Hydrogen atoms, THF of crystallization, and second component of disorder are omitted for clarity. Reprinted with permission from ref 52. Copyright 2011 Nature Publishing Group. (b) ORTEP plot (25% thermal probability ellipsoids) of (Mg 2 (μ-Cl) 3 •6THF)(Ph 2 AlCl 2 ) (APC); 50% thermal probability ellipsoids; hydrogen atoms omitted for clarity. Reprinted with permission from ref 9.

Research leading to the construction of an ambient temperature rechargeable magnesium battery based on organic electrolytes and positive electrodes capable of reversible intercalation of Mg § ions is discussed. The number of combinations of solvent, solute, and intercalation cathode which give reasonable battery performance is much more limited for Mg than for alkali metals. The only electrolytes which allowed Mg dissolution and deposition were solutions of organomagnesium compounds in ethers or tertiary amines; many of these were unstable in the presence of transition metal oxides or sulfides which were found to function acceptably as intercalation electrodes. Possible directions for future research which could solve these problems are discussed, as well as theoretical aspects of magnesium compound behavior in nonaqueous solvents.

Magnesium is an ideal metal anode that has nearly double the volumetric capacity of lithium metal with a very negative reduction potential of -2.37 vs SHE. A significant advantage of magnesium is the apparent lack of dendrite formation during charging, which overcomes major safety and performance challenges encountered with using lithium metal anodes. Here, we highlight major recent advances in nonaqueous Mg electrochemistry, notably the development of electrolytes and cathodes, and discuss some of the challenges that must be overcome to realize a practical magnesium battery.

Magnesium metal is a superior anode which has double the volumetric capacity of lithium metal and has a negative reduction potential of -2.37 V vs. the standard hydrogen electrode. A major benefit of magnesium is the apparent lack of dendrite formation during charging which is one of the crucial concerns of using a lithium metal anode. In this Review, we highlight the foremost research in the development of electrolytes and cathodes and discuss some of the significant challenges which must be overcome in realizing a practical magnesium battery.

Research and development of post lithium ion batteries is attracting considerable attention. While there have been significant advances in understanding the challenges of Li-O2(air) and Li-S batteries, the development of gas separation and ion selective membranes will be crucial in their commercialization due to their potential to separate O2 from air and impede lithium polysulfide dissolution while permitting rapid diffusion of lithium ions. In addition, research leading to novel and highly conductive and selective polymer electrolytes will be essential in overcoming the deficiencies of liquid based electrolytes in both the air and sulfur based battery systems