Aliovalent Substitution of V3+ for Co2+ in LiCoPO4 by a Low-Temperature Microwave-Assisted Solvothermal Process

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• 作者：Karl J. Kreder III ; Gaurav Assat ; Arumugam Manthiram
• 刊名：Chemistry of Materials
• 出版年：2016
• 出版时间：March 22, 2016
• 年：2016
• 卷：28
• 期：6
• 页码：1847-1853
• 全文大小：579K
• ISSN：1520-5002

文摘

Electrical and ionic conductivity has proven to be a major limiting factor in the adoption of high-voltage polyanion cathode materials, specifically LiMPO₄ (M = Mn, Co, Ni). While the aliovalent substitution of V³⁺ for Fe²⁺ in LiFePO₄ has been shown recently, no conclusive evidence is available for aliovalent substitutions in the analogous LiCoPO₄. This study presents a low-temperature microwave-assisted solvothermal synthesis and characterization of aliovalently substituted LiCo_1–3x/2V_x□_x/2PO₄ for x ≤ 0.07. The as synthesized LiCo_1–3x/2V_x□_x/2PO₄ samples belonging to the Pn2₁a space group are transformed to the Pnma polymorph via calcination in an inert atmosphere at 525 °C. The LiCo_1–3x/2V_x□_x/2PO₄ samples are characterized with scanning electron microscopy, X-ray diffraction, Rietveld refinement, inductively coupled plasma optical emissions spectroscopy, Raman and infrared spectroscopy, galvanostatic charge/discharge, electrochemical impedance spectroscopy, and cyclic voltammetry. Unlike the prior reports of aliovalent substitution via high-temperature methods, the LiCo_1–3x/2V_x□_x/2PO₄ samples presented here experienced a systematic decrease in the unit cell volume with increasing vanadium substitution. The electrochemical performance and cyclability of LiCo_1–3x/2V_x□_x/2PO₄ is greatly improved compared to the unsubstituted LiCoPO₄.