Synthesis and Electrical Characterization of NaxNi1-xO2 Compositions

Abstract

Sodium layered oxide compounds (NaxM1-xO2) have drawn significant attention as cathode materials for Na-ion batteries (NIB). Their Li analogues have already been comprehensively understood. In this study, powder compositions of (NaxNi1-x)O2, (x = 0.1, 0.25, 0.5, 0.75) were prepared by the Pechini method. For that, metal nitrates of NaNO3 and Ni(NO3)2.6H2O were mixed according to stoichiometric formula of the nominal compositions. The powder synthesis process was completed by calcining the ash product at 800 °C for two hours in air. The synthesized powders were uni-axially pressed at 150 MPa and the green pellets were subsequently sintered at 800 °C for two hours in static air. The electrical conductivity of these materials were determined by performing d.c. electrical conductivity measurements on sintered pellets by the four-probe method. The conductivity measurements were performed in a cyclic manner on heating and cooling in air, in the temperature range 25 - 200 oC. This study revealed the possibility of synthesizing NaxNi1-xO2, x = 0 - 0.75 compositions by the Pechini wet chemical synthesis technique. All these prepared materials showed an increase in conductivity in an exponential manner with increasing ambient temperature. This is a good indication of the semiconducting nature, which is the main requirement for an electrode material. In this NaxNi1-xO2 system, the x = 0.1 composition showed a sufficiently high electrical conductivity of 3.5 x 10-3 S/cm at room temperature. These achievements in electrical conductivity indicate the potential of NaxNi1-xO2 compositions for NIB cathode application.