Boston College team demonstrates nanonet-based heterostructure strategy for high-performance Li-ion cathode materials; high-power and high-capacity vanadium oxide electrode
Using a highly conductive two-dimensional TiSi2 nanonet technology they had earlier developed, a team from Boston College has synthesized a vanadium oxide (V2O5)-based cathode material that demonstrates a specific capacity of 350 mAh/g, a power rate of 14.5 kW/kg, and capacity retention of 78% after 9,800 cycles of repeated charge/discharge. In a paper published in the journal ACS Nano, they note that these results demonstrate “a cathode material significantly better than V2O5 of other morphologies.”
The strategy of having multiple components at the nanoscale—heteronanostructures—offers a critical advantage of achieving desired electronic and ionic properties on the same material by tailoring the constituent components, the team suggests in its paper.
Nanoscale materials are expected to contribute significantly to realizing an important goal in the lithium ion battery research of achieving high capacity and power rate and long cycle lifetime simultaneously...How to solve these issues in a concerted fashion, however, remains a challenge because they are intricately correlated at relevant length scales (e.g., charge and ionic behaviors at the nanoscale). Here we present a strategy that has the potential to meet this challenge.
...The key to our design is the capability to control the features of materials on multiple levels concurrently. At the atomic scale, we use Ti-doping to stabilize V2O5 upon lithiation and delithiation, which dramatically improves the cycle lifetime. At the nanoscale, the material is composed of more than one component, each designed for a specific function, the TiSi2 nanonet for charge transport, the Ti-doped V2O5 nanoparticle as the ionic host, and the SiO2 coating as a protection to prevent Li+ from reacting with TiSi2, which otherwise would lead to the destruction of the nanostructures. The strategy of having multiple components at the nanoscale offers a critical advantage of achieving desired electronic and ionic properties on the same material by tailoring the constituent components.—Zhou et al.
Zhou et al. say that their work, compared to other work using nanostructures, is distinguished by at least three features:
The two-dimensional TiSi2 nanonet inorganic framework is highly unique. The combination of mechanical strength and flexibility exhibited by the nanonet may be ideal for energy storage applications, they suggest.
The seemingly complex design is realized through simple chemical synthesis, without the involvement of catalysts or templates.
The combined power rate, specific capacity, and cycle lifetime render the nanonet-based nanostructure one of the highest performing cathode materials.
They used V2O5 to demonstrate the design principle because the addition of the conductive framework (TiSi2 nanonets) “is particularly useful to solve the key issues of poor conductivity and slow Li+ diffusion that limit the performance of V2O.”
Ti-doping stabilizes V2O5, and the SiO2 layer shields TiSi2 from the electrolyte. More critically, Zhou et al. concluded, the unique two-dimensional nanonet platform bridges different length scales from the nanoscale to the micro/macro scale.
By introducing a dedicated charge transporter, we were able to separate charge and ionic behaviors and thereby obtain unprecedented high power and high capacity on a cathode material that can be cycled extensively. We emphasize our strategy is highly modular, and other high performance cathode compounds (such as LiFePO4) should be readily integrated into the nanonet-based design. Our results demonstrated that advanced functional materials can be obtained by simple chemical synthesis. This approach should be highly complementary to existing efforts of finding highly performing compounds as battery electrode materials.—Zhou et al.
Sa Zhou, Xiaogang Yang, Yongjing Lin, Jin Xie, and Dunwei Wang (2011) A Nanonet-Enabled Li Ion Battery Cathode Material with High Power Rate, High Capacity, and Long Cycle Lifetime. ACS Nano doi: 10.1021/nn204479n