Dynamic Thermal Regulation of Li‐Mg Batteries via Microencapsulated Phase Change Materials Embedded in High‐Entropy MOF Matrices

ABSTRACT To address critical safety vulnerabilities in Li‐Mg battery (LMB), particularly internal short circuits and thermal runaway, we report a novel smart gel polymer electrolyte (HEMOF@TP@DZC GPE) that synergistically enhances electrochemical performance and intrinsic safety. The innovation centers on a hollow high‐entropy metal‐organic framework (HE‐MOF) microcapsule with a hierarchically porous structure and abundant oxygen vacancies, which significantly accelerates ion transport kinetics essential for high‐performance operation. Its unique spherical morphology with smaller curvature effectively disperses interfacial stress, actively suppressing detrimental Mg dendrite growth. For intrinsic safety, the microcapsule encapsulates flame retardant triethyl phosphate (TEP), anchored by a phase change material (PCM) serving as a smart gatekeeper. Upon temperature increase, the PCM triggers rapid TEP release, generating phosphorus‐containing radicals that efficiently terminate combustion chain reactions and prevent thermal runaway propagation. An LMB cell utilizing this multifunctional HEMOF@TP@DZC GPE demonstrated exceptional performance stability, delivering a specific capacity of 80.5 mAh g −1 at 80 C and exhibiting remarkable capacity retention with negligible degradation (only 1.55%) over an extraordinary 20 000 cycles. This work establishes a fresh, impactful avenue for designing multifunctional HE‐MOF microcapsules that seamlessly integrate advanced thermal management with superior electrochemical performance, paving the way for the next generation of intrinsically safer, higher‐energy‐density Li‐Mg batteries.