Confinement‐Engineered Thermally Programmed Ion‐Gating Separator for Decoupling Thermal–Electrochemical Feedback in High‐Energy Lithium‐Ion Batteries

ABSTRACT Thermal runaway in lithium‐ion batteries arises from the intrinsic coupling between heat generation and ion transport, yet conventional shutdown separators primarily rely on passive pore collapse without regulating the underlying electrochemical pathways. Here, we introduce a confinement‐engineered, thermally programmed ion‐gating separator that synchronizes phase transition with electrochemical disconnection. A mesoporous silica (SBA‐15) framework encapsulating Hexadecanamide (HDA) is inorporated into a PVDF‐HFP matrix to form a robust composite membrane. The high surface area and polar silanol moieties of SBA‐15 modulate the Li + solvation environment, enabling superior rate‐performance at high current densities. The nanoscale confinement stabilizes HDA via interfacial interactions, enabling controlled melting around 90–100°C and progressive pore occlusion near 120–130°C. This phase‐mediated transition induces an impedance increase of approximately 10 4 times, effectively suppressing lithium‐ion transport while preserving stable performance. Distribution of relaxation time (DRT) analysis confirms that the shutdown results from concurrent suppression of bulk and interfacial transport. In full MCMB||NMC811 cells, the separator transforms thermal‐runaway behavior from reaction‐driven escalation to a thermally moderated response, raising the onset temperature and delaying catastrophic failure under accelerating‐rate calorimetry. This work establishes a materials‐level strategy for phase‐programmed electrochemical gating, introducing a new paradigm for intrinsically safer high‐energy lithium‐ion batteries.