Polysulfide and Li Dendrite-Blocking Aramid Nanofiber/Metal–Organic Framework Composite Separators for Advanced Lithium–Sulfur Batteries

Separators are essential for supplying ion transport channels and preventing short circuits. Despite considerable effort, high-performance separators with desirable overall properties such as excellent thermostability, wettability, and impressive properties for suppressing lithium dendrites and polysulfide intermediates remain elusive. Here, we present an aramid nanofiber (ANF) and metal–organic framework (MOF) composite separator (ANF@MOFs) utilizing in situ growth of MOFs onto the extremely porous ANF network substrate. Benefiting from the features of the excellent strength, modulus, and nanoporosity of the ANF network, as well as the enormous specific surface area and sufficient metal sites of MOFs, the resultant ANF@MOFs separator exhibits excellent mechanical strength (a tensile strength of 110.7 MPa and a modulus of 3.1 GPa), improved liquid electrolyte wettability (an electrolyte uptake of 258.3%), and exceptional thermal stability (dimensionally stable after heating at 200 °C for 0.5 h). The ANF@MOFs separator not only demonstrates promising capabilities for physically blocking and chemically adsorbing Li2S2/Li2S and hence suppressing the Li2Sx shuttle effect but also suppresses the perforation of lithium dendrites, resulting in remarkable electrochemical and safety features. The battery equipped with the ANF@MOFs separator has a high first-cycle discharge capacity of 1081.92 mAh g–1 and a prolonged cycling performance with a capacity of 876.36 mAh g–1 at 0.5 C after 200 cycles. As a result, the high-performance ANF@MOFs composite separator provides significant potential for future lithium–sulfur batteries.