Aliovalent Ni in MoO2 Lattice鈥?Probing the Structure and Valence of Ni and Its Implication on the Electrochemical Performance

详细信息    查看全文

• 作者：Ofer Hirsch ; Guobo Zeng ; Li Luo ; Malwina Staniuk ; Paula M. Abdala ; Wouter van Beek ; Felix Rechberger ; Martin J. S眉ess ; Markus Niederberger ; Dorota Koziej
• 刊名：Chemistry of Materials
• 出版年：2014
• 出版时间：August 12, 2014
• 年：2014
• 卷：26
• 期：15
• 页码：4505-4513
• 全文大小：611K
• ISSN：1520-5002

文摘

Here, we present a synthesis of MoO₂ nanoparticles doped with 2 at% of Ni in a mixture of acetophenone and benzyl alcohol at 200 掳C. Based on in situ X-ray absorption near-edge structure (XANES) and ex situ extended X-ray absorption fine structure (EXAFS) measurements at Ni K-edge and Mo K-edge, we discuss scenarios on how the 鈥渄oping鈥?reaction, that is, the incorporation of Ni in the MoO₂, proceeds. We can clearly exclude the formation of NiO or Ni nanoparticles. Moreover, within the resolution of our in situ XANES experiments, we observe that the ternary compound Ni:MoO₂ nucleates directly in the final composition. Although the local structure around the Ni ion adopts the MoO₂ crystal structure pointing at the substitution of tetravalent Mo by Ni, we find that Ni remains divalent. This aliovalent substitution results in the relaxation of the local structure, which is additionally reflected in the slight shrinking of the total volume of the unit cell of Ni:MoO₂. Interestingly, such a small amount of divalent Ni has a tremendous effect on the performance of the material as anode in Li-ion batteries. The initial discharge capacity of Ni:MoO₂ based anodes almost doubles from 370 mAh/g for MoO₂ to 754 mAh/g for Ni:MoO₂ at 0.1 C (1 C = 300 mA/g). Additionally, we observed an atypical increase of capacity for both MoO₂ and Ni:MoO₂ anodes upon cycling with increasing cycling rate.