to sustain a continuous power supply for our daily life. [2] This is where rechargeable batteries can play a vital role in electrochemically storing and releasing the energy reversibly. [3] Additionally, as the majority of fossil fuel consumption is used for transportation, a shift from combustion engines to electric vehicles is essential in the 21st century. However, lithium-ion batteries, which have dominated the portable electronics over the past three decades, are unable to satisfy the high-energy requirement for electrical vehicles and next-generation energy storage. [2a,4] This is because the conventional lithium-ion batteries rely on the intercalation-type electrode materials and the lithium ions can only be intercalated topologically into certain specific sites, which limits their charge-storage capacity and energy density. [5] Therefore, exploring new battery chemistries beyond the horizon of current lithium-ion batteries is crucial for a sustainable future. [6] To realize a high energy density with new battery chemistries, seeking new types of electrode materials is a prerequisite. [7] Lithium metal, which has the highest theoretical specific capacity of 3860 mA h g −1 among the anode materials and the lowest electrochemical potential of −3.04 V versus the standard hydrogen electrode, is regarded as the "Holy Grail" anode material for next-generation batteries. [8] Sulfur, which is abundant, cheap, and environmentally benign, can offer a high theoretical specific capacity of 1675 mA h g −1 when paired with lithium metal, which is among the highest in solid cathode materials. [9] This is because the sulfur cathode undergoes a conversion reaction mechanism rather than the intercalation chemistry. Together with an average cell voltage of 2.15 V, the coupled lithium-sulfur (Li-S) battery can attain a high theoretical energy density of 2500 W h kg −1 , which is much higher than that of current lithium-ion batteries. [10] The earliest Li-S battery can be traced back to 1962 when Herbert and Ulam first introduced the concept of sulfur cathode (Figure 1). [11] Despite decades of research, the Li-S batteries had been long plagued with low discharge capacity and fast capacity decay upon cycling. Additionally, with the commercialization of lithium-ion batteries by Sony Co. in the 1990s, which have much more stable cycling performance and better safety, the research into Li-S batteries had once ceased for a period. [43] After 2000, as the rapid development of emerging applications such as electric vehicles and grid energy storage placed higher demands on the specific energy Lithium-ion batteries, which have revolutionized portable electronics over the past three decades, were eventually recognized with the 2019 Nobel Prize in chemistry. As the energy density of current lithium-ion batteries is approaching its limit, developing new battery technologies beyond lithiumion chemistry is significant for next-generation high energy storage. Lithiumsulfur (Li-S) batteries, which rely on the reversible redox reactions ...

Rechargeable magnesium batteries have attracted considerable attention because of their potential high energy density and low cost. However, their development has been severely hindered because of the lack of appropriate cathode materials. Here we report a rechargeable magnesium/iodine battery, in which the soluble iodine reacts with Mg2+ to form a soluble intermediate and then an insoluble final product magnesium iodide. The liquid–solid two-phase reaction pathway circumvents solid-state Mg2+ diffusion and ensures a large interfacial reaction area, leading to fast reaction kinetics and high reaction reversibility. As a result, the rechargeable magnesium/iodine battery shows a better rate capability (180 mAh g−1 at 0.5 C and 140 mAh g−1 at 1 C) and a higher energy density (∼400 Wh kg−1) than all other reported rechargeable magnesium batteries using intercalation cathodes. This study demonstrates that the liquid–solid two-phase reaction mechanism is promising in addressing the kinetic limitation of rechargeable magnesium batteries.

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