The Impact of Different Substituents in Fluorinated Cyclic Carbonates in the Performance of High Voltage Lithium-Ion Battery Electrolyte
Authors: Su Chi-Cheung , He Meinan , Peebles Cameron , Zhang Zhengcheng 
Published: February 2020

The development of lithium-ion batteries with high energy and power density is essential for the massive commercialization of electric vehicles. Therefore, new cathode materials with elevated operating voltages (4.6 V vs. Li+/Li) [1] and improved specific capacity [2] have been developed. However, the high voltage (>4.5 V vs. Li+/Li) instability of the state-of-the-art electrolyte, which contains 1.2 M lithium hexafluorophosophate (LiPF6) dissolved in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC)/ethyl methyl carbonate (EMC), hinders the extensive application of new cathode materials. [3] Researchers have been actively exploring new electrolytes with elevated voltage stability [4] and cathode additives that can kinetically suppress the oxidative decomposition of electrolyte by forming a passivation layer on the cathode surface.[5] The superior anodic stability of fluorinated carbonates makes them highly promising candidate for high voltage electrolytes; however, the importance of different substituents in the fluorinated cyclic carbonates has not yet been studied in detail. Herein, we present the cell performance of a graphite/LiNi0.5Mn0.3Co0.2O2 full cell system using various fluorinated cyclic carbonates as electrolyte components.

In this work, different fluorinated cyclic carbonates including FEC, DFEC, TFPC, HFEEC and NFPEC were used in an attempt to form superior solid electrolyte interphases (SEI).Cyclic fluorinated carbonates with various chemical structures were designed, synthesized and characterized by different analytical methods including NMR, GC-MS and FT-IR. Electrolytes were prepared by dissolving 1.0 M LiPF6 in a mixture of fluorinated cyclic carbonate and FEMC in a volume ratio of 3 to 7. The performance of full cells (graphite/LiNi0.5Mn0.3Co0.2O2) using an electrolyte composition containing FEC and TFPC showed the best capacity retention. With the addition of 1 wt.% additive (DTD), the cell performance of the TFPC based electrolyte can be further improved as indicated from the exceptional capacity retention of the TFPC cell at high temperature (55 oC). In conclusion, various fluorinated cyclic carbonates were synthesized and among all the carbonates, TFPC based electrolyte displayed promising properties for their application in high voltage lithium-ion batteries.

References:

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