Influence of Electrochemical Performance of Lithium Ion Batteries with the Adding of LiF and LiCl

doi:10.6023/A16080394

Abstract

In the past few decades, lithium hexafluorophosphate (LiPF₆) is the most widely employed ionic component in organic electrolyte solutions for commercial lithium ion battery, which is manufactured using PCl₅, LiF and HF as raw materials via the HF solvent method in the large scale production, and then it commonly contains LiF and LiCl impurities besides water and acid. However, the influence of LiF and LiCl on the performance of lithium ion battery is still not clear. Thus, in this paper, the influence of LiF and LiCl on the electrochemical performance of graphite electrode was investigated using charge-discharge test and cyclic voltammetry (CV) combining with scanning electron microscope (SEM) and electrochemical impedance spectrum (EIS). Charge-discharge test results showed that the electrochemical performance of graphite electrode such as reversible capacity and cycling stability were significantly improved in 1 mol/L LiPF₆-EC:DEC:DMC electrolyte with the saturation of LiF. The initial charge capacity of graphite electrode in 1 mol/L LiPF₆-EC:DEC:DMC electrolyte with the saturation of LiF is 331.0 mAh/g, which is higher than that in 1 mol/L LiPF₆-EC:DEC:DMC electrolyte (307.9 mAh/g). After 65 charge-discharge cycles, the charge capacity of graphite electrode in 1 mol/L LiPF₆-EC:DEC:DMC electrolyte with the saturation of LiF is 340.1 mAh/g, which is also higher than that in 1 mol/L LiPF₆-EC:DEC:DMC electrolyte (297.0 mAh/g). However, although the first charging capacity of graphite electrode was enhanced in 1 mol/L LiPF₆-EC:DEC:DMC electrolyte with the saturation of LiCl, the charge-discharge cycling stability was serious deteriorated. The initial charge capacity of graphite electrode in 1 mol/L LiPF₆-EC:DEC:DMC electrolyte with the saturation of LiCl is 334.2 mAh/g, yet after 65 charge-discharge cycles, the charge capacity of graphite electrode in 1 mol/L LiPF₆-EC:DEC:DMC electrolyte with the saturation of LiCl is 251.2 mAh/g. CV results showed that the influence of LiF and LiCl on the decomposition process of EC in electrolyte is small. SEM and EIS results stated that the SEI film which was formed on the graphite electrode is thinner and has a smaller resistance in 1 mol/L LiPF₆-EC:DEC:DMC electrolyte with the saturation of LiF than that in 1 mol/L LiPF₆-EC:DEC:DMC electrolyte. Thus the reversible cycle capacity of graphite electrode was increased and its cycle stability was improved. Nevertheless the SEI film which was formed on the graphite electrode is thicker and its resistance is higher in 1 mol/L LiPF₆-EC:DEC:DMC electrolyte with the saturation of LiCl than that in 1 mol/L LiPF₆-EC:DEC:DMC electrolyte, which leads to the deterioration of electrochemical performance of graphite electrode.

Key words: lithium ion battery, graphite electrode, LiPF₆, LiF, LiCl

Cite this article

Ren Tong, Zhuang Quanchao, Hao Yuwan, Cui Yongli. Influence of Electrochemical Performance of Lithium Ion Batteries with the Adding of LiF and LiCl[J]. Acta Chim. Sinica, 2016, 74(10): 833-838.

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