Toward all-solid lithium batteries

Most batteries are composed of two solid, electrochemically active layers called electrodes, separated by a polymer membrane infused with a liquid or gel electrolyte. But recent research has explored the possibility of all-solid-state batteries, in which the liquid (and potentially flammable) electrolyte would be replaced by a solid electrolyte, which could enhance the batteries’ energy density and safety.

Now, for the first time, a team at MIT has probed the mechanical properties of a sulfide-based solid electrolyte material, to determine its mechanical performance when incorporated into batteries.

Lithium-ion batteries have provided a lightweight energy-storage solution that has enabled many of today’s high-tech devices, from smartphones to electric cars. But substituting the conventional liquid electrolyte with a solid electrolyte in such batteries could have significant advantages. Such all-solid-state lithium-ion batteries could provide even greater energy storage ability, pound for pound, at the battery pack level. They may also virtually eliminate the risk of tiny, fingerlike metallic projections called dendrites that can grow through the electrolyte layer and lead to short-circuits.

“Batteries with components that are all solid are attractive options for performance and safety, but several challenges remain,” Van Vliet says. In the lithium-ion batteries that dominate the market today, lithium ions pass through a liquid electrolyte to get from one electrode to the other while the battery is being charged, and then flow through in the opposite direction as it is being used. These batteries are very efficient, but “the liquid electrolytes tend to be chemically unstable, and can even be flammable,” she says. “So if the electrolyte was solid, it could be safer, as well as smaller and lighter.”

Lithium metal anodes exhibit a significant increase in capacity compared to state-of-the-art graphite anodes. This could translate into about a 100 percent increase in energy density compared to [conventional] Li-ion technology.

Advanced Energy Materials – Compliant Yet Brittle Mechanical Behavior of Li2S–P2S5 Lithium-Ion-Conducting Solid Electrolyte

Young’s modulus, hardness, and fracture toughness are measured by instrumented nanoindentation for an amorphous Li2S–P2S5 Li-ion solid electrolyte. Although low elastic modulus suggests accommodation of significant chemomechanical strain, low fracture toughness can facilitate brittle crack formation in such materials.

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