Supercapacitor electrode fabrication through chemical and physical routes

In recent years, efficient energy storage devices that exhibit superior power and energy densities have attracted major attention to meet the demands of emerging applications such as wearable systems. In this regard, supercapacitors (SCs) in various forms offer attractive solutions. The performance of SCs is highly dependent on the synthesis route used for electrode materials preparation. This review outlines various techniques for electrode materials fabrication, such as i) solution-based chemical techniques, ii) physical methods, and iii) deposition techniques. Accordingly, different solution-based procedures such as hydrothermal/solvothermal, sol-gel, microwave, and in-situ polymerization techniques offer facile and cost-effective routes to synthesise electrode materials. Physical deposition techniques such as vacuum filtration and mechanochemical methods are also explained. The scalability to develop flexible structures is an attractive feature of physical approaches. Chemical vapour deposition, electro-polymerization/electrochemical deposition and direct growth techniques are also discussed in detail. It is suggested that incorporating electrode materials with 3D conductive substrate and hierarchical structures minimizes the excessive mass loading in commercial scale-up of SCs. Supercapacitor electrodes with shape memory properties for developing smart textiles are also presented. It is concluded that incorporating more than one synthetic approach makes it possible to obtain the electrode material for excellent electrochemical properties.