Fluorinated Electrolytes for 5 V Li-Ion Chemistry
Authors: Zhang Zhengcheng , Hu Libo , Xue Zheng , Azimi Nasim 
Published: February 2020

Lithium-ion battery is considered as an ideal power source for electrified vehicles due to its long cycle life and high energy and power density.1 To further increase the energy density, the general approach is to use cathode materials with high operating voltages (5 V vs. Li+/Li) and high specific capacity (250 mAh/g). Tremendous efforts have been taken in this direction. Cathode materials with a potential of more than 5 V have been proposed, for example, olivine-type LiNiPO4
3 and LiCoPO4
4 and normal spinel-type LiNi0.5Mn1.5O4
5 and LiCoMnO4
6. However, these cathode materials require an electrolyte with intrinsic oxidation stability to deliver the full capacity. The state-of-the-art (SOA) organic carbonate-based electrolyte (mixtures of ethylene carbonate with dimethyl carbonate, diethyl carbonate and/or ethyl methyl carbonate dissolved with LiPF6 salt) decomposes above 4.5V vs Li+/Li limiting its application to cathode chemistry with a higher charging voltage plateau to deliver the capacity.3,7 Therefore, the demand for high voltage electrolyte has become an upmost priority for high energy density lithium-ion battery.

Fluorinated organic solvents have long been investigated for many applications in lithium-ion batteries.8,9 Compared with the SOA electrolytes, fluorinated solvents bring a variety of benefits to the electrolyte. For example, fluorinated cyclic carbonate has been used as a co-solvent or as a solid electrolyte interface (SEI) formation additive for graphite10 and silicon anodes.11 Fluorinated carbonates and fluorinated ethers are reported as non-flammable electrolytes non-aqueous lithium ion batteries.12 However, there is little study about the performance of these fluorinated solvents in the high voltage Li-ion battery. Since fluorinated molecules have higher oxidation potentials than their non-fluorinated counterparts due to the strong electron-withdrawing effect of the fluorine atom, fluorinated solvents are good candidates for high voltage electrolyte application. In this talk, we will present our recent results on the fluorinated electrolytes which can significantly improve the performance of the high voltage Li-ion cell based on LiNi0.5Mn1.5O4/graphite couple.

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