eth-zurichScientists and researchers from ETH Zurich and IBM Research Zurich have built an extremely small redox flow battery – it’s only around 1.5mm thick, and can potentially provide energy to tightly packed electronic components, while at the same time dissipating the heat that’s produced by these components. Redox means reduction-oxidation, and the redox flow battery is rechargeable, thanks to two chemical components that are dissolved in liquids that are contained inside the battery system, and separated by a thin membrane. 3D printing technology was used to keep the batteries efficiently supplied with electrolytes.

Conventional batteries store energy in two fixed electrodes, but flow batteries store it in two liquid electrolytes, and it’s pumped into the battery through two circuits. Electrochemical reactions convert a battery’s energy from its stored chemical form into electricity. Flow batteries can convert chemical energy into electrical energy and vice versa, but fuel cells can only convert one direction, chemical into electrical, and not both. Flow batteries are also lighter than regular batteries – while regular batteries are heavier depending on how much energy, or fuel, is stored inside, flow batteries can get fuel from outside and don’t have to store it. The only problem is that flow batteries need a liquid supply system.

ibm-research-zurichThe work by IBM Research Zurich and ETH Zurich, the latter of which introduced a method for metal 3D printing on a nano level last year, was outlined in a research paper, titled “3D-printed fluidic networks for high-power-density heat-managing miniaturized redox flow batteries,” and published in Energy & Environmental Science; co-authors on the paper were Lorenz Brenner, Neil Ebejer, Julian Marschewski, Bruno Michel, Dimos Poulikakos, and Patrick Ruch. The tiny redox flow battery that the researchers constructed means that future computer chip stacks could not only receive electrical power, but also be cooled at the same time – basically, an electrochemical reaction produces electricity using two liquid electrolytes, “pumped to the battery cell from outside via a closed electrolyte loop.”

Poulikakos, Professor of Thermodynamics at ETH Zurich, said, “The chips are effectively operated with a liquid fuel and produce their own electricity.”

Three-dimensional chip stacks could be used in computers in the future. Integrated microscale flow batteries could both power and cool them. [Image: IBM Research Zurich]

Three-dimensional chip stacks could be used in computers in the future. Integrated microscale flow batteries could both power and cool them. [Image: IBM Research Zurich]

Chip stacks would essentially be built in layers – first a computer chip, then a battery micro-cell to both supply electricity to the computer chip and cool it, then another computer chip is added, and so on and so forth. The liquids used to fuel the batteries cause cooling: the same circuit will spread any excess heat from the stack of chips. Up until now, flow batteries have been large-scale, and used to temporarily store energy produced by solar power plants or wind farms, so the energy can be used at a later time. So not only are these new flow batteries smaller than the norm, their energy outputs are also record-breaking: 1.4 watts per square centimeter of battery surface.

ETH Zurich doctoral student Marschewski said, “We are the first scientists to build such a small flow battery so as to combine energy supply and cooling.”

polymer-channel-walls

3D-printed polymer channel walls (raised). The liquid electrolyte flows in the recesses. The enlarged image shows a 3 x 4 millimetre section. [Image: Marschewski et al. Energy and Environmental Science 2017]

In an experiment, the electrolyte liquids were shown to cool the chip, and also to spread the heat out a lot more than a conventional battery would be able to generate as electrical energy.

According to the paper’s abstract, “The miniaturization of redox flow cells (RFCs) paves the way to novel energy conversion concepts combining power delivery and heat regulation. Envisioning the integration of high-power-density RFCs into electronic devices such as microprocessors, lasers, or light-emitting diodes for the purpose of providing power and heat management simultaneously, we introduce and investigate interdigitated, tapered multiple-pass microfluidic networks in miniaturized flow cells. Employing 3D-printing for the facile and inexpensive fabrication of these networks, we demonstrated RFCs with maximum power densitites of up to 1.4 W cm−2 at room temperature and net powder densities of up to 0.99 W cm−2 after subtracting pumping power losses. The electrolytes employed modest concentrations of 0.4 M K4Fe(CN)6 and 0.2 M2,6- dihydroxyanthraquinone in alkaline electrolyte. We thereby show that rational tailoring of fluidic networks in RFCs is key for the development of devices effectively combining power delivery and thermal management.”

The researchers explained that the most important obstacle they had to surmount while building the micro-flow batteries was to work out a method to keep them efficiently supplied with electrolytes, while also maintaining a low pumping power. The battery’s electrochemical reactions happen in two thin, porous electrode layers that, as previously mentioned, are kept separate thanks to a membrane. The research team built a polymer channel system, thanks to 3D printing technology, to efficiently press the electrolyte liquid into the porous electrode layer. Wedge-shaped convergent channels were deemed to be the most effective design.

 

channel-networks

The channel networks ensure that the liquid electrolytes fully penetrate the porous electrodes and react electrochemically. [Image: Marschewski et al. Energy and Environmental Science 2017, adapted]

An initial proof-of-concept for building a small flow battery was recently completed by the scientists. Even though the micro-flow battery’s power density is high, it still doesn’t produce enough electricity to entirely operate a computer chip, so further research and industry partner optimization is needed to determine how to use the flow batter in a chip stack. Applications like lasers, which need to be supplied with energy and then cooled, or solar cells, where the produced electricity can be stored in the battery cell for later use, would benefit from the scientists’ new approach. Discuss in the Redox Flow Battery forum at 3DPB.com.

[Source: ETH Zurich]

 



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