Research On The Variation Characteristics Of Capacity And Internal Resistance Of Lithium-ion Batteries Echelon Use

ABSTRACT:The echelon use of lithium ion batteries retiring from electric vehicles are the efficient means to elevate the using value of batteries as well as reducing the whole life cycle cost of batteries.The recycle lifetime of batteries retiring from the vehicles is one of the key issues that restricting the batteries echelon use. From the perspective of degradation mechanism of the echelon use batteries during the recycle, this paper concentrates on researching the cycling characteristics of capacity-. resistance and the relationship between them, the detailed research content and conclusion as follow:(1) Deeply analyzing the recycle characteristics of batteries capacity and resistance based on different charging-discharging rates stress and SOC cycling ranges stress, using multiple linear regression method establishes function model of ohm resiatance growth rate and polarization resistance growth rate between different SOC cycling ranges and the full cycling range,and verifying the effectivity of this model and reducing the time cost of batteries life prediction from comparing with the full cycling range data.(2) Quantifiably analyzing the themodynamic loss and the kinetics loss during the recycle use of batteries,it can be seen that the loss of lithium ion and active material are the main parts of batteries capacity degredation,and the differences between the path of using history have a significant influence on batteries capacity degredation during the recycle use,therefore, the old batteries may emerge some phenomenons which different from the new batteries. using the incremental capacity analysis method analyzes the capacity degradation mechanism and the material degradation rule on the influence of rates、SOC cycling range coupling with aging of echelon use batteries. Establishing life predication model of batteries echelon use based on the degredation path, this model confirms the mathematic relationship between the batteries life and the SOC cycling range, which has a vital significance on the life predication of echelon use batteries in the energy storage operating condition.(3) Using the canonical correlation analysis method, establishes the model between capacity degradation rate%ohm resistance growth rate as well as polarization resistance rate, this model has relatively high precision and universality, it is evident from the eight batteries data that the capacity degradation rate and resistance growth rate conform to certain plane relation.(4) Establishing the electrochemical impedance spectrum, comparing the old and new batteries electrochemical parameters, it is obvious that ohm resistance electrochemical polarization impedance、electrical double-layer capacitance and lithium ion diffusion coefficient vary considerably. Comparatively analyzing some external characteristic parameters such as SOC-OCV curves, ICA curves, the rate of charge and discharge efficiency of the old and new batteries, it is apparent from the information supplied that the SOC-OCV curve vary greatly in the high and low sections during aging; the electrode material losse and the change of the dynamic characteristics make markedly position shift and decrease of peaks in ICA curves with aging; When capacity decline rate within a certain range, the battery has a good ratio characteristics and charge-discharge efficiency, while when the recession to50%capacity, ratio characteristics and charging and discharging efficiency significantly reduced.