens up new avenues for further extension of the commercialized carbon electrode-organic electrolyte system's potential. A novel non-Faraday organic ferroelectric salt additive is reported for the first time, which significantly improves the specific capacitance of carbon-based supercapacitors by compressing the thickness of the dielectric layer and/or modulating the relative dielectric constant of the electrolyte.image