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

Abstract

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 Mg²⁺ cannot maintain the structural integrity of intercalation-type cathodes even for open framework prototypes. The lack of high-voltage electrolytes and sluggish Mg²⁺ 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.