Simulation of Impedance Changes with Aging in Lithium Titanate-based Cells Using Physics-Based Dimensionless Modeling

Abstract

Quantifying aging effects in lithium-ion cells with chemistries that have a flat open circuit potential is challenging. We implement a physics-based electrochemical model to track changes in the electrochemical impedance response of lithium titanate-based cells. Frequency domain equations of a pseudo two-dimensional model are made dimensionless, and the corresponding non-dimensional parameters are estimated using a Levenberg-Marquardt routine. The model weighs the relative contributions of changes in diffusion, ionic conduction within the electrolyte phase against solid phase electronic conduction towards cell aging. Solid-phase diffusion, charge transfer resistance and double layer capacitance at the solid-liquid interface are accounted for in the particle impedance. The estimation routine tracks dimensionless parameters using accelerated cycling data from full cells over 1000 cycles. The model can be deployed within a short time for state estimation using physics-based models without requiring prior knowledge of the battery chemistry, format, or capacity.

Extracting and Interpreting Electrochemical Impedance Spectra (EIS) from Physics-Based Models of Lithium-Ion Batteries

“…[9][10][11] The impedance spectra can be used to characterize electrochemical and physical phenomena (i.e., ionic transport, solid-phase diffusion, charge-transfer process), and to identify and track internal degradation processes. [11][12][13] By applying a low-amplitude harmonic current (galvanostatic mode) or voltage (potentiostatic mode) signal over a range of frequencies, the impedance spectra can be obtained by measuring the amplitude and phase shift of the output voltage or current, respectively. Figure 1 illustrates the physical meaning of electrochemical impedance.…”

“…The analytical solutions are obtained in the frequency domain after linearization and using Laplace/Fourier transformations of the coupled transient nonlinear partial differential equations. 13,[17][18][19][20][21][22][23][24][25][26][27] Because deriving the analytical solution is complex and tedious, different levels of simplification of the P2D models are generally applied. These analytical approaches are primarily concerned with the linear (first-order) system response, but recently efforts are underway to study higher-order frequency responses to uniquely identify internal parameters that were previously undetectable.…”