Influence of impurities on the recycling process of NCM active materials

Summary:

One of the challenges in the future of lithium battery recycling technology is to obtain a stable resynthesis process of recycled materials which leads to new usable active materials (e.g., NCM). Besides that, this process should be robust to contaminations such as iron, aluminum, copper, and other ions, coming from battery casings, current collectors or electronic circles. In the hydrometallurgical recycling process the discharged battery cells are being dismantled, crushed and leached. After separation from undissolved materials the leached solutions are processed further to remove contaminations and recover the materials (nickel, cobalt, manganese) needed for the resynthesis. However small amounts of impurities can remain and affect the resynthesis process afterwards. The impurities can indeed be incorporated during the coprecipitation of NCM precursors, leading to an irreversible contamination in the cathode active material. The effects however might vary. Depending on the impurity itself and on its content in the NCM-structure, the impurities can have positive and negative effects on the active materials. Therefore, a robust concept and masking strategies are required to allow an acceptable concentration of impurities to incorporate into the active materials without critical disadvantages. The preliminary research to investigate the influence of impurities on the NCM active materials is shown in the current work. The literature study revealed the most relevant impurities, their origin and the scale that can be tolerated in the synthesized active material.

A lab-scale process for the synthesis of NCM was set up the following. Ammonia solution (25 %) was added to the aqueous solutions of nickel sulfate, cobalt sulfate and manganese sulfate as a chelating agent to form a complex with the metal ions. This step is important for better reaction control and uniform precursor particle growth. A coprecipitation with natrium hydroxide is then conducted. The coprecipitated precursors obtained are subsequently calcinated with lithium hydroxide, leading to the desired NCM active material.

The synthesized active materials are characterized with SEM to study the morphology and particle size. With EDX and XRD composition and purity of the calcined active material is characterized.