Sustainable hydrothermal carbon for advanced electrochemical energy storage

The development of advanced electrochemical energy storage devices (EESDs) is of great necessity because these devices can efficiently store electrical energy for diverse applications, including lightweight electric vehicles/aerospace equipment. Carbon materials are considered some of the most versatile materials, which play a vital role in EESDs, since their properties (e.g., high porosity and electrical conductivity) can fulfill diverse requirements of EESDs. Hydrothermal carbon is recognized as a very promising electrode material for EESDs. Therefore, in this review, we have firstly introduced the concept of hydrothermal technologies (hydrothermal carbonization, hydrothermal liquefaction and hydrothermal gasification) for the controllable preparation of hydrothermal carbon with insights into its production and characteristics. Subsequently, we have interpreted the mechanisms involved in the formation of carbon in response to different hydrothermal technologies. It is well known that the application of hydrothermal carbon directly produced from the hydrothermal processing of biomass in EESDs is limited by its relatively low storage sites and low diffusion sites. Consequently, functionalized hydrothermal carbon materials have been engineered via pore structure tailoring and surface modulation, enabling the rational tuning and tailoring of their surface area, porosity, surface chemistry, and morphology and to promote their electrochemical performance. Herein, we shed light on the function of modification (such as pore structure tailoring and surface recombination) in the production of effective hydrothermal carbon materials with different textural and surface properties. Subsequently, we focus on the state-of-the-art results documented for sustainable hydrothermal carbon materials in advanced EESDs (i.e., supercapacitors, hybrid capacitors, and alkaline metal ion batteries). Hydrothermal carbon with porous structures and doped heteroatoms has been demonstrated to be capable of achieving high capacity, improving rate performance, and prolonging cycling stability in both batteries and supercapacitors. Ultimately, the current knowledge gaps and challenges involved in the development of hydrothermal carbon materials for practical application in advanced EESDs are discussed with suggestions for further perspectives. The development of advanced electrochemical energy storage devices (EESDs) is of great necessity because these devices can efficiently store electrical energy for diverse applications, including lightweight electric vehicles/aerospace equipment.