Rechargeable lithium-ion batteries are an emerging technology that could one day power cell phones and laptops for days on a single charge. Offering significantly improved energy density, they are a safer alternative to the flammable lithium-ion batteries currently used in consumer electronics, but they are not environmentally friendly. Current recycling methods focus on the limited recovery of metals contained in the cathodes, while everything else is discarded.
A team of researchers from Penn State University may have solved this problem. Led by Enrique GomezInterim Associate Dean for Equity and Inclusion and Professor of Chemical Engineering in the Penn State College of Engineering, the team redesigned these solid-state lithium batteries so that all of their components could be easily recycled. They published their findings in ACS Energy Letters.
“As the need for rechargeable batteries increases, we need to think about the end of life of this technology,” Gomez said. “We hope our work will shed light on the possibilities for recycling solid-state batteries, using some key design elements.”
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Traditionally, most of the basic components of batteries are discarded because they mix together during the recycling process, forming a “black mass,” according to the researchers. This black mass is rich in materials needed for batteries, but separating them remains a challenge. In solid-state batteries, the use of solid electrolytes compounds this problem because they mix with the black mass.
To more easily separate these components from other metal components of a button cell, the researchers inserted two layers of polymer at the interfaces between the electrode and the electrolyte before the recycling process began.
“We suggested that by dissolving the polymer layer during the recycling process, it is possible to easily separate the electrode from the electrolyte,” said Yi-Chen Lan, a doctoral student in chemical engineering and first author of the paper. “Without the polymer layer separating them, the electrode and electrolyte would be mixed, making them difficult to recycle.”
Once the researchers were able to separate the components, they made a composite with the recovered metals and electrodes using cold sintering — the process of combining powder-based materials into dense shapes at low temperatures using pressure applied using solvents. Cold sinteringwas developed in 2016by a team of researchers led byClive Randall Penn State DirectorMaterials Research Instituteand Distinguished Professor of Materials Science and Engineering. Gomez and his team have recently demonstrated the recycling of solid electrolytes by cold sintering.
“We used cold sintering to combine the recovered electrodes with the recovered composite solid electrolyte powders, and then rebuilt the battery with the added polymer layers,” said Po-Hao Lai, a chemical engineering doctoral student and co-author of the paper. “This allows us to recycle the entire battery, which we are then able to recycle again after its use.”
After testing its performance, they found that the rebuilt battery achieved between 92.5% and 93.8% of its original discharge capacity.
“While the commercialization of all-solid-state lithium-ion batteries is still in its early stages, our work provides important insights and ideas for designing recyclable versions of these batteries,” Lan said. “While we’re not quite there yet, the long-term goal is to apply this innovation to larger batteries that could be used in devices such as cell phones and laptops once all-solid-state technology becomes more widespread.”
Reference: Lan YC, Lai PH, Vogt BD, Gomez ED. Interfacial layers to enable recyclability of all-solid-state lithium batteries. ACS Energy Lett. 2024;9(7):3324-3334. doi: 10.1021/acsenergylett.4c01153
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