A new solid-state battery surprises the researchers who created it
Engineers create a high performance all-solid-state battery with a pure- silicon anode

Date:
September 23, 2021
Source:
University of California - San Diego
Summary:
Engineers created a new type of battery that weaves two promising
battery sub-fields into a single battery. The battery uses both
a solid state electrolyte and an all-silicon anode, making it a
silicon all-solid-state battery. 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 from grid storage
to electric vehicles.



FULL STORY ========================================================================== Engineers created a new type of battery that weaves two promising battery
sub- fields into a single battery. The battery uses both a solid state electrolyte and an all-silicon anode, making it a silicon all-solid-state battery. 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 from grid storage to electric vehicles.


==========================================================================
The battery technology is described in the 24 September, 2021 issue of
the journal Science. University of California San Diego nanoengineers
led the research, in collaboration with researchers at LG Energy Solution.

Silicon anodes are famous 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 other hand, silicon anodes are infamous
for how they expand and contract as the battery charges and discharges,
and for how they degrade with liquid electrolytes. These challenges
have kept all-silicon anodes out of commercial lithium ion batteries
despite the tantalizing energy density. The new work published in
Science provides a promising path forward for all- silicon-anodes,
thanks to the right electrolyte.

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

Next-generation, solid-state batteries with high energy densities
have always relied on metallic lithium as an anode. But that places restrictions on battery charge rates and the need for elevated temperature (usually 60 degrees Celsius or higher) during charging. The silicon anode overcomes these limitations, allowing much faster charge rates at room
to low temperatures, while maintaining high energy densities.

The team demonstrated a laboratory scale full cell that delivers
500 charge and discharge cycles with 80% capacity retention at room temperature, which represents exciting progress for both the silicon
anode and solid state battery communities.



========================================================================== Silicon as an anode to replace graphite Silicon anodes, of course, are
not new. For decades, scientists and battery manufacturers have looked to silicon as an energy-dense material to mix into, or completely replace, conventional graphite anodes in lithium-ion batteries.

Theoretically, silicon offers approximately 10 times the storage capacity
of graphite. In practice however, lithium-ion batteries with silicon added
to the anode to increase energy density typically 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 UC San Diego nanoengineering
professor Shirley Meng, the corresponding author on the Science paper,
and director of the Institute for Materials Discovery and Design at UC
San Diego. "We needed a totally different approach," said Meng.

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



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

"This new work offers a promising solution to the silicon anode problem,
though there is more work to do," said professor 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 focus on
silicon- graphite composites, or on combining nano-structured particles
with polymeric binders. But they still struggle with poor stability.

By swapping out the liquid electrolyte for a solid electrolyte, and at
the same time removing the carbon and binders from the silicon anode, the researchers avoided a series of related challenges that arise when anodes become soaked in the organic liquid electrolyte as the battery functions.

At the same time, by 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.

This two-part move allowed the researchers to fully reap the benefits
of low cost, high energy and environmentally benign properties of silicon.

Impact & Spin-off Commercialization "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 Darren H. S. Tan, the first author on the Science paper.

Sulfide-based solid electrolytes were often believed to be highly
unstable.

However, this was based on traditional thermodynamic interpretations used
in liquid electrolyte systems, which did not account for the excellent
kinetic stability of solid electrolytes. The team saw an opportunity to
utilize this counterintuitive property to create a highly stable anode.

Tan is the CEO and cofounder of a startup, UNIGRID Battery, that has
licensed the technology for these silicon all solid-state 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 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," added Kim. LG Energy Solution said it plans to further
expand its solid-state battery research collaboration with UC San Diego.

The study had been supported by LG Energy Solution's open innovation,
a program that actively supports battery-related research. LGES has been working with researchers around the world to foster related techniques.

========================================================================== Story Source: Materials provided by
University_of_California_-_San_Diego. Original written by Ioana
Patringenaru. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Darren H. S. Tan, Yu-Ting Chen, Hedi Yang, Wurigumula Bao, Bhagath
Sreenarayanan, Jean-Marie Doux, Weikang Li, Bingyu Lu, So-Yeon Ham,
Baharak Sayahpour, Jonathan Scharf, Erik A. Wu, Grayson Deysher,
Hyea Eun Han, Hoe Jin Hah, Hyeri Jeong, Jeong Beom Lee, Zheng Chen,
Ying Shirley Meng. Carbon-free high-loading silicon anodes enabled
by sulfide solid electrolytes. Science, 2021; 373 (6562): 1494 DOI:
10.1126/ science.abg7217 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/09/210923165942.htm

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