Researchers develop nontoxic, recyclable binder for batteries

Electric vehicles (EVs) made up more than 10 percent of global vehicle sales last year and are on track to reach 30 percent by 2030, according to research from the International Energy Agency in Paris. As EV sales increase, the need for critical materials used to manufacture EV batteries also will increase. 

Some companies like Redwood Materials and Toronto-based Li-Cycle have announced plans to build large-scale recycling facilities across North America to recover material from end-of-life batteries. While recycling companies prepare for the influx of batteries currently circulating, other groups are looking to improve the design of lithium-ion (li-ion) batteries to make recycling them safer and less toxic to the environment. 

Scientists atLawrence Berkeley National Laboratory in California have created a new battery binder called the Quick-Release Binder. Battery binders are a paste-like substance that hold together the active material particles within the electrode of a li-ion battery to maintain a strong connection between the electrode and the contacts. Due to their properties, they can be molded to fit different sizes of battery specifications. Standard binders are made with either styrene-butadiene rubber (SBR) or polyvinylidene fluoride (PVDF) and often contain per- and polyflourokyl substances (PFAS). 

“The binder has to be very stable for it to work properly in a battery [and] it also has to be able to hold in the components of a battery almost forever,” says Gao Liu, senior scientist at the Berkeley lab and head researcher on the binder project. “However, the binders that are currently being used can’t be easily recycled due to their chemical makeup.” 

Liu notes the difference between his team’s binder and the standard binder is its composition. The group’s new Quick-Release Binder is made from two commercially available polymers, polyacrylic acid (PAA) and polyethyleneimine (PEI), joined together through a bond between positively charged nitrogen atoms in PEI and negatively charged oxygen atoms in PAA. 

When the solid binder material is placed in alkaline water containing sodium hydroxide, the sodium ion pops into the bond site, breaking the two polymers apart. The separated polymers dissolve into the liquid, freeing any electrode components embedded within, according to Berkley. 

Alkaline water is essential to this process because it allows quick release of components and, as a result, Liu says recyclers can recover around 99 percent of the battery. 

“Our process allows operators to recover much more than what the standard binders allow,” Liu says. “You can also recover the copper and aluminum foil, which act as the current collectors in the battery. These materials are typically burned to ash when being recycled because the standard method requires heat to burn off the binder holding everything together.” 

Liu and his team created the binder while working on lithium-sulfur (Li-S) batteries, a possible alternative to traditional li-ion batteries. Liu says Li-S batteries can be made without rare cobalt and have a higher theoretical energy density than li-ion, but Li-S batteries still are years from commercialization because of issues with corrosion caused by the electrolytes necessary for power storage. While the binder was made for Li-S batteries, the team realized with the similar electrode coating process to li-ion battery, the Quick-Release Binder also could be used in li-ion batteries. 

Now, the team is working with Bend, Oregon-based recycler OnTo Technology to finish testing the binder and bring it to the market. Steve Sloop, founder of OnTo, says the company will build prototype li-ion batteries with the binder to analyze its performance comprehensively and showcase its functionality with regard both utility and recyclability. Through these tests, the company hopes to determine how well the binder works in batch recycling, what obstacles there might be in recycling and what costs will be involved in maintaining the process. 

“We plan to do some recycling studies on the binder and show the scalability these could have on the recycling side,” Sloop says. 

Sloop says the company also will investigate ways to manage byproducts created from this process, including salts and electrolytes that power the battery. By managing these byproducts, Sloop says the company can better maintain the water used to deconstruct the battery. 

Lawrence Berkley researchers provided samples of the binder to OnTo for smaller-scale testing. In the future, OnTo hopes to find a battery manufacturer to join the pilot and create a larger batch of batteries to scale the process from creation to recycling. 

The binder can be shaped as needed, which makes it ideal for several li-ion battery applications like electric vehicles. 

Sloop says the partnership aims to improve the design of batteries using the binder, and by improving the consistency of the design, it can easily be adopted by manufacturers. A consistent battery also means the recycling process will produce similar results every time. 

The pilot currently is in preliminary phases, however, Liu says he expects the binder to get commercialized in two to five years. 

Call2Recycle, a consumer battery stewardship and collection program headquartered in Atlanta, says more than 3 million pounds of li-ion batteries were collected last year—the highest number of li-on batteries collected in Call2Recycle’s history. 

“There’s a lot of value that can be recovered from a battery, however, they are toxic in their current form,” Liu says. “We’re trying to introduce the idea of ‘design for recycling.’ This means that from the very start, we want manufacturers to think about how these batteries can have a smaller environmental footprint and how the material used to make them can be efficiently recovered.”