Clarification of particle size dependence on the rate capabilities of Li[Ni1/2Mn3/2]O4 materials and electrodes by the dilute electrode method

Abstract

Improving the rate capability of lithium insertion electrodes is essential for high-power lithium-ion batteries used in automobile applications. Several approaches have been studied to improve the rate capability of Li[Ni 1/2 Mn 3/2 ]O 4 (LiNiMO); however, no consensus has been reached owing to conflicting results of particle size dependence on rate capability. Rate capability improvement has been obtained previously using nanosized particles as well as micron-sized particles. To solve this contradiction, we examined the dependence of particle size on rate capabilities of LiNiMO materials and electrodes using the dilurted electrode method. This method allows us to measure two distinct rate capabilities of lithium insertion materials and electrodes. The rate capability of dilute-LiNiMO electrodes is improved by using nanosized particles, while that of conventional electrodes is improved by using micron-sized particles. This indicates two different rate-determining steps: Li-ion transport in LiNiMO particles for the dilute electrodes, and Li-ion diffusion in the electrolyte for the conventional LiNiMO electrodes. Moreover, the rate capability of the dilute-LiNiMO electrodes is superior to that of the conventional electrodes, indicating that Li-ion transport in LiNiMO particles is faster than Li-ion diffusion in an electrolyte with porous electrodes. These findings provide important insights for designing electrodes with excellent rate capabilities. • Two types of rate capabilities of Li[Ni 1/2 Mn 3/2 ]O 4 materials and electrodes were measured. • The rate capability of dilute electrodes is improved by using nanosized particles. • The rate capability of conventional electrodes is improved by using micro-sized particles. • The rate capability of the dilute LiNiMO electrodes is superior to that of the conventional electrodes. • Li-ion transport in LiNiMO particles is faster than Li-ion diffusion in an electrolyte with porous electrodes.