Designed synthesis of TiO2-modified iron oxides on/among carbon nanotubes as a superior lithium-ion storage material

Abstract

Various transition metal oxide-based nanostructures with outstanding lithium-ion storage properties are considered as the most appealing candidates to substitute conventional carbonaceous anode materials in lithium-ion batteries. However, the rational design and tailored synthesis of hybrid materials with specific components, morphologies and structures are crucial to achieving superior electrochemical performances. In this paper, we have designed the synthesis of nanostructured anatase TiO₂-modified iron oxides (Fe_xO_y) on/among carbon nanotubes (CNTs) (denoted as TFCs) by a simple and inexpensive bottom-up assembly approach. In the as-designed TFCs, TiO₂ modifications include two forms: TiO₂-coated on Fe_xO_y, and TiO₂ nanoparticles distributed among TFCs, which play a significant role in avoiding the aggregation and pulverization of the Fe_xO_y nanoparticles. With the introduced TiO₂ as a buffer material, and the CNTs framework as a porous 3D conducting/buffering network and an effective substrate for anchoring Fe_xO_y nanoparticles, as compared to all of the existing analogues reported, the as-designed TFCs display overwhelmingly superior Li⁺ storage properties, to be specific, good capacity retention with 922 mAh g⁻¹ at 500 mA g⁻¹ and 1089 mAh g⁻¹ at 200 mA g⁻¹, excellent rate capability with current densities varying from 50 mA g⁻¹ to 10 A g⁻¹ and remarkable cycling performance with the capacity increased from 584 to 922 mAh g⁻¹ at 500 mA g⁻¹ over 450 cycles (remaining stable at around 920 mAh g⁻¹ after the 420th cycle) after the rate tests for the same tested cell. We believe that the fascinating TFCs as well as other hybrids with similar structures can be easily extended for diverse applications, such as supercapacitors and catalysts, thus exhibiting broad prospects in the design of high-performance hybrid materials.