Development and Validation of a Reduced Order Model Incorporating a Semi-Empirical Degradation Model for Pouch Type LiFePO4/Graphite Cells

Paper #:
  • 2017-01-1218

Published:
  • 2017-03-28
Abstract:
Experimental and modeling investigations are conducted by commercial pouch type LFP/graphite cells, whose nominal capacity is 20Ah. The characteristics of two-phase transition and path dependence are taken into account in a reduced order model (ROM). Two-phase transition during galvanostatic charge/discharge with a moving interface between the lithium-rich phase and lithium-deficient phase, was estimated by a shrinking core. Different current (0.1/1/3/4C) were applied to fresh cells at different ambient temperatures (25/35/45°C). Comparison between validation results of ROM and collected experimental data shows good consistency. The experimental evidence of path dependence is also shown in the paper. Side reaction is treated as the predominant cause for degradation of cycled cells, which could be affected by the operating conditions, such as temperature and SOC cycling range. The cycling tests were interrupted every 30 or 40 cycles to measure the capacity and EIS of five cycled cells under different temperatures and SOC cycling ranges. The final capacity fade are 5.81%, 10.95%, 12.17%, 14.17%, and 23.54%, respectively. Degradation can be accelerated by high temperature and SOC cycling range. Postmortem analysis conducted at the end of experiments revealed morphology change on composite negative electrode. A semi-empirical degradation model was incorporated into the former developed ROM. Three key parameters, volume fraction of active anode material, resistance of SEI and deposit layer, and effective diffusion coefficient in electrolyte, were extracted from experiments based on nonlinear least square method. The simulation results and experimental data are in a pretty good match.
Also in:
  • SAE International Journal of Alternative Powertrains - V126-8EJ
  • SAE International Journal of Alternative Powertrains - V126-8
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