Influence of carbon content, particle size, and partial manganese substitution on the electrochemical performance of LiFexMn1-xPO4/carbon composites

• DOI: 10.1007/s11581-015-1366-6
• Publication Date: 2015-01-23T17:29:53Z
• Authors: N. A. Hamid; S. Wennig; A. Heinzel; C. Schulz; H. Wiggers
• Keywords: Lithium iron phosphate; Carbon fibers

LiFePO4/C and LiFexMn1-xPO4/C (x = 0.7) nanocomposites were successfully synthesized via scalable spray-flame synthesis followed by solid-state reaction. A solution of iron (III) acetylacetonate and tributyl phosphate in toluene was used to produce amorphous, nanosized FePO4⋅H2O in a spray-flame reactor which was then milled with Li2CO3 and glucose to produce a LiFePO4/C composite material in a solid-state reaction. The influence of calcination temperature and carbon content on the properties of the resulting material was investigated using specific surface area measurements (BET), X-ray diffraction (XRD), electron microscopy, and electrochemical characterization. The impact of manganese addition on the electrochemical behavior was analyzed using cyclic voltammetry (CV) and constant-current (CC) measurements. XRD shows that the combination of gas-phase synthesis and subsequent solid-state reaction yields highly pure LiFePO4/C. BET measurement revealed that the particle size of LiFePO4 in the composite depends on the amount of glucose. A discharge capacity of more than 140 mAh/g at C/20 is achieved for LiFePO4/C with a carbon content of 6 wt%. This material supports high charge as well as discharge rates delivering more than 60 mAh/g at 16 C and sustains good cycle stability providing 115 mAh/g at 1 C. The energy density of the olivine increases about 10 % by substituting 30 mol% of iron by manganese while preserving the electrochemical performance of pure LiFePO4/C.