High Energy Capacity TiB₂/VB₂Composite Metal Boride Air Battery

Abstract

Transition metal borides, such as VB 2 and TiB 2 , are studied as battery anode materials both individually and as a composite anode for an air cathode battery. The combination of VB 2 and TiB 2 is shown to enhance anodic battery performance. In alkaline media, VB 2 and TiB 2 anodically discharge to yield respectively 11 and 6 electrons per molecule with VB 2 intrinsic gravimetric charge capacity of 4,060 mAh/g and 2,314 mAh/g for TiB 2 , 3 to 5 fold higher than a conventional zinc anode. With an air cathode using external O 2 , these boride/air batteries discharge at ∼1 V, and exhibit unusually high, primary battery energy capacities. We show that the coulombic efficiency attained by the TiB 2 anode in boride/air batteries is not a strong function of the anode capacity per unit area (cm 2 ) of anode, while the efficiency of the VB 2 anode decreases with increasing anode capacity. The discharge of VB 2 shows a unique singular voltage plateau, indicating that the 11 electrons discharge at a similar potential. Two voltage plateaus are observed during the TiB 2 discharge indicating the possibility of a two-step anodic oxidation. The combination of VB 2 and TiB 2 exhibits evidence of a synergistic increase of the capacity and discharge voltage of boride/air batteries. The development of improved energy density battery systems is driven by emerging technological demands of longer operational time and lighter weight for medical, military and consumer electronic devices. A principal focus of battery research in the past decade has been the advancement of the energy capacity of rechargeable Li-ion batteries, which have a capacity of 100 to 200 Wh/kg. Despite this, the capacity of rechargeable batteries remains approximately 5-fold lower than that of primary batteries. The highest commercial primary battery energy capacity is exhibited by zinc/air batteries.1 Replacement of the air battery's zinc electrode by a higher capacity anode material has the potential to further increase the energy capacity. New materials, such as metal borides, have been studied due to their demonstrated high capacities as anodes for primary alkaline batteries. Of the large number of borides that have been investigated as anodes in alkaline media, TiB 2 and VB 2 exhibit the highest stability and demonstrated anodic capacity.2-9 Although Zn, TiB 2 , and VB 2 have similar formula weights (65.39, 69.49. 72.56 g/mol), the Zn oxidative discharge releases only two electrons, whereas TiB 2 and VB 2 are observed to discharge up to 6 and 11 electrons, respectively. While the conventional Zn anode has an intrinsic capacity of 820 mAh/g (2*FW/Faraday*mAh), TiB 2 and VB 2 have respective intrinsic capacities of 2,314 and 4,060 mAh/g. Coupled with an air cathode, vanadium diboride has been reported to have among the highest energy density of any primary battery (5,300 kWh/kg). 9 The 11 electron discharge reaction of the VB 2 /air battery is given by the following half cell and full cell reactions: It is interesting to note that VB 2 discharges each of its 11...

FeNi-LDH Intercalation for Suppressing the Self-Discharge of the VB2–Air Battery

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