Thermally Resistant, Mechanically Robust, Enamel‐Inspired Hydroxyapatite/Polyethylene Nanocomposite Battery Separator

Abstract Microporous polyethylene (PE) membrane is a representative lithium‐ion battery (LIB) separators but regularly shrinks especially in high‐temperature conditions, and is facilely pierced while growing Li dendrites, leading to severe consequences such as short circuits, thermal runaway, and even explosion. Herein, this article reports a quasi‐continuous strategy that utilizes in situ enamel mineralization engineering followed by thermal treatment to easily develop a large‐area, 3D interlaced hydroxyapatite nanosheets array‐reinforced PE nanocomposite separator with robust mechanical properties and excellent resistance to thermal shrinkage. Specifically, the 120 °C‐heated nanocomposite possesses excellent breaking stress, an ultrahigh toughness of ≈434.4 MJ m⁻³, and an enhanced friction coefficient of ≈0.69, which are distinctly higher than those of commercial PE separators, respectively, and far exceeding those of reported ceramic modified‐PE separators. The elongation of the resultant nanocomposite can achieve an extraordinary ≈2456.4% without any fracture under a 180 °C‐heating temperature. In situ observation and finite element simulation indicate that the impressive mechanical and thermostable integration profits from the co‐effect of efficient energy dissipation at organic–inorganic interfaces and mechanically interlocked, mutually‐supported hybrid microstructure. The enamel‐inspired separator can be potentially applied in safer high‐temperature LIBs and this strategy provides a valuable guide to develop other high‐performance polymer‐based nanocomposites.