Self-Discharge Kinetics Behavior of Li-Si Anode Within Thermal Batteries: Modeling and Quantification Upon Characteristic Preparation and Operation Conditions

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