Recycling streams for lithium-ion batteries and modelling to compensate performance loss of recycled cathode active materials

Introduction The increasing demand of lithium-ion batteries (LIBs) for electric vehicles, combined with the lack of critical raw materials (e.g., cobalt, nickel, lithium) and the necessity to dispose spent batteries, is pushing proper recycling strategies to recover these materials for their re-use in new batteries. Pyrometallurgical and hydrometallurgical processes are rather established, while direct recycling processes are promising. In any case, the regenerated cathode materials might have a lower quality than those prepared from virgin precursors. In order to meet the stringent requirements of the automotive sector, changes in the electrode design may be required when recycled cathode active materials are used. Material and Methods An extensive survey of the main recycling processes is provided, focusing specifically on the ones which are currently at industrial level. A Doyle-Fuller-Newman electrochemical model is used to provide guidelines to the electrode design to compensate the performance loss of recycled cathode materials, focusing mainly on LiNixMnyCo1-x-yO2 (NMC) chemistry for which an extensive parametrization and validation is performed. Results Pyrometallurgical processes can handle a broader variety of LIB chemistries compared to hydrometallurgical processes, although with a lower recycling efficiency. Hydrometallurgical processes, instead, are limited by initial mechanical separation treatments to obtain the black mass, which affect the material recovery rate and flexibility to treat different LIB chemistries. The electrochemical model is validated against experimental data of a commercial cell (Samsung SDI 94 Ah), showing accurate predictions of voltage and capacity. When recycled active materials with reduced solid-state diffusivity and nominal capacity are simulated, the model shows a decrease in accessible capacity of a few percentages at 0.3-1 C, which can be compensated by increasing marginally the electrode thickness, ultimately resulting in a minor decrease in specific energy density of the battery pack. Discussion The analysis shows that the current recycling processes have some limitations, namely the loss of lithium in the slag in pyrometallurgical processes and the sensitivity to mechanical separations for the recovery of the black mass in hydrometallurgy. Nevertheless, electrochemical modelling indicates that recycled active materials can be effectively used to re-build new batteries with minor modifications to the cell design, suggesting that a sustainable chain for LIBs is feasible.