As a type of next-generation secondary batteries, the magnesium ion battery achieves high energy capacity by using metal magnesium anodes. However, stable battery operation has only been confirmed when using a metal sulfide cathode [1], whose energy capacity and operating potential are lower than those of the latest lithium ion batteries.

One way to increase the output voltage is establishing a cathode / electrolyte interface that is compatible with the cathode redox reaction at a higher potential, where the liquid electrolyte is subjected to oxidization. To accomplish this, a solid-state electrolyte on the thin film cathode could be used to suppress the oxidative decomposition of liquid electrolyte in the magnesium battery. Since the electronically insulating solid state electrolyte inhibits the unwanted electron transfer between the cathode and the electrolyte solution, the electrochemical potential window of the liquid electrolyte could be widened. This solid-state electrolyte coating may be regarded as an artificial solid-electrolyte interphase (ASEI) [2]. We prepared a cell with V₂O₅ thin film cathode coated by a MgZrSiO amorphous solid-state electrolyte using RF sputtering technique. As a result, the cell had higher oxidative stability (decomposition at 4.5 V vs Mg²⁺/Mg) than the cell with the uncoated cathode (3.3 V vs Mg²⁺/Mg) (Figure 1).

Reference

[1] D. Aurbach, Nature, 407, 724 (2000).

[2] N. J. Dudney, J. Power Sources, 89, 176 (2000).

Figure 1 The cyclic voltammogram of the MgZrSiO-coated and bare V₂O₅ thin film cathodes in 0.5M Mg(TFSA)₂/triglyme at 55℃. The scanning rate was 0.1 mV/s.