Preparation and Electrochemical Performance of Mo6V9O40 Nanorods as Cathode Materials for Li-Ion Batteries

Searching for cathode materials for Li ions batteries with high energy density is a key mission in recent years [1]. Among various candidates, vanadium and molybdenum oxides have been intensively studied due to their high capacity, easy preparation, and low cost. For example, Li ions can reversibly intercalate/deintercalate into the lattice layers of V₂O₅ and MoO₃. Their hybrid oxides, molybdenum-vanadium based oxides, have been reported to be more sustainable to over discharge (to 1.5 V vs. Li/Li⁺), including solid solution (V_1-yMo_y)₂O₅ (0≤y≤0.3) and Mo₆V₉O₄₀ [2]. Introduction of Mo into the structure increases the M-O bond length, and the structure is more flexible for Li ion intercalation/deintercalation. In addition, substituting Mo⁶⁺ for V⁵⁺increases the electronic conductivity [3].

Pure-phase molybdenum and vanadium mixed oxides are difficult to be obtained due to the multiphase equilibrium. Extremely long annealing time at high temperatures (above 600ºC) is needed to eliminate the impurity phases (such as V₂O₅ and MoO₃). However, long time at high temperatures results in large particles, which degrades the electrochemical performance and is unfavorable for large-scale production. In this work, Mo₆V₉O₄₀ nanorods with the diameters of ~200 nm were prepared through a sol-gel route, and the calcining time decreased to 2 h. The Mo₆V₉O₄₀ nanorods exhibited an initial discharge capacity of 369 mA h g^-1 at a current density of 100 mA g^–1, and Li⁺ intercalation is partly irreversible, which is similar to V₂O₅. The discharge capacities of the second cycle were 276.2 and 212 mA h g^-1 at 100 mA g^–1 and 1 A g^–1, and retained 214.8 and 181.8 mA h g^-1after 50 cycles, exhibiting good cyclic stability and rate performance.

Figure 1. (a) SEM, (b) TEM, (c) charge/discharge curves at 100 mA g^–1, and (d) cyclic performance at 100 mA g^–1 and 1 A g^–1 of Mo₆V₉O₄₀nanorods.

References

[1] M. Hu, X. Pang, Z. Zhou, J. Power Sources 237 (2013) 229-242.

[2] A. Tranchant, R. Messina, J. Power Sources 24 (1988) 85-93.

[3] M. Uchiyama, S. Slane, E. Plichta, M. Salomon, J. Electrochem. Soc. 136 (1989) 36-42.