New Material Offers Promise for Solid-State Batteries

May 1, 2022

Argonne National Laboratory, DuPage County, IL

Researchers from the University of Waterloo, Canada, who are members of the Joint Center for Energy Storage Research (JCESR), headquartered at the U.S. Department of Energy's (DOE) Argonne National Laboratory, have discovered a new solid electrolyte that offers several important advantages.

Chlorine-based electrolytes like the one shown here are offering improved performance for solid-state lithium-ion batteries. (Photo: Linda Nazar/University of Waterloo)

This electrolyte, composed of lithium, scandium, indium, and chlorine, conducts lithium ions well but electrons poorly. This combination is essential to creating an all-solid-state battery that functions without significantly losing capacity for over a hundred cycles at high voltage (above 4 volts) and thousands of cycles at intermediate voltage. The chloride nature of the electrolyte is key to its stability at operating conditions above 4 volts -meaning it is suitable for typical cathode materials that form the mainstay of today's lithium-ion cells.

Current iterations of solid-state electrolytes focus heavily on sulfides, which oxidize and degrade above 2.5 volts. Therefore, they require the incorporation of an insulating coating around the cathode material that operates above 4 volts, which impairs the ability of electrons and lithium ions to move from the electrolyte and into the cathode.

The team wasn't the first to devise a chloride electrolyte, the decision to swap out half of the indium for scandium based on their previous work proved to be a winner in terms of lower electronic and higher ionic conductivity.

One chemical key to the ionic conductivity lay in the material's crisscrossing 3D structure called a spinel. The researchers had to balance two competing desires – to load the spinel with as many charge carrying ions as possible, but also to leave sites open for the ions to move through.

It is not yet clear why the electronic conductivity is lower than many previously reported chloride electrolytes, but it helps establish a clean interface between the cathode material and solid electrolyte, a fact that is largely responsible for the stable performance even with high amounts of active material in the cathode.

The research was funded by the DOE's Office of Science and Office of Basic Energy Sciences with some support from Canada's National Sciences and Engineering Research Council.

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