Synthesis and Evaluation of Fluorinated Carbonates As Solvents for High-Voltage Lithium-Ion Battery Electrolyte

High-voltage Li-ion battery draws great interest due to the promise to deliver high power and energy which are essential to transportation applications. The bottleneck to this technology is the anodic stability of the organic electrolyte. Approaches to solve this problem include developing additives to kinetically stabilize the cathode/electrolyte interface and developing novel electrolyte systems that are intrinsically stable toward oxidation at high potential . Our group has been taking the second approach with a focus on fluorinated compounds as electrolyte solvents. We have synthesized a series of fluorinated cyclic carbonates and linear carbonates and evaluated their electrochemical stability and other physical characteristics. Electrolytes formulated from these fluorinated compounds have demonstrated excellent anodic stability and some of the formulations also showed enhanced cell performance for LiNi0.5Mn1.5O4(LNMO)/ graphite full cells. Characterization of harvested electrolyte with NMR and GC-MS revealed that less soluble decomposition products were generated in the fluorinated electrolyte compared with the conventional electrolyte. Investigation of the cycled electrodes with SEM and TEM revealed that the high stability of the fluorinated electrolyte on the cathode not only helped with the electrolyte decomposition problem, but also reduced the degradation of the electrode material as well.