Research Status of Cathode Materials for Magnesium-Ion Batteries

Excessive consumption of traditional energy sources such as oil and natural gas has led to increasingly serious environmental pollution and ene-rgy crises. Therefore, it is imperative to develop environmentally friendly, large-scale and efficient energy storage devices to obtain intermittent energy such as wind and solar energy continuously. Among various energy storage technologies, secondary batteries have the best research and development prospects for their advantages of high energy conversion efficiency, long service life, and low cost. In comparison with the widely studied lithium-ion batteries, the magnesium-ion batteries can theoretically provide more electrons, which makes their capacity 2 to 3 times as large as that of the lithium-ion batteries. Furthermore, magnesium-ion batteries, owing the advantages of abundant resources, environmental friendliness, non-toxicity and low prices, are considered as one potential candidate for portable devices and heavy-duty energy equipment. A lot of studies on magnesium-ion batteries have been carried out since a successful prototype of magnesium-ion battery appeared in early 2000. However, the commercial development of rechargeable magnesium-ion batteries (RMBs) is still hampered by some challenges. At present, due to the high charge density, strong polarization effect and slow diffusion kinetics of Mg2+, it is still a great challenge to develop cathode materials that can meet the current commercial needs. RMBs cathode materials mainly include transition metal sulfides, transition metal oxides, polyanionic compounds and Prussian blue analogs. The transition metal sulfides have a low rigidity structure that is difficult to collapse during the charge-discharge cycle. However, some defects such as ion trapping effect and slow diffusion kinetics are found in transition metal sulfides. Transition metal oxides have higher voltage than sulfides but great structural rigidity and poor cycle performance of them can't be ignored. The polyanionic compounds with mesoporous structure are beneficial to improving the electrochemical performance of RMBs, but the conductivity needs to be improved. The Prussian blue analogue with an open and adjustable structure is conducive to the rapid deintercalation of Mg2+ while its compatibility with aqueous electrolytes is poor. In recent years, researchers have mainly optimized the design of cathode materials from the aspects of nanocrystallization, structural adjustment, doping modification and coating modification in response to the present challenges. In this paper, the domestic and foreign research status of various types of RMBs cathode materials including the information of crystal structure, research status and existing problems is reviewed. Meanwhile, challenges of RMBs cathode materials are also analyzed to provide reference for synthesizing RMBs cathode materials with high energy density and high cycle stability. © 2022, Materials Review Magazine. All right reserved.