부산대학교 도서관

Glass samples with general formula NaCo(VO)PO ( x = 0.1, 0.3, 0.5 and 0.7) are synthesized via a simple melt quenching method followed by high-energy ball milling for 30 h to form the homogeneous nanoscaled glass powders. DTA traces of all the glass and glass-ceramic samples indicated exothermic processes confirming selective crystallization induced in the glass network. The formation of major crystalline phase [sodium cobalt pyrophosphate (NaCoPO)] with an ordered layered structure was monitored by X-ray diffraction and the same was justified by SEM images. Structural illustration of major crystalline NaCoPO phase offered more intra-layer Co-Co distance (7.12 Å) than inter-layer Co-Co distance (5.37 Å) which facilitates two-dimensional Na-ion diffusion pathways to achieve the fast intercalation and de-intercalation phenomenon along the a and c directions. The ionic conductivity was monitored by Impedance analysis and achieved to be highest (6.41 × 10 S cm) for the glass-ceramic cathode x = 0.3, NaCo(VO)PO. The initial discharge capacity for the highest conducting NaCo(VO)PO cathode is obtained as 93 mA h g in 0.1 C and had 65% capacity retention even at high rate 10 C. [ABSTRACT FROM AUTHOR]