Search

With excellent specific capacity, superior cycle stability, safety and strong practical, Nb2O5 has been considered as one of the prospective anode materials for lithium-ion batteries (LIBs). However, current study suggests that Nb2O5 electrode materials for LIBs still face the vital issues of low electrical conductivity and poor rate performance. Therefore, carbon-coated TT-Nb2O5 materials are designed and synthesized through solid state method in this work, which present high specific capacity (228 mA h g−1 at 0.2C), satisfactory rate properties (107 mA h g−1 at 20 C). The outstanding electrochemical property can not only give the credit to the pseudocapacitance effect of TT-Nb2O5, but also attribute to introduction of carbon. The homogeneous carbon-coated materials enhance the electrical conductivity, increase the electron transmission speed and alleviate particle crushing. This research not only offers a new method for preparing excellent electrode materials, but also provides a kind of excellent anode material with prospective application for LIBs.

In this reported study, Li3NbO4-based, Li-excess cathode materials xLi3NbO4•(1-x)LiMnO2 (0.2 ≤ x ≤ 0.5) were synthesized using a solid state reaction method. XRD results showed that the fabricated powders with x = 0.3–0.5 could be indexed to a typical rock-salt structure (Fm-3m space group). Rietveld refinements showed that the lattice parameters increased with the increase in Nb5+ content. SEM and TEM images of the product showed that the elements Nb, Mn and O were evenly distributed in the samples, which further confirmed the cubic rock-salt structure of the product. Electrochemical tests of the samples showed that the sample with x = 0.4 exhibited the best electrochemical performance (232 mAh/g in the first cycle and more than 175 mAh/g in 50 cycles, as well as relatively high discharge capacity at high discharge current density). The redox mechanism analysis of the experimental results indicated that there were two stages in charge process: one was the Mn3+/4+ oxidation reaction below 4.3 V, and the other was related to the oxidation of O2− to O− or the release of O2, which improved the reversible capacity of the material. The structural evolution analysis of the samples showed that a spinel phase structure was present during the cycling process and the shift in the XRD peaks indicated that the sample with x = 0.4 exhibited the best structural stability. The electrochemical impedance spectroscopy analysis showed that the sample with x = 0.4 had the smallest Rct. The results for the kinetics of lithium ion diffusion indicated that the sample with x = 0.4 had largest DLi+, which was consistent with the best electrochemical performance for this material, especially the rate capability.

Columbite CuNb2O6 anode materials are prepared at 800–1000 °C through the typical solid-state reaction. CuNb2O6 sintered at 900 °C exhibits not only an exceptional rate capability (still 154.9 mAh·g−1 at the ultra-large current rate of 5 A·g−1) but also outstanding cyclic stability (the capacity retention of 90.3% at 500 mA·g−1 after 1000 cycles). These properties indicate that columbite CuNb2O6 may be a potential anode material for lithium-ion batteries.