Automotive Engineering - May 2022 - BET15

need to continue development, mainly of solid electrolyte materials. "
He also stressed that the company would prefer to first
launch solid-state batteries in hybrid-electric vehicles (HEVs).
" One of the reasons that Toyota is starting with HEVs is because
it wants to introduce solid-state batteries to the market as soon
as possible, gain customer feedback and continue to evolve them,
Maeda said. " Rather than building a large-scale production line
for BEVs, which require a large number of batteries, it is better to
start with HEVs, which have smaller batteries and a development
process with which Toyota is familiar. This would allow solid-state
batteries to be introduced to the market faster, as well as enable
improvement of the manufacturing technology for them. "
Pushing Ahead with Silicon
Graphite (carbon) mostly has served as the industry's choice for
anode material during lithium-ion batteries' initial volume-production
phases. But attention is shifting to anode material with improved
characteristics; silicon and lithium metal are front-runners
and silicon - currently used in small ratios in the anode of some
production-battery lithium-ion chemistries - remains the focus of
new and emerging research efforts and various startup companies.
Late 2021 saw the announcement of new research from the
University of California at San Diego (UCSD) pairing solid-state
electrolyte with an all-silicon anode to create what the scientists
are calling " a silicon all-solid-state battery. " As reported by UCSD's
News Center, the work resulted in a " laboratory-scale full cell that
delivers 500 charge and discharge cycles with 80 percent capacity
retention at room temperature, which represents exciting progress
for both the silicon anode and solid-state battery communities. "
Although silicon can deliver up to 10 times the storage capacity
of a graphite anode, lithium-ion batteries with silicon added to the
anode to boost energy density see impact on the number of charge
cycles and energy retention. Much of those performance compromises
is due to the interaction of silicon anodes and the liquid
electrolytes used in all current production lithium-ion batteries.
" For silicon anodes, we know that one of the big issues is the liquid
electrolyte interface instability, " said UCSD nanoengineering professor
Shirley Meng, the corresponding author on a paper about
the research published in the journal Science. " We needed a totally
different approach, " Meng, Director of the Institute for Materials
Discovery and Design UCSD, told the UCSD News Center.
The UCSD researchers reported that they eliminated the carbon
and the binders usually employed with all-silicon anodes.
They also looked to micro-silicon, which is not as highly processed,
and thus less-expensive, than nano-silicon typically used
for anodes. The micro-silicon anode then was teamed with a
sulfide-based solid electrolyte that experiments demonstrated is
extremely stable for use with all-silicon anodes. By totally eliminating
carbon in the anode, the team markedly reduced the interfacial
contact (and corresponding performance-reducing effects)
with the solid electrolyte, avoiding continuous capacity
loss common with liquid-based electrolytes.
" 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 of the Science paper. Tan also is
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the CEO and co-founder of a startup, UNIGRID Battery, which has
licensed the technology for the silicon all-solid-state battery.
Meanwhile, any number of startups also continue to concentrate
silicon-based solid-state battery designs. StoreDot, for one,
aims to have a silicon-based solid-state battery (dubbed XED, or
Extreme Energy Density) sometime in the 2028 timeframe. The
company has said resulting energy density from silicon-based
lithium-ion batteries can enable DC fast charging that delivers
up to 25 miles (40 km) of range per minute while reducing longterm
performance degradation. Another, Colorado's Solid Power,
is developing its own silicon-intensive anode and pairs it with a
proprietary sulfide-based solid electrolyte. BMW and Ford have
invested in Solid Power and BMW has intimated it targets a mid2020s
launch for EVs using solid-state technology.
Another solid-state battery developer, QuantumScape, has
said graphite anodes are responsible for many of the limitations
of contemporary lithium-ion batteries. QuantumScape, which
since 2015 has collaborated with the Volkswagen Group, is hoping
for energy density of " close to " 1000 Wh/liter for its novel
battery design that is manufactured without an anode -
charging the cell causes an anode of pure lithium metal to form.
This article was written by Bill Visnic, Editorial Director, Mobility
Media, SAE International. For more info visit http://info.hotims.
com/82321-423. 
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