The growing demand for lithium-ion batteries may, in the future, limit the available lithium resources, significantly influencing the cost and the own survival of technology. Therefore, new materials are investigated to replace the non-abundant and expensive raw materials that constitute the available cathode active material on lithium-ion batteries. Among the emerging technologies, the one that uses sodium ion and iron stands out. Sodium orthoferrite, NaFeO2, shows polymorphism with the α-phase stable up to 770 ºC and the β-phase stable at higher temperatures. The phase α-NaFeO2 presents a lamellar structure that allows the diffusion of sodium ions in two dimensions, enabling its use as a cathode of Na+ based batteries. The investigation of this material is essential for the commercial application of these batteries. Thus, the aimed of this study was to synthesize α-NaFeO2 via sol-gel route, not yet described in the literature, and to verify its crystallographic, morphological and electrochemical properties. The effect of the concentration of chelating agent (citric acid), of the calcination temperature and time, on the synthesis, were studied. X-ray diffraction shows the tendency to the formation of the α-phase in the ratio of 1:2 of citric acid and metals. By Rietveld’s refinement of the calcined sample at 600 ºC for 4 days it was verified that the only phase containing the iron was α-NaFeO2 with contamination with Na2CO3 of less than 5%. Spherical grains of the order of 200 nm were observed by scanning electron microscopy. Using the BET method, it was observed that the α-NaFeO2 phase synthesized by the sol-gel route had a surface area 4 times greater than that described in the literature for solid state synthesis. Electrochemical performance measurements revealed a charge capacity for the first cycle of about 113 mA h g-1 in the potential range of 1.00 to 4.00 V vs. Na+/Na. Even higher discharge capacity values, as well as superior electrochemical performance can be achieved by improving the synthetic parameters of the new route are in progress.

New sodium orthoferrite synthesis route for green sodium-ion batteries

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