New solid-state battery surprises researchers who created it

Engineers have created a new type of battery that weaves two promising battery subfields into a single battery. The battery uses both a solid electrolyte and an all-silicon anode, making it an all-solid silicon battery. The first rounds of tests show that the new battery is safe, durable and energy dense. It shows promise for a wide range of applications, from network storage to electric vehicles.

Battery technology is featured in the September 24, 2021 issue of the journal Science. Nanotechnology engineers from the University of California at San Diego led the research, working with researchers from LG Energy Solution.

Silicon anodes are renowned for their energy density, which is 10 times greater than the graphite anodes most often used in today’s commercial lithium-ion batteries. On the flip side, silicon anodes are infamous for the way they expand and contract as the battery charges and discharge, and how they degrade with liquid electrolytes. These challenges have kept all-silicon anodes from commercial lithium-ion batteries despite the enticing energy density. The new work published in Science offers a promising path for all-silicon anodes, thanks to the right electrolyte.

“With this battery configuration, we are opening up new territory for solid-state batteries using alloy anodes such as silicon,” said Darren HS Tan, lead author of the article. He recently completed his doctorate in chemical engineering. at the Jacobs School of Engineering at UC San Diego and co-founded a startup UNIGRID Battery that licensed this technology.

New generation high energy density solid-state batteries have always used metallic lithium as the anode. But this places restrictions on battery charge rates and the need for a high temperature (typically 60 degrees Celsius or more) while charging. The silicon anode overcomes these limitations, allowing much faster charge rates at low ambient temperatures, while maintaining high energy densities.

The team demonstrated a complete lab-scale cell that delivers 500 charge and discharge cycles with 80% capacity retention at room temperature, representing an exciting advancement for anode communities. silicon and solid-state batteries.

Silicon as an anode to replace graphite

Silicon anodes, of course, are nothing new. For decades, scientists and battery manufacturers have turned to silicon as an energy-dense material to mix or completely replace conventional graphite anodes in lithium-ion batteries. Theoretically, silicon offers about 10 times the storage capacity of graphite. In practice, however, lithium-ion batteries with silicon added to the anode to increase energy density usually suffer from real performance issues: in particular, the number of times the battery can be charged and discharged while still maintaining the performance is not high enough.

Much of the problem is caused by the interaction between silicon anodes and the liquid electrolytes with which they have been associated. The situation is complicated by the large volume expansion of silicon particles during charging and discharging. This results in significant capacity losses over time.

“As battery researchers, it is essential to solve the fundamental problems of the system. For silicon anodes, we know that one of the big problems is the instability of the interface of the liquid electrolyte”, said Shirley Meng, professor of nanotechnology at UC San Diego, corresponding author of the Science paper, and director of the Institute for Materials Discovery and Design at UC San Diego. “We needed a totally different approach,” Meng said.

Indeed, the team led by UC San Diego took a different approach: they removed the carbon and binders that came with all-silicon anodes. In addition, the researchers used micro-silicon, which is less processed and cheaper than nano-silicon, which is used more often.

A solid solution

In addition to removing all carbon and binders from the anode, the team also removed the liquid electrolyte. Instead, they used a solid sulfide-based electrolyte. Their experiments have shown that this solid electrolyte is extremely stable in batteries with all-silicon anodes.

“This new work offers a promising solution to the silicon anode problem, although there is still work to be done,” said Prof Meng, “I see this project as a validation of our research approach. on the batteries here at UC San Diego. We combine the most rigorous theoretical and experimental work with creativity and thought outside the box. We also know how to interact with industry partners while pursuing difficult fundamental challenges. ”

Past efforts to commercialize silicon alloy anodes have mainly focused on silicon-graphite composites, or on combining nanostructured particles with polymer binders. But they still struggle with poor stability.

By replacing the liquid electrolyte with a solid electrolyte and at the same time removing carbon and binders from the silicon anode, the researchers avoided a series of related challenges that arise when the anodes are soaked in the organic liquid electrolyte. while the battery is working.

At the same time, by removing carbon in the anode, the team dramatically reduced interfacial contact (and unwanted side reactions) with solid electrolyte, thus avoiding continued capacity loss that typically occurs with electrolytes. liquids.

This two-part approach allowed researchers to take full advantage of the properties of silicon at low cost, high energy and environmentally friendly.

Impact and spin-off marketing

“The solid state silicon approach overcomes many limitations of conventional batteries. It presents exciting opportunities for us to meet market demands for higher volumetric energy, lower costs and safer batteries, especially for grid energy storage, ”said Darren HS Tan, Senior author. on the Science paper.

Solid sulfide electrolytes were often considered very unstable. However, this was based on traditional thermodynamic interpretations used in liquid electrolyte systems, which did not take into account the excellent kinetic stability of solid electrolytes. The team saw an opportunity to use this counterintuitive property to create a very stable anode.

Tan is the CEO and co-founder of a startup, UNIGRID Battery, which licensed the technology for these solid-state silicon batteries.

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

“LG Energy Solution is delighted that the latest research in battery technology with UC San Diego has been published in the journal of Science, a significant recognition, ”said Myung-hwan Kim, president and chief purchasing officer of LG Energy Solution. “With the latest discovery, LG Energy Solution is much closer to realizing solid-state battery techniques, which would significantly diversify our battery product line.”

“As a leading battery manufacturer, LGES will continue its efforts to foster cutting-edge techniques in next-generation battery cell research,” Kim added. LG Energy Solution has announced plans to further expand its solid-state battery research collaboration with UC San Diego.