Water-free titania-bronze thin films with superfast lithium-ion transport

Stable Supercapacity of Binder-Free TiO2(B) Epitaxial Electrodes for All-Solid-State Nanobatteries

Owing to its pseudocapacitive, unidimensional, rapid ion channels, TiO2(B) is a promising material for application to battery electrodes. In this study, we align these channels by epitaxially growing TiO2(B) films with the assistance of an isostructural VO2(B) template layer. In a liquid electrolyte, binder-free TiO2(B) epitaxial electrodes exhibit a supercapacity near the theoretical value of 335 mA h g-1 and an excellent charge-discharge reproducibility for ≥200 cycles, which outperform those of other TiO2(B) nanostructures. For the all-solid-state configuration employing the LiPON solid electrolyte, excellent stability persists. Our findings suggest excellent potential for miniaturizing all-solid-state nanobatteries in self-powered integrated circuits.

Nanostructure and Advanced Energy Storage: Elaborate Material Designs Lead to High-Rate Pseudocapacitive Ion Storage

The drastic need for development of power and electronic equipment has long been calling for energy storage materials that possess favorable energy and power densities simultaneously, yet neither capacitive nor battery-type materials can meet the aforementioned demand. By contrast, pseudocapacitive materials store ions through redox reactions with charge/discharge rates comparable to those of capacitors, holding the promise of serving as electrode materials in advanced electrochemical energy storage (EES) devices. Therefore, it is of vital importance to enhance pseudocapacitive responses of energy storage materials to obtain excellent energy and power densities at the same time. In this Review, we first present basic concepts and characteristics about pseudocapacitive behaviors for better guidance on material design researches. Second, we discuss several important and effective material design measures for boosting pseudocapacitive responses of materials to improve rate capabilities, which mainly include downsizing, heterostructure engineering, adding atom and vacancy dopants, expanding interlayer distance, exposing active facets, and designing nanosheets. Finally, we outline possible developing trends in the rational design of pseudocapacitive materials and EES devices toward high-performance energy storage.

Tunable Pseudocapacitance in 3D TiO2-δ Nanomembranes Enabling Superior Lithium Storage Performance

Nanostructured TiO₂ of different polymorphs, mostly prepared by hydro/solvothermal methods, have been extensively studied for more than a decade as anode materials in lithium ion batteries. Enormous efforts have been devoted to improving the electrical conductivity and lithium ion diffusivity in chemically synthesized TiO₂ nanostructures. In this work we demonstrate that 3D Ti³⁺-self-doped TiO₂ (TiO_2-δ) nanomembranes, which are prepared by physical vapor deposition combined with strain-released rolled-up technology, have a great potential to address several of the long-standing challenges associated with TiO₂ anodes. The intrinsic electrical conductivity of the TiO₂ layer can be significantly improved by the in situ generated Ti³⁺, and the amorphous, thin TiO₂ nanomembrane provides a shortened Li⁺ diffusion pathway. The fabricated material shows a favorable electrochemical reaction mechanism for lithium storage. Further, post-treatments are employed to adjust the Ti³⁺ concentration and crystallinity degree in TiO₂ nanomembranes, providing an opportunity to investigate the important influences of Ti³⁺ self-doping and amorphous structures on the electrochemical processes. With these experiments, the pseudocapacitance contributions in TiO₂ nanomembranes with different crystallinity degree are quantified and verified by an in-depth kinetics analysis. Additionally, an ultrathin metallic Ti layer can be included, which further improves the lithium storage properties of the TiO₂, giving rise to the state-of-the-art capacity (200 mAh g^-1 at 1 C), excellent rate capability (up to 50 C), and ultralong lifetime (for 5000 cycles at 10 C, with an extraordinary retention of 100%) of TiO₂ anodes.

Nanoscale self-templating for oxide epitaxy with large symmetry mismatch

Direct observations using scanning transmission electron microscopy unveil an intriguing interfacial bi-layer that enables epitaxial growth of a strain-free, monoclinic, bronze-phase VO₂(B) thin film on a perovskite SrTiO₃ (STO) substrate. We observe an ultrathin (2–3 unit cells) interlayer best described as highly strained VO₂(B) nanodomains combined with an extra (Ti,V)O₂ layer on the TiO₂ terminated STO (001) surface. By forming a fully coherent interface with the STO substrate and a semi-coherent interface with the strain-free epitaxial VO₂(B) film above, the interfacial bi-layer enables the epitaxial connection of the two materials despite their large symmetry and lattice mismatch.

Li intercalation mechanisms in CaTi5O11, a bronze-B derived compound

A first-principles study was performed to elucidate the electrochemical properties of CaTi₅O₁₁, a recently discovered compound that is a crystallographic variant of TiO₂(B) and that shows promise as an anode material for Li-ion batteries. The crystal structure of CaTi₅O₁₁ was further refined and two symmetrically distinct interstitial sites that can accommodate Li at positive voltage were identified. A statistical mechanics study relying on density functional theory (DFT) calculations predicted that interstitial Li in CaTi₅O₁₁ forms a solid solution with Li insertion resulting in a sloping voltage profile. Li diffusion within CaTi₅O₁₁ was found to be highly anisotropic with low barrier diffusion pathways forming one-dimensional channels parallel to the c axis.

Ultrafast Microwave Nano-manufacturing of Fullerene-Like Metal Chalcogenides

Metal Chalcogenides (MCs) have emerged as an extremely important class of nanomaterials with applications ranging from lubrication to energy storage devices. Here we report our discovery of a universal, ultrafast (60 seconds), energy-efficient, and facile technique of synthesizing MC nanoparticles and nanostructures, using microwave-assisted heating. A suitable combination of chemicals was selected for reactions on Polypyrrole nanofibers (PPy-NF) in presence of microwave irradiation. The PPy-NF serves as the conducting medium to absorb microwave energy to heat the chemicals that provide the metal and the chalcogenide constituents separately. The MCs are formed as nanoparticles that eventually undergo a size-dependent, multi-stage aggregation process to yield different kinds of MC nanostructures. Most importantly, this is a single-step metal chalcogenide formation process that is much faster and much more energy-efficient than all the other existing methods and can be universally employed to produce different kinds of MCs (e.g., MoS₂, and WS₂).

Reaction kinetics for the solid state synthesis of the AlH3/MgCl2 nano-composite by mechanical milling

The process of mechanical milling has been proved to be a cost-effective way to synthesize the AlH3/MgCl2 nano-composite by using MgH2 and AlCl3 as reagents. However, so far there is no comprehensive knowledge of the kinetics of this process. In an effort to predict the reaction progress and optimize the milling parameters, the kinetics of the synthesis of the AlH3/MgCl2 nano-composite by mechanical milling of MgH2 and AlCl3 is experimentally investigated in the present work. The reaction progress or the transformation fraction upon milling for different times is evaluated using the isothermal hydrogen desorption test of the as-milled samples at 220 °C, which is much lower than the threshold temperature for the de-hydriding of the reagent MgH2 but enough for the de-hydriding of the as-synthesized nano-sized AlH3. The effects of milling parameters on the reaction kinetics as well as the underlying mechanism are discussed by referring to the mechanical energy input intensity, the vial temperature and the Gibbs free energy change for the reaction. Furthermore, it is found that the Johnson-Mehl-Avrami (JMA) model can well describe the kinetics theoretically. By fitting the experimental data with the JMA expression, the theoretical kinetics expressions, the equation parameters, and the activation energy are obtained.

Creating high quality Ca:TiO2-B (CaTi5O11) and TiO2-B epitaxial thin films by pulsed laser deposition

Highly crystalline TiO₂-B/Ca:TiO₂-B dual layer fabricated by pulsed laser deposition.

Electroless deposition of Ni3P–Ni arrays on 3-D nickel foam as a high performance anode for lithium-ion batteries

The array structure of Ni₃P–Ni can accommodate volume changes during the lithiation/de-lithiation progress and promote high-rate capability because the interspaces in such structure can act as ideal volume expansion buffers.

Atomic structure of defects and interfaces in TiO2-B and Ca:TiO2-B (CaTi5O11) films grown on SrTiO3

An atomic-scale analysis of the interfacial structure and defects in CaTi₅O₁₁grown on SrTiO₃and TiO₂-B grown on CaTi₅O₁₁is presented.