Mechanisms and Performances of Na1.5Fe0.5Ti1.5(PO4)3/C Composite as Electrode Material for Na-Ion Batteries

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• 作者：Siham Difi ; Ismael Saadoune ; Moulay Tahar Sougrati ; Rachid Hakkou ; Kristina Edstrom ; Pierre-Emmanuel Lippens
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：November 12, 2015
• 年：2015
• 卷：119
• 期：45
• 页码：25220-25234
• 全文大小：778K
• ISSN：1932-7455

文摘

The properties, insertion mechanisms, and electrochemical performances of the Na_1.5Fe_0.5Ti_1.5(PO₄)₃/C composite as electrode material for Na-ion batteries are reported. The composite was obtained by solid-state reaction and consists of porous secondary particles of submicron-sized particles coated by carbon. Detailed characterizations were performed by combining theoretical and experimental tools. This includes the determination of the crystal structure of Na_1.5Fe_0.5Ti_1.5(PO₄)₃ from both first-principles calculations and X-ray diffraction providing Na distribution over M1 and M2 interstitial sites, which is of importance for ionic conductivity. Na_1.5Fe_0.5Ti_1.5(PO₄)₃/C was used as an electrode material at 2.2 V versus Na⁺/Na⁰, exhibiting good Na-storage ability with a specific capacity of 125 mAh g^鈥?, close to the theoretical value, for the first discharge at C/10, good capacity retention, and Coulombic efficiency of 95% and 99.5% at the 60th cycle, respectively, and high power rate with a decrease of the specific capacity of only 14% from C/10 to 2C. These good performances have been related to the morphology of the composite and the substitution of Fe for Ti, leading to an insertion mechanism that differs from that of NaTi₂(PO₄)₃. This mechanism was quantitatively analyzed from operando ⁵⁷Fe M枚ssbauer spectroscopy used for the first time in both galvanostatic and GITT modes.