Defect effects on the physical and electrochemical properties of nanoscale LiFe0.92PO4 and LiFe0.92PO4/C/graphene composites

Abstract

Nanoscale LiFe_0.92PO₄ and LiFe_0.92PO₄/C/graphene composites including defects as performance-improved cathode materials for lithium-ion batteries were prepared by a carbothermal reduction method. The physical and electrochemical properties of samples were characterized by means of X-ray diffraction, inductively coupled plasma optical emission spectrometry, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and electrochemical testing techniques. The results confirmed that defects existed within the nanoscale LiFe_0.92PO₄ lattice and had significant effects on improving the electrochemical properties of samples. The excellent graphene sheets covered on nanoparticles and formed a three-dimensional conductive network in nanoscale LiFe_0.92PO₄/C/graphene composites. The composites exhibited a discharge capacity of 90 mA h g⁻¹ at 10 C and capacity retention ratios of 98% after 100 cycles at various rates, implying outstanding high-rate capability and cycling stability.