Making batteries from sugar? That’s quite a stretch

When it comes to choosing a career, it’s not uncommon for a son to follow in his father’s footsteps. Cynics might be quick to accuse any family-run enterprise of nepotism but it makes sense that many people end up working in the same, or similar, areas as their parents. We do what we know.

This is also true for Prof Guihua Yu, an expert in materials science and mechanical engineering at the Texas Materials Institute, part of University of Texas, Austin. "When I was just a boy living in China my father worked in a huge state-owned sugar-making factory," he says. "Sugar used to be one of the core industries for China and my dad worked alongside 3,000 other staff in his warehouse alone."

It might seem like a bit of a stretch to connect Yu's career as a materials scientist in the largest university in the United States with his dad's job at the local sugar factory back in China in 1981.

But that’s where he found his inspiration for a potential solution to one of material sciences’ biggest conundrums: a stretchable battery structure that could be woven into wearable tech.

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Specifically, Yu has developed the first all-stretchable-component sodium-ion full battery based on graphene-modifed polydimethylsiloxane sponge electrodes and an elastic gel membrane.

He has created this all-stretchable battery for wearables using sugar cubes as a platform for designing the battery materials. The sugar is used as a framework and then melted away leaving behind an architecture that’s conductive and stretchable.

Undervalued material

In layman’s terms, this is a battery prototype that can stretch and bend and is small enough to potentially be woven into, say an item of clothing developed with wearable tech in mind.

“Sugar cane is an undervalued material with many useful properties,” he says. Apart from being a staple daily food across the world, sugar cane is a natural framework material – a kind of microstructure with lots of space inside, almost like a sponge. “The problem with sponges, however, is that they are usually too porous, whereas sugar cane has ideal levels of porosity for certain storage requirements.”

Batteries convert chemical energy into electrical energy in the form of voltage. This causes electrical current to flow. Crudely speaking, a basic battery will comprise two plates, made from different metals, immersed in a chemical solution called an electrolyte.

The metals react with the electrolyte to make charges flow that gather on the negative plate, known as the anode. The charge stored in the positive plate, or cathode, is literally siphoned dry of charge and, as a result, a voltage is formed. One last crucial component is the separator, which prevents the battery from short circuiting or overheating.

Stretchable energy-storage devices have been the focus of materials scientists around the world on account of their promising applications in future wearable technologies.

But several challenges remain, including “low utility of active materials, limited multidirectional stretchability, and poor stability under stretched conditions. In addition, most proposed designs use one or more rigid components that fail to meet the stretchability requirement for the entire device”.

“Materials scientists have been grappling with various stretchable battery prototypes for years now, but what you find in all existing scientific research is a focus on making one specific component – the electrodes, or separator, or the packaging itself stretchable. We have succeeded in making all components flexible.”

Rigorously tested

Researchers working on stretchable power storage prototypes need frameworks, or scaffolding, in order to work on the various materials intrinsic to developing batteries. If your scaffolding doesn’t provide the right kind of support, it may not be able to sustain large amounts of the active materials you are trying to load on to it. “If you go beyond its storage limit, the materials may quickly detach from the framework and dissolve into it,” says Yu.

Yu and his research team have rigorously tested and retested the performance of their stretchable battery against a more conventional and commonly used VOPO4 battery. Our prototype “exhibits reasonable electrochemical performance and robust mechanical deformability, meaning it can perform almost as well as battery materials we’re already using. In other words, when comparing non-stretchable to stretchable, one doesn’t lose any major intrinsic properties in exchange for stretchability.

Like every new research breakthrough with potential commercial viability, the next step is finding the best fit for the tech in the real world and assessing its scalability. “Stretchable battery tech is in big demand in the wearable tech sector. Our battery can be built or woven into clothes or any textile. So that is the most likely commercial application I see for it.”

Previous frameworks, or scaffolding, for research in this area had all proven to be too porous or not porous enough for effective analysis. But like Goldilocks, Prof Yu has discovered the properties of sugar cane to be “just right” for the development of stretchable battery technology.

So perhaps connecting he and his father’s seemingly disparate career paths isn’t that much of a stretch after all.