Abstract
Impedance-based temperature detection (ITD) is a promising approach for rapid estimation of internal cell temperature based on the correlation between temperature and electrochemical impedance. Previously, ITD was used as part of an Extended Kalman Filter (EKF) state-estimator in conjunction with a thermal model to enable estimation of the 1-D temperature distribution of a cylindrical lithium-ion battery. Here, we extend this method to enable estimation of the 2-D temperature field of a battery with temperature gradients in both the radial and axial directions. An EKF using a parameterised 2-D spectral-Galerkin model with ITD measurement input (the imaginary part of the impedance at 215 Hz) is shown to accurately predict the core temperature and multiple surface temperatures of a 32113 LiFePO$_4$ cell, using current excitation profiles based on an Artemis HEV drive cycle. The method is validated experimentally on a cell fitted with a heat sink and asymmetrically cooled via forced air convection. A novel approach to impedance-temperature calibration is also presented, which uses data from a single drive cycle, rather than measurements at multiple uniform cell temperatures as in previous studies. This greatly reduces the time required for calibration, since it overcomes the need for repeated cell thermal equalization.
Highlights
Monitoring the temperature of Li-ion batteries during operation is critical for safety and control purposes
The conventional approach to temperature estimation is to use numerical electrical-thermal models coupled with online measurements of the cell surface temperature and/or the temperature of the heat transfer medium [1] (Figure 1)a)
Shi.zhao, Preprint submitted to Journal of Power Sources david.howey}. Using this approach in conjunction with state estimation techniques such as Kalman filtering, the cell internal temperature may be estimated with high accuracy [2, 3, 4, 5]
Summary
Monitoring the temperature of Li-ion batteries during operation is critical for safety and control purposes. Rapid fluctuations in internal temperature may not be registered by surface mounted temperature sensors, regardless of the sampling frequency This may mean thermal runaway cannot be detected, since associated timescales are often shorter than those associated with heat conduction through the cell [8]. One approach to overcome these problems is to embed flexible thin film micro-temperature sensors within the cell to enable in-situ internal temperature measurement [9, 10, 11, 12, 13] Whilst this has some obvious advantages, the additional manufacturing and instrumentation requirements would significantly increase the cost and complexity of the system
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