Solid-State Batteries Why There is No Single Production Process

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Those who speak of producing a solid-state battery fall short. Depending on the solid electrolyte, completely different process chains emerge—with far-reaching consequences for machine builders, equipment manufacturers, and battery producers.

Solid-state batteries are considered a promising candidate for the next generation of energy storage. While new electrolyte materials, higher energy densities, or improved safety features are often discussed, another question comes to the forefront when considering industrial scale-up: How can these batteries be produced economically and in large quantities?

The third edition of the guide *Production of a Solid-State Battery Cell* by the PEM of RWTH Aachen and VDMA addresses precisely this issue. Instead of describing a universally applicable process chain, the publication demonstrates that production is significantly determined by the respective cell concept. The choice of solid electrolyte not only affects the properties of the battery but also the production processes, plant technology, and quality requirements.

Four Electrolyte Classes—Four Different Process Chains

A key finding of the guideline: There is no single production process for solid-state batteries. Instead, the manufacturing steps differ significantly depending on the solid electrolyte used.

The authors distinguish four fundamental material classes: oxides, sulfides, polymers, and halides. Each of these classes has specific electrochemical properties and imposes different requirements on industrial manufacturing.

Oxide electrolytes are characterized by high chemical stability but usually require high-temperature processes such as sintering. Sulfide electrolytes offer high ion conductivity and are relatively easy to densify but are sensitive under normal atmospheric conditions. This creates specific requirements for the production environment, plant technology, and occupational safety. Polymer electrolytes enable relatively simple processing methods and flexible cell designs but often do not achieve the conductivity of ceramic systems. Halide electrolytes combine high electrochemical stability with good conductivity and are considered a promising alternative for future cell designs.

The consequence: The choice of electrolyte already determines which manufacturing processes can be used and how a future production line must be structured.

Proven Manufacturing Steps Remain Intact

Despite the technology shift, the production of a solid-state battery does not start from scratch. Numerous established processes from the manufacturing of conventional battery cells essentially remain unchanged. These include mixing active materials, coating electrodes, drying processes, and calendaring.

However, the guideline also makes it clear that these known process steps only constitute a part of the subsequent production chain.

The Solid Electrolyte Itself Becomes Part of the Manufacturing Process

While the liquid electrolyte in today's batteries is introduced relatively late in the manufacturing process, the solid electrolyte in all-solid-state batteries forms its own distinct production area. Depending on the material system, different methods are used—such as strip casting, pressing processes, or high-temperature processes like the sintering of ceramic electrolytes.

This brings new quality characteristics to the forefront of manufacturing. Layer thickness, homogeneity, porosity, and the quality of interfaces directly influence the performance of the resulting cell and place high demands on process control.

Precision is Key in Cell Assembly

Cell assembly also changes compared to current battery concepts. The guideline shows that many solid-state cell concepts rely on stacked cell architectures, as the materials used often are not well-suited for wound designs.

This makes high-precision stacking processes, exact positioning, and defined pressing forces significantly more important. Even minor deviations at the interfaces between electrodes and solid electrolytes can impair ion transport and thus affect the performance of the entire cell.

Mechanical Engineering Becomes the Key to Series Production

The guideline highlights that the success of solid-state batteries will not depend solely on new materials. Equally important is the development of suitable production equipment capable of manufacturing the various cell concepts reproducibly, economically, and in large quantities.

This opens up a new field of development for machine and plant manufacturers. While individual process steps from today's battery production can be adopted, numerous new requirements also arise—from the production of the solid electrolyte to cell assembly and the management of complex material and interface processes. The production line of the future will therefore not be universal but will differ significantly depending on the cell chemistry and manufacturing concept.

Further information: The guide *Production of a Solid-State Battery Cell (3rd Edition)* by the PEM of RWTH Aachen and the VDMA provides a detailed description of the various cell concepts, material systems, and associated production processes.