By Kyle Proffitt
September 4, 2024 | A method for recycling battery materials was recently described that promises major savings in cost, greenhouse gas emissions, energy usage, and time. The work is led by Professor James Tour of Rice University, and it is based on his development of the flash Joule heating (FJH) technique. “This method allows us to flash the cathode and rejuvenate it; then you can just put the cathode right back into a battery,” Tour explained. The work was published July 24 in Nature Communications. DOI: 10.1038/s41467-024-50324-x
Battery Power Online spoke with Dr. Tour and first author Weiyin Chen to learn more about the technique and the current outlook for battery recycling. “Most methods take the cathode and decompose it to its base metals that they now dissolve in some acid… the whole cathode structure is broken down,” Tour told Battery Power Online. “You have to isolate those metals and use them again to build a whole new cathode.” In contrast, this FJH method can now be used without cathode destruction.
Battery Recycling Now
There’s a statistic that is commonly repeated: only 5% of lithium ion batteries are recycled. Fortunately, this isn’t quite true, or at the very least it is no longer true. A report last year looked at the entire landscape of battery reuse and recycling using data from 2019, and ultimately estimated a global recycling rate of 59%. It’s pretty complicated to track, because batteries are reused in other applications such as grid storage, exported, or may be still sitting in your drawer inside that old cell phone. Of course, when talking about the major drivers of demand and need for recycling, EVs take the biggest slice of pie, about 80%; it takes about a thousand laptop batteries to equal one EV battery. In any case, recycling efforts have only expanded since 2019.
It is also true that recycling batteries isn’t as clear cut as with, for example, glass. “When you look at it, they may be only pulling out one metal, and the rest is going to landfill,” Tour warned. Recycling batteries right now never really means you reuse all of the material. However, there is significant market value for the critical materials present in battery waste, including lithium and cobalt, and it makes little sense to simply discard these and then mine for new raw materials. Estimates have also suggested that global cobalt reserves could be depleted by 2040; new sources are needed if this holds true.
Efforts have ramped up to meet this demand, and there are several major players now. More than 200 businesses are in operation with a combined capacity to recycle over 1 million metric tons of end-of-life (EOL) batteries per year. That’s great news, but of course there’s room for improvement, and other estimates say we will produce 2 million tons of EOL waste per year by 2030. As Tour indicated, most of these methods are pretty destructive. This includes pyrometallurgical, hydrometallurgical, and biometallurgical approaches, making use of heat, acids and solvents, or microbes, primarily to strip out the metals. In addition to their destructive nature, these methods vary in terms of energy required, waste and greenhouse gas emissions created, and recovery of useful basic materials.
Flash Joule Heating
The flash Joule heating (FJH) method Dr. Tour uses is comparatively straightforward. A high voltage is applied across a somewhat resistive material, which causes rapid heating to temperatures upwards of 2000 °C. Back in 2020, Tour and his group used FJH to “upcycle” waste materials ranging from tires to banana peels to prepare graphene, a useful material in various coatings, sensors, and electronics, including batteries. Since then, they’ve used FJH for “urban mining” of metals from electronic waste, and to recycle battery materials, both in recovering anode graphite and in metal recovery from black mass—a pulverized powder of mixed battery materials.
“After the previous black mass recycling project, we started to think about direct cathode recycling,” first author Weiyin Chen said in an email. To use FJH more directly, they also wanted to get away from the solvents and acids used prior for separating desirable material from waste. “Separation methods based on physical properties hold more promise than those relying on chemical reactions,” Chen explained. “We realized the metal will be reduced from the surface and the as-formed phase should be magnetic.”
They were correct, a simple magnet does the trick. For their experiments, they used old laptop batteries and 18650 cylindrical cells from a local recycler, manually isolated the cathodes, pulverized them, and mixed the powder with conductive carbon black or graphite before applying the flash procedure. Tour described the process. “You take this material and you flash it—you put it between two electrodes, you apply a high current and a high voltage.” This frees up the metals, and then to separate them, “you take a magnet, and the parts that you want are magnetic,” Tour said.
As anticipated, the FJH process causes some metal reduction at the surface of cathode particles, most importantly the reduction of Co3+ to Co2+, forming Co3O4, which is magnetic, whereas non-flashed materials are not. In the process, the internal structure of particles is unchanged, but the magnetic surface allows the entire particle to come along for the magnetic ride, including lithium and whichever metal oxides are present, such as nickel, manganese, and cobalt. As Tour explains, the bulk “3-D hierarchical structure remains, so you don’t have to rebuild that.” The recovery is also really good. With NMC mixed cathode waste, the researchers were able to recover between 92% and 97% of Li, Co, Ni, and Mn. The non-magnetic materials accounted for about 10% by weight, and even this remnant could be collected, pooled, and re-flashed to further improve yield.
Reformed Cathodes Function Like New
The researchers took their flashed cathodes, relithiated them to maximize available lithium for cycling, and put them back into complete batteries containing a lithium anode. Whereas the waste cathode material that had not undergone FJH showed very low specific capacity and cycled poorly, the flashed cathode material was essentially indistinguishable from fresh commercial cathodes over 100 cycles of testing. The method was applicable to NMC and LCO, and Tour says it will be even easier with solid-state versions. It may be useful with other chemistries as well. “We have not yet tested cathode materials other than LCO and NMC; we think LFP could undergo a similar magnetic separation process if the formation of Fe2O3 or Fe3O4 is well controlled, Chen said.
Cost and Economic Factors
“The flashing lowers the cost so much,” Tour said. “It’s such an inexpensive method.” From modeling estimates in their report, FJH was associated with at least 80% reduction in water consumption, 60% reduction in energy consumption, 70% reduction in greenhouse gas emissions, and 40% reduction in cost, relative to hydrometallurgical or pyrometallurgical methods.
“People often think high voltage, high current, high energy, high cost. No! Because we only flash for such short time periods, the amount of electricity we put in is very small… we’re only putting in the electricity for a second or less… we’re not heating a furnace,” Tour said. The comparison is favorable compared to fresh mining too, according to Chen, who said that the FJH cost “is much lower than the whole process including mining cobalt, synthesizing lithium carbonate, and producing cobalt-based cathode.”
Infinite Recyclability
Battery recycling has an important distinction from some other recycling that we’re used to. “Metals are infinitely recyclable,” Tour said. They’re not like paper or plastic, which lose quality as a result of impurities. Tour pointed out that the gold in a wedding ring is unlikely to be in its first use after coming out of the ground, and these metals are no different. Here, FJH applied to battery materials recovered “exactly the same thing that came out of the mining process,” according to Tour. As such, there’s no loss of quality, and a true circular ecosystem for these metals’ use in batteries can be developed.
The Future
While the experiments in this publication were conducted at gram scale, the FJH technology has been demonstrated at one-ton-per-day scale for graphene production. The method is also licensed to MTM Critical Metals Ltd., a mining company based out of Australia, and their subsidiary, Flash Metals USA, Inc., is “moving on battery recycling” using the technique, according to Tour.
“I think flash is going to start doing a lot of things for recycling, and one of them is in this battery technology,” Tour said. However, he sees a need for regulatory changes. “One of the big problems is that there’s no standardization in how to package a battery.” Original manufacturers are not necessarily thinking about recycling, and for the FJH approach to work most efficiently, they will need to, because the first step involves manual disassembly. According to Chen, the new method “requires separated cathode waste and is not favorable using different kinds of cathode materials.” Unlike other recycling approaches that mix and grind different battery types together, this approach will work best on one cathode type at a time. “What we’re going to have to do is have legislation… you’re going to have to have your car batteries have a standard unpackaging method,” Tour suggested. For the time being, “we think the previous recycling method using black mass is more versatile, as the final battery chemistry composition can be adjusted by monitoring the total concentration of metal cations,” Chen added.
Tour and Chen pointed to one more factor that is beyond their control. As manufacturers continually update cell chemistries, the value of a recycled cathode may well change. If NMC811 falls out of favor, then in 15 years when the majority of EV batteries using this chemistry could be headed for recycling, the EV makers may have lost interest in this cathode. “The demand for different battery recycling methods is closely tied to the types of new battery chemistries being adopted by automotive companies,” Chen explained.
