04: The Issues with Lithium-Ion Battery Recycling

Hi everyone! In this post, I will look at the current issues with lithium-ion battery recycling.

There are many reasons to the low purity results of lithium ion battery recycling. Some of which (high energy and complexity) I have discussed in blog 03. In this blog, I will be looking a bit deeper and finding flaws that I might be interested in finding a solution to.

Successful Recycling of Lead-Acid Batteries

To evaluate the future of lithium ion battery recycling it is helpful to compare it with the successful lead acid battery market. These batteries were used to power the first EVs back in 1859 (they were later replaced by internal combustion engines).

The lead acid cell has, through numerous iterations, become standardized and is designed for recycling. Modern lead acid batteries are able to reuse >98% by mass of the material. This is due in part to the simplicity of their design, where the anode and cathode are Pb and PbO2, respectively. The lead acid battery is self-contained in one unit, not assembled into modules and packs, so it needs no disassembly prior to recycling. Finally, recycling a lead acid battery is also relatively simple: the case is crushed, allowing the sulphuric acid electrolyte to escape, and the lead electrodes are separated from the polypropylene casing and separator by density. The lead is smelted and the polypropylene can be reused in new casings.

Thus, it is economical to recycling lead acid batteries due to the relatively high cost of lead, and the process is an efficient one due to the uniformity of the materials used and battery design. The materials recycled from the lead acid batteries are then used to manufacture new batteries, closing the loop. This is why recycling rates of these batteries are almost 100% in the USA, Japan and most of Europe.

Structure & Design

Unlike the lead acid battery, the structure of lithium ion batteries is much more complex, with a series of small cells being collected together to make a module and a number of modules are assembled to make the overall battery pack. An automotive battery pack is composed of hundreds or thousands of cells, which not only have to be individually opened but also disassembled from the ensemble. The complex structure and risks associated with electric shock and potential fires make safe dismantling slow and labor intensive. For this reason, current approaches start with crushing the battery, in the same approach to lead acid batteries, but, for LIBs, this requires more steps, more energy and more chemicals.

There is also great variation in lithium ion battery cathode chemistries (such as variations of NCA, NMC, LMO, LCO and LFP). As there is no one-size-fits-all battery recycling method, and individually processing each type is costly and time consuming, the battery recycling method is generalized and ends up being economical. This is exasperated by the rapid advances in battery technology: two versions of the same car model may even have different battery chemistries. Thus, a desire for quick treatment and simple recycling, given present modest volumes, has led to processing techniques that are chemistry agnostic, resulting in lower purity products.

Module Issues

In automotive applications, battery packs need to be both power and energy dense, which can only be achieved by aggregating cells into modules, and modules into packs. Increasing the number of cells in a module decreases the ratio of active material to cell case and complicates the issue of opening cells.

One of the main issues is the way in which the cells, modules and packs are assembled. The cells themselves are hermetically sealed and the modules and packs are often glued together with adhesives. This provides rigidity, but means that they can often only be dissolved in molecular organic solvents. This prevents disassembly from becoming a viable recycling method due to the time and solvent requirements. Thus, the structures are clearly established for safety and potentially cell longevity, but at the expense of recycling efficiency.

Cell Issues

As I have discussed previously, there are various form factors of cells, each with their own shapes and sizes. The cells themselves are also constantly being improved to increase safety and performance, which usually comes at the cost of recycling efficiency.

For example in consumer electronics, prismatic cells are often stacked using a Z-fold configuration with parallel terminal tags (this design allows for easy automated manufacturing of the cells). To maximize the energy density, thinner current collectors, tags and separators are utilized where possible, and high loadings of active material are coated upon the current collectors, with low porosities. For safety reasons separators are often either slightly thicker to further separate the anode and cathode, or coated in a thin ceramic layer to help prevent short circuiting. For larger cell formats Z-fold configurations are more difficult, and therefore stacking or winding is more prevalent, for example in electric vehicle cell manufacturing. Stacking with individual separator sheets leads to an excess of separator, which is then incorporated into the pouch sealing, reducing the excess, but adding complexities in the separation of the anode and cathode from the cell during disassembly.

There is also development in the area of safety, as batteries are famously known to catch on fire easily. Some solutions, including shear thickening electrolytes to limit puncture damage, strengthened separators to stop dendrite penetration, redox shuttle additives to stop overcharging, and flame retardants in the electrolyte
and separator, add to the complexity of the cell and will reduce recycling efficiency.

Lack of Standardization

While the hazard labelling of lithium ion batteries is strongly regulated, there is a lack of compositional labelling for easy identification. Most battery packs contain no information about the chemistry of the anode, cathode or electrolyte, meaning that cells from the different packs need to be dealt with by the same process. The presence of different elements and binders can affect the efficiencies of separation and lead to contamination. Improved battery labelling would enable different battery chemistries to be separated before processing and would prevent contamination between different chemistries.

With no standardization of cells and the predominance of cells from small portable devices, this means that initial recycling approaches will be more similar to solid municipal waste, producing streams of lower purity. Additionally, the lack of standardization on pack and cell level coupled with the complexity of storage, transportation and handling of batteries all contribute to the increased cost and decrease the incentive to recycle.

Sources

Thompson, D. L.; Hartley, J.; Lambert, S.; Shiref, M.; Harper, G.; Kendrick, E.; Anderson, P. A.; Ryder, K. S.; Gaines, L.; Abbott, A. P. The importance of design in lithium ion battery recycling – a critical review. Green Chemistry 2020, 22 (22), 7585–7603. https://doi.org/10.1039/d0gc02745f.

Mao, J.; Ye, C.; Zhang, S.; Xie, F.; Zhou, R.; Davey, K.; Guo, Z.; Qiao, S. Toward practical lithium-ion battery recycling: adding value, tackling circularity and recycling-oriented design. Energy and Environmental Science 2022, 15 (7), 2732–2752. https://doi.org/10.1039/d2ee00162d.