Solvothermal Synthesis of LiMn1鈥?i>xFexPO4 Cathode Materials: A Study of Reaction Mechanisms by Time-Resolved in Situ Synchrotron X-ray Diffraction

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• 作者：Jianming Bai ; Jian Hong ; Haiyan Chen ; Jason Graetz ; Feng Wang
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：February 5, 2015
• 年：2015
• 卷：119
• 期：5
• 页码：2266-2276
• 全文大小：686K
• ISSN：1932-7455

文摘

We applied time-resolved in situ synchrotron X-ray diffraction (XRD) to study the reaction processes and pathways during the solvothermal synthesis of the olivine-structured LiFePO₄, LiMnPO₄, and LiFe_0.4Mn_0.6PO₄ with ethylene glycol C₂H₆O₂ (EG) as the solvent by following the evolution of the crystal structures of the Fe/Mn-containing phases. We identified a stable intermediate phase in the synthetic reaction process of LiFePO₄, viz., a ferrous oxalate EG complex (FeC₂O₄路C₂H₆O₂), and resolved its structure; thus, we established a two-step reaction mechanism involving dissolution鈥損recipitation followed by interface-coupled dissolution鈥搑eprecipitation for the synthesis of LiFePO₄. The synthetic reactions in an LiFe_0.4Mn_0.6PO₄ solid solution also followed a two-step process via the formation of a metastable intermediate phase bearing a structural similarity to FeC₂O₄路C₂H₆O₂ that, however, has a slightly larger unit-cell, indicating that the substitution of Fe by Mn occurred at the intermediate stage. In contrast, the reaction in the synthesis of LiMnPO₄ proceeds through a simple process of precipitation. Our findings provide important information for optimizing the synthesis of olivine cathode materials. The in situ XRD method we developed in this work offers a new way of exploring a wide range of solvothermal synthesis reactions, which is valuable for the rational design of new batteries.