Lithium ion batteries have dominated the portable electronics market and have the potential to dominate large-scale battery applications including hybrid and electric vehicles as well as grid storage because of their high energy and power densities.[1] It is well known that conventional electrolytes (such as 1.2 M LiPF₆ in EC/EMC 3/7) show poor anodic stabilities above 4.5 V versus Li/Li⁺.[2] However, high voltage electrolytes play an intrinsic role in many applications such as hybrid and electrical vehicles, aerospace uses and power grids. As a result, high voltage electrolytes are essential for the development of next generation lithium ion batteries. One possible solution is to develop fluorinated electrolytes which not only form kinetically stable SEI interphase, but also are resistant to oxidative decomposition due to their high oxidation potential. [3] In this work, a novel fluorinated electrolyte was introduced in a graphite-LiNi_0.5Mn_0.3Co_0.2O₂ full cell operated between 3.0 - 4.6 V. The electrolyte contains 1.0 M LiPF₆ dissolved in a mixture of FEC and HFDEC solvent with 1wt % LiDFOB used as the additive. Compared to a conventional EC and EMC based electrolyte, the fluorinated electrolyte shows an excellent cycle life under a 4.6V cut off voltage. NMR and GC-MS were used to analyze the harvested electrolyte post-cycling while SEM, XPS and FTIR were employed to study the interface between the electrolyte and the bulk electrodes. Most importantly, HR-XRD and XANS were conducted to investigate and compare the cycled bulk cathode electrode in different electrolytes. To the best of our knowledge, the structural change of the cycled cathode material in different electrolytes has never been reported. Therefore, we believe this research is a crucial breakthrough for studying the interaction between the electrolyte and electrode. The methodology developed could be fundamental in the design and investigation of better electrolytes for next generation lithium ion batteries.

[1]Xu, Kang. "Nonaqueous liquid electrolytes for lithium-based rechargeable batteries." Chemical reviews 104.10 (2004): 4303-4418.

[2] Xu, Kang. "Electrolytes and interphases in Li-ion batteries and beyond." Chemical reviews 114.23 (2014): 11503-11618.

[3] Zhang, Zhengcheng, et al. "Fluorinated electrolytes for 5 V lithium-ion battery chemistry." Energy Environ. Sci. 6.6 (2013): 1806-1810.