A team of MIT researchers has announced that they have developed a new battery electrode that could lead to more powerful batteries. The breakthrough is based on what MIT calls the “long-sought goal” of using pure lithium metal as the anode of the battery. MIT’s design comes from the lab of Ju Li and is part of a concept for developing all-solid-state batteries.
The concept would ditch the liquid or polymer gel that is used as an electrolyte between the two electrodes inside the battery. The electrolyte in current batteries allows lithium ions to travel back and forth during charge and discharge cycles. Scientists say that an all-solid version would be safer than liquid electrolytes that have high volatility and have been the source of explosions in lithium batteries in the past.
One of the biggest challenges for solid-state batteries is that as they are charged, atoms stack up inside the lithium metal, causing it to expand with charging, and the metal shrinks during discharge. This repeated change in the shape of the battery makes it hard for solids to maintain constant contact and tend to cause the solid electrolyte to fracture or detach.
Another challenge is that none of the proposed solid electrolytes are truly chemically stable when in contact with lithium metal making it degrade over time. Li and his team used an unusual design that uses two additional classes of solids known as “mixed ionic-electronic conductors” (MIEC) and “Electron and Li-ion insulators” (ELI). Both of those are chemically stable in contact with lithium metal.
They developed a 3D nanoarchitecture in the form of a honeycomb-like array of hexagonal MIEC tubes partially infused with solid lithium metal to form one electrode of the battery with extra space in each tube. As the lithium expands in charging, it flows into the empty space in the tubes. That flow relieves pressure from expansion during charging. ELI is used as a “crucial mechanical binder” between the MIEC walls and the solid electrolyte layer. The team is working on scaling up their invention now.