Lithium Metal Batteries with Improved Thermal Stabilities

<b>Lithium Metal Batteries with Improved Thermal Stabilities</b><br/>Xia Cao, Wu Xu, Ji-Guang Zhang^*<br/>Energy and Environment Directorate, Pacific Northwest National Laboratory<br/>Richland, Washington 99354, United States<br/> <br/>Development of lithium (Li) metal batteries (LMBs) has attracted worldwide attention in recent years due to their much higher theoretical energy densities than those of conventional Li ion batteries.^1,2 Other metal batteries (MBs), such as Na metal batteries (NMBs) and potassium metal batteries (PMBs) also attracted more and more attention due to their abundance in earth crust and low cost.^3,4 Although long cycle life of metal batteries have been demonstrated,^2,5,6 their large-scale applications are still hindered by several barriers. One of the main barriers is the thermal stability of the electrolytes, especially when they are in contact with high voltage cathode. Therefore, development of electrolyte with improved thermal stability is critical for large scale application of metal batteries<br/> <br/>In this work, factors affecting thermal stability of electrolytes for Li metal batteries will be discussed. First, electrolyte components should be selected to enable preferential decomposition of its salt rather than solvent so an inorganic rich interphase layer can be formed on electrodes, especially on metal anode to block its continuous reaction with electrolyte. These inorganic rich SEI layers can also enable the formation of large size of metal particles instead of nano powders, therefore minimize the surface area of anode. Formation of a stable SEI layer can not only minimize the formation of powdered metal particles, but also can prevent exposure of large amount of pure metal powder to ambient air in case of mechanical damage of batteries. Second, electrolyte solvents with high boiling point, low vapor pressure, and low reactivity with oxygen species are desired. These features will largely slow down the formation of flammable vapor when the cell is exposed to ambient air. Third, electrolyte should be stable at elevated temperature even at fully charged (high voltage) conditions. In any case, selection of solvent properties should not compromise electrochemical property es of the electrolytes. At last, examples of novel electrolytes based on these design principles will be reported in this work.<br/> <br/>1 Whittingham, M. S. History, Evolution, and Future Status of Energy Storage. <i>Proceedings of the IEEE</i> <b>100</b>, 1518-1534, (2012).<br/>2 Niu, C.<i> et al.</i> Balancing interfacial reactions to achieve long cycle life in high-energy lithium metal batteries. <i>Nature Energy</i>, (2021).<br/>3 Jin, Y.<i> et al.</i> Low-solvation electrolytes for high-voltage sodium-ion batteries. <i>Nature Energy</i>, (2022).<br/>4 Zhang, W., Liu, Y. & Guo, Z. Approaching high-performance potassium-ion batteries via advanced design strategies and engineering. <i>Science Advances</i> <b>5</b>, eaav7412, (2019).<br/>5 Hu, Q. Li-Metal Batteries. <i>https://s29.q4cdn.com/695431818/files/doc_presentation/2022/03/March-2022-Investor-Presentation.pdf</i>, (2022).<br/>6 Zheng, J.<i> et al.</i> Extremely Stable Sodium Metal Batteries Enabled by Localized High-Concentration Electrolytes. <i>ACS Energy Letters</i> <b>3</b>, 315-321, (2018).