Abstract
For reliable lifetime predictions of lithium-ion batteries, models for cell degradation are required. A comprehensive semi-empirical model based on a reduced set of internal cell parameters and physically justified degradation functions for the capacity loss is developed and presented for a commercial lithium iron phosphate/graphite cell. One calendar and several cycle aging effects are modeled separately. Emphasis is placed on the varying degradation at different temperatures. Degradation mechanisms for cycle aging at high and low temperatures as well as the increased cycling degradation at high state of charge are calculated separately. For parameterization, a lifetime test study is conducted including storage and cycle tests. Additionally, the model is validated through a dynamic current profile based on real-world application in a stationary energy storage system revealing the accuracy. Tests for validation are continued for up to 114 days after the longest parametrization tests. The model error for the cell capacity loss in the application-based tests is at the end of testing below 1% of the original cell capacity and the maximum relative model error is below 21%.
Highlights
Cell degradation models are necessary. Physicochemical models that include aging mechanisms are based on a detailed set of parameters which are often not readily available, computationally costly and require experimental parameterization of degradation rates.[2,3,4] Instead, purely empirical models can be parameterized without knowledge of internal cell setup through extensive testing
For reliable lifetime predictions, cell degradation models are necessary
State of charge dependence.—The capacity loss attributed to the additional term for the mechanism at low temperatures at a high state of charge is calculated from experimental data of the constant current (CC)-Constant Voltage (CV) tests by subtraction of the previously developed terms of the calendar model and the cycle model for low and high temperature: QL,Exp,Cycle,High State of Charge (SOC)
Summary
Cell degradation models are necessary. Physicochemical models that include aging mechanisms are based on a detailed set of parameters which are often not readily available, computationally costly and require experimental parameterization of degradation rates.[2,3,4] Instead, purely empirical models can be parameterized without knowledge of internal cell setup through extensive testing. This equation for the calendar aging capacity loss is fitted to experimental data for a test with constant temperature and SOC, Downloaded on 2018-02-13 to IP 192.174.37.50 address.
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