A Promising Solid-State Synthesis of LiMn_1-yFe_yPO₄ Cathode for Lithium-Ion Batteries

LiMn_1-yFe_yPO₄ (LMFP) is a significant and cost-effective cathode material for Li-ion batteries, with a higher working voltage than LiFePO₄ (LFP) and improved safety features compared to layered oxide cathodes. However, its commercial application faces challenges due to a need for a synthesis process to overcome the low Li-ion diffusion kinetics and complex phase transitions. Herein, we propose a solid-state synthesis process using LFP and nano LiMn_0.7Fe_0.3PO₄ (MF73). The larger LFP acts as a structural framework fused with nano-MF73, preserving the morphology and high performance of LFP. Our results demonstrate that the solid-state reaction occurs quickly, even at a low sintering temperature of 500 °C, and completes at 700 °C. However, contrary to our expectations, the larger LFP particles disappeared and fused into the nano-MF73 particles, revealing that Fe ions diffuse more easily than Mn ions in the olivine framework. This discovery provides valuable insights into understanding ion diffusion in LMFP. Notably, the obtained LMFP can still deliver an initial capacity of 142.3 mAh g^-1, and the phase separation during the electrochemical process is significantly suppressed, resulting in good cycling stability (91.2% capacity retention after 300 cycles). Our findings offer a promising approach for synthesizing LMFP with improved performance and stability.