Dodecylamine-derived thin carbon-coated single Fe₃O₄ nanocrystals for advanced lithium ion batteries

Dodecylamine (DDA) was functionalized on Fe₂O₃ nanocrystals (NCs) by a solvothermal process to allow electrostatic interaction on Brønsted acid sites induced on the surface of NCs, followed by carbonization to convert DDA into a thin layer of carbon on single Fe₃O₄ NCs. The obtained carbon composite (IOC-Fe₃O₄) is composed of Fe₃O₄ NCs a few nanometers in size, each uniformly coated with a thin carbon layer. The carbon coating reduces the resistance at the NC-to-NC interface within the composite and retains a short lithium diffusion length by inhibiting crystal growth, as well as accommodating the volume change of Fe₃O₄ during charge-discharge. The composite electrode exhibited a high reversible capacity of 1027 mA h g^-1 in a lithium ion battery, as well as 100% capacity retention after 300 cycles and rate performance of 563 mA h g^-1 at 3 A g^-1, which was achieved with only 4.2 wt% carbon in the composite. The relationship between the enhanced diffusion kinetics of IOC-Fe₃O₄ and excellent electrochemical performances is demonstrated through a voltammetric charge technique.