Zhonghe Bi

Mesoporous TiO2–B Microspheres with Superior Rate Performance for Lithium Ion Batteries

Advanced energy storage systems such as lithium ion batteries are important approaches to mitigate energy shortage and global climate warming issues that the world is currently facing. High power and high energy density are essential to batteries for applications in electric vehicles, stationary energy storage systems for solar and wind energy as well as smart grids. Because conventional lithium ion batteries are inadequate to meet these needs, advanced materials with high capacity and fast chargedischarge capability are critical for next generation lithium ion batteries. [ 1 ] Titanium dioxide (TiO 2 ) with various polymorphs (anatase, rutile, and TiO 2 –B (bronze)) have been widely investigated as lithium ion battery anode materials, due to their advantages in terms of cost, safety and rate capability. [ 2 ] In particular, the polymorph of TiO 2 –B shows a favorable channel structure for lithium mobility, which results in fast chargedischarge capability of a lithium cell. [ 3 ] It has been identifi ed that the lithium intercalation in TiO 2 –B features a pseudocapacitive process, rather than the solid-state diffusion process observed for anatase and rutile. [ 4 ] Theoretical studies have uncovered that this pseudocapacitive behavior originates from the unique sites and energetics of lithium absorption and diffusion in TiO 2 –B structure. [ 5 ] As a result, TiO 2 –B nanoparticles, [ 6 ] nanotubes, [ 7 ]

Studies on supercapacitor electrode material from activated lignin-derived mesoporous carbon.

We synthesized mesoporous carbon from pre-cross-linked lignin gel impregnated with a surfactant as the pore-forming agent and then activated the carbon through physical and chemical methods to obtain activated mesoporous carbon. The activated mesoporous carbons exhibited 1.5- to 6-fold increases in porosity with a maximum Brunauer-Emmett-Teller (BET) specific surface area of 1148 m(2)/g and a pore volume of 1.0 cm(3)/g. Both physical and chemical activation enhanced the mesoporosity along with significant microporosity. Plots of cyclic voltammetric data with the capacitor electrode made from these carbons showed an almost rectangular curve depicting the behavior of ideal double-layer capacitance. Although the pristine mesoporous carbon exhibited a range of surface-area-based capacitance similar to that of other known carbon-based supercapacitors, activation decreased the surface-area-based specific capacitance and enhanced the gravimetric specific capacitance of the mesoporous carbons. A vertical tail in the lower-frequency domain of the Nyquist plot provided additional evidence of good supercapacitor behavior for the activated mesoporous carbons. We have modeled the equivalent circuit of the Nyquist plot with the help of two constant phase elements (CPE). Our work demonstrated that biomass-derived mesoporous carbon materials continue to show potential for use in specific electrochemical applications.

High performance Cr, N-codoped mesoporous TiO2 microspheres for lithium-ion batteries

Cr, N-codoped TiO2 mesoporous microspheres have been successfully synthesized by a facile hydrothermal reaction followed by annealing under an ammonia atmosphere. Through introduction of Cr, the nitrogen doping level was increased from 2.81 at.% for N-doped TiO2 to 5.68 at.% for Cr, N-codoped TiO2, which improves the electrical conductivity of TiO2. When used as an anode for lithium-ion rechargeable batteries, the Cr, N-codoping TiO2 microspheres led to an enhanced performance of 159.6 mA h g−1 at 5 C with a drop of less than 1% after 300 cycles.

Orienting oxygen vacancies for fast catalytic reaction.

A strategy to enhance the catalytic activity at the surface of an oxide thin film is unveiled through epitaxial orientation control of the surface oxygen vacancy concentration. By tuning the direction of the oxygen vacancy channels (OVCs) in the brownmillerite SrCoO2.5 , a 100-fold improvement in the oxygen reduction kinetics is realized in an epitaxial thin film that has the OVCs open to the surface.

Tailored recovery of carbons from waste tires for enhanced performance as anodes in lithium-ion batteries

Morphologically tailored pyrolysis-recovered carbon black is utilized in lithium-ion battery anodes with improved capacity as a potential solution for adding value to waste tire-rubber-derived materials. Micronized tire rubber was digested in a hot oleum bath to yield a sulfonated rubber slurry that was then filtered, washed, and compressed into a solid cake. Carbon was recovered from the modified rubber cake by pyrolysis in a nitrogen atmosphere. The chemical pretreatment of rubber produced a carbon monolith with higher yield than that from the control (a fluffy tire-rubber-derived carbon black). The carbon monolith showed a very small volume fraction of pores of widths 3–5 nm, prominent nanoporosity (pore width < 2 nm), reduced specific surface area, and an ordered assembly of graphitic domains. Electrochemical studies revealed that the recovered-carbon-based anode had a higher reversible capacity than that of graphite. Anodes made with a sulfonated tire-rubber-derived carbon and a control tire-rubber-derived carbon exhibited an initial coulombic efficiency of 71% and 45%, respectively. The reversible capacity of the cell with the sulfonated tire rubber-derived carbon as the anode was 390 mA h g−1 after 100 cycles, with nearly 100% coulombic efficiency. Our success in producing a higher performance carbon material from waste tire rubber for potential use in energy storage applications adds a new avenue to tire rubber recycling.

A POM–organic framework anode for Li-ion battery

Rechargeable Li-ion batteries (LIBs) are currently the dominant power source for portable electronic devices and electric vehicles, and for small-scale stationary energy storage. However, one bottleneck of the anode materials for LIBs is the poor cycling performance caused by the fact that the anodes cannot maintain their integrity over several charge–discharge cycles. In this work, we demonstrate an approach to improving the cycling performance of lithium-ion battery anodes by constructing an extended 3D network of flexible redox active polyoxometalate (POM) clusters with redox active organic linkers, herein described as POMOF. This architecture enables the accommodation of large volume changes during cycling at relatively high current rates. For example, the POMOF anode exhibits a high reversible capacity of 540 mA h g−1 after 360 cycles at a current rate of 0.25C and a long cycle life at a current rate of 1.25C (>500 cycles).

An integrated approach for structural characterization of complex solid state electrolytes: the case of lithium lanthanum titanate

Neutron scattering and first principles simulation are integrated to reveal the atomic-level to nano-scale structure of lithium lanthanum titanate (LLTO), a representative solid electrolyte material with applications in Li-ion batteries. The integrated approach solves the hierarchical local structure of LLTO in detail, including the coupled chemical order and topological distortion, as well as their correlation length scale and the spatial modulation with coherent boundaries. Ab initio molecular dynamics simulations are used to map out the distribution of the mobile ions and identify the migration pathway. Overall, this integrated approach provides powerful means for detailed study of materials with complex local chemical and topological environment.

In situ TEM observation of the electrochemical lithiation of N-doped anatase TiO2 nanotubes as anodes for lithium-ion batteries

Due to their high specific capacity and negligible volume expansion during cycling, anatase titanium dioxide (a-TiO2) nanotubes have been considered as a prime candidate for anodes in lithium-ion batteries. However, their rate capability for electrochemical cycling is limited by the low electronic conductivity of a-TiO2 nanotubes. Here, we show that a desirable amount of nitrogen doping can significantly enhance the electronic conductivity in a-TiO2 nanotubes, resulting in improvements in both the capacity stability and the rate capability at fast charge–discharge rates. Electron energy loss spectroscopy revealed a high doping concentration of nitrogen (∼5%) by substituting for oxygen ions in a-TiO2 nanotubes. The lithiation mechanism of N-doped a-TiO2 nanotubes was further investigated using in situ transmission electron microscopy, where a three-step lithiation mechanism was revealed. Lithium ions initially intercalate into the a-TiO2 lattice structure. Further insertion of lithium ions triggers a phase transformation from a-TiO2 to orthorhombic Li0.5TiO2 and finally to polycrystalline tetragonal LiTiO2. Our results reveal that nitrogen doping significantly facilitates lithiation in TiO2 through enhanced electronic conductivity, while the structural and chemical evolutions during the lithiation process remain similar to those of undoped TiO2.

The influence of the local structure on proton transport in a solid oxide proton conductor La0.8Ba1.2GaO3.9

The local structure around the mobile ions influences their dynamics. The knowledge about the relationship between these properties is of fundamental importance and may lead the way for development of improved solid state ionic conductors. In this study, we use inelastic neutron scattering and ab initio modeling to study a representative proton conductor, La0.8Ba1.2GaO3.9, where different local structures are possible for the same stoichiometry. The intrinsic correlations between the local bonding environment and the dynamical behavior of protons are presented. In particular, we identify how the local Ba/La concentration affects the proton vibrational frequencies, hydrogen bond strength, O–H rotations and in turn long-range proton mobility. Further, possible mechanism for proton transport, through the inter-tetrahedral bond switching, O–H rotations and tetrahedral reorientation is anticipated.