High Rate Magnesium-Sulfur Battery with Improved Cyclability Based on Metal-Organic Framework Derivative Carbon Host.

Mg batteries have the advantages of resource abundance, high volumetric energy density, and dendrite-free plating/stripping of Mg anodes. However the injection of highly polar Mg ²⁺ cannot maintain the structural integrity of intercalation-type cathodes even for open framework prototypes. The lack of high-voltage electrolytes and sluggish Mg ²⁺ diffusion in lattices or through interfaces also limit the energy density of Mg batteries. Mg-S system based on moderate-voltage conversion electrochemistry appears to be a promising solution to high-energy Mg batteries. However, it still suffers from poor capacity and cycling performances so far. Here, a ZIF-67 derivative carbon framework codoped by N and Co atoms is proposed as effective S host for highly reversible Mg-S batteries even under high rates. The discharge capacity is as high as ≈600 mA h g ^-1 at 1 C during the first cycle, and it is still preserved at ≈400 mA h g ^-1 after at least 200 cycles. Under a much higher rate of 5 C, a capacity of 300-400 mA h g ^-1 is still achievable. Such a superior performance is unprecedented among Mg-S systems and benefits from multiple factors, including heterogeneous doping, Li-salt and Cl ^- addition, charge mode, and cut-off capacity, as well as separator decoration, which enable the mitigation of electrode passivation and polysulfide loss.
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