关键词: LiMn_0.7Fe_0.3PO₄/C, 碳包覆, 固相法, 电化学, 正极材料

Abstract:

The olivine structure of lithium manganese iron phosphate lithium composite materials can combine the advantages of lithium iron phosphate and lithium manganese phosphate，achieving higher energy density.However，an excessively high manganese iron ratio can reduce the materials's ionic and electronic conductivity.To improve conductivity and reduce material impedance，a two-step solid-phase method with the surfactant oleic acid was used to obtain LiMn_0.7Fe_0.3PO₄/C cathode material（LFMP/C-3） with smaller morphology，uniform pore distribution，and moderately even carbon coating thickness.Cycling charge and discharge test results showed that cycling discharge capacity at 1C was 119.6 mA·h/g，which decreased to 102.8 mA·h/g after 100 cycles with a cycling efficiency of 88.87%.Rate capability testing revealed average discharge capacities at 0.1C，0.5C，1C，2C，5C，and 10C rates were 141.08，132.70，128.44，105.86，89.10 and 83.40 mA·h/g respectively，and it could recover to the initial 5-cycle average at 0.1C rate.Cyclic voltammetry and electrochemical impedance spectroscopy showed that the LFMP/C-3 sample exhibited the lower polarization degree，the lowest charge transfer impedance（139.75 Ω/s^1/2），and a higher lithium ion diffusion coefficient（1.46×10^-14 cm²/s）.The results indicated that the addition of oleic acid could improve the morphology characteristics，facilitate lithium ion intercalation，enhance material ionic and electronic conductivity，and improve the electrochemical performance of lithium manganese iron phosphate cathode materials.

Key words: LiMn_0.7Fe_0.3PO₄/C, carbon coating, solid-phase method, electrochemistry, cathode materials