Prototype systems for rechargeable magnesium batteries

Abstract

The thermodynamic properties of magnesium make it a natural choice for use as an anode material in rechargeable batteries, because it may provide a considerably higher energy density than the commonly used lead-acid and nickel-cadmium systems. Moreover, in contrast to lead and cadmium, magnesium is inexpensive, environmentally friendly and safe to handle. But the development of Mg batteries has been hindered by two problems. First, owing to the chemical activity of Mg, only solutions that neither donate nor accept protons are suitable as electrolytes; but most of these solutions allow the growth of passivating surface films, which inhibit any electrochemical reaction. Second, the choice of cathode materials has been limited by the difficulty of intercalating Mg ions in many hosts. Following previous studies of the electrochemistry of Mg electrodes in various non-aqueous solutions, and of a variety of intercalation electrodes, we have now developed rechargeable Mg battery systems that show promise for applications. The systems comprise electrolyte solutions based on Mg organohaloaluminate salts, and Mg(x)Mo3S4 cathodes, into which Mg ions can be intercalated reversibly, and with relatively fast kinetics. We expect that further improvements in the energy density will make these batteries a viable alternative to existing systems.

Intercalation and Push‐Out Process with Spinel‐to‐Rocksalt Transition on Mg Insertion into Spinel Oxides in Magnesium Batteries

“…Moreover, the cyclability is significantly affected by the thermal stability of the PVDF binder (in the compoisite active material) that cannot be endurable around 150 °C. To return to the subject, in the 1st discharge process, the converted working potential is shown to be 2–2.5 V vs. Mg 2+ /Mg, which is much higher than that of the Chevrel compounds,8 and the capacity amounts to about 120 mAh g −1 above 2 V vs. Mg 2+ /Mg and also amounts to 170 mAh g −1 above 1 V vs. Mg 2+ /Mg at a rate of 1/10 C.…”

“…For example, there are no appropriate electrolytes with wider electrochemical windows and without causing passivation on the Mg‐electrode surface. Furthermore, despite that several candidates for the MRB cathode materials have been reported,5, 6, 7 there are few cathode materials for MRBs that can work at ambient temperature except for Chevrel compounds;8, 9 even though the Chevrel compounds are used, the electromotive force delivers about 1.0–1.2 V, and the energy density of Mg battery is less than 150 mWh g −1 (currently 370 mWh g −1 in electrode energy density of LiCoO 2 vs graphite). Therefore, unless more talented cathode materials that can accommodate polyvalent cations are sought out, PSBs would not be comparable to Li ion batteries in terms of the energy density.…”

Understanding the Initial Stages of Reversible Mg Deposition and Stripping in Inorganic Nonaqueous Electrolytes

“…3,7,8,10,11 In all cases, Cl aligns toward the Mg surface, with adsorption on the HLW site preferred over the TOP site as shown in Figure 1 (also see Figure S2 in Supplementary Information), because in comparison to TOP, HLW and SIDE oriented adsorption (shown in Figure 5) maximizes the interaction of the Cl ion with the Mg surface sites as well as that of some dangling C and H atoms from the THF molecules with the Mg surface. Of all the charged magnesium-chloro complexes, (MgCl) + coordinated by 5 THF in the hollow site exhibits the strongest adsorption energy (-84.7 ± 10.5 kJ mol −1 ), and in general the strength of the adsorption reduces with sequential THF removal, as seen in the trend of adsorption energies of Figure 5.…”

“…3,11,31 Negative ∆Es indicate that spontaneous adsorption is preferred. Referencing to the THF gas state would make the adsorption energies more negative (see Supplementary Information Figure S1) by adding the gas to liquid bonding energy (∼ -46 kJ mol −1 ).…”

“…One of the most promising approaches is to build on the traditional robust three-component Li-ion battery architecture (intercalation or metal anode, non-aqueous electrolyte, and intercalation cathode), but with a multivalent chemistry such as Mg 2+ , 3,4 where multiple electrons are transported per ion (i.e. 2 electrons for each Mg 2+ compared to 1 for Li + ).…”