The effect of electrolyte temperature on the passivity of solid electrolyte interphase formed on a graphite electrode

摘要

The effect of electrolyte temperature on the passivity of solid electrolyte interphase (SEI) wasinvestigated in 1M LiPF_6-ethylene carbonate/diethyl carbonate (50:50 vol.%) electrolyte,using galvanostatic charge-discharge experiment,and ac-impedance spectroscopy combined with Fourier transform infra-red spectroscopy,and high resolution transmission electron microscopy (HRTEM).The gavanostatic charge-discharge curves at 20degC evidenced that the irreversible capacity loss during electrochemcial cycling was markedly increased with rising SEI formation temperature from 0 to 40degC.This implies that the higher the SEI formation temperature,the more were the graphite electrodes exposed to structural damages.From both increase of the relative amount of Li_2CO_3 to ROCO_2Li and decrease of resistance to the lithium transport through the SEI layer with increasing SEIformation temperature,it is reason able to claim that,due to the enhanced gas evolution reactions during transformation of ROCO_2Li to Li_2CO_3,the rising SEI formation temperature increased the number of defect sites in the SEI layer.From the analysis of HRTEM images,no significant structural destruction in bulk graphite layer was observed after charge-discharge cycles.This means that solvated lithium ions were intercalated through the defect sites in the SEI,at most,into the surface region of the graphite layer.