Dual-Precursor Coating Strategy for One-Step Upgrade of LiFePO4 to LiMn0.6Fe0.4PO4 Cathodes with Atomic-Level Mn/Fe Uniformity and Enhanced Electrochemical Performance

Abstract

Lithium manganese iron phosphate (LMFP) has emerged as an ideal alternative to lithium iron phosphate (LFP) due to its higher operating voltage and resultant energy density. However, the long-standing issues of uneven element distribution and manganese dissolution in traditional synthesis have hindered its widespread adoption. This study proposes a dual-precursor coating strategy that involves the uniform mixing of manganese/iron sources with an LFP template via a mechanochemical method, followed by a two-step carbon coating and rapid thermal treatment to achieve directed diffusion and in situ conversion of Mn2+ ions into the LFP lattice. X-ray absorption spectroscopy (XAS) indicates that Mn atoms were successfully incorporated into the olivine lattice, achieving an atomic-level uniform distribution. XPS depth profiling confirms that the Mn/Fe atomic ratio remains stable at 0.59:0.41, eliminating the surface manganese enrichment. Owing to the atomic-level uniform distribution of Mn and Fe within the lattice, the lithium-ion diffusion coefficient of the material was enhanced to 1.2×10-10 cm2 s-1, while the charge transfer resistance was as low as 99 Ω. At a 0.5 C rate, the discharge specific capacity reached 140.6 mAh g-1, and was maintained at 105.4 mAh g-1 at a high rate of 5 C. After 800 cycles at 0.5 C, the capacity retention rate was as high as 99.2%. Notably, when spent LFP was used as the raw material, the structure of the synthesized LMFP was consistent with that of the sample synthesized from fresh LFP, delivering a specific capacity of up to 163.5 mAh g-1 at 0.1 C. This synthesis method, which integrates atomic-level element regulation and resource recycling concepts, provides a new approach for preparation of LMFP in the lithium battery industry.