Carbon From Old Tires Used in Car Batteries

Old tires are finding a new life on the road as the rubber is recycled to make anodes for electric car batteries.

Scientists at the U.S. Department of Energy’s Oak Ridge National Laboratory, led by Parans Paranthaman and Amit Naskar, have discovered a way to take old tires and remove the carbon black from them. The substance is then used for anodes on improved lithium-ion batteries. While graphite is a natural carbon usually used in battery anodes, carbon black is man-made.

What is Carbon Black?

Fillers are used as diluents in tire composition and to lower the cost of the tire. Elastomers are special fillers that can enhance certain properties of a tire. Carbon black is a distinctive filler that can considerably improve the properties of any base polymer while keeping costs down. In car tires, the carbon black helps keep heat away from the tread and the belt, thereby increasing the life of the tire.

It’s also used in copiers, as toner in laser printers, and can be used as a pigment for inks, polymers and coatings. Carbon black is added to polypropylene (PP) because it absorbs UV rays that can cause PP to break down. It has also been used in electronics, and in food and beverage and product packaging.

Carbon black is an extremely fine particulate form of basic carbon with an amorphous molecular composition. Random orientations of microcrystalline groups of concentrated rings are buried inside the amorphous structure. The groups are similar to graphite, another form of carbon, which has layered rings. A large percentage of the arrays within the carbon black have open ends with unsatisfied carbon molecules allowing for chemical activity to occur at these points.

Carbon black procedures always start with smoke production — it’s the component of smoke that makes it black.

How Is Carbon Black Reclaimed?

The carbon black is removed by using a pretreatment on the tire and then using a method called pyrolysis, the burning off of organic material without oxygen present. This process reclaims the pyrolytic carbon black from the tire.

Paranthaman said:

Using waste tires for products such as energy storage is very attractive not only from the carbon materials recovery perspective but also for controlling environmental hazards caused by waste tire stock piles.

The capacity (a measure of charge stored per gram of weight) of the carbon black anode was tested in the lab and measured at 390 milliamp-hours per gram (mAh/g), an improvement on graphite’s 370 mAh/g capacity. The rise in capacity is attributed to the microstructure of the reclaimed carbon black increasing its surface area. After 100 charge cycles the anode capacity remained the same. More testing needs to be done to replicate the thousands of charge cycles a battery sustains in real-world conditions. Naskar said:

This technology addresses the need to develop an inexpensive, environmentally benign carbon composite anode material with high-surface area, higher-rate capability and long-term stability.

It seems carbon black may be the new material of choice for anodes for lithium-ion batteries. However, there are many other materials being tested for the same job, including nanostructured silicone or graphene, which both show higher capacity rates. For now, the recycled tires will fit the bill for improvement in car batteries. In the future, we may find other applications for reclaimed carbon black.