Exploring hybrid Mg2+/H+ reactions of C@MgMnSiO4 with boosted voltage in magnesium-ion batteries

Abstract

MgMnSiO4 is a promising cathode material for rechargeable magnesium batteries, however, it still suffers from unsatisfactory electrochemical performances. Although the modulation of electrolyte formulation and cell configuration are critical to enhancing the electrochemical behavior of MgMnSiO4, few works focused on these important issues. Therefore, to get cathode materials operating at high voltage and overcome the electrostatics problems of bivalent Mg2+ ion, we adopt an unconventional approach of engaging water in a conventional nonaqueous solution such as 0.5 M Mg(TFSI)2 in DME (dimethoxyethane). The electrochemical reaction of Mg/electrolyte/C@MgMnSiO4 cell occurs at 2.8 – 0.5 V (vs. Mg2+/Mg) with 160 mA h g-1 entailing 300 W h kg−1 at the materials’ level. The results show that C@MgMnSiO4 could be a potential cathode material for high-energy magnesium secondary batteries in a bifunctional electrolytes, which not just utilized as a transmitter ... of Mg2+, but also as a source of H+. We prove that the generated H+ increases the isotropy around Mg2+, changes in the Mn oxidation states, and modifies Mg/MgO interphase. Eventually, by assembling several Mg-ion full cells versus different anodes including Li4Ti5O12, activated carbon, and Mg0.5MnSiO4, we recall the main challenges to overcome.