Investigation of thermokinetics in carbo- and aluminothermic reduction of synthesized lithium iron phosphate black mass

The rising demand for lithium-ion batteries (LIB) has led to a surge in electronic waste, accentuating the need to recycle these batteries in an environmentally sustainable way. However, to improve state-of-the-art recycling technologies for full metal recovery, further research regarding their thermodynamic and kinetic behavior has to be done. While most publications about LIB kinetics focus on Cobalt (Co) recovery from lithium cobalt oxide (LiCoO₂) chemistry, Li transition metal phosphates such as lithium iron phosphate (LiFePO₄) have been neglected. So far there is no fully working recycling solution for this cathode chemistry, considering demanding recovery targets. Carbothermic reduction could offer an elegant solution, using the carbon from the anode, to simultaneously recover Li and Phosphorous (P) via the off-gas and Iron (Fe), Copper (Cu) and other elements within an alloy. However, thermodynamic data, which are currently unavailable for LiFePO₄, are necessary for the process engineering of novel reactors, overcoming current limitations within pyrometallurgy. Therefore, this study investigates the kinetics and thermodynamic behavior of a synthesized LiFePO₄ black mass in a temperature range between 900 °C and 1200 °C. By using isothermal mass change analysis with corresponding phase and microstructure analysis, diffusion and nucleation related reactions could be identified. The phase analysis revealed the formation of highly stable phosphates such as lithium phosphate (Li₃PO₄) and aluminum phosphate (AlPO₄). Furthermore, activation energies for the early and later stages with 38 kJ/mol and 46 kJ/mol respectively, were calculated. The results of this paper have significant importance for further process engineering within recycling approaches using carbo- and aluminothermic reduction.