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Most of the nascent high energy-density battery materials—lithium-metal, silicon, solid-state electrolyte, sulphur, etcetera—require high stack pressures to aid the kinetics. Applying such pressures can obviously be done by torquing cells in place between two stiff plates, but that has two drawbacks: precision and control. We like using pneumatics to apply the pressure as they can be electronically—and thus programmatically—controlled.
For all of these we also want to send ultrasonic waves through the cells, so the transducers must be embedded in the structure, without them experiencing the pressure, so they are encased in a 3D printed structure.
We design and build these apparatuses in-house, only outsourcing threaded structural parts. I've led the design and build of three, each with a minute difference, depending on the exact application. We alternate between doing CAD in Solidworks and Shapr3D.
scanner.movtomography
The jigs shown in the previous section are all one-dimensional, i.e. they always shoot the sound wave through the cell in the same spot. Batteries are complex systems, and are typically chemomechanically heterogeneous. Probing these is of great interest in industry, and there are at least two companies that specialize in exactly that. Wes Chang, a Clüb Steingart alumnus, published on a project similar to this a couple of years ago.
Now, although building custom hardware and software would be great, it would be pretty costly and time-consuming. Enter modern 3D printers (Enders ftw). They are both cheap and preprogrammed to be controlled via simple G-Code (see nodeforwarder). We simply replace the printer nozzle with a prong with transducers on the end and raster scan the cell, see video to the side.
This results in these (still rough! work in progress) chemo-mechanical maps of the cells, showing wetting, plating, gassing etc. operando.
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