High-Performance Magnesium Electrochemical Cycling with Hybrid Mg–Li Electrolytes

• Published in: ACS applied materials & interfaces Vol. 14; no. 30; pp. 34552 - 34561
• Main Authors: Krebsz, Melinda, Johnston, Sam, Nguyen, Cuong Ky, Hora, Yvonne, Roy, Binayak, Simonov, Alexandr N., MacFarlane, Douglas R.
• Format: Journal Article
• Language: English
• Published: American Chemical Society 03.08.2022
• Subjects: Energy, Environmental, and Catalysis Applications; borohydride; Mg electrodeposition; mixed electrolyte; Mg electrochemistry; bis(trifluoromethylsulfonyl)imide
• ISSN: 1944-8244; 1944-8252
• DOI: 10.1021/acsami.2c04073

Kinetics and coulombic efficiency of the electrochemical magnesium plating and stripping processes are to a significant extent defined by the composition of the electrolyte solution, optimization of which presents a pathway for improved performance. Adopting this strategy, we undertook a systematic investigation of the Mg0/2+ process in different combinations of the Mg2+–Li+–borohydride–bis­(trifluoromethylsulfonyl)­imide (TFSI–) electrolytes in 1,2-dimethoxyethane (DME) solvent. Results indicate that the presence of BH4 – is essential for high coulombic efficiency, which coordination to Mg2+ was confirmed by Raman and NMR spectroscopic analysis. However, the high rates observed also require the presence of Li+ and a supplementary anion such as TFSI–. The Li+ + BH4 – + TFSI– combination of ionic species prevents passivation of the magnesium surface and thereby enables efficient Mg0/2+ electrochemical cycling. The best Mg0/2+ performance with the stabilized coulombic efficiency of 88 ± 1% and one of the highest deposition/stripping rates at ambient temperature reported to date are demonstrated at an optimal [Mg­(BH4)2]:[LiTFSI] mole ratio of 1:2.