On Mg batteries cycled in TFSI-based electrolytes containing polysulfides

BRACAMONTE, M. VICTORIA; ALEN VIZINTIN ; GREGOR KAPUN; JAN BITNEC; MIRAN GABERčEK; ROBERT DOMINKO

Congreso; 2020 Express Conference on the Physics of Materials and Their Applications in Energy Harvesting; 2020

Li-ion batteries have not only revolutionized portable electronics but also, started an electromobility revolution by storing more energy by volume and mass than their competing systems (Ni-MH, lead acid batteries). However, the specific capacities for Li-ion cathode and graphite anode are expected to be limited only to 400 and 370 mAh g-1, respectively.1,2 For this reason, the batteries? research has been pushed to the frontiers of new systems (Na-ion, Mg-ion, Li-S, Mg-S). Magnesium-sulfur battery is a young technology, which was firstly demonstrated by Muldoon and co-workers in 2011.3 Like Li-S battery the operation mechanism of Mg-S battery is based on a conversion reaction concept on the cathode side.4?7 Due to this, both batteries share also similar problems, e.g. self-discharge, low cycle life due to fast capacity fade, shuttle effect, high polarization, and polysulfide depletion due to MgS precipitation.6-8 Furthermore, also sluggish solid-state Mg2+ diffusion contribute to large overpotentials.10 Altough a lot of work has been done in development for weakly coordinated magnesium salts and new non-nucleophilic electrolyte concepts for Mg-S battery to overcome the low cycle lifetime, there are still a lot of questions opened on what is happening on the surface/interphase of the Mg anode. Herein, we have focus on a study of a Mg electrode interphase in an Mg(TFSI)2, MgCl2 ether-based electrolyte with and without the presence of Mg polysulfides. The electrochemical formed surface films were carefully analyzed by employing galvanostatic/potentiostatic methods, electrochemical impedance spectroscopy (EIS), focused ion beam-scanning electron microscopy (FIB-SEM).