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Ramasubramonian Deivanayagam1 Meng Cheng1 Emma Hoyt1 Reza Shahbazian-Yassar1

1, University of Illinois at Chicago, Chicago, Illinois, United States

Magnesium batteries are a class of multivalent-ion battery systems that offer the promise of high volumetric energy densities in comparison with the lithium-based counterparts. Unlike lithium metal, magnesium is relatively inexpensive and considered extremely safe because of its dendrite-free deposition. Therefore, magnesium is considered as an ideal candidate for the construction of safer next-generation battery systems. However, intercalation of magnesium-ions (Mg2+) into host crystal lattices has proven to be extremely challenging. Consequently, there are only a handful of cathode materials that can reversibly intercalate Mg2+, and their specific capacities are considerably low. Moreover, the limited availability of Mg electrolytes that have a wide voltage window, makes it difficult to screen for Mg2+ intercalation (cathode) materials. Unfortunately, the few electrolytes that do support high reversibility and possess anodic stability, make use of flammable organometallic reagents and solvents, thereby rendering the battery unsafe.

Polymers like PEO, PVdF have been known for a long time to be a robust, and highly conductive medium for solid-state Li-ion batteries.1 Their conductivity could be further enhanced by using ceramic fillers such as SiO2, Al2O3 etc. Following their successful integration into Li-battery systems, there have been several reports on such Mg-ion conducting solid polymer electrolytes having a high conductivity.2–4 However, studies to determine their Mg-deposition overpotential and cycling efficiency have been scarce.

Here we propose a safe, composite polymer electrolyte that supports high reversibility with Mg-metal anode. Its Mg-ion transport was confirmed by performing DC polarization tests, and by measuring the cationic transference number. Raman spectra of the polymer composites were obtained at different stages of the synthesis to understand the Mg chemical environment. Its compatibility with Mg-metal anode and the reversibility of the Mg-metal battery were tested by cycling a symmetric Mg | Mg two-electrode cell. When the Mg-battery was cycled at moderate current densities at room temperature, a low overpotential of < 0.2 V was observed for up to 100 cycles. We believe that this composite polymer electrolyte would be a significant step forward towards the development of safe rechargeable solid-state Mg-metal batteries.

References:
1. Xue, Z., He, D. & Xie, X. Poly(ethylene oxide)-based electrolytes for lithium-ion batteries. J. Mater. Chem. A 3, 19218–19253 (2015).
2. Pandey, G. P., Agrawal, R. C. & Hashmi, S. A. Magnesium ion-conducting gel polymer electrolytes dispersed with nanosized magnesium oxide. J. Power Sources 190, 563–572 (2009).
3. Shao, Y. et al. Nanocomposite polymer electrolyte for rechargeable magnesium batteries. Nano Energy 12, 750–759 (2015).
4. Song, S. et al. Communication—A Composite Polymer Electrolyte for Safer Mg Batteries. J. Electrochem. Soc. 164, A741–A743 (2017).

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