Improving Thermal Regulation of Lithium-Ion Batteries by Poly(vinylidene fluoride- <i>co</i> -hexafluoropropylene) Composite Separator Membranes with Phase Change Materials

Separator membranes with thermal regulation properties have been developed for battery systems by the addition of phase change material (PCM) microspheres within the polymer separator. Separator membranes based on PCM microspheres (acrylic core-shell particle) and polymer (poly-(vinylidene fluoride-<i>co</i>-hexafluoropropylene)), PVDF-HFP, composites were obtained by thermally induced phase separation (TIPS) with different amounts of PCM microspheres (4, 8, and 16 wt %). It is demonstrated that PCM content impacts the morphology of the separator membrane, leading to a decrease in the degree of porosity from 76 to 47%, the β-phase content from 86 to 78%, and the degree of crystallinity from 22 to 13%, with increasing PCM content, leading to variations in electrolyte uptake and electrochemical characteristics of the membranes. Li/C-LiFePO₄ half-cells were produced, and the best cycling behavior was achieved for the membrane with 16 wt % of PCM microspheres, showing 87 mAh.g^-1 after 200 cycles and 2C-rate without capacity fade. Consequently, this work demonstrates a separator membrane with PCM materials with low thermal shrinkage and consequently robust mechanical characteristics, showing thermal regulation properties that can be used in the next generation of safer lithium-ion batteries.