As the demand for high capacity batteries has skyrocketed, engineers have struggled to cram more capacity into ever smaller spaces. New battery technologies come and go, but lithium-ion has thus far proven to be the most effective way of storing power when you factor in capacity, stability, and longevity. That means material costs for Li-ion cells will inevitably increase as we reach a bottleneck in supply. This has long been seen as an impending crisis for lithium-ion battery technology — the already shaky economics of electric vehicles could fall apart if the finite resources needed to build them cost too much.
You might think lithium is the most pressing concern, but it’s actually the graphite for anodes that has engineers most worried. There’s a lot more graphite than lithium in each battery, after all. As Tesla makes plans to spin up its Gigafactory to churn out high-capacity Li-ion cells for electric vehicles, the cost of graphite is expected to swing strongly upward. Researchers at Oak Ridge National Laboratory are hoping to head off the price hike with a new process that harvests carbon for battery anodes from an unlikely (but very fitting) source — old cars. Specifically, the tires of old cars.
The rubber in tires is largely composed of carbon (just like graphite), but getting it into a form that can be used in batteries without expending too much energy has always proven a challenge. The process devised by Oak Ridge National Laboratory (ORNL) has the potential to keep battery costs low, make them more efficient, and to top it all off, it’s all based on recycled materials. It really doesn’t get much better, especially when you consider all the trouble surrounding many rare earth elements needed in technology.
Feeding old tires to new cars starts with shredding the tires in a gigantic (and very awesome) industrial shredder. (There’s a video of a generic industrial tire shredder below, just so you have some idea of what these beasts look like.) The pulverized tires are then chemically treated to produce a sulfur-rich slurry of rubber that can be filtered and dried into solid cakes (not the kind for eating). This step in the process is what sets the Oak Ridge process apart from past attempts at carbon reclamation from tires.
The super-dense rubber cakes then undergo pyrolysis in a nitrogen atmosphere — they’re heated, basically. The substance left at the end of the process is called carbon black, which has a microstructure that makes it perfect for use in Li-ion anodes. In fact, carbon black produced by this process is even more efficient than the best commercial-grade graphite at 390 mAh per gram of anode material after 100 charge cycles.
Most of the world’s graphite comes from China, but recycled tires are really a global resource. Scientists hope this process will keep lithium-ion cells affordable as demand increases, but clearing the graphite hurdle doesn’t completely solve the Li-ion crisis. Battery capacity is still advancing at a tremendously sluggish pace. Every new breakthrough seems to be indefinitely five years in the future.
The super-dense rubber cakes then undergo pyrolysis in a nitrogen atmosphere — they’re heated, basically. The substance left at the end of the process is called carbon black, which has a microstructure that makes it perfect for use in Li-ion anodes. In fact, carbon black produced by this process is even more efficient than the best commercial-grade graphite at 390 mAh per gram of anode material after 100 charge cycles.
Most of the world’s graphite comes from China, but recycled tires are really a global resource. Scientists hope this process will keep lithium-ion cells affordable as demand increases, but clearing the graphite hurdle doesn’t completely solve the Li-ion crisis. Battery capacity is still advancing at a tremendously sluggish pace. Every new breakthrough seems to be indefinitely five years in the future.