Mechanism and kinetics characteristic of self-discharge of FeS<sub>2</sub> cathodes for thermal batteries
Xicheng Zhang, Chao Wang, Peng Yang, Xu Zhang, Wei Chen, Jianqing Liu, Yixiu Cui, Xiaojiang Liu, Xinlu Li
Abstract
The service life of FeS2 thermal batteries is significantly affected by self-discharge of the cathode. Herein, SEM, XRD and XPS were employed to characterize the mechanism of self-discharge of the FeS2 cathode. A novel combined-discharge method, in which a tiny current (5 mA cm-2) was applied to minimize the effect of polarization on discharge capacity, was conducted to study the kinetics characteristic of self-discharge of FeS2 cathode upon discharge. Then, the self-discharge kinetics parameters which are related to the current density (20, 50 and 200 mA cm-2) and temperature (400, 450, 500 and 550 °C) were determined by the Serin-Ellickson model. Characterizations of the cells standing at 500 °C confirm that the decomposition product of the FeS2 cathode is FeS. The quantitative analysis of self-discharge rate constants (SRC) demonstrates that the reaction is a diffusion-controlling process. The kinetics process can conform to the Serin-Ellickson model. Specifically, the values of SRC increase when the cell is carried by a heavier load, since more breakage would form in FeS2 particles at the larger current density. Besides, the SRC increase at a higher temperature, and the relationship of SRC and temperature can be fitted by the Arrhenius equation. Consequently, the apparent activation energy decreases with the increase of current density.