Thermophysical characterization, kinetic analysis, and multi-response optimization of paraffin wax/eicosane binary mixtures for lithium-ion battery thermal management system

Efficient thermal management is essential for the safety, performance, and lifetime of lithium-ion batteries, especially in high-power applications such as electric vehicles, where elevated temperatures and thermal non-uniformity accelerate degradation. Passive cooling by phase change materials (PCMs) offers a compact, energy-efficient solution. In this study, eleven paraffin wax/eicosane (PW/E) binary composite PCMs were prepared across the full composition range (S1–S11; 100/0 to 0/100 wt%) for the Molicel INR 21700 P42A battery module. Simultaneous thermal analysis (STA) under argon (10 °C·min −1 ) provided combined DSC and TGA/DTG data. Increasing eicosane content shifted the melting peak from 55.00 °C (S1) to 40.26 °C (S11); total phase-change enthalpy ranged from 135.03 J·g −1 (S4) to 252.78 J·g −1 (S11), a net +35.3% from S1 to S11. A solid–solid rotator transition (24.98–31.50 °C) contributed 4.8–22.4% of the total latent heat and is critical for accurate BTMS simulations. TGA yielded onset decomposition temperatures of 170–222 °C, exceeding the 60 °C battery limit by more than 110 °C. Coats–Redfern model fitting identified D3–Jander as the best-fitting physically admissible rate function (kinetic compensation R 2 = 0.957); effective activation energies were 107.43–145.07 kJ/mol after excluding the S2 encapsulation anomaly. Filippov-based k(T) coupled with DSC-derived tanh β(T) functions captured up to a 66.6% conductivity drop across melting. Box–Cox RSM optimization (Stat-Ease 360) identified S6 (PW/E 50/50) as the global optimum (D = 0.861, β(40 °C) = 0.07). The resulting k(T), ρ(T), β(T), and Cp(T) correlations provide a self-consistent property set for passive and hybrid BTMS CFD, pending direct thermal-conductivity measurement on the composites.