Towards Circular Batteries: Investigating Particle-Size Based Separation of Active Materials from spent Li-ion batteries

Abstract

With the enormous growth of portable electronics and the market expansion of electric vehicles, the demand for lithium-ion batteries is increasing enormously. To meet this demand, efficient recovery of battery components becomes crucial. Graphite, the material of choice for lithium-ion battery anodes, faces significant supply risks as current recycling technologies primarily focus on recovering economically valuable metal components like cobalt and nickel. Therefore, the effective separation of graphite from lithium-ion batteries is essential for recycling and reusing anode materials. The key to the direct recycling of graphite is the separation of the finest material fractions of Li-ion batteries: the anode and cathode. This work tests a circular battery manufacturing principle based on the idea that the an ode and cathode could be designed to have a difference in particle size to allow easy separation by centrifugation.
We analysed the particle sizes of anode and cathode material obtained from a spent Li-ion battery. A shift in particle size distributions is observed by grinding the materials, significantly reducing the particle sizes. We calculated the velocity distributions using Stokes’ formula for the settling velocity of spherical particles in dilute suspensions from these size distributions. Combining the velocity distributions for the anode andcathode showed the overlap of the velocities. A combination of milled and unmilled material shows the smallest overlap between the velocity distributions and, therefore, the largest difference in sedimentation velocity and the highest theoretical separation.
We measured the sedimentation of anode and cathode particles in water optically using a light source. A camera tracks the moving front of the dilute suspensions over time. Experiments of different milled samples for various concentrations show insights into the anode and cathode sedimentation behaviour. Results show that increasing concentration significantly reduces sedimentation velocities for the anode material. Theseresults deviate from what would be expected from the hindered settling of dilute suspension. A significant velocity reduction is measured for the milled anode and cathode, therefore showing the potential for separation if the materials have a marked difference in size.
In this thesis, a novel method is developed for characterising the sediment structure of the mixed active materials. By freezing sedimented suspensions, sample layers are horizontally cut off to look for the spreading of the different material components through the sediment. A combination of characterisation methods offers information about the anode and cathode fractions through the sediment layers. Significant differences between the sediment’s top and bottom layers regarding morphology, elemental components and thermal stability are observed.
The results show the potential for circular batteries in the future, where centrifugation can play a vital role in separating the electrode materials if they have a marked size difference.