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

Layer manganese dioxide with its special structure, low price and large theoretical specific capacitance/capacity is considered a competitive candidate for various energy conversion and storage devices, such as supercapacitors and batteries (Li-ion, Na-ion, and Zn-ion) 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, considering the current difficulties and challenges, recent advances in strategies for electrochemical performance improvement are systematically summarized, including synthetic methods, structure design, and interlayer engineering. Finally, suggestions for the future directions and developments in preparing layer manganese dioxide cathodes with high electrochemical performance are put forward.