Fast thermal responsive separators toward long-life and safe lithium metal batteries

Lithium metal batteries (LMBs) have been extensively investigated during the past decades because of their ultrahigh energy densities. With the increasing demand for energy density, however, the safety issue of LMBs has become a significant challenge. In particular, localized areas of increased temperature (namely, hotspots) may be induced and even exacerbated within LMBs by uneven current distribution, internal short circuits, or inadequate heat dissipation, which significantly sacrifices battery safety and cycle life. Here, we report the rational design and fabrication of a fast thermal responsive separator capable of inhibiting the growth of lithium dendrites and mitigating thermal propagation, thereby reducing the risk of thermal runaway. The as-achieved separator comprises both an electrospun membrane using a phase change material with superior thermal-storage ability and a thermally conductive modification layer of hexagonal boron nitride nanosheets with a fast heat-transfer feature. It is demonstrated that such a unique integration of heat conduction and heat storage enables the functional separator with attractive abilities to mitigate hotspots and inhibit the growth of lithium dendrites upon the cycling of LMBs. Moreover, pouch cells with the thermal-responsive separator, as well as numerical simulations, verify much enhanced safety and cycle life of LMBs. This work may offer a new conceptual design of intelligent separators that acts as a functional unit encapsulated within a single cell to boost in-situ thermal management, which will help to develop high-safety and energy-dense LMBs.