Lithium ion batteries (LIBs) are used in modern day portable consumer electronics like laptops, smartphones or tablets due to their high energy density and high specific energy. Furthermore, as the most interesting battery technology for pure and hybrid electric vehicles, there exists a widespread application of LIBs in private and industrial processes.
Overall, this is directly related to the recycling of LIBs and the respective components. As an example, Ni and Co are used as transition metal oxides in cathode materials and due to their price, an economic driven necessity arises. While there are existing recycling procedures for these metals, the high purity requirements of the manufacturers diminishes the approach to directly reuse the recycling materials as cathode materials. Furthermore, recycling itself is encouraged by the legislation due to several reasons. The demand of lithium, without any actual replacement, due to the growing application can exceed the global production already in the 2020s. Especially for the EU, where only two lithium sites are available, a recycling process is mandatory. Because of this reason, the European Parliament and Council of the European Union issued several directives like the Waste of Electrical and Electronic Equipment (WEEE) 2012/19/EU and the End of Life Vehicles (ELV) 2000/53/EC which focuses on the recycling of batteries from electronic products and electric vehicles. Beginning from 2006, at least 45 wt% of electrical and electronic equipment need to be collected by the EU member and the reuse/recovery rate for end of life vehicles is set to at least 85% weight per vehicle and year. Furthermore, the Battery Directive 2006/66/EC  was released to be instituted as the most advanced battery recycling legislation worldwide. Therefore, each EU member state has to meet a collection rate of 45% and at least a recycling efficiency of 50 wt% for non-lead-acid or nickel-cadmium batteries. So far, all processes either on the lab-scale or commercial are specialized on the metals like nickel, cobalt, manganese and the lithium from the cathode material or aluminum and copper from the current collectors.
The electrolyte, with other organic components like the binder, is normally burned or disposed. However, due to the newest EU Battery Directive, recycling of more components like the electrolyte or the anode graphitic material is getting more attention.
One recent approach is the LithoRec process (fig. 1). This mechanical-hydrometallurgical process aims to meet the demands of the EU directive by the utilization of most materials from a LIB which is a central key of this process. Battery packs, which are deep discharged by either external resistance or power, are dismantled and the individual cells are afterwards shredded under an inert atmosphere. The electrolyte, normally consisting of a mixture of linear and cyclic carbonates and a conducting salt, which evaporates during this step, is condensated and collected. In the following step, the remaining electrolyte is recovered by one of several possible methods. A thermal drying step can be applied with the disadvantage of losing the conducting salt LiPF6, which is the most costly part of the electrolyte. One other way is to use dimethyl carbonate (DMC) as a liquid extractant for electrolyte recovery including LiPF6. Another extraction method is the use of subcritical or supercritical carbon dioxide (scCO2) to efficiently recover the organic carbonate solvents. With additional co-solvents added to the extractant also a high yield of the conductive salt can be obtained. Subsequently iron parts are removed via magnetic separation and transferred to scrap metal recycling. The residual non-magnetic material is fed to a zig-zag air classifier. Here, the shredded material is further separated into two fractions containing the current collectors and active materials and a fraction consisting of the separator and plastic foils. The binder is removed by heating up to 400 – 600°C which additionally causes the detachment of the current collectors from the active material particles. Due to the application of additional air jet sieves the active materials are separated from the current collectors. Furthermore, at this stage, graphite is taken out of the recycling process. Lithium is leached out of the cathode material, while the active material is dissolved in an acidic mixture, which is further refined by a hydrometallurgical step.
On a lab-scale, the recovered graphite, electrolyte and the cathode material was chemical and electrochemical characterized and reutilized in lithium ion battery cells. The proof of principle electrolyte recovery was proven by a static extraction in an autoclave setup with different electrolytes and separators. Afterwards commercial 18650er cells were extracted with good results for the organic solvents. However, only small amounts of the conducting salt could be recovered . Therefore, a flow-through setup was chosen (fig. 2) . By applying either subcritical or supercritical carbon dioxide with additional solvents, it was demonstrated that nearly 90% of the electrolyte, including the conducting salt and aging products, could be recovered from commercial LiNi0.33Co0.33Mn0.33O2 (NMC)/graphite 18650 cells. For the resynthesis of the cathode material, commercial spent lithium-ion pouch-bag cells, containing a NCM cathode, a graphite anode and a LiPF6 / organic carbonate solvent based electrolyte, as well as production rejects of the NCM electrode fabrication were taken as source for the recycling process . The cells were dissembled and the cathode active material was dissolved in 10% sulphuric acid. Afterwards, the transition metal oxides were separated by precipitation as hardly soluble carbonate salts under alkaline conditions. The actual resynthesis was a hydrometallurgical-precursor synthesis which produced NCM active material with an electrochemical performance close to material synthesized from pure solutions. Finally, the two aforementioned procedures were combined with the graphitic anode material recycling . By applying subcritical carbon dioxide for electrolyte extraction, in the best case the electrochemical performance of recycled graphite exceeded the benchmark consisting of a newly synthesized graphite anode including a 90% recovery of the electrolyte.
Overall, it is possible to reutilize nearly the entire components from a spent LIB, which is of great benefit with regard to the recycling efficiency. Furthermore, the recycled material is comparable with pristine material. In addition, the removal of the electrolyte is beneficial not only for the recycling efficiency, but also for environmental concerns and pilot plant equipment, since the fluorinated compounds inside a electrolyte represent a risk for both.
Sascha Nowak1 and Martin Winter1,2
1Universität Münster, MEET Battery Research Center Analytics and Environmental Aspects, Münster, Germany
2Helmholtz Institut Münster, IEK-12, Forschungszentrum Jülich, Münster, Germany
MEET Battery Research Center Analytics and Environmental Aspects
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