π-Conjugated Microporous Hydrocarbon Electrodes for High-Capacity and High-Voltage Lithium-Ion Capacitors.

Abstract

Carbon-based cathodes are widely utilized in lithium-ion capacitors due to their superior cycle stability, safety, and tolerance to overcharging compared to oxide-based cathodes. However, the limited capacity of carbon cathodes, primarily governed by the electric double-layer capacitance mechanism, constrains their energy storage potential. Conventional strategies like increasing surface area and pore volume have provided marginal improvements, while heteroatom doping has been restricted by low working voltage and compromised conductivity. To overcome these limitations, a novel class of π-conjugated microporous hydrocarbons (CMHs) is developed using sub-graphitic polycyclic aromatic hydrocarbons (PAH) as building blocks. These materials PPe, PPy, and PAn feature carbon-like large π-conjugated surfaces, abundant oxygen-free edge C(sp2)-H sites, and well-defined microporous structures, facilitating anion adsorption and ion transport. Among them, PPe demonstrates exceptional performance with a high voltage of 3.13 V vs Li+/Li, a remarkable capacity of 241 mAh g-1 2.5 times of commercial activated carbon (YP50), and exceptional rate performance (up to 50 A g-1), far surpassing all other reported LIC cathode materials. These findings provide a fundamental design strategy for carbon-based cathodes in LICs that highlighting the role of π-conjugation and edge chemistry in electrochemical performance, paving the way for next-generation high-capacity, high-voltage energy storage devices.