TFSI Anion Grafted Polymer as an Ion-Conducting Protective Layer on Magnesium Metal for Rechargeable Magnesium Batteries

Rechargeable Mg batteries are one of the most promising candidates for next-generation batteries because of their safety, low cost, and high energy density. However, passivation of the Mg anode by the formation of an ion-blocking interphase layer in common organic electrolytes requires an electrolyte compatible with Mg. Herein, we propose a facile and processable method to fabricate Mg2+ ion-permeable protective polymer layers for Mg metal anodes. The trifluoromethanesulfonimide (TFSI) anion can be grafted onto a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymer backbone, significantly amorphizing the structure and boosting Mg2+ ion conductivity through the polymer layer. TFSI anion grafting is validated through spectroscopic analyses, and the mechanism of grafting is primarily ascribed to the polarity of the PVDF-HFP molecule. This anion-grafted polymer can form a film-like, high-surface-coverage coating layer on the Mg surface, preventing Mg from directly contacting the electrolyte. The Mg anode with this Mg2+ ion-permeable protection layer presents markedly improved performance in both Mg symmetric cells and Mg/V2O5 full cells using a common electrolyte of Mg(TFSI)2 in propylene carbonate. We expect that this study will stimulate Mg battery research through the use of various common organic electrolytes.