Magnesium Anode Protection by an Organic Artificial Solid Electrolyte Interphase for Magnesium-Sulfur Batteries

In the search forpost-lithium battery systems, magnesium-sulfurbatteries have attracted research attention in recent years due totheir high potential energy density, raw material abundance, and lowcost. Despite significant progress, the system still lacks cyclingstability mainly associated with the ongoing parasitic reduction ofsulfur at the anode surface, resulting in the loss of active materialsand passivating surface layer formation on the anode. In additionto sulfur retention approaches on the cathode side, the protectionof the reductive anode surface by an artificial solid electrolyteinterphase (SEI) represents a promising approach, which contrarilydoes not impede the sulfur cathode kinetics. In this study, an organiccoating approach based on ionomers and polymers is pursued to combinethe desired properties of mechanical flexibility and high ionic conductivitywhile enabling a facile and energy-efficient preparation. Despiteexhibiting higher polarization overpotentials in Mg-Mg cells,the charge overpotential in Mg-S cells was decreased by thecoated anodes with the initial Coulombic efficiency being significantlyincreased. Consequently, the discharge capacity after 300 cycles applyingan Aquivion/PVDF-coated Mg anode was twice that of a pristine Mg anode,indicating effective polysulfide repulsion from the Mg surface bythe artificial SEI. This was backed by operando imaging during long-termOCV revealing a non-colored separator, i.e. mitigated self-discharge.While SEM, AFM, IR and XPS were applied to gain further insights intothe surface morphology and composition, scalable coating techniqueswere investigated in addition to ensure practical relevance. Remarkablytherein, the Mg anode preparation and all surface coatings were preparedunder ambient conditions, which facilitates future electrode and cellassembly. Overall, this study highlights the important role of Mganode coatings to improve the electrochemical performance of magnesium-sulfurbatteries.

Automated summary

Magnesium-sulfur batteries have gained attention as potential post-lithium battery systems due to their high energy density, abundance of raw materials, and low cost. However, their cycling stability is still a challenge. This study demonstrates that the protection of the anode surface with an artificial solid electrolyte interphase (SEI) through an organic coating approach can effectively improve the electrochemical performance of magnesium-sulfur batteries. The coating reduces polarization overpotentials and inhibits the loss of sulfur, resulting in enhanced cycling efficiency and higher discharge capacity.