Experimental study on trace moisture control of lithium iron phosphate

LiFePO4 is considered as one of the mainstream positive electrodes materials for power batteries. Its moisture content is closely related to the battery cycle performance and multiplier performance. When the moisture content of LiFePO4 exceeds 600 ppm, the electrochemical performance is seriously degraded. However, it is fairly difficult to reduce its moisture content to below 1000 ppm with the conventional processes. Focusing on the requirements for the trace moisture content of LiFePO4, this study investigated the airflow grinding process inside the closed nitrogen drying system at the first time. The performance in reducing the moisture content in LiFePO4 was also compared. The results demonstrated the moisture content of LiFePO4 powder was lower than 600 ppm after crushing to the particle size of d50 = 1∼1.2 μm and d100 = 6.7–7.1 μm with closed nitrogen drying system under the conditions of the classifier rotation speed 1072 r∙min−1, the steam temperature 120 °C and the pressure 0.5 MPa, and the output capacity reached 210–230 kg h−1. The process gives full play to grinding and drying advantages and break through the drying limit of the traditional processes. It could be thought as a new process for LiFePO4 industrial production, achieving trace moisture drying and relatively high output simultaneously.