Mixed polyanion NaCo1−x (VO) x PO4 glass–ceramic cathode: role of ‘Co’ on structural behaviour and electrochemical performance
Glass samples with general formula NaCo1−x (VO) x PO4 (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 (Na2CoP2O7)] with an ordered layered structure was monitored by X-ray diffraction and the same was justified by SEM images. Structural illustration of major crystalline Na2CoP2O7 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 × 10−7 S cm−1) for the glass–ceramic cathode x = 0.3, NaCo1−x (VO) x PO4. The initial discharge capacity for the highest conducting NaCo0.7(VO)0.3PO4 cathode is obtained as 93 mA h g−1 in 0.1 C and had 65% capacity retention even at high rate 10 C.
KeywordsElectrochemical Performance Cathode Material Ceramic Sample Initial Discharge Capacity Sodium Metavanadate
This work has been funded by NAVAL RESEARCH BOARD, DRDO, Govt. of INDIA, Grant No: NRB-311/MAT/13-14. The authors thank Dr. S.K. Martha, Department of Chemistry, IIT Hyderabad for his kind help in acquiring CV studies and discussions.
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Conflict of interest
R. Balaji Rao has received Grants from NAVAL RESEARCH BOARD, DRDO, Govt. of INDIA, Grant No: NRB-311/MAT/13-14.
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