Abstract：According to the moisture absorption of ultrafine lithium iron phosphate powder and its crushing requirements, the LNJST-120 HT closed-cycle airflow grinding and grading system with nitrogen gas protection were applied to the superfine processing and drying of the lithium iron phosphate powder. The operating parameters and equipment structure in the system of grinding, grading, collecting, packaging and transporting were analyzed and improved. Meanwhile, the liquidity and moisture content of the powder in the running process were also studied.Through the industrial test of processing ultrafine lithium iron phosphate powder, investigation on the improved supersonic jet milling was adopted. The results show that, when the rotational speed of the screw feeding machine and the classifier are 62 and 1 072 r/m in respectively, the air pressure and temperature are 0.5 MPa and 120 ℃, and the dew point of the packing room is controlled below-20 ℃, the moisture content of lithium iron phosphate powder is maintained from 0.35 ‰ to 0.55 ‰, the mean particle size (d₅₀) is 0.81.2 μm, the maximum particle size (d₁₀₀) is smaller than 8 μm, and the powder yield is 200~230 kg/h.

Keywords：closed system; supersonic jet milling; lithium iron phosphate powder