Electrochemical Modeling of Calendar Capacity Loss of Nickel-Manganese-Cobalt (NMC)-Graphite Lithium Ion Batteries

Abstract

Li-ion batteries with nickel-manganese-cobalt (NMC) cathode and graphite anode are popularly used in portable electronic devices and electric vehicles. Calendar loss of the lithium ion battery is a dominating factor in battery degradation. However, few modeling work was reported on studying the calendar capacity loss of NMC-graphite Li-ion batteries. In this work, an electrochemical model for NMC-graphite Li-ion battery was developed to investigate its calendar loss behavior. Various factors affecting the calendar loss of the NMC-graphite batteries were systematically investigated, with the results validated with experimental data of a Sanyo 18,650 cylindrical cell. It was found that at 25 o C working temperature and 100% SOC, the capacity drops 6.4% of its original capacity after 10 months. Also, when the anode particle size decreases from 26.2 {\mu}m to 6.55 {\mu}m, the capacity drop ratio is over 22% after 10 months under the same operation condition. Our simulation results demonstrate that a smaller SOC, a lower cell working temperature and a larger particle size could prolong the battery life during the storage period. This modeling work can help better understand the calendar loss behavior of NMC-graphite Li-ion batteries, and serve as a robust reference for the battery performance optimization in future.