Highly concentrated solutions of lithium salts in water have made sweeping strides from the time in the early 2010s where aqueous electrolytes could operate a battery within an electrochemical window no more than 1.5V wide. In this presentation, we discuss the construction of a lithium ion battery using graphite as the anode and LiCoO2 as the cathode to make a cell with a 4.2V potential. The primary electrolyte is a water:trimethylphosphate hybrid with a water mole fraction of 0.44 and LiTFSI salt at a concentration of 9 molal. This aqueous hybrid electrolyte can be formed into a gel electrolyte by directly polymerizing acrylate-based monomers and crosslinkers dissolved in the electrolyte. We demonstrate that by protecting the graphite anode using an acrylate gel with a fluoroethylene carbonate-based liquid electrolyte, the battery cell can be cycled repeatedly between 3.0V and 4.2V just like a cell using organic carbonate electrolytes. The advantage of the aqueous hybrid electrolyte is that it is non-flammable, and a cell using aqueous gel electrolytes can withstand damage and even be cut open while operating with no risk of fire or explosion. The manufacturing and performance characteristics of the aqueous 4V battery will be discussed as well as the interfacial issues that come about with the use of aqueous gel electrolytes in a 4V-capable battery system.

The development of aqueous solutions containing comparatively high amounts of dissolved salts has brought water, an unlikely solvent, into the ongoing development of new battery chemistries. Aqueous electrolytes have the advantage of being inherently non-flammable materials, while demonstrating high cation transference number behavior and cation conductivity in the range of 1-10 mS/cm 2 in the case of Li + . As a reaction medium, highly concentrated aqueous electrolytes allow for polymerization reactions such as radical polymerization to occur, and it has been demonstrated that the kinetics of these reactions are fast enough to allow rapid processing into films of solid gel electrolytes. While lithium ion batteries were one of the first applications of aqueous gel electrolytes, we have synthesized gel electrolytes for the increasingly popular sodium and zinc systems as well. This talk will focus on the kinetics of polymerization of various radicalized monomers, the formation and properties of the solid gels that result, and the electrochemical behavior and application tree that follow using the new electrolyte materials.

Water-in-salt electrolytes (WiSE) are one of a growing family of water-based lithium ion electrolytes that use high concentrations of non-hydrolyzable lithium salts such as LiTFSI. WiSE are non-flammable and have a much wider electrochemical stability window than typical dilute aqueous electrolytes through two anion-based mechanisms: the formation of a passive anode layer through the decomposition of the TFSI- anion and exclusion of water by the anion from the cathode surface. This work details the formation of a polymer gel network containing WiSE as its liquid phase using commercially available polymer and crosslinker components. WiSE gel electrolytes are thought to be a natural evolution of the water-in-salt concept, as a WiSE gel should allow for WiSE-containing batteries to decouple themselves from typical cylindrical and prismatic battery form factors. Cycling performance and mechanical properties of the gel electrolytes will be discussed, along with fundamental investigations into the electrode-electrolyte interface and the minimization of charge-transfer resistance. Additionally, the kinetics of gel reactions in WiSE as a solvent will be discussed.