advancements in the development of solid-state batteries
Cost and design considerations
towards a Li metal-based SSB. A) Typical architecture of a Li
metal-based SSB. B) Estimated cost projection for an SSB to be
competitive with an LIB based on LLZO estimations and material costs.
Processing costs are not applicable in ‘current status’, given that
there is no production at the moment. A 20 µm fully dense LLZO solid
electrolyte (SE) has been considered to estimate current materials
costs in US$ m−2 . a) The estimated solid-electrolyte production costs
for SSB is based on the processing costs for a referenced SOFC
technology (that is US$7.5 m−2 ) and a 20 µm theoretically dense LLZO
electrolyte with a price of US$10–50 kg−1 (or US$1–5 m−2 ) assuming
mass production14. b) The polymer separator cost does not include the
processing of a microlitre amount of liquid electrolyte at about
US$22 l−1 ). sint., sintered. c) Typical thickness ranges of
solid-state electrolytes reported for pellets43,63,80, tapes110,111,
wet-chemical50,88,101 and vacuum-based71,96 deposited films. LAGP,
Li-Al-Ge-PO4-based SE. Credit: Balaish et al.
Solid state batteries (SSBs) are an emerging battery technology with
high energy densities that could compete with lithium-ion batteries (LIBs),
which power a wide range of electronic devices on the market today. In
contrast with classic LIBs, SSBs have a solid 'ceramic'-based
electrolyte that separates the anode and cathode inside the battery.
In some batteries, this design enables the use of lithium as an anode.
Before SSBs can be commercialized and implemented on a large scale,
researchers must identify cost-effective strategies to produce their
individual components and develop promising battery cell designs.
Researchers at Massachusetts Institute of Technology (MIT) have
written a review paper that summarizes recent advances in the field,
outlining strategies to process the solid electrolytes and
electrolyte/cathode tandems that could be used in future SSB designs.
"As most past studies focused on pellet-type solid electrolytes, 75%
of the production costs outlined by current cost projections for SSB
were greatly overestimated, as they were based on high-temperature
classic sintering techniques for solid electrolyte processing," Moran
Balaish, one of the researchers who carried out the study, told
TechXplore, via email. "As a result, some projections have concluded
that SSB based on oxide solid electrolytes are costly and barely
compete with LIBs if cost is the decisive factor. We provide low
temperature manufacturing options that impact cell assembly,
suggesting that researchers report and reflect not only on classic
Arrhenius transport Li+ plots and electrochemical stability windows,
but also on the new 'thermal processing budget.'"
In their paper, Rupp and her colleagues highlight that there are now
ample opportunities to manufacture ceramic SSB electrolyte films at
low temperatures in the desired size range of 1-20 um. Moreover, they
suggest that existing strategies could reduce the costs of SSB
production by avoiding expensive co-sinter strategies for producing
cathodes and electrolytes.
"For instance, if one avoids high temperature co-sintering in the
design and manufacturing of SSB oxide-based cells, this allows the use
of less cobalt to produce cathode materials, which could help to avoid
geo-socio-political conflicts for resources in the future," Rupp
In the future, the alternative co-sintering strategies discussed by
Rupp and her colleagues could affect the competitiveness of
oxide-based Li-based SSBs. In addition, they could pave the way for
further research focusing on low-temperature solid batteries for
electric vehicles or portable electronics.
"To date, most lab-based research in academia selects the
manufacturing of sintered pellets as the way to test materials and
assemble cells," Rupp said. "There are only a few groups researching
alternatives, such as the development of tapes and films to adapt
realistic and competitive designs for SSBs with thin but robust
electrolytes. This has many historic reasons associated with how the
field evolved, however, it is disadvantageous that the sintering to
pellets limits too strongly the integration of mentioned Cobalt
reduced cathodes with an undesirable form factor and high process
costs, since more of these cathode materials are simply (by phase
diagram) unstable in high temperature co-sintering with the
The review paper authored by Rupp and her colleagues ultimately
conveys a fairly simple message. More specifically, it highlights the
benefits of transitioning to the synthesis of SSB electrolytes in ways
that enable dimensions similar to those of classic polymer separators
in LIBs. According to the researchers, such a transition would be
valuable both to improve the SSBs' structure and to reduce their
costs, while also opening up new possibilities for the integration of
cathodes that are not made of cobalt on a much wider scale.
"To our surprise, even though there is the technological need for SSB
designs with thin and robust electrolytes, there was still a lack in
the field showing most Arrhenius diagrams and electrochemical windows
based on data of sintered pellets with mm-sized form factors," Juan
Carlos Gonzalez-Rosillo one of the first authors said.
While several studies have highlighted the potential of SSBs with
components that are a few microns thick, so far very few teams have
proposed effective strategies to produce these components on a
large-scale. In their paper, Rupp and her colleagues propose ways in
which this could ultimately be achieved, basing their hypotheses on
research evidence gathered over the past few years.
"Some of the questions we asked in our paper are: what methods are
suited for developing these components and, importantly, how will
these methods affect the thermal processing budget to reduce costs,
and provide options to avoid co-sintering for cathode/electrolyte
assemblies? Our review is a humble effort to motivate other teams to
explore options for the alternative manufacturing of thin and robust
SSBs, as well as electrolytes for SSBs," Rupp added.
In their future research, the researchers plan to focus on two main
aspects of SSB development. Firstly, they would like to outline a
variety of other strategies that could be used to process cathodes and
electrolytes for SSB without relying on co-sintering processes.
"These are challenging and far more time-consuming alternatives then
processes based on classic powder-to-pellet or tape routes, as there
is a vast parameter field and best densification protocols while
keeping stoichiometries of the solid chemistries are not as
straightforward," Rupp explained. "However, if challenges are
resolved, these could offer valuable alternative ways of manufacture
and this is the door opener towards integration of more Cobalt-reduced
cathode materials on the long run."
Rupp and her colleagues also plan to conduct new studies exploring
ways to accelerate the large-scale development and implementation of
SSBs. Currently, the design, development and manufacturing of SSB
electrolytes in a laboratory setting is estimated to take over 10
years on average. Reducing these components in size factors can take
an additional 5-10 years. These times are exceedingly long,
highlighting the need for faster processing techniques.
"In our present study, we explore and give a perspective on fast
screening and rapid automated processing of ceramic compounds and
their chemistries, to test properties and iterate best manufacture
routes more quickly to the optimum," Rupp said. "This is not as
straightforward as one may think, since the traditional solid state
battery processing routes from academia via powders or sintered
compound have some complexity for fast screening and run automated
loops. We hope to support our work with concrete examples and analyses
on potential methods that are more suited to do fast looping and
automation of seeking the best processing condition to make components
and cells for future solid state battery designs."
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