Particle Size Effect in LMO Cathodes for LTO/LMO Li-Ion Batteries

ROZENBLIT, ABIGAIL; TORRES, WALTER R.; TESIO, ALVARO Y.; CALVO, ERNESTO J.

Workshop; 7th International Workshop on Lithium, Industrial Minerals and Energy; 2020

Lithium ion batteries based on LTO/LMO have advantages that make them useful in renewable energy storage with very long cycle life.Lithium ion battery intercalation electrodes are comprised of ensembles of nanoparticles with size distribution. An uneven distribution of active particles size can lead to diminished battery performance due to capacity loss and/or material degradation [1,2]. Particle size is a very important factor in determining if a particle will be active within an ensemble. In this work, we have investigated the effect of LMO particle size in an LTO-LMO battery with an electrolyte conformed by 1.2 M LiPF6 in a 3:7 wt % mixture of ethyl carbonate (EC) and ethyl methyl carbonate (EMC) using multiscale simulations under COMSOL 5.4 environment. Our results with a bimodal distribution of particles show that smaller particles can withstand higher currents than their larger counterparts, without losing capacity while maintaining the applied current density (Figure 1). A simulation is presented with an LMO load of 0.0246 mg with a cell capacity of 3.45 mAh under a current of 6.913 mA for 100 nm particles and 0.6913 mA for 1 m particles. All simulations were validated with experimental and simulation data from the literature for the same systems.The operation of the battery at higher currents results in larger overpotentials while keeping the same charge capacity. This study can aid in optimizing particle size for a desired battery capacity, weighing in the amount of power loss that the battery can bear due to overpotentials. Simulations based on the porous-electrode theory developed by Newman et al. [3] were carried out in COMSOL 5.4, parametrically studying particle sizes and their impact on battery capacity. Also, a multiple-material model [4] has been adapted to include a bimodal distribution of two particle sizes within the same cathode. In line with the study of uniformly distributed particle sizes, when more than one particle size is available in the active material ensemble, larger currents (and hence more readily available power) is obtained as the proportion of small particles increases. An overpotential penalty has also been observed in this case, given that even though the current density is constant, the overall current is proportionally higher for smaller particles.This study shows that systems with 100 nm particles can work with currents that are 10 times higher than systems with particles of 1µm, maintaining both cell capacity and current density. These findings highlight the importance of microstructure and particle size in batteries? energy density.