(Invited) The Role of Electrolyte Solution in Next-Generation Batteries

Abstract

Lithium-ion electrolytes are predominantly base on carbonate solvents and have been instrumental in the success of the lithium-ion battery.1 Uniquely, their ability to form a stable solid-electrolyte interphase (SEI) at lithiated carbon electrodes underpins the battery.2 Unfortunately, the lithium-ion battery is approaching maturity and attention is turning to alterative next-generation batteries that are able to deliver enhancements in energy, power, sustainability and cost. Often, the challenges in next-generation batteries are very different from those found in the lithium-ion battery.3 New understanding and advancements in electrolyte chemistry will be needed to realize these technologies.Here, we look at how electrolyte chemistry and impurities can control charge/discharge reactions in next-generation batteries. For example, the lithium-air battery has one of the highest specific energies of any known secondary battery chemistry, but faces significant challenges.4 The battery operates via oxidation of lithium metal at the anode, coupled to reduction of oxygen and formation of lithium peroxide at the cathode and these reactions are heavily influenced by the electrolyte chemistry.5 Moreover, to operate in air they must tolerate H2O, and here we describe how solvent chemistry is able to control the discharge route from a 2-electron reaction to an irreversible 4-electron reaction. This theory explains why cells are able to tolerate 1 M H2O,6, 7 and we show that with judicious selection of the electrolyte, up to 4 M H2O can be tolerated at the positive electrode of the battery. The impact of electrolyte chemistry on anode reactions will also be discussed. Recently, there has been significant research into magnesium anodes due to their high volumetric capacity (twice that of metallic lithium) and limited dendrite formation.8 Here we consider the nature of SEI films at magnesium in simple salt glyme ether electrolytes and how this impacts the cyclability of magnesium metal. Our results demonstrate the formation of a dynamic SEI at magnesium. Reference s G. E. Blomgren, J. Electrochem. Soc., 164, A5019–A5025 (2017).E. Peled, J. Electrochem. Soc., 126 (1979).D. Larcher and J. M. Tarascon, Nat. Chem., 7, 19–29 (2015)W. J. Kwak et al., ACS Appl. Mater. Interfaces (2020).L. Johnson et al., Nat. Chem., 6, 1091–1099 (2014)K. U. Schwenke, M. Metzger, T. Restle, M. Piana, and H. A. Gasteiger, J. Electrochem. Soc., 162, A573–A584 (2015).N. B. Aetukuri et al., Nat. Chem., 7, 50–56 (2015)R. Attias, M. Salama, B. Hirsch, Y. Goffer, and D. Aurbach, Joule, 3, 27–52 (2019)