CR1620 battery

CR1620 battery offer lightweight energy storage solutions

Most batteries consist 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 improve the battery's energy density and safety.

Now, for the first time, a team at MIT has explored the mechanical properties of a sulfide-based solid electrolyte material to determine how it would perform when incorporated into a battery.

CR1620 battery offer lightweight energy storage solutions that have enabled many of today's high-tech devices, from smartphones to electric cars. But replacing the traditional liquid electrolyte with a solid electrolyte in such batteries could have significant advantages. Such all-solid-state CR1620 battery could offer higher energy storage capabilities at the pack level. They could also virtually eliminate the risk of tiny finger-like metallic protrusions, called dendrites, that can grow through the electrolyte layers and cause short circuits.

"Batteries with all the components are an attractive option for performance and safety, but several challenges remain," the researchers said. In CR1620 battery, which dominate the market today, lithium ions travel from one electrode to the other through a liquid electrolyte when the battery is charged, and then flow in the opposite direction when it is used. These batteries are very efficient, but "liquid electrolytes tend to be chemically unstable and can even be flammable," she said. "So if the electrolyte is solid, it could be safer, smaller and lighter."

But a big question about using such all-solid-state batteries is what kind of mechanical stresses might occur within the electrolyte material as the electrodes are repeatedly charged and discharged. This cycling causes the electrodes to expand and contract as lithium ions move in and out of the crystal structure. In a rigid electrolyte, these dimensional changes would result in high stresses. If the electrolyte is also brittle, then the constant changes in size could lead to cracks that quickly degrade battery performance and could even provide pathways for disruptive dendrite formation, as happens with liquid-electrolyte batteries. But if the material can resist fracture, then these stresses could be accommodated without rapid cracking

Until now, however, the sulfide's extreme sensitivity to ordinary laboratory air has posed a challenge to measuring mechanical properties, including its fracture toughness. To address this issue, members of the research team performed mechanical tests in a mineral oil bath, protecting the samples from any chemical interactions with air or moisture. Using the technique, they were able to obtain detailed measurements of the mechanical properties of conductive sulfides, which are considered promising candidates for electrolytes in all-solid-state batteries.

There are a lot of different solid electrolyte candidates. Other research groups have studied the mechanical properties of lithium-ion-conducting oxides, but so far, sulfides have been less studied, even though they are particularly promising because they conduct lithium ions easily and quickly.

Previous researchers have used acoustic measurement techniques, sending sound waves through a material to probe its mechanical properties, but this method cannot quantify resistance to fracture. But the new study uses a fine probe to probe the material and monitor its response, giving a more complete picture of important properties, including hardness, fracture toughness, and Young's modulus (a measure of a material's ability to stretch reversibly under applied pressure).

The research team has measured the elastic properties of sulfide-based solid electrolytes, but not the fracture properties. The latter is crucial for predicting whether a material will crack or shatter in battery applications.

The researchers found that the material has properties somewhat similar to putty or saltwater taffy: it can deform easily when stressed, but at high enough stress, it breaks like brittle glass.

By understanding these properties in detail, it is possible to calculate how much stress the material can withstand before breaking, and design battery systems that take this information into account.

The material is more brittle than those used in batteries, but it could still potentially be used for such purposes, as long as its properties are known and the system is designed accordingly. “You have to design around this knowledge.”

The cycle life of state-of-the-art CR1620 battery is primarily limited by the chemical/electrochemical stability of the liquid electrolyte and its interaction with the electrodes. In solid-state batteries, however, mechanical degradation could affect stability or durability. Therefore, understanding the mechanical properties of the solid electrolyte is important.

The capacity of lithium metal anodes is significantly increased compared to state-of-the-art graphite anodes. This can translate into an energy density increase of about 100% compared to [conventional] lithium-ion technology.

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