Particle-Scale Path-Dependent Behavior of Li x Ni 0.5 Mn 1.5 O 4 Electrode in Li-Ion Batteries: Part II

A mathematical model was developed to study the voltage behavior of Li_xNi_0.5Mn_1.5O₄(LNMO) electrode at particle scale. The phase transition process of Li₁ → Li_0.5 → Li₁ in spinel LNMO was modeled by Avrami equation, which was incorporated into lithium transport process in the particle. By simulating the charge and discharge process, numerical results indicated that phase distributions in the LNMO particle are different between charge and discharge at the same SOC condition, which can lead to different capacity utilization in practical battery operation. Results of average phase fractions also qualitatively demonstrated the existence of path dependent behavior of phase transformation inside LNMO electrode, which can be attributed to the competition between diffusion and phase transformation. The path-dependent behavior at different SOC conditions were then studied. Results show that longer phase change time can result in more capacity utilization. The relaxation impact was investigated at last. Numerical results showed that the path-dependence behavior can be reduced by long relaxation, and this is because phase transformation reactions take place during the relaxation period and eventually can reduce the path-dependence effect.