A start-up from Paris is working to help researchers make breakthroughs in solid-state battery development.

Thanks  to intensive research by universities and industry, Lithium-ion  batteries (Li-ion) have immensely characterized the beginning of the  21st century. The battery has developed into a “technology enabler” and  battery-operated mobile devices have opened the door to nearly all  markets. From cars to cordless drills, nearly every device is now  electrified and wireless.

In addition to the technology, the  Lithium-ion battery satisfies another market trend — the strong demand  for environmentally friendly use of technology. The electric car is  exactly in tune with the times. Politicians and the population are  demanding a “clean” version of the internal combustion engine. Nothing  comes without a price however, the material costs are a major factor of  this technology and account for around 60% of the total cost. There is  also an energy-intensive, costly production process responsible for the  remaining 40% of the cost.

In  the end, the price for the battery in an electric car is between $5000 —  $20000+, depending on its size. Certainly one reason why not all cars  are battery-powered. In addition, there is the actual environmental  footprint of the Li-ion battery issues relating to overall CO2  emissions, and human rights situations such as cobalt-mining in the  Democratic Republic of the Congo, one of the most important raw  materials for modern batteries, to which people often turn a blind eye.

However,  one of the most critical reasons why not all cars are powered by  batteries today is the limited energy density of liquid Li-ion  batteries. All industries, and especially the automotive industry, would  like batteries that are half the size, twice as powerful and  significantly safer than those currently available. The electrolyte is  the determining factor for battery potential and liquid electrolytes  have given rise to the high performance batteries we have now. However,  in the unfavorable event of a “thermal runaway”, it serves as a fire  accelerator, currently a major issue for both researchers and  manufacturers.

With  Lithium-ion batteries at their limits, creativity is required to push  battery technology and develop the next generation of cells that are  cheaper, more powerful, safer and truly environmentally friendly. But  how?

Innovative  companies are breaking new ground here and radically rethinking the  concept of the Li-ion cell and battery pack. At the last “Battery Day”  in September of this year, Tesla once again demonstrated how to think  outside the box. The engineers at Tesla have questioned the entire value  chain of Li-ion battery production — with the aim of simplifying,  wherever possible in order to reduce costs, eliminate unnecessary  production steps, and produce “greener” batteries. This means, for  example, reducing the enormous amount of water used. A holistic approach  with much potential.

In  addition to optimizing liquid electrolyte-based Li-ion technology,  researchers have established a new trend that could enable a big step in  the right direction — the all-solid-state battery or ASSB.

A  concept that has been around since the 1950s is on the rise again.  Scientists, start-ups and large-scale industry are working flat out to  develop an alternative to the liquid electrolyte. Huge amounts of  R&D budget, venture capital and research money are being directed  into the market. While there are some doubts about the technology, most  of the battery research groups are somehow working to contribute to the  topic of ASSBs. There are also a number of new players entering the  market: highly-funded start-ups are springing up everywhere, but also  classic chemistry and material producers — who simply want to see how  their ceramics or polymers work in an ASSB cell, are pushing into the  space. It is important for everyone to keep their eyes and ears open, so  as not to miss any opportunities or innovations from the competition.

Overview of relevant market participants

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Solid-state  technology promises higher performance through the potential use of  lithium metal as an anode and more safety through the absence of the  flammable liquid electrolyte.

Before  the technology can be successfully commercialized, however, this must  still be proven under laboratory and real conditions. Manufacturing  processes must also be defined and simplified in order to ensure  adequate amortization of large investments.

The  key to this technology is to find a stable, inexpensive and  easy-to-produce solid-state electrolyte that in combination with  metallic lithium, enables high-performance cell chemistries. A number of  potential materials are currently being explored, generally divided  into ceramics and various polymers.

The  main difference between ceramic and polymer-based solid state  electrolytes lies in their mechanical, chemical and electrochemical  properties. Ceramics are particularly convincing with their “high” ionic  conductivity and stability, however they are relatively demanding in  terms of processing. Oxide-based ceramics are largely considered to be  electrochemically stable, but sulfide-based ceramics require so-called  “coatings” in order to have a sufficiently high electrochemical  stability. Nonetheless, sulfide-based ceramics are currently considered  to be the most promising materials, as they combine favorable  conductivity and stability with good advances in processability.  Although polymers are easier and cheaper to process, their low ionic  conductivity and chemical stability compared to both electrodes have so  far been limiting.

The  development of halide electrolytes (X = F, Cl, Br, I) is also  particularly interesting; these could be a promising approach to further  increase the ionic conductivity by optimizing the vacancy concentration  or increasing the stability towards Li metal by adjusting the chemical  composition or combination of functional intermediate layers.

Overview of the performance factors of solid-state electrolytes:

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While  players like Solid Power and Ilika have begun testing prototypes of  solid-state batteries, the industry is still in its infancy and there  are a number of fundamental challenges that stand in the way of scaling.  Electrochemical stability, material fatigue, and the control of  metallic lithium deposition/cycling have not yet been adequately  researched. Additionally, the dependence of the conductivity on the  mechanical stack pressure and temperature. This currently restricts both  the scalability and ability to research these materials compared to  conventional lithium-ion batteries. Academic and industrial research  laboratories are not yet equipped for this type of technology. The  classic methods using “coin” or “pouch cells” do not work here,  especially in basic research. The strong pressure and temperature  dependency of solid-state systems call for new test procedures that  allow precise control of these parameters.

In  order to implement an idea in an experiment today, researchers first  have to synthesize new materials, possibly add binders, solvents or  other additives in order to then form a so-called “pellet” (consisting  of anode, electrolyte and cathode) in order to find a suitable test cell  in which a test can then be implemented.

Currently,  the industry does not yet have set standards, and without access to  standardized test cells that are designed to meet these challenges,  laboratories have only had to build test cells themselves. This has  resulted in test results for the same materials often being greater than  the differences between different materials (Nature article), making them of extremely limited use to industry.

Examples of self-made battery test cells

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For  these reasons, research in the field of solid-state batteries,  especially with regard to test procedures and equipment, needs to focus  on the connection between science and industry.

This  is exactly where the start-up Sphere-Energy comes in. The team, coming  from this research area themselves, has made it its mission to use  innovative hardware and test cells to achieve new standards in the  quality and comparability of measurement data for solid-state batteries.

Overview of traditional ASSB test process vs. Sphere-Energy test process

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Sphere-Energy’s  test cells are designed to give every laboratory quick access to highly  standardized test processes and reliable results. Researchers should be  able to take care of thinking and experimenting, be able to control all  relevant parameters, and produce clean data in order to close the gap  between research and manufacturing. The Sphere-Energy team has a clear  goal: “We want to advance the research on solid state batteries with  meaningful and precise tools, allowing a more efficient and successful  market entry for different solid state battery technologies”.