Solid-state batteries are considered the holy grail of battery development

Hoymann: The energy turnaround is advancing by leaps and bounds, but the storage problem has not yet been satisfactorily solved. It’s clear that both stationary and mobile storage systems are needed but the storage performance of both systems must be improved. However, the demands for stationary and mobile storage systems are extremely different – which system is best suited for what?

Partsch: Stationary storage covers storage classes ranging from 10 kWh to several GWh with very different requirements for the charge/discharge dynamics. For mobile storage, on the other hand, it is important that the systems are safe and have very high energy and power density. That’s why lithium batteries are particularly important for mobile storage systems.

Hoymann: What technologies are used for stationary storage?

Partsch: For example, redox flow batteries, which are already in use, or high-temperature battery storage systems like sodium-nickel-chloride batteries.

Hoymann: Particularly car manufacturers are conducting worldwide research on the solid-state battery – and the technology sounds promising. Where can it be applied most effectively?

Partsch: Solid-state batteries are particularly suitable where high energy density and improved safety are especially important, for example in the automotive sector.

Hoymann: How did the solid-state battery become so safe?

Partsch: This trait is due to their structure. In terms of the electrode materials used, they are very comparable to today's lithium batteries as similar storage materials are used. The difference lies primarily in the choice of electrolytes, which are solids, as the name suggests.

Hoymann: What electrolytes are we talking about?

Partsch: It varies. For example, polymer electrolytes or inorganic electrolytes based on sulfidic, oxidic or phosphatic ceramics. The main aim is to make batteries even safer by using solid electrolytes. And solid electrolytes also enable the use of so-called lithium anodes, which lead to a further increase in energy density at cell level.

Hoymann: What are the greatest hurdles for developing a market-ready solid-state battery – in terms of availability of raw materials and recyclability?

Partsch: For solid-state batteries, the challenges with regard to availability of raw materials are comparable to those of today's lithium-ion batteries. Similar materials are used, so their availability must also be taken into account. Development focuses on finding substitutes for particularly critical raw materials. And of course, newly developed electrolyte materials must first be manufactured and made available on an appropriate scale for a market launch in the future.

Hoymann: This means you also take a look at production, right?

Partsch: Yes, we’re currently looking at what future production processes for solid-state batteries might look like. In some cases, different technologies will have to be used than for today's lithium-ion batteries. It’s quite a challenge to produce a stable interface between the electrolyte and the electrode – and suitable materials and manufacturing processes are required.

Hoymann: What about recyclability?

Partsch: We’re working hard on reparability, component recycling and raw materials recycling. For example, we expect it will only be possible to separate individual cell components to a limited extent because lithium metal and polymer electrolytes are sticky and difficult to separate. Ceramic electrolytes will probably lead to increased wear and tear on mechanical processing equipment. We therefore need to look at how separation of individual components and substances can be implemented economically, first in mechanical processes and then in hydrometallurgical processing steps.

Hoymann: When is this technology expected to reach market maturity?

Partsch: The technological maturity of solid-state batteries differs greatly depending on the electrolyte used. In electric-powered Bolloré Bluecars, for example, batteries with polymer electrolytes are already on the road today. Companies like Nissan, Volkswagen and Toyota that are banking on inorganic electrolytes have announced the start of production in the next two to four years and plan serial production for 2028 to 2030. In addition, I can imagine that solid-state batteries will also be of interest for other markets, for example for aviation where special properties like increased safety and high energy density are advantageous.

Hoymann: Who is currently among the front runners where worldwide development is concerned? Where does Germany stand? And what about China?

Partsch: Solid-state batteries are considered the holy grail of battery development. This means that task forces all over the world are working hard to find solutions for the associated problems. Intensive research is being carried out in Germany and Europe using the extensive networks of national and global partners. In the USA, there are now several young companies – for example, QuantumScape, Solid Power and SidhuLabs, to name just a few – that promote the commercialization of solid-state batteries, and German OEMs are involved in some of them. In Asia, it’s companies like Nissan, Toyota, Samsung and ProLogium that have signaled a technology breakthrough for the years ahead. I’m curious to see who will win the race!

Hoymann: Will batteries compete with hydrogen for storing electricity in the future?

Partsch: I often get asked what’s better for storing electricity: batteries or hydrogen. I believe there will be suitable applications for both technologies. Battery storage systems like lithium-ion, redox-flow or high-temperature sodium-nickel-chloride batteries have very different characteristics. This fits in with the very different requirements for stationary and mobile storage systems which we will need to convert our energy supply to renewable energy sources.

Hoymann: When does it make sense to use one and when the other?

Partsch: For photovoltaic or wind plants, direct storage in batteries makes a lot of sense because of the low conversion losses and high efficiency, but the energy density of batteries is significantly lower than with hydrogen storage. Hydrogen systems are associated with conversion losses of around 60 percent. In short, batteries are useful for mobile storage with a shorter range and in stationary applications, while hydrogen is good for storing excess electricity and for mobile storage in heavy vehicles with considerable range.

Hoymann: Speaking of smart energy utilization, to what extent do developments in battery technology take into account that batteries and storage units could communicate with solar and wind plants as well as with end devices in order to store the generated electricity smartly and thus use it more efficiently? Does "smart" storage exist?

Partsch: Integrating smart technology into storage components is an important task. My team works primarily on smart cells that make it possible to detect health status and identify failures fast. But the task of coupling storage systems with solar and wind plants and the various consumers is also becoming increasingly smart ... so smart storage does exist!

Hoymann: Many thanks for the interview!