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 ionblocking 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-cohexafluoropropylene) (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 aniongrafted 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.