Aging characteristics in graphite electrodes for LiFePO4 batteries: Effect of design parameters and optimization

The design parameters of lithium-ion batteries include electrode solid phase volume fraction, electrode thickness, electronic conductivity, separator ionic resistance, etc. Most of previous works focus on their effect on energy density and rate capacity. Here, their effect on the capacity fading is numerically investigated in terms of solid electrolyte interface (SEI), Li plating and loss of active material (LAM) in negative electrodes. Compared to the slight effect of positive electrode solid phase volume fraction, increasing negative electrode solid phase volume fraction aggravates all aging mechanisms at the electrode region near to separator. The Li plating at the interface between negative electrodes and separators aggravates with increasing negative electrode thickness or positive electrode thickness, but the region suffering from Li plating decreases for the former while increases for the latter. Increasing the electronic conductivity of negative electrodes and positive electrodes aggravates Li plating, and the latter also increases LAM and reduces SEI, but these effects becomes little after 10 S/m and 1 S/m, respectively. Whether the Li plating aggravates or alleviates with increasing the ionic resistance of separator is associated with positive particle size. Changing negative particle size is the most responsible for the aging, and the Li plating is the most sensitive to changing design parameters. A set of optimal design parameters is obtained, which reduces the battery aging by 20.76 %. The comprehensive comparison of design parameters is beneficial for overall improvement of battery performance.