Selection of Carbon Sources for Enhancing 3D Conductivity in the Secondary Structure of LiFePO₄/C Cathode

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• 作者：Xinhe Yang^a ; ^d ; ¹ ; Jiguo Tu^c ; ¹ ; Min Lei^c ; Zicheng Zuo^c ; Borong Wu^a ; ^d ; ^{wubr@bit.edu.cn" class="auth_mail" title="E-mail the corresponding author} ; Henghui Zhou^b ; ^c ; ^{hhzhou@pku.edu.cn" class="auth_mail" title="E-mail the corresponding author}
• 关键词：LiFePO4/C ; Carbon sources ; Conductivity ; Li-ion diffusion coefficients ; Low-temperature performance
• 刊名：Electrochimica Acta
• 出版年：2016
• 出版时间：1 March 2016
• 年：2016
• 卷：193
• 期：Complete
• 页码：206-215
• 全文大小：2844 K

文摘

Secondary LiFePO₄/C microspheres (LFP) are synthesized with different carbon sources by the spray drying process. The carbon sources effect on the structures, morphologies, and 3D conductivity of the secondary structure are systematically investigated. LFP samples prepared with polyethylene glycol (PEG) and beta-cyclodextrin (β-CD) as mixing carbon sources possesses the loose structure with higher specific surface area, showing the best rate capability, cycling stability and low-temperature discharge characteristic. Additionally, the differences of 3.3 V plateau performance at room temperature and 2.85 V plateau performance at −20 °C are investigated. It could be observed that the electronic and ionic conductivities are reduced gradually with the decrease of the discharge cut-off voltage, while the electronic conductivities are greater than ionic conductivities for the four LFP samples, indicating that the ionic transport is more difficult and the electrochemical reaction is more and more difficult with the increase of Li-ion intercalation. Li-ion diffusion coefficients at the cut-off voltage of 3.30 V under room temperature and at the cut-off voltage of 2.85 V under −20 °C are both the highest for the LFP sample synthesized with PEG and β-CD, further indicating that PEG and β-CD as mixing carbon sources can decrease the charge transfer resistance and promote the 3D electronic/ionic conductivities and Li-ion diffusion coefficients in the secondary structure, thus greatly improve the rate capability, cycling stability and low-temperature capacity of LFP cathode.