Advances in layer manganese dioxide for energy conversion and storage: Mechanisms, strategies and prospects

Layer manganese dioxide with special structure, low price and large theoretical specific capacitance/capacity is considered as a competitive candidate for various energy conversion and storage devices, such as supercapacitors, Li-ion, Na-ion, Zn-ion, etc. batteries. However, challenges such as low electronic/ionic conductivity, sluggish diffusion kinetics, and structural collapse during cycling are still the main factors limiting its practical application. A solid understanding of the correlation between structure and performance will greatly promote the performance and the further application of layer manganese dioxide. In this review, the energy storage mechanism of layer manganese dioxide in different energy storage devices is discussed in detail. Additionally, in response to the current difficulties and challenges, recent advances in regards to electrochemical performance improvement are systematically summarized, including synthetic method, structure design, interlayer engineering and so on. Finally, suggestions to the future directions and developments in preparing high electrochemical performance of layer manganese dioxide cathodes are put forward.