Solid state silicon battery boost for storage systems

September 24, 2021 // By Nick Flaherty
Solid state silicon battery boost for storage systems
A solid state silicon battery technology developed at the University of California San Diego has been licensed to Unigrid Battery for energy storage systems

Researchers in the US have developed a battery with both a solid state sulfide electrolyte and an all-silicon anode and licensed the technology to a spinout.

The initial rounds of tests show that the new battery is safe, long lasting, and energy dense. It holds promise for a wide range of applications and is initially aimed at grid storage and energy storage systems.

University of California San Diego nanoengineers led the research, in collaboration with funding and researchers from LG Energy Solution.

"With this battery configuration, we are opening a new territory for solid-state batteries using alloy anodes such as silicon," said researcher Darren Tan. He recently completed his chemical engineering PhD at the UC San Diego Jacobs School of Engineering and co-founded a startup called Unigrid Battery that has licensed this technology. 

The silicon anode overcomes the limitations of using a metal lithium anode, allowing much faster charge rates at room to low temperatures, while maintaining high energy densities. 

The team demonstrated a laboratory scale full solid state cell that delivers 500 charge and discharge cycles with 80 percent capacity retention at room temperature.

Theoretically, silicon anodes offer ten times the storage capacity of graphite, but suffer from real-world performance issues: in particular, the number of times the battery can be charged and discharged while maintaining performance is not high enough. 

Much of the problem is caused by the interaction between silicon anodes and the liquid electrolytes they have been paired with. The situation is complicated by large volume expansion of silicon particles during charge and discharge. This results in severe capacity losses over time. 

"As battery researchers, it's vital to address the root problems in the system. For silicon anodes, we know that one of the big issues is the liquid electrolyte interface instability," said Prof Shirley Meng, director of the Institute for Materials Discovery and Design at UC San Diego. "We needed a totally different approach.”

The new cell eliminates the carbon and the binders, and uses micro-silicon, which is less processed and less expensive than the nano-silicon that is more often used. The team also removed the liquid lithium electrolyte and instead used a sulfide-based solid electrolyte.

Sulfide-based electrolytes are highly unstable in liquid cells, but the team found they had significant stability as a solid electrolytes with the all-silicon anodes. 

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"This new work offers a promising solution to the silicon anode problem, though there is more work to do," said Meng, "I see this project as a validation of our approach to battery research here at UC San Diego. We pair the most rigorous theoretical and experimental work with creativity and outside-the-box thinking. We also know how to interact with industry partners while pursuing tough fundamental challenges." 

Past efforts to commercialize silicon alloy anodes mainly focused on silicon-graphite composites, or by combining nano-structured particles with polymeric binders. But they still struggled with poor stability.

Eliminating the carbon in the anode, the team significantly reduced the interfacial contact (and unwanted side reactions) with the solid electrolyte, avoiding continuous capacity loss that typically occurs with liquid-based electrolytes.

"The solid-state silicon approach overcomes many limitations in conventional batteries. It presents exciting opportunities for us to meet market demands for higher volumetric energy, lowered costs, and safer batteries especially for grid energy storage," said researcher Darren Tan.

In parallel, related fundamental work will continue at UC San Diego, including additional research collaboration with LG Energy Solution. 

"LG Energy Solution is delighted that the latest research on battery technology with UC San Diego made it onto the journal of Science, a meaningful acknowledgement," said Myung-hwan Kim, President and Chief Procurement Officer at LG Energy Solution. "With the latest finding, LG Energy Solution is much closer to realizing all-solid-state battery techniques, which would greatly diversify our battery product lineup."

"As a leading battery manufacturer, LGES will continue its effort to foster state-of-the-art techniques in leading research of next-generation battery cells," he said. LG Energy Solution said it plans to further expand its solid-state battery research collaboration with UC San Diego.

www.lgensol.com; www.ucsd.edu

www.science.org/doi/10.1126/science.abg7217

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