Controllable Growth of Calcium Carbonate Nanocrystals on Collagen-Modified Polyethylene Separators with High Ionic Transport Efficiency and Stable Cycling

The commercial microporous polyethylene (PE) separators generally exhibit low thermal stability, poor electrolyte wettability, and significant safety concerns. Drawing inspiration from the formation process of biominerals, a collagen layer is first self-assembled on the PE separator surface to form a cross-linked network coating. Subsequently, the collagen matrix is mineralized with calcium carbonate nanocrystals, which undergo oriented growth within the collagen fibrils, thereby generating a stable inorganic mineral layer on the PE substrate (Mc@CaCO₃-PE). The organized structure markedly enhances the thermal stability and mechanical strength of the composite separator. Moreover, compared with conventional PE separators, it demonstrates superior electrolyte wettability, achieving an electrolyte absorption rate as high as 161.6%. Notably, the mineralized layer facilitates the sustained release of Ca²⁺ ions, which facilitates the desolvation process of Li⁺ ions. It not only increases the lithium-ion transference number (0.82) but also promotes the formation of a stable solid-electrolyte interphase (SEI). At a current density of 0.5 mA cm^-2, Li||Li symmetric cells with a Mc@CaCO₃-PE separator can be stably cycled for more than 1200 h. This composite separator shows great potential as a high-performance separator for lithium metal batteries, and this strategy provides valuable guidance for the development of other high-performance composite separators.