Engineers design a high-performance all-solid-state lithium-ion battery that is highly efficient and has a pure-silicon anode.

Engineers have created a new type of battery that combines two promising sub-fields of battery technology into one. This battery is a combination of a solid-state electrolyte as well as an all-silicon anode. It’s a silicon-all, solid-state battery. Initial tests have shown that the battery is safe, durable, and energy-dense. It is well-suited for many applications, including grid storage and electric vehicles.

Science published a detailed description of the battery technology in its September 24, 2021 issue. Nanoengineers led the research at the University of California San Diego in collaboration with researchers from LG Energy Solution.

The energy density of silicon anodes is ten times higher than graphite anodes used in commercial lithium-ion battery packs. However, silicon anodes are notorious for their ability to expand and contract with battery charges and discharges and for how they react with liquid electrolytes. Despite their high energy density, all-silicon anodes have been unable to be used in commercial lithium-ion battery applications. Thanks to the proper electrolyte, all-silicon anodes can move forward with this new work in Science.

This battery configuration opens up new possibilities for solid-state batteries that use alloy anodes like silicon,” stated Darren H. S. Tan (lead author). He has just completed his Ph.D. in chemical engineering at the UC San Diego Jacobs School of Engineering. He also co-founded UNIGRID Battery, which licensed this technology.

Solid-state batteries of high energy density have relied on metallic lithium for anodes in the future. This limits battery charge rates and requires charging at an elevated temperature (usually 60° Celsius or more). The silicon anodes overcome these limitations, allowing faster charging rates at low temperatures and high energy densities.

The team presented a full-sized laboratory-scale battery that can deliver 500 charges and discharge cycles at room temperature with 80% retention. This is a significant step forward for the solid-state and silicon anode communities.

Silicon as an alternative to graphite

Silicon anodes aren’t new, though. Scientists and battery makers have been looking to silicon as an energy-dense material to replace or mix with conventional graphite anodes in their lithium-ion batteries for decades. According to theory, silicon has approximately ten times greater storage capacity than graphite. However, in practice, lithium-ion batteries with silicon added to the anode to increase energy density often have performance issues. This includes the fact that the battery can’t be charged or discharged enough times while still maintaining its performance.

The interaction of silicon anodes with the liquid electrolytes they were paired with is a significant cause of the problem. This is made worse by the considerable volume expansion caused by silicon particles being charged and discharged. This causes severe capacity loss over time.

“It’s crucial that we address the root causes of the problems in our battery research. ” We know that the main problem with silicon anodes is the electrolyte liquid interface instability,” stated Shirley Meng, UC San Diego professor of nanoengineering and the Institute for Materials Discovery and Design director. Meng said, “We needed to take a completely different approach.”

The UC San Diego team used a different approach. They eliminated carbon and other binders associated with all-silicon anodes. The researchers also used micro silicon, which is cheaper and more processed than nano-silicon.

All solid-state solutions

The team removed all carbon and binding agents from the anode. They also removed the liquid electrolyte. They instead used a solid electrolyte based on sulfide. They found that this solid electrolyte was highly stable in all-silicon batteries.

Professor Meng said, “this new work offers a promising resolution to the silicon anode issue, though there is still more to be done.” He also stated, “I see this as a validation for our approach to battery research at UC San Diego.” We combine the most rigorous theoretical and experimental work with creativity and outside-the-box thinking. We can also work with industry partners and tackle complex fundamental problems.

The commercialization of silicon alloy anodes has been dominated by silicon-graphite compounds or the combination of nano-structured particles and polymeric binders. They still have poor stability.

Researchers avoided problems arising from anodes becoming soaked in the organic liquid electrolyte during battery function.

The team also eliminated the carbon from the anode to reduce interfacial contact and unwanted side reactions with the solid electrolyte. This avoided the continuous capacity loss that is common with liquid-based electrolytes.

By combining these two actions, the researchers could reap the full benefits of silicon’s low cost, high energy, and environmentally friendly properties.

Impact & Spin-off Commercialization

Solid-state silicon overcomes many limitations of conventional batteries. It offers exciting opportunities to meet market demand for higher volumetric and lower cost energy, safer batteries, especially for grid storage,” stated Darren H. S. Tan (first author of the Science article).

Many people believed that solid electrolytes containing sulfide were volatile. This was based on the traditional thermodynamic interpretations of liquid electrolyte systems. These interpretations did not account for solid electrolytes’ excellent kinetic stability. This counterintuitive property was an opportunity to create an incredibly stable anode.

Tan is the CEO of UNIGRID Battery and the cofounder. The company has licensed the technology to make these silicon all-solid-state batteries.

Parallel to this, UC San Diego will continue related fundamental work, which includes additional research collaborations with LG Energy Solution.

“LG Energy Solution is pleased that the latest research on batteries with UC San Diego was published in the journal of Science. This acknowledgment is meaningful,” stated Myung-hwan Kim (Chief Procurement Officer, LG Energy Solution). LG Energy Solution is closer to realizing all-solid-state battery technologies, which will significantly diversify our product range.

Kim said that LGES, a top battery manufacturer, will continue promoting state-of-the-art techniques in leading research into next-generation batteries. LG Energy Solution intends to expand its solid-state battery research collaborations with UC San Diego.