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A new approach to the determination of the thermal parameters of high-power batteries is introduced here. Application of local heat flux measurement with a gradient heat flux sensor (GHFS) allows determination of the cell thermal parameters in different surface points of the cell. The suggested methodology is not cell destructive as it does not require deep discharge of the cell or application of any charge/discharge cycles during measurements of the thermal parameters of the cell. The complete procedure is demonstrated on a high-power Li-ion pouch cell, and it is verified on a sample with well-known thermal parameters. A comparison of the experimental results with conventional thermal characterization methods shows an acceptably low error. The dependence of the cell thermal parameters on state of charge (SoC) and measurement points on the surface was studied by the proposed measurement approach.

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A novel method for the state of health (SoH) estimation and determination of the degradation mechanisms of cylindrical Li-ion cells after long storage time is presented. The proposed method is based on differential curves obtained with the help of temperature and heat flux measurements on the surface of a cylindrical lithium iron phosphate (LFP) cell. The applicability and advantages of the proposed differential curves for the SoH estimation and determination of degradation mechanisms are discussed and verified based on a comparison with currently existing in-situ diagnostic methods such as differential voltage (DV) analysis method. The results of the comparison show that the proposed differential curve can provide information about capacity fading and prevailing degradation mechanism at higher than 1 Crate discharging current while the application of the DV curve may not be possible. Moreover, the presented method allows identification of the changes in the entropic heat generation, which may improve the SoH estimation and the determination of the degradation mechanisms in a cylindrical Li-ion cell after a storage period.