Progress in development of electrolytes for magnesium batteries
Over the last few years, there has been an increased interest in developing safe, next-generation battery systems that offer energy densities higher than those of lithium-based batteries. In this context, batteries based on multivalent-ions (Mg 2+ , Zn 2+ , Ca 2+ , and Al 3+ ) have developed their own niche with their capability to achieve at least twice the energy density of monovalent-ion systems such as Li-ion and Na-ion batteries. Among the multivalent-ion battery candidates, magnesium (Mg) batteries appear to be the most viable choice to eventually replace the Li-ion technology because of the high electrode potential, superior safety, and high abundance of Mg-metal. However, the limited development in electrolytes and cathodes has prevented their commercialization to date. There is a lack of suitable electrolytes that can be used at high voltages required for Mg 2+ insertion into cathode hosts. The limited compatibility of organic electrolytes with Mg-metal anode is also a challenge, which requires extensive studies of the metal/electrolyte interactions. Such studies over the last two decades were critical in developing state-of-the-art Mg electrolytes that possess voltage windows of >4.0 V and simultaneously be compatible with Mg-metal anodes. Here, we present a review on the development of Mg battery electrolytes, challenges that impede their performance, and promising strategies that have been adopted to address them. As a result, we believe that this comprehensive review covering all three categories of Mg electrolytes (liquids, polymers, and solids) would enable researchers to get a quick grasp of the prevailing challenges, and consequently motivate them to develop novel electrolyte candidates.