Self-supported transition metal oxide electrodes for electrochemical energy storage

Electrode materials are of decisive importance in determining the performance of electrochemical energy storage (EES) devices. Typically, the electrode materials are physically mixed with polymer binders and conductive additives, which are then loaded on the current collectors to function in real devices. Such a configuration inevitably reduces the content of active species and introduces quite some undesired interfaces that bring down the energy densities and power capabilities. One viable solution to address this issue is to construct self-supported electrodes where the active species, for example transition metal oxides (TMOs), are directly integrated with conductive substrates without polymer binders and conductive additives. In this review, the recent progress of self-supported TMO-based electrodes for EES devices including lithium-ion batteries (LIBs), sodium-ion batteries (SIBs), aluminum-ion batteries (AIBs), metal-air batteries, and supercapacitors (SCs), is discussed in great detail. The focused attention is firstly concentrated on their structural design and controllable synthesis. Then, the mechanism understanding of the enhanced electrochemical performance is presented. Finally, the challenges and prospects of self-supported TMO-based electrodes are summarized to end this review.