|Energy density comparison of the 3D nanotextile electrode and conventional LiMn2O4, LiCoO2, LiFePO4, and LiNi0.5Mn1.5O4 electrodes. Credit: ACS, Fing et al. Click to enlarge.|
A team from University of Science and Technology of China and Max Planck Institute in Germany has synthesized 3D V6O13 nanotextiles from interconnected 1D nanogrooves with diameter of 20–50 nm.
Used as cathode materials in Li-ion batteries, the 3D nanotextiles delivered reversible capacities of 326 mAh g–1 at 20 mA g–1 and 134 mAh g–1 at 500 mA g–1, and a capacity retention of above 80% after 100 cycles at 500 mA g–1. The textiles showed a specific energy as high as 780 Wh kg–1, 44–56% higher than those of conventional cathodes such as LiMn2O4, LiCoO2, and LiFePO4. Furthermore, the 3D architectures retain good structural integrity upon cycling, the researchers reported in their paper in the ACS journal Nano Letters.
Although low-dimensional nanomaterials, such as 0D nanoparticles, 1D nanostructures (nanowires, nanorods, and nanotubes), and 2D nanomaterials (nanosheets, nanoflakes) have shown superior electrochemical performance in LIBs [Li-ion batteries], they still suffer from self-aggregation and pulverization, which lead to poor cycling stability. One effective way out is to assemble nano building blocks into a robust 3D architecture (nano-0D/1D ⊂ micro-3D), which synergistically combines the advantages of both nanostructures and micro-structures. In such structures, Li+ insertion/extraction is much faster than that in the bulk counterpart because of the nanoscaled dimension, while the 3D architecture at the submicrometer or micrometer scale can effectively avoid the self-aggregation of active nanomaterials.—Ding et al.
Vanadium oxides have been extensively studied due to multiple vanadium oxidation states (V2+, V3+, V4+, V5+), high specific capacities, low cost and wide availability, the authors note. Mixed-valence V6 O13 is a relatively less-studied vanadium oxide, although it has shown better electrochemical performance.
Theoretically, V6O13 can electrochemically incorporate up to 8 Li per formula unit with all the V ions being reduced to 3+ oxidation state, yielding a high theoretical specific capacity and energy of 417 mAh g-1 and 900 Wh kg-1, respectively— much higher than LiMn2O4 (148 mAh g−1, 500 Wh kg−1), LiCoO2 (140 mAh g−1, 540 Wh kg−1), or LiFePO4 (170 mAh g−1, 500 Wh kg−1). V6O13 also has a metallic character at room temperature, which is beneficial for high-rate charge and discharge, the authors said.
Nevertheless, as a mixed-valence vanadium oxide, it faces the challenges of controllable structural synthesis. … as mentioned previously, the large volume expansion/contraction of simplex nanostructure during Li+ intercalation and deintercalation results in self-aggregation or pulverization that may interrupt the electronic and ionic contact pathways in the electrodes, leading to a rapid capacity fading. Hence, it is highly desirable to build an electrode that consists of a robust 3D cross-linked architecture assembled by continuous interconnected 1D nanoscaled building blocks, which provide not only direct and rapid electron/ion transport pathways in the radial direction, but also long-range electron conduct channels along the axis direction. … The fabrication of 3D V6O13 architectures with interconnected nanoscaled building blocks through a simple synthesis procedure remains a great challenge.—Ding et al.
The researchers fabricated their 3D materials via a facile solution-redox-based self-assembly route at room temperature. The materials feature mesh structures resulting from the formation and simultaneous self-assembly of vanadium oxide nanogrooves. The mesh size in the textile structure can be controllably tuned by adjusting the precursor concentration.
|Schematic illustration of the formation of 3D V6O13 nanotextiles constructed by interconnected nanogrooves. Credit: ACS, Ding et al. Click to enlarge.|
The team attributed the formation of the 3D fabric structure to the rolling and self-assembly processes of produced V6O13 nanosheet intermediates. The researchers also said that the excellent electrochemical performance of the nanotextiles might be related to the structure in several ways:
Nanogrooves offer adequate electrode and electrolyte contact and facilitate rapid electron/ion transport. Furthermore, the cross-linked networks provide continuous electronic migration pathways in all directions.
A large number of nanomesh in the 3D nanotextile architecture is favorable for the penetration of electrolyte into the whole 3D structure and also for accommodating volume changes upon cycling. Self-aggregation of nanogrooves can be effectively impeded or mitigated due to the mechanical stability of cross-linked networks.
Compact textured architectures exhibit a relatively high packing density and deliver high volumetric energy and power density.
When employed as cathodes in LIBs, the 3D nanotextiles exhibit excellent lithium storage properties and also maintain the structural integrity upon cycling. Such findings show the usefulness of combining different dimensionalities on different length scales, a future that offers a great potential for further optimization.—Ding et al.
Yuan-Li Ding, Yuren Wen, Chao Wu, Peter A. van Aken, Joachim Maier, and Yan Yu (2015) “3D V6O13 Nanotextiles Assembled from Interconnected Nanogrooves as Cathode Materials for High-Energy Lithium Ion Batteries” Nano Letters doi: 10.1021/nl504705z