A review on the application of lignin-based carbon materials in supercapacitors: Fabrication of multi-dimensional morphologies and heteroatom doping

Supercapacitors are essential components in renewable energy storage systems due to their remarkable power density, swift charging/discharging speeds, extended lifespan across cycles, and ability to function effectively under diverse temperature conditions. Lignin, the second most plentiful biomass resource in nature following cellulose, is renowned for its wide availability, cost-effectiveness, and a rich array of bioactive components. It can be abundantly sourced as a by-product of pulp and biomass refineries. Given the growing concerns over environmental pollution and energy depletion, lignin is increasingly being recognized as a viable alternative to conventional petrochemical feedstocks. This paper presents a comprehensive overview of supercapacitors, outlining their fundamental principles and classification. This study delves into the structural characteristics and origins of lignin, highlighting the potential for optimizing crystallinity and properties of carbon materials derived from lignin through meticulous modifications of structural and carbonization parameters. This approach facilitates the tailored synthesis of polymorphic carbon materials, resulting in improved performance characteristics. Furthermore, the study investigates the substantial impact of non-metallic doping elements, including sulfur, phosphorus, and nitrogen, in conjunction with metallic elements such as copper, manganese, and nickel, on the enhancement of the electrochemical properties of carbon materials derived from lignin.