Limiting factors for low-temperature performance of electrolytes in LiFePO4/Li and graphite/Li half cells

• Published in: Electrochimica acta 2012, Vol.59, p.69-74
• Main Authors: Li, Jie, Yuan, Chang Fu, Guo, Zhi Hong, Zhang, Zhi An, Lai, Yan Qing, Liu, Jin
• Format: Article
• Language: English
• Subjects: Activation energy; Applied sciences; Constraining; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Electrochemical impedance spectroscopy; Electrodes; Electrolytes; Electrolytic cells; Exact sciences and technology; Graphite; Ionic conductivity
• ISSN: 0013-4686; 1873-3859
• DOI: 10.1016/j.electacta.2011.10.041

Low-temperature performance of LiBF4 and LiPF6-based electrolytes in LiFePO4/Li and graphite/Li half cells was investigated. In the temperature range from 0 degree C to -40 degree C, electrochemical impedance spectroscopy (EIS) results show that the charge-transfer resistance (Rct) of graphite/Li cell decreases, the Rct of LiFePO4/Li cell increases, and sum resistance of LiFePO4/Li and graphite/Li cell decreases when replacing LiPF6 with LiBF4. In the temperature range from 25 degree C to -40 degree C, energy barrier (W) for Li-ion jump at the solid electrolyte interface (SEI) alters slightly from 16.04 kJ/mol to 13.60 kJ/mol in LiFePO4/Li cells, but declines greatly from 46.47 kJ/mol to 19.81 kJ/mol in graphite/Li cells when using LiBF4 instead of LiPF6, meanwhile, activation energy ( Delta G) of electrode reaction is approximately the same (~60 kJ/mol). The above results indicate that the ionic conductivity is the main limiting factor for low-temperature performance of electrolytes in LiFePO4/Li cell, while factors related with electrolyte-interface are more crucial in graphite/Li cell than in LiFePO4/Li cell.