Abstract
In recent years, the amount of spent lithium-ion batteries (LIBs) from electric vehicles (EVs) has grown dramatically due to the increase of production of EVs as an alternative to the traditional internal combustion engine vehicles. For this reason, it is necessary to develop a proper recycling process for spent LIBs. Recycling will contribute to the circular economy in EVs battery production and alleviate depletion of critical metals such as Ni and Li present in the battery cathodes.
The co-precipitation of the cathode active metals (CAM) Li, Ni, Co, and Mn after a leaching process of the electrodes, following a novel hydrometallurgical approach for recycling of spent LIBs from EVs was performed in this master thesis. A final calcination step was also conducted to convert the precipitated metal hydroxide into the metal oxide LiNixCoyMn(1-x-y)O2 that forms the CAM. This is a well-studied technique in regenerating LIB cathode material due to the very similar properties of Ni, Co, and Mn. The challenge in recycling LIBs cathode material is the constant evolution and variety of the cathode composition and chemistry. Normally LIBs have a lifetime of 10 years and the CAM might be outdated according to the chemistry and composition by the time it is recycled. In most of the previous studies reported about this hydrometallurgical recycling route of the CAM, the cathode precursor is resynthesized with a Ni: Co: Mn molar ratio of 1: 1: 1. However, following the current and future development of the new cathode materials based on rich Ni stoichiometric ratios, recovering the highest Ni: Co: Mn molar ratio was aimed when co-precipitating the active metals in this project. The recycling of CAM according to future chemistry demands represents the novelty of the work with respect to the current state-of-the-art.
In the first stage of the hydrometallurgical recycling route, the leaching kinetics study showed that Ni, Co and Cu follow the diffusion controlled model at 80ºC. To achieve the goal of high Ni content in the resynthesized CAM, a multi-step precipitation to selectively separate Ni over Co and Mn using NaOH, and furthermore Li using Na2CO3, was studied. The selective precipitation of Ni is based on the solubility difference between the Ni, Co, and Mn hydroxides formed, which lead to different pH values of precipitation. The results demonstrated that 96% of Ni, 86% Co, and 28% of Mn could be precipitated from the leaching liquor. In the final calcination step, Ni-rich metal hydroxide was converted into the metal oxide, of which the CAM is composed. As a result, a LiNi0.47Co0.42Mn0.11O2 was resynthesized, achieving effective resource recycling from cathode scrap of spent LIBs.
