Multidisciplinary development of a novel pyrometallurgical recycling approach for lithium-ion batteries

The increasing share of electric vehicles within the transportation sector and renewable energies within the energy-intensive industries represent two central pillars of global decarbonization efforts. Electric vehicles and stationary energy storage systems are crucial in reducing anthropogenic CO₂ emissions and integrating renewable energy into power grids. However, the highly fluctuating supply of renewable energy necessitates suitable storage technologies. Lithium-ion batteries (LIBs) are a promising storage technology due to their excellent electrochemical properties. The growing demand for this battery technology inevitably leads to vast amounts of waste streams, as well as economic and political dependency on resource-rich third countries. Recycling used batteries can not only reduce the dependence on primary resources but also significantly decrease the environmental footprint of battery production.
Worldwide pyrometallurgy is a well-established recycling route for LIBs, due to their simplicity, high productivity, and flexibility in processing mixed waste streams. However, the simplicity of this approach also comes with disadvantages, including the loss of lithium through slagging, which impacts both resource efficiency and economic viability. An alternative to state-of-the-art technologies is carbothermic reduction using the InduRed reactor concept. The primary advantage of the reactor lies in the extraction of volatile elements such as lithium and phosphorus via the gas phase while concentrating valuable metals like cobalt, nickel, and copper in an alloy. This work focuses on a multidisciplinary approach to gradually optimize the InduRed reactor, where “multiple” stands for different fields of science including metallurgy, material science, physical chemistry and others. The goal of this multidisciplinary approach lies in identifying key challenges along a closed-loop recycling approach, to industrialize this novel technology.



In the context of a circular economy, this work included investigations into the potential influence of pre-treatment steps on the melting- and reaction behaviour of black mass, as well as potential downstream processing strategies for the generated alloys. It was found that especially agglomerations caused by incompletely removed binders, is hindering the effectiveness of the reactors working principle, highlighting the importance of a carefully evaluated pre-treatment process. Determining kinetic parameters, such as reaction constants and activation energies for diffusion and nucleation-controlled processes, further provided essential information about the high temperature behavior of the oxidic input material. This was supported by thermodynamic simulations and phase analyses of shock-cooled samples from isothermal melting experiments. The developed method provides an important foundation for future research projects involving higher temperature ranges. The resulting products, with a particular focus on the alloy, were examined under both open- and closed-loop recycling scenarios. Thermodynamic calculations in FactSageTM, along with subsequent biohydrometallurgical approaches, identified potential pathways, both open- and closed-loop, for processing the recovered materials.
Another key investigation to further provide industrial viability was ensuring the durability of the crucible materials. Previous studies have shown that the environment of reducing gases and chemically aggressive input materials, results in severe wear of refractory ceramics. Corrosion caused by cobalt and iron, as well as diffusion of lithium and phosphorus, not only compromises material durability but also negatively impacts recovery yields and economic efficiency. After literature comparison, alternative materials including silicon carbide, chromium oxide, and zirconium oxide were tested. It was demonstrated that silicon carbide provides increased corrosion resistance, while chromium oxide offers enhanced diffusion resistance, making them suitable for use in the InduRed reactor, either alone or in combination. Additionally, it was investigated whether graphite-based coatings could further reduce the diffusion of volatile elements such as lithium and thus decrease wear on the reactor's inner walls.
The findings of this work are crucial for the development of future-proof recycling strategies that not only ensure resource security but also provide an environmentally friendly alternative within pyrometallurgy. Future work can build upon the results of the crucible tests to create an optimal setup that minimizes lithium and phosphorus diffusion. Additionally, the developed methodology for determining kinetic parameters can be applied to other cathode materials and higher temperature ranges. Ultimately, special focus must be placed on continuous operation to elevate the process to a higher technology readiness level and thus to an industrial scale.