San Jose-based 3D-printing startup Sakuu (originally KeraCel) reckons it may have finally cracked the code and discovered the holy grail that could at last make solid-state batteries a practical reality in everything from microelectronics to big electric vehicles. We explained the many virtues of solid-state batteries here, including their inherent fire safety, insusceptibility to freezing, improved energy density, etc. Sakuu’s advance is as much a 3D-printing breakthrough as it is one of battery chemistry, and its Swift Print battery technology promises to enable production of batteries in custom form factors that may look nothing like today’s pouch, prismatic, or cylindrical cells.

What’s the Chemistry?

Solid-state battery articles often compare performance with “lithium-ion” chemistry, which always means, generically, the prevailing Li-ion chemistries that employ liquid electrolytes. Sakuu’s battery also features lithium-ion chemistry (as opposed to lead-acid or zinc-air for example), with its sub-category being lithium metal, as opposed to the most popular nickel-manganese-cobalt (NMC) or lithium-iron-phosphate (LFP) for example. This means the anode is pure lithium.

As for the electrolyte—which is crucial to any lithium-based battery’s long-term health and safety—that’s still a jealously guarded secret, despite the protection of 80-plus patents. What we do know about what separates the anode and cathode in this 3D printed solid-state battery, is that it was developed at Harvard’s John A. Paulson School of Engineering and Applied Science and consists of differing materials of varying characteristics designed to control and contain the lithium metal filaments or “dendrites” that can form on the anode, particularly during fast charging, threatening to pierce the separator layers and short-circuit the battery.

How Does the Kavian 3D-Printing Process Work?

The concept utilizes a binder-jet technique developed by MIT, in which powder particles are deposited and then a liquid agent is applied to cure them. In this way Sakuu’s Kavian process can combine bulk deposition with binder-jet application of the curing agent to form a thicker layer, maybe 25 microns thick. Then the same equipment can come back and apply a metallic current collector that is just a couple microns thick, using metal-jet deposition (a human hair measures 70 microns thick).

The Kavian platform can print ceramic, glass, metals, and polymer in a single layer—though the company has yet to reveal exactly which materials go into the 3D printed solid state battery. The process is also designed to incorporate artificial-intelligence quality checks of every layer, to minimize defects and scrappage. And the process inherently reduces waste by only applying necessary material and recycling any excess right inside the machine.

3D Printing a Solid-State Enabler

3D printing is key to the success of Sakuu’s solid-state battery, because this type of battery is like a layer cake, in which the layers need to be extremely thin. This makes them hard to handle, and ensuring a continuous bond between them without any liquid is tricky. Using a 3D printer to deposit each layer directly on the one beneath eliminates this problem. Another special sauce/enabler is Sakuu’s own support material called PoraLyte. This material can be strategically deposited wherever a channel or void is needed, because it burns away during a sintering process. Compatibility issues can arise when layering dissimilar materials, but Sakuu has a whole team of materials scientists devoted to resolving and preventing such problems.

Simpler, Smaller. Cheaper Manufacturing

With the Sakuu Kavian process, raw materials enter the machine and functioning batteries come out, passing through vastly less equipment. Relative to today’s roll-to-roll battery manufacturing process, for a given output, Sakuu believes this approach can reduce factory footprint by 44 percent, lower capital expenditure by 23 percent, slash the number of operations by 69 percent, resulting in a total reduction in manufacturing cost of 33 percent. A single 30-foot-long machine like the one pictured above is expected to be able to produce 40 mWh/yr worth of batteries (about 500 individual EV’s worth), incorporating all deposition and inspection steps to turn raw materials into working batteries.

What About the Batteries Themselves?

Sakuu’s stated goal is to deliver double the energy density at 30 percent less weight than prevailing lithium-ion chemistries. And while the company claims its Kavian 3D printing process can be applied to other battery chemistries, inherently improving energy density on the order of 10-15 percent (by eliminating wasted space in the battery), the lithium-metal design in discussion here is currently building out at 800 watt-hours per liter. The company sees a pathway to 1,200 Wh/l but notes that cycle-life can decrease at higher densities, so if longer life is the goal, a more modest energy density may make more sense. The lithium-ion batteries powering today’s EVs typically average around 350-500 Wh/l by comparison.

An as yet unexplored opportunity is the freedom of form-factor proposed by 3D printed batteries. Last year we explored the possibility of incorporating battery materials into a vehicle’s body structure. Sakuu’s Kavian process for producing Swift Print batteries certainly seems like another potential enabler of this concept, and when the battery’s mass is serving a dual purpose that would otherwise be performed by another material, it’s no longer a burden to the propulsion system.

When Can You Drive a 3D Printed Battery?

Perhaps soon, if you’re in the market for an electric two-wheeler. Sakuu isn’t ready to disclose any of its clients, but one of the company’s backers is Musashi Seimitsu, which produces motorcycle gearboxes and gearing for EV reduction transmissions, and the company has admitted an e-bike of some sort will be its first mobility application. The company also disclosed to MotorTrend that it appears to be the first to have successfully 3D-printed a fully-functioning battery with custom shapes and sizing.

Sakuu’s facility in San Jose has also entered limited production of cells for testing and verification purposes and will soon begin shipping these to undisclosed clients in automotive, mobility, aerospace, and industries ranging from IoT devices to medical equipment. The company has retained the services of Porsche Consulting to help design gigafactories for commercial production of 3D-printed lithium-metal and solid-state batteries, and it’s announced a partnership with NGK to provide ceramic materials. Sakuu is not alone. A German company called Blackstone Resources AG also purports to be working on 3D-printed batteries, with a solid-state variant in the works. We promise to keep you posted on all the latest developments.

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