The Influence of Fluoroethylene Carbonate on the LiCoO2/Electrolyte Interface

Lingli Kong, Zhijiang Su, Junkui Gao, Jie Sun Tianjin Lishen battery Joint-Stock Co. Ltd, 6 Lanyuan Road, Huayuan Hi-Tech Industry Park, China Introduction The outstanding SEI formed on the anode/electrolyte interface by adding fluoroethylene carbonate (FEC) additive had been reported many times . While, there are few publications about the effect of FEC on the LiCoO2/electrolyte interface. In this paper we aims to clarify the effect of FEC on the LiCoO2 electrode. Experimental About 1.0M LiPF6 in a 1:1:1(vol) mixture of EC, EMC, DEC was used as the standard electrolyte and 5wt% FEC were added to the standard electrolyte. Li/ LiCoO2 coin-type cells 2430 were assembled in dry room. EIS were used to measure the impedance of Li/LiCoO2 coin cell (full charged) after 3 cycles, and the cells were used to monitor the voltage change for storage test after EIS test. The electrode was removed from cell after 10 cycles in dry room and washed with DMC, then dried at room temperature in vacuum. The surface composition of cathode surface was analyzed by XPS. The thermal stability of the LiCoO2 powder gathered from the mentioned electrode above was evaluate using TG -DTA method. Results and Discussion It shows that the potential of cells with 5%FEC keeps more stable than the control one in the storage duration (Fig. 1), it may ascribe that FEC participates in the formation of SEI on the LiCoO2 electrode surface in the first cycle. And The TG-DTA and EIS data also indicate the influence of FEC on the LiCoO2/ electrolyte interface. The XPS data of C1s and F1s on LiCoO2 surface are summarized in Fig.2. It indicates that there are C-C(284.6ev), R-OCOO-(290.2ev) , and C-F(687.1ev) on LiCoO2 surface, which prove the effect of FEC on LiCoO2/electrolyte interface. We suppose that FEC was oxidized to form SEI(containing C, F polymeric substance) on the LiCoO2 surface during first charge. The further study of the influence of FEC on the LiCoO2 cathode is underway. References [1] M. Mogi, M. Inaba, S.K. Jeong, Y. Iriyama, T. Abe, Z. Ogumi, J. Electrochem. Soc. 2002, 149: A1578. [2]P. Irina. A., K. Sung-Soo, C Nam-Soon, Electrochimica Acta, 2009, 54: 4445~4450 275 280 285 290 295 300 0 500