Solid State Batteries — What Does It Take For A Breakthrough?

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

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:

Reference: https://onlinelibrary.wiley.com/doi/full/10.1002/advs.201903088

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

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

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”.