Self-discharge kinetics behaviors of the Li-Si anode for thermal batteries: Modeling, quantifying and fitting analysis

Self-discharge has significant influence on the service life of thermal batteries. The kinetics process of self-discharge depends on both the structure evolution and intrinsic property of electrodes. Herein, the kinetics model to quantify the self-discharge degree of the Li-Si anode is constructed according to the structure of thermal cells. Typical operation and preparation parameters, i.e. temperature, discharge current and electrode thickness, are evaluated based on the specially designed combined-discharge scheme. Then the effective diffusion coefficients (Deff) of soluble lithium (Li0) that are affected by the three variables are calculated and fitted. The calculation results consequently confirm self-discharge process of the Li-Si anode can be described by the derived equations exactly, and then the process is demonstrated to be diffusion-controlled. Further, Deff increase at the higher temperature and larger discharge current, while decrease with the increased electrode thickness, which is analyzed by scanning electron microscope and X-ray microcomputed tomography. The entire effects on Deff can be coupled in one fitting expression based on Arrhenius equation, and the apparent activation energies decrease under the larger discharge current and smaller electrode thickness. Finally, the additional experiments were conducted to verify the accuracy of the fitting expression.