of lithium resources in the earth's crust (0.0022 wt%). [9] Therefore, it is critical to develop new battery systems. [10] Multivalent-ion batteries can in principle provide higher energy density than monovalent LIBs, which could overcome the aforementioned problems by employing a non-Li metallic anode. [11][12][13] Among various candidates, rechargeable magnesium batteries have many advantages over LIBs, such as abundant Mg resources, small ionic radius (0.72 Å) and high theoretical volumetric capacity (3833 mAh cm −3 ) (Figure 1a). Particularly, RMBs are inherently safer than LIBs because metallic Mg anodes are dendrite-free upon cycling. [14][15][16][17] In addition, Mg also possesses higher oxidative stability than lithium. [18] The configurations and working mechanisms of RMBs are similar to those of LIBs (Figure 1b,c). However, the current research on RMBs still faces many challenges. Particularly, metallic Mg anodes have a strong tendency to form an insulated and passivating surface layer, which kinetically blocks electrochemical reactions at room temperature. [19][20][21] Such passivating layers engender difficulty for choosing compatible electrodes and electrolytes. [22,23] In addition, many RMBs electrolytes are air-sensitive, highly corrosive and flammable, [24,25] which poses a threat to their practical applications. Additionally, it is challenging to quest for suitable cathode materials with the rapid intercalation/ deintercalation of Mg 2+ at room temperature, considering the complex reaction mechanism of Mg-based electrochemistry. Many useful pioneering works have been devoted to developing cathode materials for RMBs (Figure 1d). [26][27][28] The strong electrostatic interaction of Mg 2+ inevitably results in sluggish kinetics, which is kinetically slower than Li + , especially at room temperature. [19] In this review, we summarize recently developed cathode materials for rechargeable magnesium-ion batteries. The anode materials beyond Mg metal are also discussed. Furthermore, we explored other Mg-based energy storage technologies, including Mg-air batteries, Mg-sulfur batteries, and Mg-iodine batteries. This review could also provide basic knowledge and valuable strategies for the advancement of high-energy-density rechargeable magnesium-based batteries.
Cathode MaterialsSimilar to LIBs, the working mechanism of RMBs batteries are based on the shuttle of Mg 2+ ions between cathode and anode Benefiting from higher volumetric capacity, environmental friendliness and metallic dendrite-free magnesium (Mg) anodes, rechargeable magnesium batteries (RMBs) are of great importance to the development of energy storage technology beyond lithium-ion batteries (LIBs). However, their practical applications are still limited by the absence of suitable electrode materials, the sluggish kinetics of Mg 2+ insertion/extraction and incompatibilities between electrodes and electrolytes. Herein, a systematic and insightful review of recent advances in RMBs, including intercalation-based cathode materials and conversion...
