Overpotential-Dependent Phase Transformation Pathways in Lithium Iron Phosphate Battery Electrodes

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• 作者：Yu-Hua Kao ; Ming Tang ; Nonglak Meethong ; Jianming Bai ; W. Craig Carter ; Yet-Ming Chiang
• 刊名：Chemistry of Materials
• 出版年：2010
• 出版时间：November 9, 2010
• 年：2010
• 卷：22
• 期：21
• 页码：5845-5855
• 全文大小：1204K
• 年卷期：v.22,no.21(November 9, 2010)
• ISSN：1520-5002

文摘

An objective in battery development for higher storage energy density is the design of compounds that can accommodate maximum changes in ion concentration over useful electrochemical windows. Not surprisingly, many storage compounds undergo phase transitions in situ, including production of metastable phases. Unique to this environment is the frequent application of electrical over- and underpotentials, which are the electrical analogs to undercooling and superheating. Surprisingly, overpotential effects on phase stability and transformation mechanisms have not been studied in detail. Here we use synchrotron X-ray diffraction performed in situ during potentiostatic and galvanostatic cycling, combined with phase-field modeling, to reveal a remarkable dependence of phase transition pathway on overpotential in the model olivine Li_1-xFePO₄. For a sample of particle size 113 nm, at both low (e.g., <20 mV) and high (>75 mV) overpotentials a crystal-to-crystal olivine transformation dominates, whereas at intermediate overpotentials a crystalline-to-amorphous phase transition is preferred. As particle sizes decrease to the nanoscale, amorphization is further emphasized. Implications for battery use and design are considered.