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New study provides overview of challenges, requirements for large-scale production of all-solid-state Li-ion and Li-metal batteries

Researchers from the Technical University of Munich (TUM), with colleagues from the Helmholtz Institute Ulm (HIU), have evaluated the current challenges and requirements for the large-scale production of all-solid-state lithium-ion and lithium metal batteries. In a paper in the Journal of Power Sources, they report their findings from workshops with experts from research institutes, material suppliers, and automotive manufacturers.

With the aim of bridging the gap between materials research and industrial mass production, the team presents possible solutions for the chain of production of sulfide- and oxide-based all-solid-state batteries (ASSB) from electrode fabrication to cell assembly and quality control.

They provide a detailed comparison of the production processes for a sulfide-based ASSB with a conventional lithium-ion cell, and show that while processes for composite electrode fabrication can be adapted with some effort, the fabrication of the solid electrolyte separator layer and the integration of a lithium metal anode will require completely new processes.

Schnell1
Comparison of conventional lithium-ion battery and all-solid-state lithium battery at the cell, stack, and pack levels with potentials for increased energy density. Schnell et al. Click to enlarge.

Despite their current pervasiveness in consumer, industrial and automotive applications, conventional Li-ion batteries suffer from a number of issues, including raw materials availability, safety concerns, and limited energy storage capacity.

“To meet the demands for automotive applications in 2025, energy densities of 800 Wh l−1 and specific energies above 300 Wh kg−1 will be required.”
—Schnell et al.

Conventional Li-ion cells are built with two electrodes, a separator, and a liquid electrolyte mainly composed of aprotic organic solvents and a conductive salt.

Many of the issues that current LIBs are facing can be traced back to this liquid electrolyte, the researchers say. The flammability of the solvents leads to safety concerns and side reactions of the solvents and the conductive salt lead to capacity fading and aging. During cell production, the electrolyte filling and wetting process as well as the extensive formation procedure contribute to high costs, they note.

By contrast, ASSBs are inherently safer due to the lack of flammable components, and offer the potential for a significant increase in energy density. ASSBs replace the liquid electrolyte with a solid electrolyte which serves both as electrical insulator and ionic conductor. The solid physical barrier also enables the use of lithium metal as the anode material by preventing the formation of dendrites. As a result, increases in volumetric energy densities of up to 70% are possible compared to conventional graphite, the team notes.

As a further benefit, the electrochemical stability of a solid electrolyte can facilitate the use of high capacity (e.g., sulfur) or high-voltage cathodes.

The aforementioned advantages compared to conventional LIBs make ASSBs highly promising candidates for the application in electric vehicles and stationary applications. The implementation of ASSBs on the market will have to be accompanied by a scale up from laboratory research to industrial mass production. … However, a direct transfer of laboratory preparation methods to high volume fabrication processes on industrial scale is in many cases not possible. … The up-scaling of the materials, volume and mass reduction of inactive components for satisfactory energy densities, and implementation of scalable production processes will become the next big steps towards industrial fabrication of ASSBs.

Hence, this perspective manuscript contributes to paving the way to mass commercialization of ASSBs by investigating the multiple challenges from the perspective of production engineering and developing possible production scenarios for the fabrication of ASSBs.

—Schnell et al.

Schnell2
Illustration of the process chains for the production of a sulfide-based all-solid-state battery (pouch format) and a conventional lithium-ion pouch cell. Schnell et al.Click to enlarge.

The paper details the requirements and properties of ASSBs with regards to industrial mass production, then presents different production scenarios and process chains. The researchers also make recommendations for the respective stakeholders: chemical industry, component suppliers, machine engineering, cell producers, and original equipment manufacturers (OEMs).

Broadly, the researches observe that—despite a need for ongoing improvement and development on the material level to address challenges such as limited interface stability and conductivity—future research will have to focus more strongly on material and production cost to enable rapid and successful market implementation.

First, for material development, scaling-up to larger batch sizes implies research on cheaper materials and their synthesis. Additionally, efforts are required to reduce processing temperatures and reactivity of the materials. Although final conclusions on the processing cost for ASSBs will have to be further evaluated, the inert processing environment for sulfides and the high sintering temperatures for oxides are expected to be among the biggest cost drivers next to raw material prices. On the other hand, cost savings are expected since no electrolyte filling and—possibly—no formation procedure is needed.

Second, in contrast to polymer and, possibly, hybrid solid electrolytes, fabrication of sulfide and oxide ASSBs with state-of-the-art production lines for LIBs seems unlikely due to the atmospheric requirements or the need for high-pressure/high-temperature process steps. Nonetheless, several advanced technologies that have already been applied in the manufacturing of current LIBs can be adapted for implementation into ASSB production, as shown for the exemplary process chain of a sulfide based ASSB.

This allows for a modular in-tegration of new technologies into existing LIB production lines, but could also be of particular interest for related sectors, such as fuel cell, capacitor, and semiconductor industry, as well as respective suppliers. Here, for example, knowledge can be transferred from the processing and handling of thin ceramic layers and the production in encapsulated environments. The implementation of new technologies, such as thin-film application and single sheet stacking also provide chances for machine engineering.

—Schnell et al.

Resources

  • Joscha Schnell, Till Günther, Thomas Knoche, Christoph Vieider, Larissa Köhler, Alexander Just, Marlou Keller, Stefano Passerini, Gunther Reinhart (2018) “All-solid-state lithium-ion and lithium metal batteries – paving the way to large-scale production,” Journal of Power Sources, Volume 382, Pages 160-175 doi: 10.1016/j.jpowsour.2018.02.062

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