A number of transition-metal borides were studied as anodic materials for neutral aqueous batteries. These borides are shown to have considerably high electrochemical activities in neutral electrolytes. The discharge capacities for TiB2 reach 1,350 mAh g−1 at a constant current density of 50 mA g−1, exceeding those for all the metal electrodes reported so far. Amorphous CoBx can deliver a discharge capacity of >650 mAh g−1, and even simply ball-milled FeBx can also give a discharge capacity of >200 mAh g−1. These results suggest the possible use of boride compounds as a large family of new anodic materials for constructing neutral aqueous batteries with high electrochemical capacity and rate capability.
