Surface treatment of LiFePO₄ cathode material with PPy/PEG conductive layer

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• 作者：Andrea Fedorkov谩 ; Ren谩ta Ori艌谩kov谩 ; Andrej Ori艌谩k ; Hans-Dieter Wiemh枚fer ; Du拧an Kaniansky and Martin Winter
• 关键词：Lithium ; ion battery ; Polypyrrole coating ; LiFePO4 ; Cathode particles ; Impedance
• 刊名：Journal of Solid State Electrochemistry
• 出版时间：December 2010
• 出版年：2010
• 期刊代码：79_1432-8488
• 类别：ch
• 卷：14
• 期：12
• 页码：2173-2178
• 数据来源：sp

摘要

In this work, we studied LiFePO₄ particles coated with thin films of highly conductive polypyrrole (PPy) and their electrochemical performance in cathode layers of lithium cells. Carbon-free LiFePO₄ particles were synthesized by a solvothermal method. Besides this, a part of the experiments were carried out on commercial carbon-coated LiFePO₄ for comparison. Polypyrrole coated LiFePO₄ particles (PPy-LiFePO₄) were obtained by a straightforward oxidative polymerization of dissolved pyrrole on LiFePO₄ particles dispersed in water. The use of polyethylene glycol (PEG) as an additive during the polymerization was decisive to achieve high electronic conductivities in the final cathode layers. The carbon-free and carbon-coated LiFePO₄ particles were prepared with PPy and with PPy/PEG coating. The obtained PPy-LiFePO₄ and PPy/PEG-LiFePO₄ powders were characterized by SEM, EIS, cyclic voltammetry, and galvanostatic charge/discharge measurements in lithium-ion cells with lithium metal as counter and reference electrode. Carbon-free LiFePO₄ coated with PPy/PEG hybrid films exhibited very good electrode kinetics and a stable discharge capacity of 156 mAh/g at a rate of C/10. Impedance measurements showed that the PPy/PEG coating decreases the charge-transfer resistance of the corresponding LiFePO₄ cathode material very effectively, which was attributed to a favorable mixed ionic and electronic conductivity of the PPy/PEG coatings.