Lithium　metal　battery　(LMB)　is　considered　to　be　one　of　the　most　promising　electrochemical　energy　storage　devices　due　to　the　high　theoretical　specific　capacity　and　the　lowest　redox　potential　of　metallic　lithium;　however,　some　key　issues　caused　by　lithium　dendrites　on　the　lithium　metal　anode　seriously　hinder　its　real-world　applications.　As　an　indispensable　part　of　LMBs,　the　separator　could　serve　as　a　physical　barrier　to　prevent　direct　contact　of　the　two　electrodes　and　control　ionic　transport　in　batteries;　it　is　an　ideal　platform　for　the　suppression　of　lithium　dendrites.　In　this　review,　the　mechanism　of　lithium　dendrite　nucleation　and　growth　are　firstly　discussed　and　then　some　advanced　techniques　are　introduced　for　the　precise　characterization　of　lithium　dendrites.　On　the　basis　of　dendritic　nucleation　and　growth　principle,　several　feasible　strategies　are　summarized　for　suppressing　lithium　dendrites　by　utilizing　functional　separators,　including　providing　a　mechanical　barrier,　promoting　homogeneous　lithium　deposition,　and　regulating　ionic　transport.　Finally,　some　challenges　and　prospects　are　proposed　to　clear　the　future　development　of　functional　separators.　We　anticipate　that　this　paper　will　provide　a　new　insight　into　the　design　and　construction　of　functional　separators　for　addressing　the　issues　of　lithium　dendrites　in　high-energy　batteries.　©　The　Royal　Society　of　Chemistry.