New electrode design may lead to more powerful batteries

New research from Professor Ju Li's lab could lead to batteries that can pack more power per pound and last longer, based on the long-sought goal of using pure lithium metal as one of the battery’s two electrodes, the anode.  

The design is part of a concept for developing safe all-solid-state batteries. Typically, a liquid or polymer gel is used as the electrolyte material between the battery’s two electrodes. An all-solid version could be safer than liquid electrolytes, which have high volatility and have been the source of explosions in lithium batteries. While there has been a lot of work on solid-state batteries, these efforts have faced a number of issues, including maintaining contact between the solids and chemical stability between the solid electrolytes and lithium metal.

The researchers developed a three-dimensional nanoarchitecture in the form of a honeycomb-like array of hexagonal MIEC tubes, partially infused with the solid lithium metal to form one electrode of the battery, but with extra space left inside each tube. When the lithium expands in the charging process, it flows into the empty space in the interior of the tubes, moving like a liquid even though it retains its solid crystalline structure. This flow, entirely confined inside the honeycomb structure, relieves the pressure from the expansion caused by charging, but without changing the electrode’s outer dimensions or the boundary between the electrode and electrolyte. The other material, the ELI, serves as a crucial mechanical binder between the MIEC walls and the solid electrolyte layer. Because the walls of these honeycomb-like structures are made of chemically stable MIEC, the lithium never loses electrical contact with the material, Li says. Thus, the whole solid battery can remain mechanically and chemically stable as it goes through its cycles of use. The team has proved the concept experimentally, putting a test device through 100 cycles of charging and discharging without producing any fracturing of the solids.