An Additive Study for Water-in-Salt Electrolyte (WiSE) with Lithium Manganese Oxide (LMO) and Titanium Niobate (TNO) Electrodes

Author(s):

Jackson Carter, Matthew Sieh, Janet Sun, Brett Sweeney, Arthur von Cresce, Glenn Pastel, and Marshall A Schroeder

Abstract:

Aqueous electrolytes are poised to eliminate numerous safety concerns relative to state-of-the-art organic electrolytes; however, they continue to suffer from parasitic side reactions that consume lithium and limit performance. In this study we performed additive screening of 10 species for water-in-salt electrolytes (WiSEs) with the goal of forming a more robust and resilient anode solid-electrolyte interphase against hydrogen evolution at the anode. Coin cells consisted of a high-loading LiMnO₂ cathode (13.32 mg cm-2) and a low-loading TiNb₂O₇ anode (3.32 mg cm-2) to isolate the impact on anode performance. Down-selections were performed over the course of four experiments including 1) solubility, 2) impedance, 3) cycling retention, and 4) storage, with the baseline WiSE electrolyte outperforming all other WiSE-plus-additive compositions. However, the baseline WiSE electrolyte also suffered a 37% drop in energy density relative to similar cells with conventional organic electrolyte (1.0 M LiPF₆ in ethylene carbonate:diethyl carbonate [EC:DEC]). Storage tests proved particularly useful for determining the amount of parasitic current at certain cell potentials (2.3, 2.4, and 2.5 V), which correlates to coulombic inefficiency. These results indicate a pressing need to reduce parasitic reactions at the anode by investigating protective coatings and less-catalytic anode materials.