Carbon-encapsulated Fe_3O_4 nanoparticles as a high-rate lithium ion battery anode material

摘要

A facile and scalable in situ synthesis strategy is developed to fabricate carbon-encapsulated Fe_3O_4 nanoparticles homogeneously embedded in two-dimensional (2D) porous graphitic carbon nanosheets (Fe _3O_4@C@PGC nanosheets) as a durable high-rate lithium ion battery anode material. With assistance of the surface of NaCl particles, 2D Fe@C@PGC nanosheets can be in situ synthesized by using the Fe(NO _3)_3·9H_2O and C6H 12O6 as the metal and carbon precursor, respectively. After annealing under air, the Fe@C@PGC nanosheets can be converted to Fe _3O_4@C@PGC nanosheets, in which Fe_3O_4 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 Fe_3O_4 to the electrolyte and preserve the structural and interfacial stabilization of Fe_3O_4 nanoparticles. Meanwhile, the flexible and conductive PGC nanosheets can accommodate the mechanical stress induced by the volume change of embedded Fe_3O_4@C nanoparticles as well as inhibit the aggregation of Fe_3O_4 nanoparticles and thus maintain the structural and electrical integrity of the Fe_3O _4@C@PGC electrode during the lithiation/delithiation processes. As a result, this Fe_3O_4@C@PGC 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 Fe_3O_4-based electrode including various nanostructured Fe_3O_4 anode materials, composite electrodes, etc.