A Generic Cycle Life Model for Lithium-Ion Batteries Based on Fatigue Theory and Equivalent Cycle Counting

Abstract

This paper proposes a cycle life model for lithium-ion batteries. The main objective of this work is to facilitate the electrical simulation of lithium-ion battery aging (due to cycling), and its impact on battery capacity and internal resistance. Most of the reported cycle life models are either: a) physics based, with parameters difficult to retrieve or b) semi-empirical, where the parameter identification process requires large amount of experimental data, huge manpower and test duration lasting from months to years. Moreover, these models tend to be valid only for the underlying battery and not for other battery types. This makes the simulation of lithium-ion batteries cycling effects, difficult to achieve, expensive and time consuming. The model proposed in this paper is based on simple physical equations from fatigue theory and equivalent cycle counting. The parameter identification process is straightforward and requires only few data from battery datasheets and limited (or short duration) cycling experiments. The proposed model is generic and able to represent the impact of common cycle life factors such as: depth-of-discharge (DoD), temperature and C-rate. The model is validated using two lithium-ion battery types (LFP-LiFePO4 and NMC-LiNiMnCoO2) and simulation results are close to reality with an error within ±1.5% compared to experimental results.

Keywords

• Battery cycle life model
• capacity loss curves
• equivalent cycle counting
• generic battery model
• lithium-ion batteries