Designing Janus separators reinforced by hydrogen/ionic bonds for stable lithium metal anodes

Lithium metal batteries (LMBs), with their ultra-high theoretical energy density, are considered the most promising high-density energy storage devices. However, uncontrolled lithium dendrites and safety issues have seriously hindered the widespread application of LMBs. Separators are a vital component in ensuring the safety of batteries, preventing direct electrical contact between the cathode and anode while allowing ion transport. Here we report a Janus separator with an electrically and thermally conductive layer of carbon nanotubes on one side and a solid-solid phase change layer on the other side. Meanwhile, hydrogen/ionic bonds are introduced to enhance the internal structural connectivity of the separator, leading to a significant improvement in mechanical strength. The electrically and thermally conductive layer of the Janus separator regulates lithium deposition by eliminating local current density and hot spots, to mitigate the growth of lithium dendrites. When lithium dendrites inevitably pierce the separator and cause short circuit, the solid-solid phase change layer can serve as safety compensation, absorbing heat through the solid-solid phase change and alleviating the temperature rise caused by the short circuit. Experimental results and theoretical simulations show that the Janus separator can effectively suppress lithium dendrites and alleviate the temperature rise of the battery during short circuit. More importantly, the Janus separators exhibit superior electrochemical performance to commercial polyolefin separators. The as-designed Janus separator with the functions of lithium dendrite suppression and solid-solid phase change thermoregulation provides an effective strategy for enhancing the safety of LMBs.