Behavior of LiFePO4/CPVDF/Ag-based cathode materials obtained using polyvinylidene fluoride as the carbon source

Abstract

Li1-хFe1-2x(NiIn)xPO4/CPVDF and Li1-хFe1-2x(NiIn)xPO4/CPVDF/Ag (х=0, 0.005) nanocomposites with the olivine structure were obtained using sol–gel method and polyvinylidene fluoride (PVDF) as the carbon source. The materials were characterized with the use of XRD analysis, SEM, TGA, impedance spectroscopy. Their electrochemical behavior has been investigated with the use of charge/discharge tests. It was shown that fluorination of the olivine type phosphate takes place and a uniform highly conductive carbon coating is formed. The electrical conductivity of the cathode material is additionally increased upon the addition of silver nanoparticles to the composite. The increase in the conductivity of the grain boundary and fluorine-doped LiFePO4 results in improved charge/discharge characteristics of cathode materials during low-rate charge/discharge (the specific discharge capacity of LiFePO4/CPVDF was 160mAh/g at a current 20mA/g). High capacity values for high-rate charge/discharge were achieved by depositing a silver-containing carbon coating on lithium iron phosphate co-doped with divalent and trivalent cations. Most likely, this indicates that the insertion of fluorine is limited only by the surface of LiFePO4 particles. The specific discharge capacity of Li0.995Fe0.99(NiIn)0.005PO4/CPVDF/Ag was 161, 78, and 58mAh/g at currents of 20, 3000, and 5000mA/g, respectively.