September 23, 2021-Engineers created a new type of battery, weaving two promising battery sub-fields into one battery. The battery uses a solid electrolyte and an all-silicon anode at the same time, making it a silicon all-solid-state battery. The first few rounds of testing have shown that the new battery is safe, long-lasting and energy-intensive. It is expected to be used in a wide range of applications from grid storage to electric vehicles.

Battery technology is described in "Science" magazine. University of California (UC) San Diego nanoengineers and LG Energy Solution researchers collaborated to lead the research. 

Silicon anodes are known for their energy density, which is 10 times higher than the graphite anodes most commonly used in commercial lithium-ion batteries today. On the other hand, silicon anodes are notorious for how they expand and contract during battery charging and discharging and how they degrade with the liquid electrolyte. Despite its attractive energy density, these challenges make it impossible to use commercial lithium-ion batteries for all-silicon anodes. Thanks to the correct electrolyte, the new work published in the journal Science provides a promising path for all-silicon anodes.

"With this battery configuration, we have opened up a new field for solid-state batteries that use alloy anodes such as silicon," said Darren HS Tan, the first author of the paper. He recently completed his Ph.D. in chemical engineering at the Jacobs School of Engineering at the University of California, San Diego, and co-founded UNIGRID Battery, a start-up company that has licensed the technology. 

Next-generation solid-state batteries with high energy density have always relied on metallic lithium as an anode. But this imposes restrictions on the battery charging rate and the temperature that needs to be raised during the charging process (usually 60 degrees Celsius or higher). The silicon anode overcomes these limitations and can achieve a faster charging rate from room temperature to low temperature while maintaining high energy density. 

The team demonstrated a laboratory-scale full battery that can provide 500 charge and discharge cycles at room temperature with a capacity retention rate of 80%, which represents an exciting advancement in the silicon anode and solid-state battery communities.

Of course, silicon anodes are not new. For decades, scientists and battery manufacturers have regarded silicon as a material with high energy density to mix or completely replace traditional graphite anodes in lithium-ion batteries. In theory, the storage capacity of silicon is about 10 times that of graphite. However, in practice, lithium-ion batteries in which silicon is added to the anode to increase energy density usually encounter real-world performance problems: in particular, the number of times the battery can be charged and discharged while maintaining performance is not high enough.

Most of the problems are caused by the interaction between the silicon anode and its paired liquid electrolyte. In the process of charging and discharging, the volume of silicon particles expands greatly, which complicates the situation. Over time, this can lead to severe capacity loss. 

"As a battery researcher, it is very important to solve the fundamental problems in the system. For silicon anodes, we know that one of the big problems is the instability of the liquid electrolyte interface," said Shirley Meng, professor of nanoengineering at the University of California, San Diego, who is a science The corresponding author of the paper is also the director of the Materials Discovery and Design Institute at the University of California, San Diego. Diego. "We need a completely different approach," Meng said.

In fact, the team led by the University of California, San Diego took a different approach: They eliminated the carbon and binder used with the all-silicon anode. In addition, the researchers used micro-silicon, which has less processing and lower cost than the more commonly used nano-silicon.

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

"This new work provides a promising solution to the silicon anode problem, although there is more work to be done," Meng said. "I think this project is a validation of our battery research method at the University of California, San Diego. We pair the most rigorous theoretical and experimental work, with creativity and out-of-the-box thinking. We also know how to interact with industry partners while pursuing serious basic challenges." 

In the past, efforts to commercialize silicon alloy anodes mainly focused on silicon-graphite composite materials, or combining nanostructured particles with polymer binders. But they are still struggling with the problem of poor stability.

By replacing the liquid electrolyte with a solid electrolyte while removing carbon and binder from the silicon anode, the researchers avoided a series of related challenges that arise when the anode is immersed in an organic liquid electrolyte while the battery is running. 

At the same time, by eliminating carbon in the anode, the team significantly reduced the interfacial contact (and unwanted side reactions) with the solid electrolyte, avoiding the continuous capacity loss that usually occurs with liquid electrolytes.

This two-part initiative allows researchers to fully benefit from the low-cost, high-energy, and environmentally friendly properties of silicon.

"The solid-state silicon method overcomes many of the limitations of traditional batteries. It provides us with exciting opportunities to meet the market's demand for higher volume energy, lower cost and safer batteries, especially for grid energy storage. Battery," Tan said. 

Sulfide-based solid electrolytes are generally considered to be highly unstable. However, this is based on the traditional thermodynamic interpretation used in liquid electrolyte systems and does not take into account the excellent dynamic stability of solid electrolytes. The team saw an opportunity to use this counterintuitive property to make highly stable anodes.

Tan is the CEO and co-founder of UNIGRID Battery, a start-up company that has licensed the technology for these silicon all-solid-state batteries.

At the same time, the University of California, San Diego will continue to carry out related basic work, including additional research collaboration with LG Energy Solution (LGES). 

Myung-hwan Kim, President and Chief Procurement Officer of LG Energy Solution, said: “LG Energy Solution is very pleased that the latest research on battery technology from the University of California, San Diego was published in the journal Science. This is a meaningful recognition.” “According to The latest discovery, LG Energy Solution is closer to the realization of all-solid-state battery technology, which will greatly enrich our battery product lineup."

"As a leading battery manufacturer, LGES will continue to work hard to cultivate the most advanced technologies and lead the research of next-generation batteries," Kim added. LG Energy Solution said it plans to further expand its solid-state battery research cooperation with the University of California, San Diego.

-This press release was originally published on the University of California San Diego website

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