N-Doped Carbon Nanofiber-based LiMnxFe1-xPO4 cathodes via Imidazolium Ionic Liquid-Assisted Electrospinning for High-Performance Batteries

The olivine-structured LiMn_xFe_1-xPO₄ (LMFP) cathode material fabricated via traditional methods exhibits rapid capacity fade during the cycling process and poor rate capability, leading to a relatively short cycle life, which constrains its widespread application and commercialization. To enhance the electrochemical performance of LMFP, polyacrylonitrile (PAN) was employed as the spinning medium to form a nanoscale network structure after heat treatment. Concurrently, a rheological ionic liquid (IL) was utilized as the precursor in the electrospinning process of lithium ferromanganese phosphate. This method facilitates the penetration and coverage of the inherent active material, promoting the formation of a continuous and thin carbon layer on its surface. Moreover, it serves as a soft template for generating uniform pores that enhance ion transport kinetics. Through systematic investigation of PAN concentration, optimization of the experimental parameters, and adjustment of the annealing conditions, an increase in unit cell volume was successfully achieved, resulting in a high reversible capacity. In addition to the rational design of nanofibers with uniform thickness and stable structure, the even distribution of active particles contributes to the material's excellent cycling stability. The LiMn_0.8Fe_0.2PO₄/PAN 12 nanofiber cathode material prepared under optimized annealing conditions delivers an initial discharge specific capacity of up to 164.1 mAh · g⁻¹ at 0.1 C. In the multi-rate charge-discharge tests conducted from 0.1 C to 5 C, the material exhibited discharge specific capacities of 136.2, 120.5, and 93.8 mAh·g⁻¹ at 1 C, 2 C, and 5 C rates, respectively. Upon reverting to 0.1 C, nearly no capacity loss was observed. During long-term cycling tests, the material displayed excellent capacity retention, maintaining 85.9% of its initial capacity after 200 cycles at 1 C. This study proposes a novel synthesis strategy for LMFP, offering promising potential for its application in high-performance power sources.