A novel boron-based electrolyte system for rechargeable Mg batteries

Batteries are now powering our world and an ideal battery that is characterized by high capacity, safety, environmental friendliness and low cost is very important for today's society. Mg is abundant in resource and much cheaper than lithium. It possesses a very negative electrode potential (-2.37V vs. SHE) and a high theoretical specific capacity (2205Ah Kg-1). Moreover, owing to its lower chemical reactivity than metallic lithium, high safety can be expected when metallic Mg is used as negative electrode material. Given these advantages, rechargeable Mg batteries have gained more and more attentions as next-generation energy-storage devices in heavy load applications [1, 2]. One of the key challenges for developing practical rechargeable Mg batteries is to establish a reversible redox process of Mg. However, it is not easy to achieve sufficient reversibility of Mg in most electrolyte systems because Mg metal tends to form passive films not only in aqueous but also in non-aqueous media. Aurbach et al. developed a family of aluminum based electrolyte solutions of Mg(AlCl4-nRn’Rn”)2 (R, R= alkyl or aryl groups, n’+ n” = n) in ethereal solvents. The optimized composition of THF solution of Mg(AlCl2BuEt)2 complex and AlCl3-(PhMgCl)2 complex exhibited the improved anti-oxidation capability and excellent reversible Mg deposition/dissolution characteristics, which greatly promoted the development of rechargeable Mg batteries[2,3]. Fig.1 Typical steady-state voltammograms of Pt electrodes i