Molten salt activation combined with in-situ surface graphitization towards wood-derived self-supporting carbon electrodes with high volumetric specific capacity for zinc-ion hybrid supercapacitors

Despite significant advancements in enhancing the gravimetric and areal specific capacities of carbon electrodes for zinc-ion hybrid supercapacitors (ZHSCs), the attainment of a high volumetric specific capacity remains a pivotal challenge. This research suggests an innovative method to boost the volumetric specific capacity of carbon electrodes by constructing self-supporting carbon electrodes derived from wood. The process involves a synergistic application of molten salt activation and in-situ surface graphitization. Specifically, pine wood (Pinus sylvestris var. mongolica Litv.) undergoes initial carbonization, followed by treatment with a molten salt electrolyte, generating a carbon material distinguished by a penetrating channel structure, a rich micro-mesoporous network, and distinct characteristics such as self-support and surface graphitization. These qualities contribute to a significant increase in the volumetric specific capacity of the resultant carbon electrode, achieving up to 26.3 mAh cm^–3 at 2 mA cm^–2, surpassing commercial activated carbon and analogous materials in ZHSC applications. Additionally, a coin-cell ZHSC utilizing this innovative carbon electrode demonstrates exceptional performance, reaching up to 5.6 mAh or 12.6 F per individual ZHSC, equivalent to 12.5 F cm^–3 by volume. This performance not only outperforms commercial coin-cell supercapacitors but also aligns closely with the performance metrics of certain commercial coin-cell aqueous batteries. This approach provides a viable solution for augmenting the volumetric specific capacity of carbon electrodes in ZHSCs.