Complete recycle of solid-state batteries possible, thanks to polymer layers

The rechargeable lithium-ion batteries that power your cellphone, laptop, and other gadgets use liquid or gel electrolytes. Scientists want to replace these batteries with rechargeable solid-state lithium batteries, but why? This is because solid-state batteries are stable, have a higher energy density, and are much safer since they are not flammable like conventional Li-ion batteries. For instance, an electric vehicle powered by a solid-state lithium battery would offer a greater range and perform well under different temperature conditions compared to a similar EV with a conventional lithium battery. Similarly, a cellphone with a solid-state battery will last multiple days on a single charge. There is one big problem, though. Recycling solid-state lithium batteries is much more complex and challenging, making them a disaster for the environment. Even at present, about 95 percent of conventional lithium batteries (which are easier to recycle) go unrecycled and end up polluting land and water. Solid-state lithium batteries can worsen the situation. However, a new study from researchers at Penn State University (PSU) reveals a practical and efficient way to recycle solid-state batteries. Here’s how it works:

Using polymers to recycle solid-state lithium batteries

When lithium batteries are recycled, they turn into a black mass comprising different materials. “This black mass is rich in materials needed for batteries but separating them out remains a challenge,” the study authors note. This is probably because many of these materials have similar chemical properties and may also contain various impurities. In lithium batteries with liquid or gel electrolytes, identifying and separating different materials from the black mass is possible to some extent. However, in solid-state batteries, the use of solid electrolytes compounds this problem, as they become intermixed with the black mass, the study authors added. The PSU team figured out an interesting way to solve this problem. They took a solid-state lithium coin cell battery and placed two polymer layers at the junctions between its electrode and electrolyte. Next, they subjected the battery to the recycling process used to recycle conventional Li-ion batteries. This caused the polymer to dissolve between the electrolyte and electrode, preventing them from mixing. “Without the polymer layer separating them, you would have the electrode and electrolyte mixed together, which makes them hard to recycle,” Yi-Chen Lan, first author of the study and a doctoral student at PSU, said. The researchers then separated the different battery materials. They combined the recovered metals and electrodes using cold sintering. It is a process in which a powdered mixture of different materials is pressed and treated with a solvent at low temperatures until it turns into one solid object that can be used to make a new battery. “We used cold sintering to combine the recovered electrodes with recovered composite solid electrolyte powders, then reconstructed the battery with the polymer layers added. This enables us to recycle the whole battery, which we are then able to recycle again after its use,” Po-Hao Lai, one of the study authors, said.

Testing the recycled solid-state battery

The PSU team integrated the recycled solid material from the coin cell into a new battery and tested its performance. The recycled battery had over 92 percent of the discharge capacity of the original coin cell battery. “Fully recovered full cells with Li-metal and LTO anodes show 92.5% and 93.8% of original discharge capacity at 0.05 C and room temperature,” the study authors note. Solid-state battery technology is still in the early development phase. However, this experiment successfully demonstrates that it is possible to recycle such batteries and harness their potential without harming the environment. “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 like cell phones and laptops, once all-solid-state technology becomes more prevalent,” Lan said. The study is published in the journal ACS Energy Letters.