Carbon-Encapsulated Fe3O4 Nanoparticles as a High-Rate Lithium Ion Battery Anode Material

Abstract

A facile and scalable in situ synthesis strategy is developed to fabricate carbon-encapsulated Fe₃O₄ nanoparticles homogeneously embedded in two-dimensional (2D) porous graphitic carbon nanosheets (Fe₃O₄@[email protected] nanosheets) as a durable high-rate lithium ion battery anode material. With assistance of the surface of NaCl particles, 2D [email protected]@PGC nanosheets can be in situ synthesized by using the Fe(NO₃)₃·9H₂O and C₆H₁₂O₆ as the metal and carbon precursor, respectively. After annealing under air, the [email protected]@PGC nanosheets can be converted to Fe₃O₄@[email protected] nanosheets, in which Fe₃O₄ nanoparticles (∼18.2 nm) coated with conformal and thin onion-like carbon shells are homogeneously embedded in 2D high-conducting carbon nanosheets with a thickness of less than 30 nm. In the constructed architecture, the thin carbon shells can avoid the direct exposure of encapsulated Fe₃O₄ to the electrolyte and preserve the structural and interfacial stabilization of Fe₃O₄ nanoparticles. Meanwhile, the flexible and conductive PGC nanosheets can accommodate the mechanical stress induced by the volume change of embedded Fe₃O₄@C nanoparticles as well as inhibit the aggregation of Fe₃O₄ nanoparticles and thus maintain the structural and electrical integrity of the Fe₃O₄@[email protected] electrode during the lithiation/delithiation processes. As a result, this Fe₃O₄@[email protected] electrode exhibits superhigh rate capability (858, 587, and 311 mAh/g at 5, 10, and 20 C, respectively, 1 C = 1 A/g) and extremely excellent cycling performance at high rates (only 3.47% capacity loss after 350 cycles at a high rate of 10 C), which is the best one ever reported for an Fe₃O₄-based electrode including various nanostructured Fe₃O₄ anode materials, composite electrodes, etc.