Fig. 2

Thermal treatment for the commercially available structure (a) and fabricated structure (b). a1 Metallic oxide nanoparticles can be obtained on the surface of an metal structure via a simple thermal oxidation progress [34]. a2 The active materials can be synthesized on the surface of conductive structure by thermal treatment [35]. a3 Biomass can be carbonized to achieve the carbon architecture [32]. b1 The mixture of polymer and active materials can be carbonized to achieve the binder-free electrode [36]. b2 Hierarchical structure can be obtained by multiple processes [37]. b3 Binder-free electrode can be obtained by thermal treatment the electrospinning membrane [38]