Effect of particle size in Li4Ti5O12 (LTO)-LiMn2O4 (LMO) batteries: A numerical simulation study

Abstract

Multiscale numerical simulations based on the porous-electrode theory developed by Newman et al. have been carried out in COMSOL 5.4 environment for different particle sizes (PS) of LiMn2O4 cathode material in Li4Ti5O12 (LTO)-LiMn2O4 (LMO) batteries. The electrolyte used in the simulations was 1.2 M LiPF6 in a 3:7 wt % mixture of ethyl carbonate (EC) and ethyl methyl carbonate (EMC). The model has been validated against experimental data from the literature for half cells (LTO-Li and LMO-Li) and full LTO-LMO cells. A multiple-material model has been adapted to describe an LMO cathode as a material blend with two PS (100 and 1000 nm radii), representing a binary PS distribution (PSD) within the material. The simulation results show that larger populations of small particles at constant cathode material load and constant current density over the electroactive area can effectively allow for larger currents to be applied due to the compensating larger active surface area per unit volume, which decreased the local current density at the LMO crystal interface with the electrolyte. However, higher overpotentials were obtained for cells with higher proportions of small particles, meaning that there is a compromise between electrical work output and C-rate. These findings highlight the importance of microstructure and PS in battery design, particularly in the LTO-LMO system.