Three-dimensional chip stacks  Credit: IBM Research ZurichThree-dimensional chip stacks Credit: IBM Research ZurichResearchers at ETH Zurich and IBM Research Zurich have built a proof-of-concept redox flow battery tiny enough to both power and cool stacks of computer chips.

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 research team chose two liquids that act both as electrolytes and as a medium to remove heat from the circuit.

Existing flow batteries are most often large, used for stationary energy storage applications. The new dual-purpose battery is 1.5 millimeters thick, with a net power density of 1 watt per square centimeter. The size factor makes it feasible to interleave the battery with chips, an important space-saving consideration as electronic devices shrink in size.

According to the scientists, the most serious challenge in constructing the new micro-flow batteries was to build them in such a way that they are supplied with electrolytes as efficiently as possible while at the same time keeping the pumping power as low as possible.

The power producing electrochemical reactions occur in two thin and porous electrode layers that are separated by a membrane. Using 3D printing, the research team created a polymer channel system that presses the electrolyte liquid into the porous electrode layer as efficiently as possible.

Initial testing confirmed that the electrolyte flow from one battery is more than adequate to cool one microchip. Power density, however, is not entirely sufficient to power the chip. The team expects industrial partners to further optimize the design.

Additional applications suitable for these tiny batteries include lasers and solar cells. The technique of pressing the electrolyte into porous electrodes could also be adapted for larger batteries.

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