As per the first author of a recent paper detailing the team’s work, Grayson Deysher, a PhD candidate at UC San Diego, “no one has been able to successfully combine these three ideas although there have been previous sodium, solid-state, and anode-free batteries, until now.”
The study team had to develop a novel architecture for the sodium battery in order to produce a sodium battery, which is said to have an energy density comparable to that of lithium ion batteries.
It chose to use an anode-free battery architecture, which eliminates the anode and stores the ions directly on the current collector by the electrochemical deposition of alkali metal. Although it presents its own difficulties, eliminating the anode allows for less weight and space, higher cell voltage, cheaper cell cost, and increased energy density.
According to Deysher, “a good contact between the electrolyte and the current collector is necessary in any anode-free battery.” When employing a liquid electrolyte, this is usually quite simple because the liquid can spread out and moisten all surfaces. This is not possible for a solid electrolyte.
But as the liquid electrolytes gradually deplete the active components, they produce a buildup known as the solid electrolyte interphase, which shortens the battery’s life.
The team from UC San Diego approached this issue in a unique way. They built a current collector that encircles the electrolyte rather than utilizing an electrolyte that does so.
They utilized aluminum powder, a solid that has the ability to flow like a liquid, to make their current collector.
As previously not possible with conventional aluminum foil, the researchers reported that “an aluminum current collector is found to achieve intimate solid–solid contact with the solid electrolyte, which allows highly reversible sodium plating and stripping at both high areal capacities and current densities.”
In order to enable low-cost and high-efficiency cycling during battery assembly, the powder was densified under high pressure to produce a solid current collector while keeping a liquid-like interface with the electrolyte. According to the researchers, a whole cell of an all-solid-state battery without a sodium anode has shown steady cycling over several hundred cycles.
Deysher stated, “We hope that this paper can invigorate more push into the sodium area by demonstrating that it can work well, even better than the lithium version in some cases.” Sodium solid-state batteries are typically considered as a technology that is far off in the future.
Through the Office of Innovation and Commercialization at UC San Diego, the researchers have submitted an application for a patent on their work. The article “Design principles for enabling an anode-free sodium all-solid-state battery,” which was published in Nature Energy, goes into greater detail about their findings.