Control of Electrolyte Reactivity: A New Design of Electrolyte Additives for High Voltage Lithium Ion Batteries

Abstract

To reach a higher energy density, lithium ion batteries have been pushed to cycle at a higher voltage. The development of new high voltage electrolytes and additives are essential as the fading mechanism at high voltages is tied up with exacerbating oxidation, cathode electrolyte interface formation, as well as the blockage of accessible active Li+. The additive development strategy has mostly followed the trial and error principle, and a paradigm shift is hard.Here we report a development strategy which tames the spontaneity of electrolyte reactivity and opens an avenue to new additives that would be impossible to achieve otherwise. The talk will cover the recent development of a series of in-situ additives that utilize the reactivity of bistrimethylsilyl carboxylates with two -OSiMe3 groups to react with LiPF6 and form highly moisture sensitive lithium carboxylato phosphate additive (Figure 1).1,2 These additives targets at alleviating cathode impedance rise and show exceptional performance with NMC 532//Gr cell at 4.4 V. Figure 1. Structure of in-situ additives and the exchange reaction between -O-TMS and LiPF6. Recently we were also able to use a rational design to expand the family of in-situ additives to include functionality of - N-SiMe3 (TMSML, see Figure 1).4 High nickel cathodes show better performance with the -N-SiMe3 containing additive as they prevent the hydrolysis of LiPF6 caused by traces of water in a carbonate electrolyte, both ex and in situ. It also inhibits oxidative decomposition of electrolytes on the energized cathode through deactivation of the Transition Metal-Oxide (-TM-O.) radical center. We trace these beneficial functions to the ease of nucleophilic substitution and the formation of TM-O.N< that reduce electrolyte oxidation.Overall, a new design of additives has been implemented with invention of two classes of new additives that improve the performance of high voltage lithium ion batteries.References I. Shkrob, B. Han, R. Sahore, A. P. Tornheim, L. Zhang, D. P. Abraham, F. Dogan, Z. Zhang, C. Liao,* Chemistry of Materials 2019, 31, 2459-2468.Yang, I. Shkrob, Q. Liu, N. L. Dietz Rago, Y. Liu, K. Liu, Z. Zhang, C. Liao,* Journal of Power Sources 2019, 438, 227039.Yang, I. Shkrob, K. Liu, J. Connell, N. L. Dietz Rago, Z. Zhang a and C. Liao*, J. Electrochemical Society, 167 (7), 070533 Figure 1