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

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• 作者：Jie Li ; Chang Fu Yuan ; Zhi Hong Guo ; Zhi An Zhang ; Yan Qing Lai ; Jin Liu ; ^{csulightmetals09@163.com}
• 关键词：Li-ion battery ; Low temperature ; Electrolyte ; LiBF4 ; LiPF6
• 刊名：Electrochimica Acta
• 出版年：2012
• 出版时间：1 January, 2012
• 年：2012
• 卷：59
• 期：Complete
• 页码：69-74
• 全文大小：775 K

文摘

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 ¡ãC to ?0 ¡ãC, electrochemical impedance spectroscopy (EIS) results show that the charge-transfer resistance (R_ct) of graphite/Li cell decreases, the R_ct 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 ¡ãC to ?0 ¡ãC, 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 (¦¤G) of electrode reaction is approximately the same (?0 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.