Caltech researchers use DLP 3D printing to improve Li-ion battery performances

A team of researchers from the California Institute of Technology (Caltech) have developed a novel method of 3D printing electrodes for lithium-ion batteries.

Using DLP 3D printing technology, a visible light-based form of vat photopolymerization, the researchers were able to fabricate complex polymer structures before converting them into useful electrode materials via a thermal post-processing treatment. The final carbon and lithium cobalt oxide structures were shown to function as anodes and cathodes respectively, with reports of excellent battery performance and stability.

Kai Narita, a graduate student at Caltech, explains, “Pyrolysis of polymers has been known to result in the formation of carbon. Our approach exploits this phenomenon to fabricate 3D carbon materials. We simply use a commercially available photoresin with digital light process printing to create 3D polymer structures, which we then pyrolyze at 1000˚C to convert into carbon ones.”

A complex electrode geometry 3D printed via DLP. Image via Caltech.
A complex electrode geometry 3D printed via DLP. Image via Caltech.

Limitations of lithium-ion batteries

Since their invention around five decades ago, lithium-ion batteries have become integral to modern human life, powering everything from consumer electronics to military satellites. As such, there is a mountain of research in the field of electrochemistry aimed specifically at improving the capacity of energy storage devices, all while making them smaller, cheaper, and faster charging.

Beyond just letting us sit on our phones all day, higher-quality batteries also have major implications for climate change as they can help reduce society’s dependence on fossil fuels and promote the use of renewable energy sources instead. Unfortunately, applications such as electric vehicles and grid-scale energy storage for wind and solar farms are still limited by the energy densities and charging rates currently available, even at the cutting edge.

In conventional lithium-ion batteries with planar electrodes, the energy densities (amount of energy that can be stored) and power densities (rate of energy release) are often coupled. For example, increasing the mass of an electrode will increase its energy density but reduce its power density due to an increase in electrode thickness, whereby ions and electrons are forced to travel a greater distance before discharging. If this relationship were to be decoupled, both the energy and power densities of energy storage devices could be improved simultaneously. This is where 3D printing comes in.

SEM imaging of a 3D printed carbon electrode. Image via Caltech.
SEM imaging of a 3D printed carbon electrode. Image via Caltech.

3D printing to the rescue

While 3D printing has actually been explored for the application in recent years, previous attempts have largely relied on nano-ink extrusion, which doesn’t lend itself to high resolution parts. Vat photopolymerization, on the other hand, solves the resolution issue but isn’t typically compatible with electrode materials as it is based on polymer chemistry.

Using the DLP-pyrolysis technique, the Caltech team was able to combine the best of both worlds and produce high-resolution electrodes with electrode materials. Owing to the technology’s affinity for complex geometries, they were able to print thick electrode structures with micro- and nano-sized sub-structures. This effectively increased the mass loading of the custom electrodes while alleviating the power density issues associated with longer transport lengths, paving the way for a new method of high-performance battery production.

Professor Julia Greer, lead author of the studies, concludes, “Creating 3D-sculpted electrodes, with full control over their architectural design, dimensions, and now – materials, is bringing us even closer to the eventual attainment of the Holy Grail, i.e. a scalable and reliable fabrication methodology of solid-state batteries that are safe, mechanically robust, and efficient.”

Further details of the studies can be found in Advanced Energy Materials and Advanced Materials Technologies. The co-authors of the papers include Julia Greer, Michael Citrin, Daryl Yee Et Al.

Close-up of the 3D printed carbon electrode layers. Image via Caltech.
Close-up of the 3D printed carbon electrode layers. Image via Caltech.

Back in September, 3D printer OEM Photocentric announced the launch of a new division that’s dedicated to the development of eco-friendly 3D printed electric batteries. The Peterborough-based firm stated that it had committed to a “significant investment,” which includes an entire research team, in a bid to design and 3D print more energy-efficient storage devices.

Elsewhere, in the aerospace sector, NASA’s Marshall Space Flight Center has previously awarded KULR Technology Group a dual-use technology agreement which could see future space missions utilizing 3D printed spare battery packs. As part of the collaboration, KULR will build 3D printed battery systems for crewed and autonomous space applications using its passive propagation resistant (PPR) and internal short circuit (ISC) technologies.

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Featured image shows a complex electrode geometry 3D printed via DLP. Image via Caltech.