New High Energy Capacity VB2/TiB2 Composite Transition Metal Boride Air Battery

Transition metal borides, such as vanadium diboride (VB₂) and titanium diboride (TiB₂), are studied as alkaline battery anode materials both individually and as a composite anode for an air cathode battery. Composite batteries containing various amounts of VB₂ and TiB₂ show evidence of a synergistic enhancement of the cells both in their discharge voltage and in their efficiency. In alkaline media, VB₂ and TiB₂ individually electrochemically oxidize to yield 11 and 6 electrons per molecule, respectively. These anodes deliver an intrinsic gravimetric charge capacity of 4,060 mAh/g for VB₂ and 2,314 mAh/g for TiB₂, which is 3 to 5 fold higher than a typical zinc anode. High energy densities are obtained by using a cathode active material, oxygen, located outside the battery itself. The discharge of nanoscopic-VB₂ shows a single voltage plateau of ~1V as a result of the simultaneous oxidation of all 11 electrons, though the coulombic efficiency (the actual charge capacity vs. the theoretical charge capacity) is greatly dependent upon the capacity of the anode; on the other hand, two distinct plateaus are reported for the macroscopic-TiB₂ discharge curve (the first at ~1V, the second at ~0.85V), indicating the possibility of a two-step anodic oxidation occurring, but the coulombic efficiency of these cells remains constant despite changes in anode capacity.