Controllable preparation of green biochar based high-performance supercapacitors

With the higher demand for energy storage device performance, supercapacitors have attracted increasing interest because of their high power density, stable cycling capability, and wide range of operating temperatures. Various carbon materials are used as electrode materials for supercapacitors. To deal with the worsening energy crisis, biomass, as a green renewable resource, has been widely used in many fields. Biochar, with its naturally porous structure and abundant surface functional groups, is considered a promising candidate for the development of energy storage. However, their inherent inhomogeneity and random uncontrollability result in relatively low performance, greatly limiting their future applications. There is a great need to develop effective methods to produce more desirable carbon materials from this rich and diverse renewable resource. This critical review points out the significance of controllable production for improving the electrochemical performance of biochar supercapacitors, and the recent research achievements of controllable design and development of new biochar materials. Factors affecting the electrochemical performance of biochar materials are discussed from the perspective of structural design and control. An in-depth summary of various promising approaches used in recent years to achieve major research breakthroughs and innovations is provided. Finally, current challenges, future research directions, and opportunities in the renewable energy storage field of biochar-based supercapacitors are discussed. Graphical abstract