Microwave-absorbing properties of cathode material during reduction roasting for spent lithium-ion battery recycling

As a hazardous material to the environment and human health, spent lithium-ion batteries need to be recycled in a reasonable way. To explore the effect of microwave heating on spent lithium-ion batteries (LIBs) recycling, the microwave-absorbing properties of a spent cathode powder (LiNi_xCo_yMn_zO₂) were studied by measuring its dielectric properties from 25-900 °C at 2450 MHz under different conditions (temperature, carbon dose and apparent density). X-ray diffraction and thermogravimetric analysis (TGA) were used to study decomposition and reduction reactions in the heating process. The results indicated that the cathode material has good microwave-absorbing properties over the entire temperature range (25-900 °C), especially when mixed with carbon. As the reduction reactions proceed, the dielectric properties of the material increase rapidly from 600 °C, which means that microwave heating can promote a carbothermal reduction reaction. The effect of the carbon dose on the dielectric properties indicates that the carbothermal reduction reaction can fully occur when the carbon dose reaches 18%. Furthermore, the best microwave-absorbing performance can be achieved when the apparent density of the material is 1.41 g/cm³. These studies have established a basis for research towards the direct recovery of lithium from LIBs by microwave reduction roasting.