©　2018　Elsevier　B.V.　Despite　promising　high-capacity　of　lithium　metal　anode,　one　major　obstacle　for　its　wide　application　is　the　uncontrolled　dendrite　growth,　causing　low　Coulombic　efficiency　(CE),　irreversible　capacity　loss　and　short　circuit.　Here,　we　report　a　facile　separator　engineering　to　suppress　Li　dendrites　growth　through　single-side　deposition　of　magnesium　(Mg)　nanoparticles.　The　lithiophilic　Mg　nanoparticles　on　the　separator,　servering　as　heterogeneous　nucleation　sites,　exhibits　a　strong　guiding　effect　to　form　inerratic　Li　crystal　seeds　in　the　early　plating　process,　resulting　in　a　dense　Li　anode　with　dendrite-free　morphology　after　long　cycling.　The　unique　characteristics　of　this　functional　separator　are　further　demonstrated　in　Li|LiCoO2　full　cells　with　a　high　capacity　retention　(＞80%　after　400　cycles).　Accordingly,　our　strategy　offers　a　scalable　low-cost　and　efficient　approach　for　advanced　rechargeable　Li　metal　batteries.