Crystal Structure, Physical Properties, and Electrochemistry of Copper Substituted LiFePO4 Single Crystals

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• 作者：Shailesh Upreti ; Natasha A. Chernova ; Jie Xiao ; Joel K. Miller ; Olga V. Yakubovich ; Jordi Cabana ; Clare P. Grey ; Vincent L. Chevrier ; Gerbrand Ceder ; Janice L. Musfeldt ; M. Stanley Whittingham
• 刊名：Chemistry of Materials
• 出版年：2012
• 出版时间：January 10, 2012
• 年：2012
• 卷：24
• 期：1
• 页码：166-173
• 全文大小：432K
• 年卷期：v.24,no.1(January 10, 2012)
• ISSN：1520-5002

文摘

Copper substituted lithium iron phosphate, with the olivine structure, has been synthesized hydrothermally as dark-brown single crystals with 15% of the iron sites occupied by cupric ions. Single crystal X-ray diffraction and magnetic susceptibility,combined with Li solid state NMR studies performed on powder sample, showed that 5% of the lithium ions also reside on the iron site, giving the formula Li_0.95[(Fe²⁺)_0.70(Fe³⁺)_0.10(Cu²⁺)_0.15Li_0.05)]PO₄. The compound exhibits anisotropic magnetic susceptibility and orders antiferromagnetically at 48 K. The magnetic moments are aligned along [010] as in LiFePO₄. The optical measurements indicate that the dark brown color originates from interionic d-d transitions. A part of the lithium ions can be cycled in an electrochemical cell, corresponding to the oxidation/reduction of the iron ions. An onset of a second electrochemical process is observed at about 4.1 V, tentatively attributed to the removal of Li ions from the Fe site. The first principles calculations indicate above 5 V redox potential for the Cu²⁺/Cu³⁺ pair in the olivine structure, much higher than experimentally observed. The diffusion coefficient is determined from galvanostatic intermittent titration data, as part of the delithiation process proceeds as a single-phase reaction in this disordered compound.

Keywords:

copper olivine; hydrothermal synthesis; redox behavior