Metal-air batteries represent a leap forward in battery technology. They comprise of a metal anode with the cathode in ambient air. Crucially they have an energy density that is much higher than typical lithium-ion batteries meaning that you can get more electricity from one charge. For this reason, metal-air batteries have been intensely researched in order to develop the next generation of batteries, especially in applications such as electric vehicles.
The reason that metal-air batteries have not been more widely used is that their development has repeatedly come up against roadblocks, from the batteries being non-rechargeable to the metal anode corroding and reducing the lifetime of the batteries. Now the future looks a lot brighter for metal-air batteries and researchers have overcome many of the barriers to their widespread use, however some still remain.
One remaining obstacle is that the metal air cathodes require a multistep manufacturing process which makes production more difficult as well as increasing the cost. The more wet chemistry or solid-state synthesis that is required in battery production can also have a negative impact on the sustainability of the battery.
A collaboration between researchers in the UK and China used the electron Physical Science Imaging Centre (ePSIC) at Diamond to understand new substrates for the air interface of their zinc-air batteries. They discovered that carbon paper could become self-activated and perform exceptionally well as the air interface of a zinc-air battery. They left the carbon paper untreated and discovered that the resulting battery had favourable properties with an impressive cycling stability, a small discharge volage gap and a high current density. In fact, they found that the performance of the battery incorporating self-activated carbon paper performed better than many reported electrocatalysts with much more complex synthesis procedures.
The research team performed extensive characterisiation experiments and discovered how the carbon paper was able to produce such an effective battery. They saw that the battery had improved wettability with optimised three-phase boundaries. Wettability affects the way that current density is distributed on the electrode surface. They also found the cause of the self-activation which was oxygen-rich functional groups forming on carbon paper, which behaved as active species for electron transfer. Finally, the team saw that using self-activated carbon paper led to large electrochemical surface areas, which are known to improve the performance of batteries.
By fully characterising this somewhat serendipitous observation, the research team have shown a way for metal-air batteries to be produced more easily and cost effectively in the future.
The work published in Energy Storage Materials provides a new method for producing self-standing air-cathodes for metal-air batteries in a cheap and simple way. The data gathered from the experiments at Diamond were not only important for validating the method and battery performance, but also for generating the data needed for rational design of high-performance batteries in the future. The research team acknowledge that even more characterisiation can be done in the future to fully understand how these cathodes work. While this is being done, research can also begin to optimise the performance of the metal-air batteries.
Reducing the cost and complexity of battery technology going into the future has many important implications for society and the environment. Producing energy that has little to no effect on the environment is becoming increasingly important and reducing the cost of energy has a large impact on society and industry. In the future, this work could lead to longer ranges in electric cars and sustainable power for our homes and workplaces.
Jian Guo et al. Self-activated cathode substrates in rechargeable zinc–air batteries. Energy Storage Materials 35,(November 2020). DOI: 10.1016/j.ensm.2020.11.036)
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