Probing the Functionality of Halogen-Free Electrolytes Using Succinonitrile Additive in Magnesium-Sulfur Batteries

Abstract

Rechargeable magnesium batteries have attractive features as a post-lithium battery owing to their high volumetric capacity, safety, and low cost. However, the high charge density of Mg2+ causes sluggish interfacial charge transfer kinetics at the electrode/electrolyte interface. This paper is an attempt to optimize the electrochemical performance of a halogen-free liquid electrolyte (HFE)-based magnesium nitrate (Mg(NO3)2) and variable additive of succinonitrile (SN). A polymer layer interface (PLI) consisting of Mg (CF3SO3)2, polyvinylidene fluoride (PVDF), SN, and G4 has been introduced to isolate the Mg anode's surface from HFE in order to reduce the growth rate of the passivation layer at the surface of the Mg anode. The introduction of SN regulates the ionic conductivity, overpotential of Mg plating/stripping, and the ion transference number of the HFE. A prototype of the Mg/HFE_SN/S full cell delivers a high initial discharge/charge capacity of ~ 1200/500 mAh g−1 with a rapid capacity fade, while (Mg/PLI/HFE_SN/S) cell offers low capacity with long cycle life over (Mg/HFE_SN/S) counterpart. Postmortem analysis of sulfur electrodes at different electrochemical states reveals the reversible back and forth movement of Mg2+ ions in Mg/S cells via conversion reaction.