Surface Modification of Biochar for Electrochemical Energy Storage: Focused Mini Review on Supercapacitors and Batteries

Abstract

This brief review explores the synthesis, functionalization, and deployment of biochar as an electrode material for electrochemical energy storage, particularly in relation to supercapacitors and lithium‐ion batteries (LIBs). Biochar, generated via the pyrolysis of diverse biomass feedstocks, offers tunable porosity, surface chemistry, and conductivity; however, electrochemical performance is limited by structural heterogeneity and insufficient activity. In order to mitigate these issues, the review analyzes significant functionalization techniques—including chemical activation (e.g., KOH), heteroatom doping (nitrogen [N], sulfur [S], and phosphorus [P]), metal impregnation, and plasma‐assisted modification—that improve surface area, redox activity, and charge transport. Characterization techniques such as scanning electron microscopy (SEM), X‐ray diffraction (XRD), Raman spectroscopy, and electrochemical evaluations (cyclic voltammetry [CV], galvanostatic charge–discharge [GCD], electrochemical impedance spectroscopy [EIS]) are investigated to establish relationships between structure and performance. Functionalized biochar has exhibited specific capacitance values surpassing 377 F/g and energy densities reaching 54 Wh/kg in supercapacitors, while biochar‐based battery anodes have attained capacities up to 1483 mAh/g with significant coulombic efficiency. The review concludes by delineating prospective research trajectories, including biochar/MXene hybrids, integration of flexible devices, and environmentally sustainable synthesis methods, as promising avenues to enhance scalable, high‐performance energy storage technologies that align with principles of a circular economy.