Iron oxide-carbon nanocomposites modified by organic ligands: Novel pore structure design of anode materials for lithium-ion batteries

Iron oxide-carbon nanocomposites modified with organic ligands (L-iron oxide-carbon) were prepared by a hydrothermal process and subsequent thermal treatments for application as lithium-ion battery anode materials. The use of polyacrylic acid as the organic ligand effectively inhibited the agglomeration and additional growth of iron oxide nanoparticles, helping to form the porous composite structure. The molecular weights of the as-employed polymeric organic ligands were further regulated (high-molecular-weight ligands (HMLs) and low-molecular-weight ligands (LMLs) were used) to control the pore structure of the composite. Interestingly, since the pore structure of the composite depended on the molecular weight (or radius of gyration) of the polymeric organic ligand, HML-based composites possessed a larger pore volume and larger pore size than those of the LML-based one. The as-formed HML-iron oxide-carbon composite contained homogeneously distributed iron oxide nanoparticles in the porous graphitic carbon matrix obtained by regulated thermal treatments involving carbonization and oxidation. In the comparative electrochemical (EC) test for the samples (HML-iron oxide-carbon and controls), HML-iron oxide-carbon exhibited superior performance (retained capacity: 835 mAh/g after 100 cycles at 1 A/g; rate capability: 628 mAh/g at 3 A/g) compared to that of the controls (LML-iron oxide-carbon, iron oxide-carbon, iron oxide, and porous carbon). HML-iron oxide-carbon also exhibited an increased capacity of 835 mAh/g at 1 A/g after prolonged cycling (after 100 cycles). This outstanding EC performance of HML-iron oxide-carbon can be attributed to its unique composite structure design obtained by the introduction of HMLs and consecutive thermal treatments.