Thermodynamic properties of sodium hexatitanate (Na2Ti6O13) at high temperature (298.15–1573 K)

Sodium hexatitanate (Na 2 Ti 6 O 13 ) was reported as an anode side material for Sodium ion batteries owing to low material cost, high energy efficiency, good thermal stability and long cycle life. Therefore, studies pertaining to the thermodynamic properties of Na 2 Ti 6 O 13 are indispensable for improving its service performance. However, a significant number of literature reviews concerning thermodynamic properties indicated that heat capacity of Na 2 Ti 6 O 13 at high temperatures should be confirmed. In this study, the 99.5% purity of Na 2 Ti 6 O 13 sample was successfully prepared via solid-state reaction using TiO 2 and Na 2 CO 3 as initial materials. Heat capacity of the as-synthesized samples in the temperature range of 573–1523 K was measured using a multi-high temperature calorimeter 96 line. Heat capacity, Cp, from 298.15 to 1573 K was modeled as a polynomial formula with a prediction error of 3%: Cp = 474.08143 + 0.06286T-8.04068 × 10 6  T −2 (J⋅mol −1 ⋅K −1 ). In combination with the low-temperature data, heat capacity of Na 2 Ti 6 O 13 from 0 to 1573 K was given in present study. Values of changes in enthalpy, Gibbs free energy and entropy in the temperature range of 298.15–1573 K were calculated based on the temperature dependence of heat capacity.