Solid-state reaction synthesis and characterization of Mn-doped LiFePO₄ cathode material

Abstract

Olivine type LiFePO4 has great advantages for Li-ion batteries due to its non-toxicity, high safety, and good cycle life performance. However, its low-rate capability and low energy density make some challenges for this LiFePO4. Several methods like doping with transition metals were used, and Mn ion was used in this work to improve the overall electrochemical properties. LiMn x Fe1-x PO4 is promising cathode material owing to high voltage, structural and chemical stability. However, the electrochemical performance of these materials depends on phases and structures obtained from synthesis. In this work, the effect of solid-state reaction conditions, including calcination temperature and duration, on morphology, structure, and electrochemical properties of LiMn x Fe1-x PO4 cathode materials with the composition of x = 0.5 was investigated. The morphology, crystallography and local structure of the synthesized materials were examined by field emission scanning electron microscope (FE-SEM), X-ray diffractometer (XRD) and Fourier-transform infrared spectrometer (FTIR), respectively. The surface area was also determined by the Brunauer-Emmett-Teller (BET) model. The effect of calcination temperature and reaction time upon the morphology, structures of the synthesized cathode materials were studied and discussed. The results could be essential for further development and employment of LiMn x Fe1-x PO4 in Li-ion batteries.

Ammonia-free synthesis of lithium manganese iron phosphate cathodes via a co-precipitation reaction

“…18,[21][22][23] By partially substituting Mn 2+ for the Fe 2+ to form LiMn x Fe 1−x PO 4 (LMFP), the energy density can be enhanced due to the higher operating voltage of Mn 2+/3+ redox (∼4.0 V) compared to Fe 2+/3+ redox (∼3.4 V). [24][25][26] While LMFP can theoretically provide a 10-20% improvement in energy density compared to LFP, such improvement is difficult to achieve in practice due to the kinetic limitations of Mn 2+/3+ redox, which results in low practical capacity with high Mn contents (>50%). These kinetic limitations arise from the Jahn-Teller distortion of the Mn 3+ ion, which leads to increased lattice strain and worsened Li + diffusion kinetics.…”