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Battery electrodes: take several portobello mushrooms....

30 September 2015

The porous structure and high potassium salt concentration of portobello mushroom tissue makes it an ideal candidate for battery electrodes.

No, it's not April 1st. Researchers at the University of California (UC) Riverside Bourns College of Engineering have created a new type of lithium-ion battery anode using the skin from the caps of portobello mushrooms - suitably processed, of course.

The current industry standard for rechargeable lithium-ion battery anodes is synthetic graphite, which comes with a high cost of manufacturing because it requires tedious purification and preparation processes that are also harmful to the environment.

With the anticipated increase in batteries needed for electric vehicles and electronics, a cheaper and sustainable source to replace graphite is needed. Using biomass as a replacement for graphite has drawn recent attention because of its high carbon content, low cost and environmental friendliness.

The UC Riverside engineers were drawn to using mushrooms as a form of biomass because past research has established they are highly porous, meaning they have a lot of small spaces for liquid or air to pass through. That porosity is important for batteries because it creates more space for the storage and transfer of energy, a critical component to improving battery performance.

In addition, the high potassium salt concentration in mushrooms allows for increased electrolyte-active material over time by activating more pores, gradually increasing its capacity.

A conventional anode allows lithium to fully access most of the material during the first few cycles and capacity fades from electrode damage occurs from that point on. The mushroom carbon anode technology could, with optimisation, replace graphite anodes. It also provides a binder-less and current-collector free approach to anode fabrication.

"With battery materials like this, future cell phones may see an increase in run time after many uses, rather than a decrease, due to apparent activation of blind pores within the carbon architectures as the cell charges and discharges over time," says Brennan Campbell, a graduate student in the Materials Science and Engineering programme at UC Riverside.

The skin from the caps of portobello mushrooms, once processed, provides a material for battery anodes (diagram: UC Riverside)

The nano-ribbon-like architectures transform upon heat treatment into an interconnected porous network architecture which is important for battery electrodes because such architectures possess a very large surface area for the storage of energy, a critical component to improving battery performance.

One of the problems with conventional carbons, such as graphite, is that they are typically prepared with chemicals such as acids and activated by bases that are not environmentally friendly. This has prompted the UC Riverside team, under the leadership of Professor Mihri Ozkan, to focus on naturally-derived carbons, such as the skin of the caps of portobello mushrooms.

It is expected that nearly 900,000 tons of natural raw graphite would be needed for anode fabrication for nearly six million electric vehicles, forecast to be built by 2020. This requires that the graphite be treated with harsh chemicals, including hydrofluoric and sulphuric acids, a process that creates large quantities of hazardous waste. The European Union projects this process will be unsustainable in the future.

Earlier this year the UC Riverside Bourns College of Engineering team, led by Professor Ozkan, published details of a paper-like material for lithium-ion batteries that they had created from sponge-like silicon nanofibres. Silicon suffers significant volume expansion, which can quickly degrade a battery. However, Professor Ozkan's silicon nanofibre structure circumvents this issue and allows the battery to be cycled hundreds of times without significant degradation.

The current work with mushroom tissue is published in the journal, Scientific Reports.

Les Hunt


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