Surfactant and Dispersant Coassisted Synthesis of High-Performance Lithium Manganese Iron Phosphate Cathode Material for Li-Ion Batteries

The practical application of lithium manganese iron phosphate (LMFP) is hampered by its low electrical conductivity and poor Li⁺ diffusion kinetics. Herein, high-rate Li_0.98Na_0.02Mn_0.6Fe_0.4PO₄/C cathode material has been prepared through ball milling, spray drying, and carbothermal reduction methods using glucose and PEG as carbon sources, along with a water-soluble dispersant maleic acid acrylic acid copolymer (MA-AA) and a zwitterionic surfactant dodecyl dimethyl betaine (BS-12). It is found that the addition of MA-AA can improve the grinding efficiency and reduce the viscosity of the ball-milled slurry, thereby leading to a smaller primary particle size with enhanced homogeneity. The unique structure of BS-12 makes its hydrophobic hydrocarbon chains adsorb and encapsulate raw material particles, increasing the compactness between particles. Meanwhile, the hydrophilic groups are oriented toward water, thereby enhancing the wettability between raw material particles and water-soluble carbon sources, which finally leads to the formation of a thin and uniform carbon coating layer. Therefore, the synergistic effect of MA-AA and BS-12 significantly reduces the primary particle size and improves the uniformity of the carbon layer, thereby enhancing the Li⁺ diffusion rate and electrical conductivity of the cathode material. The as-prepared sample exhibits discharge capacities of 159.1, 131.1, and 117.9 mAh g^-1 at 0.2, 5, and 10 C rates, respectively, and a capacity retention rate of 97.02% after 200 cycles at 1 C. The cooperative use of a dispersant and a surfactant during the ball-milling process is an effective approach to enhance the high-rate capability and cycling stability of olivine-based cathode materials.