Engineers have created a new type battery that combines two promising sub-fields of batteries into one. This battery is a combination of a solid-state electrolyte as well as an all-silicon anode. It's a silicon allsolid-state battery. Initial tests have shown that the battery is stable, durable, and energy dense. It is well-suited for many applications, including grid storage and electric vehicles.
Science, 24 September 2021: The Battery Technology is discussed. The research was conducted by nanoengineers at the University of California San Diego in collaboration with researchers from LG Energy Solution.
The energy density of silicon anodes is 10 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 as well as for how they react to liquid electrolytes. All-silicon anodes have been unable to use commercial lithium ion battery despite their attractive energy density. Science published a new study that shows all-silicon anodes can be made more efficient by using the right electrolyte.
"With this battery configuration we are opening a new territory solid-state batteries using alloy aniodes such silicon," stated Darren H. S. Tan (lead author). He has just completed his PhD 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). These limitations are overcome by the silicon anode, which allows for 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 battery 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 for decades as an energy-dense materials to replace or mix with conventional graphite anodes in their lithium-ion batteries. According to theory, silicon has a storage capacity that is approximately 10 times greater than graphite. However, in practice, lithium-ion battery with silicon added to 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 with which they were paired is a major cause of the problem. This is made worse by the large volume expansion caused by silicon particles during discharge and charge. This causes severe capacity loss over time.
"As researchers in battery technology, it is essential to identify the root causes of the problems. We know that the main problem with silicon anodes is the electrolyte liquid interface instability," stated Shirley Meng, a UC San Diego professor of nanoengineering and the corresponding author of the Science paper. She is also the director of the Institute for Materials Discovery and Design. 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-siliconanodes. The researchers also used microsilicon, which is cheaper and more processed than the 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 extremely stable in all-silicon batteries.
Professor Meng said that "this new work offers a promising resolution to the silicon anode issue, though there are 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 work and experimental work with creativity, outside-the-box thinking. We are also able to work with industry partners and tackle difficult 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 several related problems that can arise from anodes becoming soaked in 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.
The researchers were able to reap the full benefits of silicon's low cost, high energy, and environmentally friendly properties by combining these two actions.
Impact & Spin-off Commercialization
Solid-state silicon overcomes many limitations of conventional batteries. This paper, which was first published by Darren H. S. Tan (the Science paper's first author), presents us with exciting opportunities to satisfy market demand for more volumetric energy, lower costs, and safer batteries, especially for grid energy storage."
Many people believed that solid electrolytes containing sulfide were highly unstable. 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 seen as an opportunity to create an extremely 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, UCSan Diego will continue related fundamental work, which includes additional research collaborations with LG Energy Solution.
"LG Energy Solution is pleased that the most recent research on battery technology with UC San Diego was published in the Journal of Science. This acknowledgement is meaningful," stated Myung-hwan Kim (Chief Procurement Officer, LG Energy Solution). LG Energy Solution is now closer to realizing all solid-state battery technologies, which will greatly diversify our product line.
Kim said that LGES, a top battery manufacturer, will continue to promote state-of the-art techniques in leading research into next-generation batteries. LG Energy Solution stated that it intends to expand its solid-state battery research collaborations with UC San Diego.
LG Energy Solution's open innovation supported the study. This program actively supports research in battery-related fields. LGES collaborates with other researchers to promote similar techniques.