Researchers in the US have developed a way to prevent dendrite formation in lithium-ion batteries using a solid electrolyte in contact with an electrode made of sodium and potassium.
The team say they solved the safety issue by developing a semi-solid electrode— that can flow and be shaped like the amalgam dentists use to fill a cavity— that provides a “self-healing surface” at the interface.
The solid electrolyte is a ceramic compound called sodium beta-alumina.
The findings were described in a paper by Massachusetts Institute of Technology (MIT) graduate student Richard Park, professors Yet-Ming Chiang and Craig Carter, and seven others at MIT, Texas A&M University, Brown University, and Carnegie Mellon University.
The paper was published in the journal Nature Energy.
The team demonstrated it was possible to run the system at 20 times greater current than using solid lithium, without forming any dendrites.
A spokesman for MIT told BEST that at room temperature, the current density (current per unit area, units of mA/cm^2) that a lithium metal electrode could run without causing dendrites in a solid electrolyte was 1 mA/cm^2.
They said: “For our sodium-potassium semisolid electrode at room temperature, we were able to run up to 20 mA/cm^2. The C-rate that this corresponds to depends on the capacity per unit area of the electrode, which has units of milliamp-hours per unit area.
“For a typical area capacity used in lithium-ion of 3mAh/cm^2, the 20 mA/cm^2 current density corresponds to 6.7C rate, whereas the 1 mA/cm^2 current density is only C/3.”
In the case of the 20 mA/cm^2 capability, the electrode is a mix of sodium and potassium metal.
In a second version of the solid battery, the team introduced a very thin layer of liquid sodium potassium alloy in between a solid lithium electrode and a solid electrolyte. This approach also prevented dendritic growth, providing an alternative approach for further research.
The new approaches could easily be adapted to many different versions of solid-state lithium batteries that are being investigated by researchers around the world, say the scientists.
The idea was inspired by experimental high-temperature batteries, in which one or both electrodes consist of molten metal.
If commercially viable, the technology could unleash the potential of solid-state batteries that, theoretically, are both safer and boast higher energy densities than the liquid variant.
Chiang said solid-state batteries only made sense with metal electrodes, but attempts to develop such batteries had been hampered by the growth of dendrites, which form more rapidly when the current flow is higher.
Park, the first author of the paper, said high temperatures in the experimental molten-metal batteries would never be practical for a portable device, but the work had demonstrated that a liquid interface can enable high current densities with no dendrite formation.
He said: “The motivation here was to develop electrodes that are based on carefully selected alloys, in order to introduce a liquid phase that can serve as a self-healing component of the metal electrode.”
Chiang says the team’s next step will be to demonstrate this system’s applicability to a variety of battery architectures.
Co-author Viswanathan, professor of mechanical engineering at Carnegie Mellon University, says, “We think we can translate this approach to really any solid-state lithium-ion battery. We think it could be used immediately in cell development for a wide range of applications, from handheld devices to electric vehicles to electric aviation.”
The team also included Christopher Eschler, Cole Fincher, and Andres Badel at MIT; Pinwen Guan at Carnegie Mellon University; and Brian Sheldon at Brown University. The work was supported by the U.S. Department of Energy, the National Science Foundation, and the MIT-Skoltech Next Generation Program.
IMAGE: a metal electrode (the textured inner circle) on a grey disc of solid electrolyte. After being tested through many charging-discharging cycles, the electrolyte shows the beginnings of dendrite formation on its surface.