Scientists develop a way to restore aging EV batteries without breaking them down into raw materials

Cornell's DEER process removes performance-robbing buildup

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The big picture: Cornell University researchers have developed a way to recycle lithium-ion batteries without breaking them down into raw materials first. Their method, called Direct Electrode-to-Electrode Regeneration, or DEER, restores worn battery electrodes so they can be used again. The results suggest that some EV batteries could be refurbished at lower cost and with less energy than conventional recycling methods, though the process will not work for every degraded cell.

The work focuses on a common problem in aging lithium-ion batteries: buildup on the electrodes. As batteries are charged and discharged, a layer known as the solid electrolyte interphase, or SEI, grows on their surfaces. Some SEI is necessary, but too much of it slows the movement of electrons and reduces battery capacity.

In the Cornell process, researchers take apart used cells and place the electrodes in an electrochemical bath containing 1,3-dimethyl-2-imidazolidinone, or DMI. The treatment removes the thicker SEI layer without destroying the electrode itself. The renewed electrodes can then be used to build new battery cells.

The researchers reported that regenerated cells recovered up to 95% of their original capacity. They also found that treated batteries degraded more slowly than untreated ones. Untreated degraded batteries lost capacity at a rate of 0.072% per cycle, compared with 0.042% per cycle for batteries restored through DEER. The lower degradation rate held for about 800 cycles before increasing.

A second round of treatment brought a previously regenerated battery back to 90% of its original capacity. That suggests the process could extend the working life of electrodes more than once, depending on the condition of the battery.

The approach differs from most commercial recycling methods. Conventional systems typically shred or crush spent batteries into a mixture called black mass. Recyclers then use high heat, chemicals, or both to recover lithium, cobalt, nickel, manganese, copper, and aluminum.

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Those methods recover valuable materials, but they also destroy electrodes and other parts that may still be usable. DEER treats the battery less as a source of metals and more as a device with components that can be repaired.

That could be useful for electric-vehicle batteries. EV battery packs are often removed from vehicles once they fall to about 70% to 80% of their original capacity. At that point, the batteries may no longer meet automotive range and performance requirements, but many of their electrodes can still function.

The Cornell method is not suited to every battery. It works best when performance loss is caused mainly by SEI buildup. Batteries with lithium loss, cracked particles, structural damage or mechanical failures would still need conventional recycling.

There are also practical hurdles. The electrodes must be removed from the battery, processed, and washed before they can be reused. Researchers tried injecting the DMI solution directly into intact cells, but the results were poor. That means a commercial version of the process would require battery disassembly and careful handling of the electrode materials.

Cornell estimates that DEER-recycled cells could cost $15.25 per kilogram, compared with $26.31 per kilogram for recycling through pyrometallurgy or hydrometallurgy. The estimate does not include recovering the DMI solution, which accounts for about 63% of the process cost. Reusing that chemical could improve the economics if the method moves beyond laboratory testing.

The research comes as battery recycling companies and researchers look for ways to handle a growing supply of aging EV batteries. While many of these methods remain focused on recovering metals, DEER offers a different option. Instead of immediately reducing a used battery to its chemical ingredients, it tries to salvage the electrode before that step becomes necessary.

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