Temperature Dependency of Sodium Ionic Activity in β-NaFeO2 Material

An investigation of temperature-dependent ionic activity of a representative sodium oxide material was carried out in the current research work due to the known importance of heat challenges in the battery development process. To assess the heat effects on the ionic conductivity capabilities, the electrochemical, electronic, and crystal structure properties of β-NaFeO2 and β-NaFeO2:Bi2Te3 composite materials were examined. The ionic conductivity of samples was slightly decreased by increasing the temperature, especially above 50–70°C. In contrast, better results were achieved for the β-NaFeO2:Bi2Te3 composite material than the parent β-NaFeO2 material as an indicator of the impacts of thermoelectric properties. At comparable temperatures, x-ray absorption (XAS) and x-ray absorption fine structure (XAFS) spectroscopic data were collected and processed to demonstrate the physical background influence of the increase in temperature on the atoms of the materials. It was found that the sodium atoms were the greatest contributors to the ionic conductivity loss at an increasing temperature among the materials. By separating from the spinel structure Fe–O ligand, sodium atoms increased the ionic capacitance by raising the temperature with a worse ionic conductivity. However, studies on the β-NaFeO2:Bi2Te3 composite material revealed a better ionic conductivity change than the β-NaFeO2 material with increasing temperature. This achievement was very clearly highlighted, particularly at the best working temperatures of Bi2Te3 material with a mechanism of absorbing waste heat and emitting free electrons. Additionally, the inactivity of β-NaFeO2 material could be determined by the instability of Na sites, which worsens with the increase in heat.