KEY CONCEPTS
• A closed-loop process for recycling cathode materials used in lithium-ion batteries involves acid leaching.
• Recovery rates for nickel, manganese and cobalt are greater than 90%. 
• Evaluation of cathodes prepared with recycled metals shows superior results compared to pristine cathode materials. 

The move toward sustainability is leading to what steps can be done in recycling components present in batteries. This will reduce operating costs and ease the growing supply chain issues that lubricant suppliers are increasingly facing.

But the question arises about whether recycled components placed in lithium-ion batteries can perform at a comparable level to pristine ones. Yan Wang, William Smith Foundation Dean’s professor in the department of mechanical and materials engineering at Worcester Polytechnic Institute in Worcester, Mass., and cofounder and chief scientist at Ascend Elements, a lithium-ion battery recycling and manufacturing company, says, “Batteries are pretty complex devices, so there is concern about introducing recycled materials due to higher costs, lower yields and inferior performance.”

Recycling is becoming a more important need because the demand for lithiumion batteries in electric vehicles could increase from 0.33 to 4 million metric tons between 2015 and 2040 as Wang indicated in a recent paper.¹ Wang says, “Industry is hesitating to use recycled batteries due to quality and safety concerns. This issue has recently arisen due to a significant battery recall that was made by the producer of an electric vehicle.”

One reason for hesitancy in using recycled battery components is the presence of impurities. Wang says, “The three main types of lithium-ion battery recycling (pyrometallurgical, hydrometallurgical and direct recycling) can all generate up to 10 different types of impurities. Candidates include copper, aluminum, iron, phosphorus, fluorine, silicon and sulfur. Even the type of derivative can be a factor as copper and copper oxide can have a different impact on battery performance.”

Another challenge to commercialize recycled battery components is the actual techniques used to evaluate their performance. Wang says, “Much of the analysis work conducted by academia uses coin cells. This occurs due to ease of use, simplicity and testing that can be done on a small scale. Industry partners do not trust results from coin cells and much prefer testing be done on actual battery cells.”

Wang and his colleagues at Ascend Elements have now developed a new approach for recycling cathode materials used in lithium-ion batteries and have shown in a recent study1 that these components can exhibit superior performance compared to pristine components in lithiumion batteries.

The Unique Hydro-to-Cathode™ closed-loop recycling process
The researchers produced recycled cathode materials using a closed-loop process (see Figure 3) that combines the benefits of hydrometallurgical and direct recycling technologies. In a first step, spent batteries are discharged to a level below two volts followed by cutting, shredding and sieving. Steel cases, current collectors, electronic circuits, plastics and pouch materials are removed and recycled. The remaining black mass contains various forms of carbon, cathode materials and some aluminum, copper and iron residues.


Figure 3. Yan Wang and his colleagues have developed a new approach for recycling cathode materials that leads to high metal yields and superior performance in the self-discharge and cold crank tests, both relevant to electric vehicles. Figure courtesy of Worcester Polytechnic Institute.

At this point, leaching in mineral acid is conducted to dissolve the metals and remove carbon based species and undissolved materials through filtration. Wang says, “We then isolate ions of key metals (nickel, manganese and cobalt) through pH adjustment. In this way remaining copper, iron and aluminum species are removed. Additional pH control is carried out through the use of sodium hydroxide to further minimize the presence of impurities. After analysis of the remaining metals through inductively coupled plasma–optical emission spectrometry (ICP–OES), the metal concentrations can be adjusted through derivatives such as nickel sulfate.”

Wang reports that recovery rates of nickel, manganese and cobalt are over 90% using this technique. In evaluating the efficacy of recycled cathode materials, the researchers used the metals isolated from the closed-loop process in the preparation of the commonly used oxide of lithium, nickel, manganese and cobalt known as NMCIII. He says, “We prepared standard lithium-ion batteries with recycled and pristine NMCIII. This is a cathode material that industry has a good deal of experience using.”

The researchers then followed U.S. Advanced Battery Consortium (USABC) Plug-in Hybrid Electric Vehicles protocol to evaluate recycled cathode materials. Recycled and pristine versions of NMCIII were incorporated into coin cells, single-layer pouch cells, one ampere-hour (AH) and 11 AH cells.

Cycle results with 1 AH cells showed that the recycled cathode material containing batteries exhibited superior results to pristine cathode materials. 1 AH cells with the recycled NMCIII have the best cycle life result reported for recycled materials and enable 4,200 cycles and 11,600 cycles at 80% and 70% retention, which is 33% and 53% better than the state-of-the-art commercial LiNi1/3Mn1/3Co1/3O₂. Meanwhile, its rate performance is 88.6% better than commercial powders at 5 C.

Other tests conducted by the researchers that are relevant to electric vehicles are the self-discharge and cold crank tests. Wang says, “The battery used in the self-discharge test is charged to 100% and then kept at an open circuit voltage where it is not connected to an external load and maintained at 50 C to accelerate the result. Every seven days, the capacity of the battery is evaluated. The battery with the recycled cathode materials loses a lower amount of energy charge than a comparable battery with pristine cathode materials.”

The cold crank test measures the voltage threshold of the battery at -30 C and state of charge. Comparable results were found for both the recycled and pristine cathode material containing batteries.

A combination of analytical techniques and modeling were used to study the recycled and pristine cathode materials after the testing was conducted. Wang says, “We found that recycled cathode materials contain a unique microstructure that contains a center hole enabling the battery to survive for longer cycles. The hole can effectively buffer the strain and deformation to mitigate capacity fading during cycling. One of the reasons that this may occur is that some electrolyte may diffuse into the hole facilitating charge diffusion. Such a phenomenon is not seen with pristine cathode materials.”

The researchers will use their recycling technique to study other cathode materials including those containing 90% nickel. Wang adds, “We also will be recycling single crystal materials, which should provide longer cycle lives.”

Additional information can be found in a recently published article¹ or by contacting Wang at yanwang@wpi.edu.

REFERENCE
1. Ma, X., Chen, M., Zheng, Z., Bullen, D., Wang, J., Harrison, C., Gratz, E., Lin, Y., Yang, Z., Zhang, Y., Wang, F., Robertson, D., Son, S., Bloom, I., Wen, J., Ge, M., Xiao, X., Lee, W., Tang, M., Wang, Q., Fu, J., Zhang, Y., Sousa, B., Arsenault, R., Karlson, P, Simon, N. and Wang, Y. (2021), “Recycled cathode materials enabled superior performance for lithium-ion batteries,” Joule, 5 (11), pp. 2955-2970.