Reaction Synthesis and Discharge Performance of Binary Vanadium Borides

Vanadium boride compound powders with different compositions were prepared by reactive synthesis at 1500℃ from elemental powders. Then, with the obtained powders as active materials, Ni powder as conductive agent and NH₄HCO₃ as space-holder, the porous anodes of V-xB/Ni (x=2/3~2) were fabricated by powder metallurgy (PM), respectively. The effects of V-xB compounds with different phases on the discharge performance of the assembled air batteries were studied. The results show that the single-phased VB₂ powder can be obtained from the raw powder with the atomic ratio of V:B=1:2, and so does the VB powder. As for atomic ratio of V:B=3:2, the synthesized powder consists of V₃B₂ and a small amount of VB, while the ratio of V:B=2:3 yields the phase composition of V₂B₃, V₃B₄ and minor VB₂. The prepared V-xB/Ni anodes with porosity of 60.25%-61.75% exhibit good discharge performance, and their capacity can reach the range of 6129-7901 mAh while specific capacity is 2724-3511 mAh/g. With the increase of B content, the discharge performance of V-xB/Ni anodes shows a significant improvement. In comparison, the porous V-2B/Ni anode possesses the superior discharge properties with discharge capacity of 3512 mAh/g, coulombic efficiency of 86.5% and specific energy of 2504 Wh/kg.