Structural, electrical conductivity and dielectric relaxation behavior of LiHf2(PO4)3 ceramic powders

Lithium hafnium phosphate LiHf2(PO4)3 (LHP) was synthesized via solid-state synthesis technique. The sintering behavior, structure, and phase composition of the as-prepared sample was analyzed using X-ray diffraction (XRD) characterization technique. The XRD-Rietveld refinement analysis showed that after sintering at low temperatures 500 to 1000 °C, it exhibited various secondary phases. However, a single phase was observed as the sintering temperature increases from 1100 to 1200 °C. LHP sintered at 1100 °C produced real features of sodium superionic conductor type (NASICON-type) with hexagonal crystal axis indicating R-3c space group. The electrical properties were studied using impedance spectroscopy technique. Frequency and temperature dependence behavior of conductivity (ac and dc) and dielectric permittivity were studied. The results obtained describes the conduction mechanism in the system. Electric modulus formalism was performed to investigate the relaxation behavior which showed that as measuring temperature increases, the relaxation frequency increases whereas relaxation time decreases. This behavior explains the hopping mechanism of the charge carriers in the system. Likewise, the correlated barrier hopping model elucidates the dominant hopping mechanism

Effects of activated carbon treatment on Li4Ti5O12 anode material synthesis for lithium-ion batteries

Conventional solid-state reaction method that is widely adopted to synthesize Li4Ti5O12 (LTO) typically generates rutile TiO2 phase at calcination temperature range between 700 and 900 °C in which two competitive reactions between anatase-to-rutile TiO2 and Li2TiO3-to-Li4Ti5O12 formations occur simultaneously. This study investigates the effectiveness of coconut shell-based activated carbon treatment to eliminate the formation of anatase-to-rutile TiO2. X-ray diffraction (XRD) results indicate that mixing LTO precursors with 3, 6, and 10 wt% activated carbon prior to calcination process could reduce the amount of rutile TiO2 phase in LTO down to 6.9, 4.6, and 3.5 wt%, respectively, versus 9.1 wt% in untreated LTO. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements show that LTO pretreated with 10 wt% AC has discharge capacity of 168.35 mAh g−1 and also Li+-ion diffusion rate of 1.2 × 10−13 cm2 s−1. These values are comparably higher than those of untreated LTO that gains lower discharge capacity of 134.93 mAh g−1 and Li+-ion diffusion rate of 6.9 × 10−14 cm2 s−1. This improvement could be attributed to the suppression of anatase-to-rutile TiO2 formation during calcination process