Clustered LiMn0.7Fe0.3PO4 Nanoparticle for Lithium Battery Cathode Materials

Abstract

LiMn0.7Fe0.3PO4 nanoplates were prepared by a polyol process at 100oC for 4h, and nanoplates with a thickness of ~ 30 nm oriented along [010] direction were obtained, followed by carbon-coating by ball-milling with Ketjen black. X-ray diffraction was performed to identify the phase of the material, resulting in Pnma of orthorhombic system. Scanning electron microscopy and transmission electron microscopy were performed to investigate the morphology and size of the particles. Average LiMn0.7Fe0.3PO4 nanoplates are about 30 nm and they were coated with an amorphous carbon layer with several nanometers. In addition, energy near edge stricture (ELNES) shows Mn L- and Fe L-ELNES spectra for LiMn0.7Fe0.3PO4. A comparison of ELNES spectra with the standard oxides [CH3COCH=C(O)CH3]2Fe, where metal atoms are octahedral synchronized by six oxygen atoms, suggests that the Fe replaced the manganese site with Fe2+/3+ ions, respectively. Moreover, dQ/dV versus voltage plot showed the charge and discharge peaks (oxidation and reduction) centered at 3.4V and 4.1V. Raman spectroscopy identified the amorphous carbon coating on the nanoplates LiMn0.7Fe0.3PO4. Electrochemical performances of the samples were tested in coin type half cells. The carbon coated LiMn0.7Fe0.3PO4 nanoplates are presented a good rate behavior and cyclic life both at 21oC and 60oC. The sample shows capacity of 161 mAh g-1 at 0.1C, 143 mAh g-1 at 1C rate (21 oC). At elevated temperature (60 oC) this material exhibited improved capacity of 165 mAh g-1 at 0.1C and 140 mAh g-1 at 1C. The electrode retained 99% of the capacity at 0.1C, after 40 cycles at 60 oC. This electrochemical stability is attributed to the structural stability by Fe ions, which decreased Mn3+ dissolution from LiMn0.7Fe0.3PO4.