Strategic Design of Ceramic‐Coated Separators for Fast‐Charging Safety Through Evaluating the Impact of Coating Methodology on Li ⁺ Flux Uniformity and Thermal Stability

The separator plays a pivotal role in governing safety and electrochemical performance in lithium‐ion batteries (LIBs), particularly under fast‐charging conditions where nonuniform lithium‐ion (Li ⁺ ) flux and thermal instability become critical challenges. Here, we investigate how coating methodology affects the structural, thermal, and electrochemical properties of ceramic‐coated separators, comparing a Al ₂ O ₃ /poly(acrylic acid) composite layer fabricated via doctor blade coating and electrospinning. The blade‐coated separator forms a dense, mechanically robust ceramic layer with superior tensile strength (4307.1 gf) and thermal stability (open‐circuit voltage retention of 765.4 s at 150 °C), but its increased tortuosity and pore‐blocking effects hinder ion transport under high‐rate conditions. In contrast, the electrospun separator forms a highly porous, interconnected network with improved ionic conductivity (0.877 mS cm ⁻¹ ), reduced charge–transfer resistance, the highest capacity retention (57.62% after 100 cycles at 0.5 C), and superior rate capability up to 5 C. Postmortem analysis confirms that the homogenized Li ⁺ flux from the electrospun architecture minimizes differential volumetric strain in the SiO _x composite anode, suppressing crack formation and resistance growth. These findings establish that pore architecture, rather than chemical composition, primarily governs Li ⁺ flux uniformity, rate performance, and thermal safety, offering design guidelines for next‐generation fast‐charging LIB systems.