University of Sydney researchers have found a solution for one of the biggest stumbling blocks preventing zinc-air batteries from overtaking conventional lithium-ion batteries as the power source of choice in electronic devices.
Zinc-air batteries are batteries powered by zinc metal and oxygen from the air. Due to the global abundance of zinc metal, these batteries are much cheaper to produce than lithium-ion batteries, and they can also store more energy (theoretically five times more than that of lithium-ion batteries), are much safer, and are more environmentally friendly.
While zinc-air batteries are currently used as an energy source in hearing aids and some film cameras and railway signal devices, their widespread use has been hindered by the fact that, up until now, recharging them has proved difficult. This is due to the lack of electrocatalysts that successfully reduce and generate oxygen during the discharging and charging of a battery.
the new method can be used to create bifunctional oxygen electrocatalysts for building rechargeable zinc-air batteries from scratch.
“Up until now, rechargeable zinc-air batteries have been made with expensive precious metal catalysts, such as platinum and iridium oxide. In contrast, our method produces a family of new high-performance and low-cost catalysts,” he said.
These new catalysts are produced through the simultaneous control of the: 1) composition, 2) size and 3) crystallinity of metal oxides of earth-abundant elements such as iron, cobalt and nickel. They can then be applied to build rechargeable zinc-air batteries.
Paper co-author Dr Li Wei, also from the University’s Faculty of Engineering and Information Technologies, said trials of zinc-air batteries developed with the new catalysts had demonstrated excellent rechargeability – including less than a 10 percent battery efficacy drop over 60 discharging/charging cycles of 120 hours.
“We are solving fundamental technological challenges to realize more sustainable metal-air batteries for our society,” Professor Chen added.
Metal oxides of earth-abundant elements are promising electrocatalysts to overcome the sluggish oxygen evolution and oxygen reduction reaction (OER/ORR) in many electrochemical energy-conversion devices. However, it is difficult to control their catalytic activity precisely. Here, a general three-stage synthesis strategy is described to produce a family of hybrid materials comprising amorphous bimetallic oxide nanoparticles anchored on N-doped reduced graphene oxide with simultaneous control of nanoparticle elemental composition, size, and crystallinity. Amorphous Fe0.5Co0.5Ox is obtained from Prussian blue analog nanocrystals, showing excellent OER activity with a Tafel slope of 30.1 mV dec−1 and an overpotential of 257 mV for 10 mA cm−2 and superior ORR activity with a large limiting current density of −5.25 mA cm−2 at 0.6 V. A fabricated Zn–air battery delivers a specific capacity of 756 mA h gZn−1 (corresponding to an energy density of 904 W h kgZn−1), a peak power density of 86 mW cm−2 and can be cycled over 120 h at 10 mA cm−2. Other two amorphous bimetallic, Ni0.4Fe0.6Ox and Ni0.33Co0.67Ox, are also produced to demonstrate the general applicability of this method for synthesizing binary metal oxides with controllable structures as electrocatalysts for energy conversion.
Zinc–air battery
Specific energy 470 (practical),1370 (theoretical) Wh/kg (1.692, 4.932 MJ/kg)
Energy density 1480-9780 Wh/L (5.328–35.21 MJ/L)
Specific power 100 W/kg
Nominal cell voltage 1.65 V
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