Exploration of Multi-Component Solvent System Electrolytes for the Extended Low-Temperature Performance of Lithium-Ion Batteries

Abstract

Optimized electrolyte design for lithium-ion batteries (LIBs) is essential for Li dendrite formation suppression and enhanced electrochemical performance. The present work illustrates an electrolyte design concept aimed at improved performance of LIBs at extremely low temperatures. Electrochemical measurements explored a temperature range from -20°C to 20°C. Thermoanalytical and electrochemical characterizations of electrolytes at low temperatures were given special focus to direct electrolyte design and explain possible limiting factors of the designed electrolytes. Electrolyte design involved different combinations, ratios, and solvent multiplicities of ethylene, dimethyl, diethyl, propylene carbonate (EC, DMC, DEC, PC) solvents with acetate- and ester-based cosolvents. Electrolyte compositions were selected with careful consideration to past studies of co-solvents that improved low temperature cycling of LIBs. In addition to characterization methods, temperature-controlled experiments of electrochemical impedance spectroscopy in combination with cyclic voltammetry were performed to further examine changes in the electrochemical properties of electrolytes over time. Contradictory to expectations and in spite of the absence of freezing point depression, the lowest-complexity 2 solvent system electrolyte exhibited good performance at extremely low temperatures. However, TTE, an ester-based cosolvent, was shown to enhance low temperature performance in the higher-complexity solvent system electrolyte. The results of this study recommend that future studies on creating high-multiplicity solvent system compositions exhibiting stable long-term performance in extremely low temperatures strive to achieve a balance in electrolyte design according to solvation energies and ionic conductivities of individual solvents components, in addition to considerations on solvent multiplicity.