Biomass-Derived Carbon: A Value-Added Journey Towards Constructing High-Energy Supercapacitors in an Asymmetric Fashion.

Currently, asymmetric supercapacitors (ASCs) produced from supercapacitors (SCs) offer more benefits for energy-storage applications because they display a high operational voltage in aqueous-based electrolytes that may enhance grid storage and zero-power transportation with high energy density in the future. At the same time, the realization of low-cost energy devices through the construction of cheap electrode materials deserves a permanent place in the market once the goals of high energy, extra power, and long cycling stability are achieved. Biomass-derived carbon retrieved from sources such as plants has attracted considerable attention because of the rich abundance, low cost, and environmentally friendliness. In addition, the utilization of porous hierarchical structures has achieved enhanced electrochemical performance with excellent capacitance, outstanding stability, and praiseworthy rate capability. However, issues still persist in procedures used to obtain biomass-derived carbon materials with a high yield and a high degree of carbonization/graphitization, surface functionality, and porous characteristics, wherein the materials are used as electrodes in ASC devices. The present review briefly addresses the need for biomass-derived carbon materials in ASCs, comprehensively categorizes SCs in the context of their historical background, and elucidates the SC mechanism. In addition, influencing factors, such as the pore size distribution, role of surface functional groups, surface area, active-material loading, heteroatom doping, and activation techniques used in the preparation of biomass-derived carbon, have been discussed in detail. Moreover, this review assesses other nanostructured carbon electrodes used in ASCs and advances made in the fabrication of ASCs by using biomass-derived carbon in aqueous electrolytes. Finally, existing challenges and mandatory solutions toward developing cost-effective and high-performance ASCs by using environmentally friendly biomass-derived carbon materials are discussed in detail.