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Modified Si nanoparticles were investigated as an anode material for lithium-ion batteries. The Si nanoparticle surfaces were modified with conductive, N-doped carbon layers and prepared by a simple pyrolysis process using an ionic liquid that contained nitrogen. After the heat treatment, the N-doped carbon layers were uniformly coated onto the Si nanoparticles. The smooth carbon layers connected the Si nanoparticles without any morphological changes. Si nanoparticles containing 34 wt.% N-doped carbon exhibited the best electrochemical performance with a capacity of ∼1145 mAh g and excellent capacity retention over 100 cycles. The high electrochemical performance was attributed to the N-doped carbon layers that improved the electrical conductivity and minimized the volume expansion associated with the alloy during cycling. [ABSTRACT FROM AUTHOR]