Superlong supercooling solvents (SSSs): Alternative green solvents to ionic liquids and deep eutectic solvents for lithium-ion batteries recycling

Water, supercritical fluids, ionic liquids and deep eutectic solvents (DESs) have been considered as green solvents for many years. The demand of green and sustainable development requires the search of novel green solvents. Some of the reported DESs might be not be the real DESs because we observe that these so-called reported liquid DESs become solid after exposure to the room temperature for many hours or days. Here, we for the first time propose a new concept of green solvents, superlong supercooling solvents (SSSs), as the green alternatives to water, supercritical fluids, ionic liquids and DESs. SSSs are the metastable liquid solvents either single component or multiple components due to the superlong supercooling effect at the temperature around or a little higher than room temperature. SSSs should condense after a superlong time; however, SSSs could be used as the green solvents before the condensation due to the superlong supercooling. Typical application example of SSSs is that SSSs could leach nearly 100% valuable metals from lithium-ion batteries cathode at low temperature, which is much higher than that by reported DESs and ILs at the same conditions. The new concept of SSSs would be very helpful for expanding the area of green solvents and green chemistry for building a greener world.