Optimization of low-temperature preheating strategy for Li-ion batteries with supercooling phase change materials using response surface method

The supercooling phase change materials (SPCMs) for preheating lithium-ion batteries (LIBs) in cold environ-ments have demonstrated efficacy and improved the discharge performance in practical applications. However, the bulky and heavy SPCM blocks and the uneven temperature distribution deteriorate the discharge perfor-mance of LIBs. In this paper, an optimization study based on the response surface method (RSM) is carried out on the low-temperature preheating strategy of LIBs using SPCMs to obtain a lightweight design with satisfactory performance. The three key factors of PCM thickness, gap, and PCM type are optimized based on six responses. The optimization goals are to minimize the preheating time, the maximum and average battery pack tempera-ture, and the temperature difference between cells, as well as to maximize the volume and mass energy densities. The PCMs with different melting points and heat of fusion, including the sodium acetate trihydrate (SAT), the sodium thiosulfate pentahydrate (STP), and the disodium hydrogen phosphate dodecahydrate (DHPD), are evaluated to preheat a 3S3P 18650 battery pack from 5 degrees C to 20 degrees C. The simulation results show that the increase of the PCM thickness will decrease the preheating time and the temperature difference, but increase cell tem-perature and mass-energy density. The decrease of the gap can reduce the temperature difference and increase the volume energy density. Optimization case studies show that the thin PCM thickness, small gap, and DHPD demonstrate high energy density and safe thermal performance, such as case 10 (PCM thickness = 3.05 mm, Gap = 1.0 mm, PCM type = DHPD).

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