A sustainable biochar-based shape stable composite phase change material for thermal management of a lithium-ion battery system and hybrid neural network modeling for heat flow prediction

Abstract

Electric vehicles are gaining global popularity lately, and along with it, efficient battery thermal management systems (BTMS) are also gaining traction amongst the research community. Phase change material (PCM) based BTMS can be an attractive solution due to its high energy density and isothermal energy exchange. However, pure PCM has some drawbacks like low thermal conductivity, volume expansion, and leakage during phase change. A shape stable composite PCM (SSCPCM) resolves these drawbacks but is an expensive solution due to the high cost of conventional supporting materials. Biochar (BC) based SSCPCM developed in this study can be a cheap and sustainable solution for BTMS. The characterization studies are carried out for combination of pure PCM (Myristyl Alcohol) and biochar at various loadings of 6 %, 12 %, 18 %, and 24 % by weight, using Fourier transform infrared analysis (FT-IR), X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), particle size analysis (PSA), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The shape stability studies reveal that the PCM with minimum of 24 % biochar (PCM-BC24) is shape stable. The thermal conductivities and effusivities of pure and shape-stable composite PCMs are also studied. Enhancement in thermal conductivity of PCM-BC24 is studied with the addition of multi-walled carbon nanotubes (MWCNT) in 0.5 % and 1 % concentrations. FT-IR and XRD results reveal that the interaction of biochar and MWCNT with pure PCM is purely physical and chemically stable. The degree of supercooling is reduced by 19.26 %, 23.49 %, and 25.17 % for PCM-BC24 with 1 % MWCNT compared to pure PCM at a heating rate of 5.0, 7.5, and 10 °C/min, respectively. Thermal conductivity and effusivity of PCM-BC24 with 1 % MWCNT are 458.72 % and 146.25 % higher than the pure PCM, respectively. The TGA results reveal that PCMs thermal stability is not adversely affected by the addition of BC & MWCNT. Furthermore, an ANFIS model is developed to predict the heat flow (mW/mg) values of PCM samples and found that the generalized bell-shaped input and linear output membership function is best suitable with a coefficient of determination (R2) of 0.971.