Coulombic　efficiency　especially　in　the　first　cycle,　cycling　stability,　and　high-rate　performance　are　crucial　factors　for　commercial　Li-ion　batteries　(LIBs).　To　improve　them,　in　this　work,　Al2O3-coated　natural　graphite　powder　was　obtained　through　a　low-cost　and　facile　sol　gel　method.　Based　on　a　comparison,　of　various　coated　amounts,　0.5　mol　%　Al(NO3)(3)　(vs　mole　of　graphite)　could　bring　about　a　smooth　Al2O3　coating　layer　with　proper　thickness,　which　could　act　as　a　preformed　solid　electrolyte　interface　(SEI)　to　reduce　the　regeneration　of　SEI　and　lithium-ions　consumption　during　subsequent　cycling.　Furthermore,　we　examined　the　advantages　of　Al2O3　coating　by　relating　energy　levels　in　LIBs　using　density　functional　theory　calculations.　Owing,　to　its　proper　bandgap　and　lithium-ion　conduction　ability,　the　coating　layer　performs　the　same　function　as　a　SEI　does,　preventing　an　electron　from　getting　to　the　outer　electrode　surface　and　allowing　lithium-ion　transport.　Therefore,　as　a　preformed　SEI,　the　Al2O3　coating　layer　reduces　extra　cathode　consumption　observed　in　commercial　LIBs.