Transition metal oxides/oxyhydroxides (TMOs) are promising high-capacity materials for electrochemical energy storage. However, the low rate and poor cyclability hinder practical applications. In this work, we developed a general electrochemical route to fabricate monolithic core/shell sandwiched structures, which are able to significantly improve the electrochemical properties of TMO electrodes by electrically wiring the insulating active materials and alleviating the adverse effects caused by volume changes using engineered porous structures. As an example, a lithium ion battery anode of porous MnO sandwiched between CNT and carbon demonstrates a high capacity of 554 mAh g-1 even after 1000 cycles at 2 A g-1. An all-solid-state symmetric pseudocapacitor consisting of CNT@MnOOH@polypyrrole exhibits a high specific capacitance of 148 F g-1 and excellent capacitance retention (92% after 10000 cycles at 2 A g-1). Several other examples and applications have further confirmed the effectiveness of improving the electrochemical properties by core/shell sandwiched structures.
Keywords: core/shell structure; electrodeposition; flexible pseudocapacitors; lithium-ion batteries; transition metal oxide.