Phase transition model of high-nickel positive electrodes: Effects of loss of active material and cyclable lithium on capacity fade

Abstract

Nickel-rich layered oxides have been widely used as positive electrode (PE) materials for higher-energy-density lithium ion batteries. However, their severe degradation has been limiting battery lifetime. Here we present a phase transition model at the particle level to describe the structural degradation in terms of loss of active material (LAM), loss of lithium inventory (LLI), and resistance increase. The particle degradation model is then incorporated into a cell-level physics-based model (e.g., P2D) to explore the e ects of LAM and LLI on capacity fade in cyclic aging tests.It is found that loss of PE active material will terminate the discharging earlier with less PE material to take lithium, thereby diminishing the discharging capacity. The loss of cyclable lithium changes the stoichiometry range of the NE but does not contribute to capacity loss in the simulated cases where LAM dominates the collective response. The shell layer resistance, similar to the SEI resistance at the negative electrode side, suppresses the accessible voltage and power. The work o ers insights into the diagnosis of degradation modes from the change pattern of the state of charge curve. The model has been implemented into PyBaMM and made available as open source codes.