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Stanford, CMU, MIT team reviews challenges to practical implementation of solid-state Li-ion batteries

Toyota, which has been working on solid-state batteries for EVs for a number of years (earlier post), is in the news with a report by the Wall Street Journal that it will be ready to commercialize a solid-state battery by 2022.

Solid-state lithium-ion batteries, with higher volumetric energy densities than currently available lithium-ion batteries, offer a number of conceptual advantages including improved packaging efficiency; improved safety; and long cycle life. However, there remain a number of unresolved issues precluding commercialization at this point. A team from Stanford, Carnegie Mellon University, and MIT recently published an open-access paper in the Journal of the Electrochemical Society reviewing the practical challenges hindering the development of solid-state Li-ion batteries.

The challenges, they note, are many:

  • Unresolved fundamental issues remain in the quest to fully understand the behavior of all-solid batteries, especially in the area of electrochemical interfaces.

  • Parameters that require robust understanding from a product development standpoint are material cost, cell lifetime and shelf life, cell energy density on a volumetric and gravimetric basis, operable capabilities for given temperature conditions, and safety.

  • The advantage of energy density remains to be realized in solid state electrolytes (SSEs) since most studies to date utilize thick SSEs or cathodes with low active loading compared to liquid counterparts.

  • The desire to use SSEs in conjunction with Li metal anodes requires understanding and managing the morphology of Li metal plating, which can impact volumetric energy density.

  • Although operation at both higher and lower temperature compared to conventional technologies is a significant potential advantage of SSE systems, reports of solid state cells achieving parity with traditional systems at room temperature or any other temperature do not currently exist.

  • The decreased flammability of SSE systems is another potential advantage but requires ongoing validation and study.

  • The manufacturability and material component costs of SSEs have not been well characterized, and thus the value of these features will need to be weighed accordingly with any added cost.

  • The operating lifetime of SSEs capturing intrinsic materials parameters such as voltage stability as well as catastrophic failure modes such as shorting have been briefly investigated, but in the absence of high energy density electrode formulations and application based testing protocols that are comparable to commercial liquid electrolyte cells.

To enable development and maturation of solid state battery technology, the value propositions of SSEs must be substantiated with relevant data in the coming years. Companies with competencies in ceramic or battery processing and with the resources to engage in a broad level of materials development and failure analysis may be well positioned to enable this technology.

—Kermana et al.

In their paper, the team references more than 200 papers, exploring critical aspects of solid-state battery technology including the basic material properties of solid state electrolytes—along with key differences in theory and understanding of material physics—and the fabrication of those materials.

They discuss the solid electrolyte interfaces, including the number of failure modes that can occur due to phenomena at the electrolyte-electrode interface. Failure modes can range from the catastrophic to mere poor performance.

The development of full cells requires understanding of material limitations, processing capabilities and cell form factor.

Noting that all energy storage devices, including batteries, possess inherent risk as energy is being confined in a closed system that can be physically or electrically damaged, they discuss risk mitigation strategies as well.

A basic fishbone diagram highlighting two of the key high level failure modes (impedance growth or electrical shorting) and the variety of potential contributing factors. Possible solutions and the consequent product risks to their implementation, including reduced safety, power, energy density, throughput, or requirement of material innovation are also shown. Understanding the interplay between material level issues and cell level ramifications are highlighted to reiterate holistic approaches. Kermana et al. Click to enlarge.

There has been incredible progress in the field of solid state electrolytes for Li ion batteries. The discussion in this work strongly emphasizes that, in the context of solid state battery technology, a holistic approach to material development, taking cell and product design considerations into account is powerful and necessary in creating resilient and far reaching solid state material technologies in the Li ion space. Highly conductive solid ionic materials have paved the way for the potentially ground breaking technology of high energy density anodes and a true solid state battery.

… Specific research vectors for advancing solid state battery technology include scalable manufacturing of low defect density thin ionic conducting solids, characterization methods to determine defect densities at relevant scales, increasing ionic conductivity of solid state electrolytes further, protective active cathode particle coatings, developing high ionic conductivity materials that are deformable or have low melting temperature, and increasing active cathode particle fraction in solid state electrodes.

—Kermana et al.


  • Kian Kermana, Alan Luntz, Venkatasubramanian Viswanathan, Yet-Ming Chiang, and Zhebo Chen (2017) “Review—Practical Challenges Hindering the Development of Solid State Li Ion Batteries” J. Electrochem. Soc. volume 164, issue 7, A1731-A1744 doi: 10.1149/2.1571707jes

  • Yuki Kato, Satoshi Hori, Toshiya Saito, Kota Suzuki, Masaaki Hirayama, Akio Mitsui, Masao Yonemura, Hideki Iba & Ryoji Kanno (2016) “High-power all-solid-state batteries using sulfide superionic conductors” Nature Energy 1, Article number: 16030 doi: 10.1038/nenergy.2016.30



TMC have been and are pouring substantial resources into battery development as well as fuel cells as like me they are interested in getting the result of low carbon and harmful emissions free transport, able to utilise a high proportion of renewables rather than seeking to be prescriptive on the means.

Their gripe against batteries has been that they couldn't get one they were happy with the safety and durability of at the right cost.

I think at least for safety and durability their view has been somewhat conditioned by not wanting to use Korean batteries, but in trying to kick Panasonic into building what the want.

For costs though materials along exceed a fully competitive price of of the order of $50kWh needed to be universal ex-subsidy and mandate.

$100kWh or so should be doable within the next few years, but not $50 with present chemistry.

So development of better batteries fully accords with Tesla's mission statement to remain at the forefront of transport whatever is powering it and to move to de-carbonised and sustainable use of resources throughout the production chain.

So they do both batteries and fuel cells, as both can actually help each other out, for instance for the billion plus cars there will be in the world in the next couple of decade with no realistic place to plug in.

And they have the resources and the long time horizons to do both.

But the talk of a 2022 for mass production does not sound at all Toyota to me.

They research and develop products, then put them into exhaustive testing for years, then limited production, and build up gradually.

They don't claim mass production when none of these things have been completed.

It sounds like journalistic hype to me.


TMC did have working prototype in 2014, they published a breakthrough using sulfide superionic conductors in 2016 ( article), going into production in 2022 does not mean worldwide scale of millions EVs, but something like we have seen with Prius in 1997 only available in small numbers in Japan.

The original article in Chunichi paper stated:
"Toyota has decided to sell the new model in Japan as early as 2022"

In that article there is also this:
"Toyota is reportedly planning to begin mass-producing EVs in China, the world's biggest auto market, as early as in 2019, although that model would be based on the existing C-HR sport utility vehicle and use lithium-ion batteries."

We can suspect that Toyota will roll out their EVs in 2019, but my guess is they won't go large scale until they have solid-state battery fully tested and ready for mass production (Around 2025?).


Yeah, Toyota are releasing a BEV, Chinese regulations pretty well compel them to, and as they have said the development of the Prius Prime batteries was aimed also at future BEVs, probably with fairly limited range at this stage of the cost cycle.

They ain't about to suddenly jump to mass producing a radically new solid state format without years of testing and a gradual ramp up though.

Toyota are normally reasonably forthcoming in their statements, and when they think they are coming close, will no doubt tell us.

Not much fun for journalists in waiting for that though, so a speculation sells more copy.


They also patented a magnesium sulfur battery, have not seen that.


No one here dare to talk of where the ones parking in the streets will charge their bev.

"Toyota spokeswoman Kayo Doi said the company would not comment on specific product plans but added that it aimed to commercialize all-solid-state batteries by the early 2020s"


Five cities in the US are already permitting or funding the installation of curbside parking. Los Angeles Department of Water and Power has installed chargers on lamp posts which are powered using the streetlamp wiring. LED bulb replacement enabled the existing wiring to be used without major upgrades.

- Electric Car Insider Q1 2017 edition


And recently, scientists have developed a new coating for lithium-ion batteries, which stabilizes their operation and extends the life of more than three times compared to standard batteries. They (researchers from the University of California) found that when adding only 0.005% methylviologen to the electrolyte, its molecules form a stabilizing coating on the electrode, so that the battery life lasts more than three times. In my study, which I write on, I found that, in principle, methyl viologen is very cheap in production and this makes it possible to widely use it. Of course, I would like to see some ready-made prototype, but I think that soon it will appear.


Curbside parking takes from 4 to 6 vehicles per street lights.

LEDs can save an average of 200 watts per street light. Unless existing wiring is over engineered, you could hardly slow charge more than a single BEV per street light. Upgrading wiring would be a must to go up to 6 slow chargers.


The authors of this post have incorrectly cited the first author's name as Kermana. It should be Kerman.


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