Remaining Useful Life Prediction for Two-Phase Hybrid Deteriorating Lithium-Ion Batteries Using Wiener Process

Owing to operating condition switching and internal degradation mechanisms, the degradation processes of some lithium-ion batteries (LIBs) exhibit non-monotone and two-phase patterns, which are composed of a linear first phase and a nonlinear second phase. The existing Gamma process and Inverse Gaussian process methods are limited to modeling the monotone degradation data. Besides, traditional single-phase nonlinear models and two-phase linear models are insufficient to describe such a degradation process effectively. Therefore, degradation modeling and remaining useful life (RUL) prediction of the hybrid deteriorating LIBs is still a compelling practical issue. In this paper, a two-phase hybrid degradation model with a linear first phase and a nonlinear second phase is formulated based on the widely used Wiener process-based model. Taking into account the random effects caused by the unit heterogeneity and the uncertainty of the degradation state at the changing point, we obtain the analytical solutions of the lifetime estimation and RUL prediction under the concept of the first passage time (FPT). In addition, to conduct model parameter identification, the expectation maximization (EM) algorithm in conjunction with a profile log-likelihood function method are utilized for offline parameter estimation. Subsequently, the Bayesian rule is adopted to conduct the online parameter updating. Finally, the numerical and practical experiments are provided for verification and show that the proposed method could achieve high estimation accuracy for the RUL prediction of the two-phase hybrid deteriorating LIBs.