Chip-scale flow batteries could power and cool 3D stacks
Using flow batteries as layers in a 3D stack would provide both power and cooling at the same time. In a flow battery, an electrochemical reaction is used to produce electricity out of two liquid electrolytes, which are pumped to the battery cell from outside via a closed electrolyte loop.
“The chips are effectively operated with a liquid fuel and produce their own electricity,” said Dimos Poulikakos, Professor of Thermodynamics at ETH Zurich.
The battery is just 1.5 mm thick and the idea is to assemble chip stacks layer by layer with the batteries in between. The output of the new micro-battery also reaches a record high of 1.4 W/cm2.
Flow batteries are usually large scale and used mainly in stationary energy storage applications, for instance in combination with wind farms and solar power plants, where they temporarily store the energy produced there so it can be used at a later time. “We are the first scientists to build such a small flow battery so as to combine energy supply and cooling,” said Julian Marschewski, a doctoral student in Poulikakos’ group.
A key part of the research is demonstrating that the electrolyte liquids are able to cool a chip and dissipate more heat than the battery generates as electrical energy.
The electrochemical reactions in the battery occur in two thin and porous electrode layers that are separated by a membrane. Marschewski and his colleagues used 3D-printing technology to build a polymer channel system to press the electrolyte liquid into the porous electrode layer as efficiently as possible. The most suitable of the various designs tested proved to be one made of wedge-shaped convergent channels.
Next: proof of concept
The scientists have now provided an initial proof-of-concept for the construction of a small flow battery but despite the high power density, it was not enough to actually operate operate a processor, and the next stage is to optimise the design for an operational system. The battery could also be used for solar cells, where the electricity produced could be stored directly in the battery cell and used later when needed. The system could also keep the operating temperature of the solar cell at the ideal level.