The world runs on batteries. They’re in our devices, in our homes, in our cars, and in our hearts (quite literally, for some). Batteries, and the electrification they enable, may be the technology that will save our planet from irreversible warming.
But for that to happen, batteries have to get better. Much better. Thankfully, there’s no shortage of researchers trying to do just that. Solid electrolytes and higher energy electrodes are just some of the active areas of research. But we can go deeper than improving the materials that make up batteries—we can improve the physical design of batteries themselves.
“While most companies try to improve batteries by focusing on the chemistry, we focus on the physics,” boasts battery startup Addionics, founded in 2018 and based in Israel and the U.K. Addionics is working to commercialize its version of 3D batteries, a promising field of battery research that hasn’t proven practical to manufacture at scale—until now, according to Addionics.
“We came up with a process to manufacture 3D structures with precision and cost-effectiveness that, to the best of our knowledge, no one else in the world can do,” explained Addionics co-founder and CEO Moshiel Biton.
What Are 3D Batteries?
There are many different chemistries of lithium-ion batteries—the most popular type of battery today—but they all share one thing in common: they’re flat. A Li-ion cell is composed of layers stacked together like a polarized sandwich. On either end is a current collector, typically aluminum foil on the positive end and copper foil on the negative end. Next in line are the electrodes, the positive cathode and negative anode. In the very middle of the sandwich is a separator soaking in a liquid electrolyte. (The sandwich can be rolled in on itself, as seen in automaker Tesla’s cylindrical cells, but it remains effectively a two-dimensional structure.)
3D batteries bring height into the equation. Rather than layering flat sheets one on top of another, 3D batteries interlock like Lego pieces. There are a number of different ways to accomplish this, but the simplest is the so-called interdigitated structure. This involves an array of electrode rods, alternating between cathode and anode, surrounded by a solid electrolyte.
Another type of 3D battery uses a concentric structure, in which rods of one electrode (e.g., the anode) are coated with an electrolyte, and the volume is filled with the other electrode (e.g., the cathode). Yet another 3D structure is called aperiodic and resembles a sponge constructed of one electrode, coated with an electrolyte, and filled in with the opposite electrode.
Why bother going 3D? Unlike TVs from the 2010s, 3D is not just a gimmick for batteries. There are two big advantages to this approach: it decouples energy and power density, and it allows for uniform electrochemical reactions.
Energy and power density are two of the most important characteristics in any battery. Energy density describes how much energy can be stored in the battery, and power density describes how quickly it can charge and discharge. With conventional 2D architectures, these two attributes trade off with one another. Adding more electrode material increases energy density, but it impacts how quickly ions can shuttle between the two electrodes, decreasing power density. Adding the dimension of height allows one to increase the amount of electrode material without compromising the effective distance between electrodes, making it possible to simultaneously achieve high energy and high power density.
Mixing the electrodes and electrolyte in three dimensions also allows 3D batteries a more uniform distribution of electrochemical reactions. Rather than hot spots of activity at the planar interface between layers, reactions take place more evenly throughout the cell volume. This relieves bottlenecks found in 2D batteries that can contribute to cell degradation.
Addionics’ Approach to 3D Batteries
The 3D battery structures described above are actively being researched, but are still far from being commercially viable. There is, however, an intermediary between these full 3D structures and conventional flat batteries. Rather than a fully 3D battery, you can keep the flat sandwich structure but add another dimension to some of the layers—in particular, the current collectors. Instead of a flat layer of metal foil, two alternative current collectors are so-called mesh and foam structures. A mesh is a periodic lattice, while a foam is an aperiodic porous structure.
The porosity of these alternative current collectors is considered a promising approach to improving energy density, but a recent review of Li-ion current collectors by Zhu et al. concluded that that there’s a “need to optimise the porous structure of current collectors, e.g. porosity, pore size and pore shape, to increase electrode mass loading as well as keep electrical resistance low and Li-ion diffusion rate high.”
This appears to be what Addionics is attempting to do with what it calls “smart 3D electrodes,” which are 3D current collector structures containing electrode active material. According to Addionics, smart 3D electrodes—both cathodes and anodes—can be swapped in place of the 2D electrodes in an otherwise conventional battery structure.
“We are replacing the metal foil with a smart 3D structure,” explained Biton. “You don’t need to synthesize new chemistries. You can change the structure and yield better performance.”
When pushed for details, the Addionics CEO was reticent. “It’s neither a mesh or a foam. It’s a real controllable 3D structure with variety and control of the z axis. I can’t disclose more than that,” Biton stated.
According to Addionics, its smart 3D electrodes provide similar benefits to fully 3D batteries. There is more space for electrode active material, meaning energy density is increased. Power density is also increased, because the homogenous distribution of electrode material lowers the internal resistance of the battery (as much as 90 percent lower than 2D batteries, Biton said, though it depends on the specific cell chemistry). This translates to faster charging and discharging as well as better thermal performance.
Biton is upfront that his company’s main contribution is not inventing 3D battery structures, but unlocking how to make them. “No one solved the manufacturing to make a commercial product in the battery domain,” Biton explained. “All our prototypes were built in existing production lines. We haven’t introduced any new tools. That’s our greatest advantage.”
With that advantage, Addionics plans to sell its 3D electrodes to battery companies around the world, offering them as a drop-in replacement for existing components. With proprietary AI-based algorithms, Addionics can customize its 3D electrodes for any battery, regardless of cell chemistry or size.
“We are agnostic to the application, as we can integrate our technology with every chemistry and in any format,” Biton claimed.
Building Future Batteries with 3D Electrodes
While Addionics technology isn’t yet in any commercial products, the startup is involved in several promising partnerships to develop next-generation batteries. In April 2021, Addionics announced a collaboration with material company Saint-Gobain Ceramics & Plastics to develop solid-state batteries employing its smart 3D electrodes. The joint project received $1 million in funding from the U.S. Department of Energy and Israel Ministry of Energy via the two nations’ BIRD (Binational Industrial Research and Development) Energy program.
Addionics has also partnered with an undisclosed American automotive tier-1 supplier to develop silicon anode batteries, a promising chemistry with one big drawback: mechanical stability. When reacting with lithium ions, silicon swells in size, and shrinks when the reaction is reversed. This constant swelling and shrinking damages the cell. According to Addionics, its smart 3D electrodes can mitigate this problem, effectively containing the silicon as it expands and contracts.
Another project involves lithium iron phosphate (LFP) cathodes, a Li-ion chemistry with growing interest due to its low cost and long lifespan. In total, Biton revealed that Addionics is currently working on six commercial projects, each in the R&D phase. These encompass several industries, including automotive, micromobility, and consumer electronics.
“We’re growing very fast in order to walk in different verticals simultaneously,” Biton summarized. “It’s not easy, but that’s our play: we are not a battery company. We are building a high-value component that can be suitable for any type of battery.”---
References
A review of current collectors for lithium-ion batteries, Zhu et al., 2021
Three-dimensional electrodes and battery architectures, Arthur et al., 2011
3D Architectures for Batteries and Electrodes, Long et al., 2020