Analysis of Ruthenium-Doping on the Electrochemical Properties of LiFePO4 Cathode Materials Prepared By Sol-Gel Synthesis for Use in Lithium-Ion Batteries

Wednesday, 12 October 2022: 17:20
Galleria 8 (The Hilton Atlanta)
C. Rodmyre, A. Numan-Al-Mobin, and A. Smirnova (South Dakota School of Mines and Technology)
In recent years, the demand for high voltage and high-capacity energy systems has grown due to the increased use of portable electronics, electric vehicles, and grid energy storage systems. LiFePO4 (LFP) shows great promise as a cathode material due to its low cost, structural stability, safety characteristics, and low environmental impact. However, LFP cathodes possess a lower Li-ion diffusion coefficient and poor electrical conductivity compared to traditional lithium cobalt oxide (LCO) that are on the market. LFP cathodes have a theoretical specific capacity of 170 mAh g-1 while studies show specific capacities around 120 mAh g-1. Doping of materials is a highly effective method of improving electrochemical characteristics in LFP cathodes. Ruthenium-doping of iron sites within LFP has shown positive effects in the promotion of Li-ion diffusion, reduction in bandgap energies, and improved electrical conductivity. Studies have shown that ruthenium-doping at 0.01 moles has an increased specific capacity of 162 mAh g-1, better cycling characteristics, and reduced resistance compared to undoped LFP. Ruthenium doping levels above 0.02 moles have shown a decrease in specific capacity, cycling characteristics, and an increased resistance due to the formation of ruthenium oxide that disrupts the crystal lattice of LFP. In this study, samples of LiFe1-xRuxPO4 (x= 0.01, 0.0075, and 0.005) and undoped LFP are prepared via the sol-gel technique using microwave synthesis to explore the effects of lower levels of ruthenium-doping on LFP electrochemical characteristics. Microwave synthesis is employed as it greatly reduced sintering time thus saving energy when compared to traditional tube furnace sintering. Furthermore, glycine and citric acid are used as the chelating agents in the sol-gel process to further study how preparation methods of LFP can affect its electrochemical characteristics and morphology. Glycine in particular has the benefit of being a zwitterion at a neutral pH thus allowing it to chelate cations and anions compared to citric acid which can only bind cations. Samples are characterized via scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive x-ray spectroscopy (EDX), C-rate testing, and electrochemical impedance spectroscopy (EIS). The authors acknowledge financial support from the NSF IUCRC program for supporting the “Center for solid-state electric power storage” (#2052631), and the South Dakota “Governor’s Research Center for electrochemical energy storage”.