Fabrication of Nb2O5 Nanosheets for High-rate Lithium Ion Storage Applications

Meinan Liu, Cheng Yan, Yuegang Zhang
2015 Scientific Reports  
Nb 2 O 5 nanosheets are successfully synthesized through a facile hydrothermal reaction and followed heating treatment in air. The structural characterization reveals that the thickness of these sheets is around 50 nm and the length of sheets is 500 , 800 nm. Such a unique two dimensional structure enables the nanosheet electrode with superior performance during the charge-discharge process, such as high specific capacity (,184 mAh?g 21 ) and rate capability. Even at a current density of 1 A?g
more » ... 1 , the nanosheet electrode still exhibits a specific capacity of ,90 mAh?g 21 . These results suggest the Nb 2 O 5 nanosheet is a promising candidate for high-rate lithium ion storage applications. L ithium ion batteries are commonly used for consumer electronics, portable electric devices, electric vehicles and other applications 1-5 . However, for high power density applications such as in electric vehicles, it is hindered by the achievement of high-rate capability of electrode materials. Recently, transition metal oxides have been extensively explored as anode replacing graphite due to their higher theoretical capacity and high packing densities, which lead to high volumetric energy densities in devices 6-10 . Among the different transition metal oxide as anode materials, lithium titanate (Li 4 Ti 5 O 12 ) and niobium oxide (Nb 2 O 5 ) have received the most study because of the considerable safety advantage that their redox potentials match to the LUMO of the organic liquid-carbonate electrolyte 11-13 . Compared with Li 4 Ti 5 O 12 with a specific capacity of 140 mAh?g 21 , Nb 2 O 5 exhibits a higher capacity (,200 mAh?g 21 ) 11,12 . Furthermore, Augustyn and Dunn et al found that the crystal structure of orthorhombic Nb 2 O 5 permits exceptionally rapid ionic transport since the mostly empty octahedral sites between (001) planes provide natural tunnels for lithium ion transport throughout the a-b plane 14,15 , which makes Nb 2 O 5 a promising anode material. However, its intrinsic poor electric conductivity (s , 3 3 10 26 S?cm 21 ) and the capacity decay resulted from pulverization during charge-discharge process limit its practical application in lithium ion batteries, and thus it is still challenging to develop efficient but simple ways to enhance the utilization of electroactive Nb 2 O 5 15-19 . Building nanostructures with desirable morphology and size is of great importance for addressing this issue 15-31 . For instance, Dunn et al developed Nb 2 O 5 mesoporous films through a simple solution process, which exhibited high-rate lithium insertion capability 16 . Wang and Lu et al reported high performance supercapacitors based on nanocomposites of Nb 2 O 5 nanocrystals and carbon nanotubes 17 . Nb 2 O 5 -carbon core-shell nanocomposites were fabricated by Li and Ma et al, which exhibited high specific capacity and rate capability 18 . Nb 2 O 5 nanobelts and hollow nanospheres were also been developed with large capacity and high rate capability 19,20 . Among these nanostructures, two dimensional structures with nano size in thickness and micro size in length have been considered to be the appropriate morphology for energy storage 22-25 . Generally, a nano-sized thickness has short ion diffusion path and large surface area; the micro-sized length can lower the internal resistance and facilitate the electron transfer rate as compared with the noncontinuous oxide framework composed of nanoparticles 22-25 . These merits encourage us to investigate Nb 2 O 5 electrode materials with two dimensional structures. In this work, Nb 2 O 5 nanosheets were developed by a two-step hydrothermal reaction and subsequent calcination process. The two dimensional sheet-like structure was composed of thin thickness (,50 nm) and long length (,800 nm), fitting the desirable structure principles as mentioned above. As expected, the nanosheet electrodes exhibited superior capacity (,184 mAh?g 21 ), much higher than commercial Nb 2 O 5 particles (,135 mAh?g 21 ). Additionally, the samples performed well at high current density (,130 mAh?g 21 at 0.4 A?g 21 and OPEN SUBJECT AREAS: BATTERIES MATERIALS CHEMISTRY
doi:10.1038/srep08326 pmid:25659574 pmcid:PMC4321166 fatcat:7f45fotec5da5muurp77a2nznu