Article Highlight: Turning leftover coffee into batteries

Coffee gives many of us a daily boost and, by recycling the leftovers, it may one day do the same for a new generation of batteries. Research into the intriguing possibility of turning coffee grounds into a key chemical component of battery electrodes is reported by an Australian research team in the open access journal Carbon Trends.

“I love coffee, and I think it’s great that we might use coffee waste to develop more sustainable batteries,” says researcher Neeraj Sharma of the University of New South Wales (UNSW) in Sydney.

The research began as a collaboration with Vaibhav Gaikwad and Veena Sahajwalla of the UNSW Center for Sustainable Materials Research and Technology (SmART). Gaikwad and colleagues wanted to test some unconventional materials in batteries. This intrigued Sharma’s research student Lisa Djuandhi, who then undertook much of the investigation into the potential of coffee grounds.

The team’s work is focused on the chemistry required for rechargeable lithium-sulfur batteries, which hold great potential for entering the next generation of everyday electrical storage technology. Li-S batteries have a higher theoretical energy storage capacity than most current batteries, including lithium-ion. The sulfur they require is non-toxic,readily available in nature, and can be obtained relatively cheaply as a by-product of the petroleum industry.

The sulfur needs to be supported, or “hosted”, on a framework of carbon to form a working sulfur electrode, which is where the coffee grounds come in. Processing the grounds at high temperatures in a procedure called pyrolysis can generate virtually pure carbon. However, carbon can exist in a wide variety of forms, with a variety of physical properties, and making the most suitable form of carbon will be vital for recycling coffee grounds into battery electrodes.

“The key feature of our work was characterising the carbon,” says Sharma. This involved understanding its structure, morphology, impurities, surface area, pore properties, and crystalline nature in both the pyrolysed powder and the resulting electrodes.

The ultimate aim of this analysis was to find the correlation between the physical properties of the different forms of pyrolysed carbon and their effectiveness as the host material of an electrode. “Characterising such materials is very challenging because many techniques are required,” Sharma adds.

The most revealing technique was a sophisticated procedure called X-ray Absorption Near Edge Spectroscopy (XANES). This was performed using a specific type of X-ray generated at the Australian Synchrotron facility. The pattern of absorption of the X-rays, followed by fluorescent emission, revealed structural details of the carbon on many different scales.

“We were also able to highlight in detail the changes in the carbon framework, the sulfur components and other compounds on the surface of the electrode during electrochemical function,” says Sharma.

The team hope that these early insights can be built on by quantifying the acceptable levels of impurity in the carbon and the minimal level of processing required to make it suitable for building electrodes. Choosing the correct carbon sources based on performance, availability and suitability for large-scale production are further factors that need to be considered before commercial application.

Article Details: Djuandhi, L. et al.: “Pyrolysed coffee grounds as a conductive host agent for sulfur composite electrodes in Li–S batteries,” Carbon Trends (2021)