Lithium-ion batteries have powered our lives for the past three decades, from cellphones and laptops to electric vehicles and other essential products. However, they are filled with flammable liquid electrolytes, which raises concerns about their safety and reliability as power and grid storage demands continue to grow.

A new, safer generation of batteries does not rely on liquids or gels. Instead, these solid-state batteries use a very thin, solid film to keep charge-generating parts (cathodes and anodes) separate and enable the battery to be charged and discharged.

Argonne chemist Lei Cheng is a technical lead for beyond lithium-ion and solid-state electrolyte research at the Argonne Collaborative Center for Energy Storage Science and focus area lead for the Liquid Solvation Science thrust of the Joint Center for Energy Storage Research.

In the Q&A below, Cheng discusses the challenges and opportunities for this next generation of batteries and how Argonne is working to improve the electrochemical performance of solid-state electrolytes and batteries and scale solid-state materials synthesis and chemical processes.

Q: Why are solid-state batteries important now? What energy storage challenges could they help solve?

A: Solid-state batteries that use a lithium metal anode will have increased specific energy and energy density, more potential for fast charging and be intrinsically safer compared with batteries using flammable organic liquid electrolyte. Not only can the current electric vehicle applications benefit from having these improved features, but the higher energy density and improved safety will also enable other applications such as electric aviation. With so much intense research effort and huge capital investment in research and development for this technology, I believe we will get there.

Q: As noted in a 2021 paper in ACS Energy Letters, expectations for solid-state batteries are high, but there are significant materials and processing challenges to overcome. What are some of those challenges and how is Argonne working to address them?

A: The materials-level challenges include the high-temperature steps required to process some of these materials, which lead to a high heat budget and cost. These steps cannot be easily scaled up to roll-to-roll manufacturing processes. It’s also not clear how the cells should be put together, whether the components are made separately and then assembled together, or the components will be casted on top of one another to ensure intimate contact. Having solid electrolyte material fully infiltrated into the space between cathode particles is not as easy as infiltration by liquid, posing another challenge. The cell performance is also another bottleneck since maintaining solid-solid interfaces is not quite straightforward.

“With so much intense research effort and huge capital investment in research and development [for solid-state batteries], I believe we will get there.” — Lei Cheng, Argonne chemist

Some of the things Argonne is working on include exploring other alternative energy steps such as microwave and light to replace the high heating step for processing. We also exploit the existing roll-to-roll technologies to make materials and optimize their performance.

We’re examining the interfaces of the electrolyte and electrode very carefully using advanced characterization techniques and modeling to shed light on the failure mechanism and the path to improvement. And of course, no material is perfect, so we are also constantly looking for new materials that have the potential to improve performance.

Q: What’s the next key innovation needed to advance solid-state battery technology?

A: For solid-state technology to be widely adaptable, the electrolyte materials need to conduct lithium ions fast, effectively suppress lithium dendrite growth at the anode and maintain stable low-resistance interfaces for thousands of cycles to ensure good battery lifetime.

We also need to know how to make and process these materials in large quantities and at low cost. Most of the material being researched now has certain superior properties but misses the mark on other requirements. For example, polymers are intrinsically more processible, but work is needed to improve their room-temperature ionic conductivity, while for hard materials such as oxides, improving the processability is the key.