"We designed this structure that gives us three-dimensional electrodes, like a honeycomb," says Ju Li, the Battelle Energy Alliance Professor of Nuclear Science and Engineering and professor of materials science and engineering. The void spaces in each tube of the structure allow the lithium to "creep backward" into the tubes, says Li, "and that way, it doesn't build up stress to crack the solid electrolyte."
The expanding and contracting lithium inside these tubes moves in and out, similar to the way a car engine's pistons move inside their cylinders, says Li. Because these structures are built at nanoscale dimensions, the result is like "an engine with 10 billion pistons, with lithium metal as the working fluid."
Because the walls of these honeycomb-like structures are made of chemically stable MIEC, the lithium never loses electrical contact with the material, says Li. Thus, the whole solid battery can remain mechanically and chemically stable as it goes through its cycles of use.
While many other groups are working on what they call solid batteries, says Li, most of those systems actually work better with some liquid electrolyte mixed with the solid electrolyte material. "But in our case," he says, "it's truly all solid. There is no liquid or gel in it of any kind."
The researchers say they have proved the concept experimentally, putting a test device through 100 cycles of charging and discharging without producing any fracturing of the solids. The new system, say the researchers, could lead to safe anodes that weigh only a quarter as much as their conventional counterparts in lithium-ion