Mg-Ion Conducting Gel Polymer Electrolyte Based on High Flash Point Solvent Adiponitrile for Magnesium Ion Batteries

Abstract

Due to some specific properties of adiponitrile (ADN) including high oxidative stability and high flash point, it is proposed as co-solvent with an ionic liquid (IL) as a promising electrolyte solvent for application in magnesium batteries. Herein, we report a flexible film of gel polymer electrolyte (GPE) comprising a polymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) in which a liquid electrolyte of Mg-trifluoromethane sulfonate (Mg-triflate) in the mixture of ADN:IL (1-ethyl-3-methylimidazolium triflate, EMITf) is immobilized for use in Mg-batteries. The structural/morphological properties of the GPE film have been characterized via different physical techniques. The high ionic conductivity (σ_RT = 5.9 mS cm⁻¹), wide potential range of oxidative stability (~4.18 V vs. Mg/Mg²⁺), high Mg-ion transport number (t_Mg²⁺ = 0.67) and thermal stability up to ~160°C ascertain the compatibility of electrolyte film in magnesium batteries with high voltage cathode materials. The comparative studies of the interfacial-stability and Mg-stripping/plating tests on the two symmetrical cells with Mg and Mg/MWCNTs nanocomposite electrodes show the improved reversibility of the electrolyte film with Mg-MWCNTs powder as anode material, compared with pure Mg-powder. The overall results indicate that the GPE based on binary solvent mixture ADN:IL is high performance flexible electrolyte for Mg-batteries with Mg-MWCNTs powder as anode material.