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

作者：Hirsch Ofer; Zeng Guobo; Luo Li; Staniuk Malwina; Abdala Paula M; van Beek Wouter; Rechberger Felix; Sueess Martin J; Niederberger Markus; Koziej Dorota^*

来源：Chemistry of Materials, 2014, 26(15): 4505-4513.

DOI：10.1021/cm501698a

Here, we present a synthesis of MoO2 nanoparticles doped with 2 at% of Ni in a mixture of acetophenone and benzyl alcohol at 200 degrees 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 "doping" 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.

• 出版日期2014-8-12