Tuning MgCl2 content in BMIMPF6 to optimize mg-ion battery performance

Abstract

This study aims to explore magnesium chloride salt-ionic liquid as an efficient electrolyte for Magnesium-ion Batteries (MIBs) using graphite as a cathode material. A complete physicochemical and electrochemical characterizations were performed on a number of electrolyte compositions and important properties including ion solvation, specific conductivity, ion transport behaviour, dominant ionic species, and electrochemical stability were tested. Also, the effect of magnesium salt concentration on specific capacity, reversibility, stability, charge retention, and rate capability were examined. Moreover, the effect of graphite electrodes on Solid Electrolyte Interphase (SEI) layer, its practicality, and cyclability of the different electrolyte compositions afforded interesting conclusions by this comprehensive comparison of electrode-electrolyte pairings. This evaluation is further supported by life cycle analysis, which gave an important information on how to keep electrodes structurally intact even after several uses. Though there were differences in the three electrolyte systems with respect to reversibility, stability, cyclicbility, capacity fading, and unexpected failures, the 0.2 M electrolyte showcased a notable feature of a high ionic conductivity (4.6 × 10−3 mS cm−1) at room temperature and strong anodic stability (4.0 V vs. Mg/Mg2+). Thus, endorsing the developed system as promising lead for further exploration. Additionally, magnesium dissolution and deposition on a Pt working electrode in this electrolyte was also thoroughly examined in this study. The process of PF6¯ ion intercalation and de-intercalation into graphite layer structure was examined using Cyclic Voltammetry (CV). Based on the analysis by Field Emission- Scanning Electron Microscopy (FE-SEM), Energy Dispersive Spectroscopy (EDS), and X-ray Photoelectron Spectroscopy (XPS), a change in the active-material morphology was observed and we hypothesize that this might be the reason for the improved performance.