Numerical analysis on the aging characteristics of a LiFePO4 battery: Effect of active particle sizes in electrodes

The lifespan of lithium-ion batteries receives increasing attention during the wide application of lithium-ion batteries. The size of active particles in porous electrodes is a key parameter in the design of lithium-ion batteries. The effect of particle sizes on the aging characteristics in negative electrodes is numerically investigated based on a cycle life model with solid electrolyte interface (SEI) formation, Li plating and loss of active material (LAM) included. Increasing the rp,neg (particle size for negative electrodes) causes the aggravation of capacity fading and the rise of the optimum temperature of batteries. The aggravation arises from the increase in SEI formation, Li plating and LAM. With increasing rp,neg, the distribution of SEI formation and LAM within negative electrodes becomes more in-uniformly, and a larger region of the negative electrode suffers the Li plating. In contrary, increasing the rp,pos (particle size for positive electrodes) alleviates the capacity fading, which primarily results from the decrease of Li plating. As the initial temperature elevates, the Li plating will be limited and consequently the capacity fading alleviation due to increasing the rp,pos becomes increasingly slight. The Li plating occurs in final stage of constant current charging, and its lasting time declines with rp,pos increasing. When the initial temperature is below a certain value (10 °C in the present study), increasing the rp,pos leads to the general aggravation of LAM, resulting from the competition between Li plating and LAM. In the competition, the decrease of Li plating leaves more electrode region that will be exposed to the LAM. For the operating condition without significant Li plating, however, the LAM actually will be reduced with the rp,pos increasing. The present study gives an insight into how the sizes of active particle affect the aging of lithium batteries, which hopefully benefits the design of batteries.