Abstract: The capacity loss of batteries results from the joint effects of the loss mechanisms of recyclable lithium and various active materials. The batteries with the same overall capacity loss may present completely different residual life decay trajectories due to the different proportions of different mechanisms. How to accurately diagnose the loss of each mechanism during battery aging is crucial for batteries’ utilization in the whole-life cycle. Therefore, an open circuit voltage(OCV) aging model which is more suitable for training-free diagnosis is selected as the study object, and aiming at the limitation of characterization accuracy at the later stage of battery aging, an improved OCV aging model for capacity-loss mechanism diagnosis in the whole-life cycle is proposed. The new model, fully considering the composite influence law of the deep loss of active material on electrode potential curves at the later stage of battery aging, realizes the effective mechanism description of the whole-life aging behavior of battery OCVs through the non-uniform compression expansion of the corresponding basic electrode potential joint coordinate system, based on the existing model. In order to verify the effectiveness of the new model in the whole-life cycle, lithium iron phosphate batteries(LFP) with available capacity decaying to 30% is taken as the experimental object, and the model fitting diagnostic tests are carried out under different aging states. The results show that the RMS error of the new model is controlled within 2 mV throughout the whole-life cycle. Furthermore, in order to ensure the reliability of the new model in the diagnosis process, its parameter identifiability is also analyzed and demonstrated.

Key words: OCV aging model, whole-life cycle, non-uniform compression, capacity-loss mechanism diagnosis