Cell to module level thermal management of batteries using partial and full coverage of multi-melting point flexible composite phase change materials

High-rate operation of cylindrical lithium-ion batteries causes excessive temperature rise and axial temperature non-uniformity, compromising safety and cycle life. Although phase-change materials (PCMs) suppress peak temperature, most strategies rely on full battery coverage or bulky external structures, increasing material usage and system mass, which is undesirable for weight-sensitive applications and may reduce pack-level gravimetric energy density. Furthermore, mismatch between the PCM melting temperature and desired battery operating window limits latent-heat utilization. This study proposes a material-efficient strategy from single cell to module level by comparing partial and full coverage using flexible composite PCM (FCPCM). Two FCPCMs with melting points of 35 °C (FCPCM-A) and 42 °C (FCPCM-B) are developed to assess the combined effects of melting-point selection and coverage configuration. Different coverage strategies are evaluated at various discharge rates, followed by cyclic testing at 30 °C with module-level validation. Partial coverage reduces peak temperature but relocates hotspots to uncovered regions, and single partial layer cannot keep temperatures within safe limits at high C-rates. While full coverage provides better cooling, the upper-middle (UM) partial-coverage configuration maintains safe temperatures range using ∼62% of the full-coverage FCPCM mass, corresponding to ∼38% FCPCM saving and ∼ 14.8% estimated module-level gravimetric energy-density improvement. UM coverage reduced peak temperature from 56.6 °C and 66.3 °C (bare cell) to below 45 °C at 3C and below 50 °C at 4C. During cycling, FCPCM-B showed more stable latent-heat buffering than FCPCM-A. Thus, melting-point-matched partial coverage saves material while maintaining safe peak temperature, though full coverage provides better temperature uniformity.