Maria Lukatskaya1
ETH Zürich1
Electrolytes are an essential component of energy storage devices. Electrolyte composition has a significant impact on the safety, price and performance of the battery. Intrinsically nonflammable aqueous electrolytes can offer safer battery operation and decreased associated toxicity but suffer from a smaller electrochemical stability window (and hence energy density) compared to traditional organic electrolytes. To circumvent the small electrochemical stability window, highly concentrated “water-in-salt”, WIS, lithium organic imide systems which demonstrate significantly wider stability windows were recently proposed.<sup>1,2</sup> However, the toxicity often associated with organic imides and high price make the practical implementation of current water-in-salt electrolyte chemistries into commercial energy storage devices challenging.<br/>We address the challenge of developing new formulations of water-in-salt electrolytes caused by the lack of lithium salts having water solubility high enough to satisfy the water-in-salt condition. The proposed mixed cation strategy can enable use of cheaper (by at least an order of magnitude) and more soluble salts featuring alkali cations beyond lithium, e.g. potassium acetate, to create the water-in-salt condition.<sup>3</sup> We study co-dissolution of corresponding lithium and zinc salts, we show that such highly concentrated electrolytes can provide the same benefits of the extended voltage window as imide-based electrolytes and, demonstrate compatibility with traditional Li-ion or Zn-ion battery electrode materials while being low-cost and environmentally benign. In addition, we demonstrate the strong effect of the solution concentration on the solvation structure of the cations and local order in the potassium acetate-based WIS systems and correlate it with the electrochemical response of different Zn-ion and Li-ion based electrode systems.<br/><br/><b>References</b><br/>L. Suo, O. Borodin, T. Gao, M. Olguin, J. Ho, X. Fan, C. Luo, C. Wang and K. Xu, Science, 2015, 350, 938<br/>Y. Yamada, K. Usui, K. Sodeyama, S. Ko, Y. Tateyama and A. Yamada, Nat. Energy, 2016, 1, 16129<br/>MR Lukatskaya, JI Feldblyum, DG Mackanic, F Lissel, DL Michels, Y Cui, Z. Bao, Energy Environ. Sci., 2018, 11, 2876-2883