Substantial oxygen loss and chemical expansion in lithium-rich layered oxides at moderate delithiation.

Delithiation of layered oxide electrodes triggers irreversible oxygen loss, one of the primary degradation modes in lithium-ion batteries. However, the delithiation-dependent mechanisms of oxygen loss remain poorly understood. Here we investigate the oxygen non-stoichiometry in LiNiMnCoO electrodes as a function of Li content by using cycling protocols with long open-circuit voltage steps at varying states of charge.

Beyond Constant Current: Origin of Pulse-Induced Activation in Phase-Transforming Battery Electrodes.

Mechanistic understanding of phase transformation dynamics during battery charging and discharging is crucial toward rationally improving intercalation electrodes. Most studies focus on constant-current conditions. However, in real battery operation, such as in electric vehicles during discharge, the current is rarely constant.

Highly Efficient Uniaxial In-Plane Stretching of a 2D Material via Ion Insertion.

On-chip dynamic strain engineering requires efficient micro-actuators that can generate large in-plane strains. Inorganic electrochemical actuators are unique in that they are driven by low voltages (≈1 V) and produce considerable strains (≈1%). However, actuation speed and efficiency are limited by mass transport of ions.

Fictitious phase separation in Li layered oxides driven by electro-autocatalysis.

Layered oxides widely used as lithium-ion battery electrodes are designed to be cycled under conditions that avoid phase transitions. Although the desired single-phase composition ranges are well established near equilibrium, operando diffraction studies on many-particle porous electrodes have suggested phase separation during delithiation. Notably, the separation is not always observed, and never during lithiation.

Metal-oxygen decoordination stabilizes anion redox in Li-rich oxides.

Reversible high-voltage redox chemistry is an essential component of many electrochemical technologies, from (electro)catalysts to lithium-ion batteries. Oxygen-anion redox has garnered intense interest for such applications, particularly lithium-ion batteries, as it offers substantial redox capacity at more than 4 V versus Li/Li in a variety of oxide materials. However, oxidation of oxygen is almost universally correlated with irreversible local structural transformations, voltage hysteresis and voltage fade, which currently preclude its widespread use.

Fluid-enhanced surface diffusion controls intraparticle phase transformations.

Phase transformations driven by compositional change require mass flux across a phase boundary. In some anisotropic solids, however, the phase boundary moves along a non-conductive crystallographic direction. One such material is LiFePO, an electrode for lithium-ion batteries.

Electrochemical trapping of metastable Mn ions for activation of MnO oxygen evolution catalysts.

Electrodeposited manganese oxide films are promising catalysts for promoting the oxygen evolution reaction (OER), especially in acidic solutions. The activity of these catalysts is known to be enhanced by the introduction of Mn We present in situ electrochemical and X-ray absorption spectroscopic studies, which reveal that Mn may be introduced into MnO by an electrochemically induced comproportionation reaction with Mn and that Mn persists in OER active films. Extended X-ray absorption fine structure (EXAFS) spectra of the Mn-activated films indicate a decrease in the Mn-O coordination number, and Raman microspectroscopy reveals the presence of distorted Mn-O environments.

Prompt and synergistic antibacterial activity of silver nanoparticle-decorated silica hybrid particles on air filtration.

There is a significant need for materials that promptly exhibit antimicrobial activity upon contact. The large-scale fabrication of monodisperse silver nanoparticle (AgNP)-decorated silica (AgNP@SiO) hybrid particles, and their prompt and synergistic antibacterial activity against both the Gram-negative bacteria Escherichia coli and the Gram-positive bacteria Staphylococcus epidermidis on air filtration units are presented. Monodisperse aminopropyl-functionalized silica colloids (406 nm) were used as a support material and were hybridized with AgNPs using a seeding, sorting-out, and growing strategy with Ag seeds (1-2 nm) into ∼30 nm AgNPs, successfully yielding 51 g of AgNP@SiO hybrid particles.

Facile synthesis of intense green light emitting LiGdF4:Yb,Er-based upconversion bipyramidal nanocrystals and their polymer composites.

A pathway for achieving intense green light emitting LiGdF4:Yb,Er upconversion nanophosphors (UCNPs) via Y(3+) doping is demonstrated. It was revealed that Y(3+) doping initiated the formation of a tetragonal phase and affected the particle size. Single tetragonal-phase LiGd0.

Highly bright multicolor tunable ultrasmall β-Na(Y,Gd)F₄:Ce,Tb,Eu/β-NaYF₄ core/shell nanocrystals.

Herein, we report highly bright multicolor-emitting β-Na(Y,Gd)F₄:Ce,Tb,Eu/β-NaYF₄ nanoparticles (NPs) with precise color tunability. First, highly bright sub-20 nm β-Na(Y,Gd)F₄:Ce,Tb,Eu NPs were synthesized via a heating-up method. By controlling the ratio of Eu(3+) to Tb(3+), we generated green, yellow-green, greenish yellow, yellow, orange, reddish orange, and red emissions from the NP solutions via energy transfer of Ce(3+)→ Gd(3+)→ Tb(3+) (green) and Ce(3+)→ Gd(3+)→ Tb(3+)→ Eu(3+) (red) ions under ultraviolet light illumination (254 nm).

Rational morphology control of β-NaYF4:Yb,Er/Tm upconversion nanophosphors using a ligand, an additive, and lanthanide doping.

We report the systematic control of the morphology of β-NaYF4:Yb,Er/Tm upconversion nanophosphors (UCNPs) from large spheres (37.9 nm) to rods (length = 60.1 nm, width = 21.

Synthesis of blue emitting InP/ZnS quantum dots through control of competition between etching and growth.

Blue (<480 nm) emitting Cd-free quantum dots (QDs) are in great demand for various applications. However, their synthesis has been challenging. Here we present blue emitting InP/ZnS core/shell QDs with a band edge emission of 475 nm and a full width at half maximum of 39 nm (215 meV) from their quantum confined states.

Effect of surface tension and coefficient of thermal expansion in 30 nm scale nanoimprinting with two flexible polymer molds.

We report on nanoimprinting of polymer thin films at 30 nm scale resolution using two types of ultraviolet (UV)-curable, flexible polymer molds: perfluoropolyether (PFPE) and polyurethane acrylate (PUA). It was found that the quality of nanopatterning at the 30 nm scale is largely determined by the combined effects of surface tension and the coefficient of thermal expansion of the polymer mold. In particular, the polar component of surface tension may play a critical role in clean release of the mold, as evidenced by much reduced delamination or broken structures for the less polarized PFPE mold when patterning a relatively hydrophilic PMMA film.

Facile synthesis and optical properties of colloidal silica microspheres encapsulating a quantum dot layer.

We present colloidal silica microspheres encapsulating a homogeneous quantum dot layer at radial equidistance from the centre by utilizing electrostatic interaction between surface-engineered silica microspheres and QDs. The microspheres show dramatically enhanced optical absorption and emission with an appropriate silica shell thickness.

Enhanced biomolecular detection based on localized surface plasmon resonance (LSPR) using enzyme-precipitation reaction.

An enzyme-catalyzed precipitation reaction was employed as a means to increase the change in the LSPR signal after intermolecular bindings between antigens and antibodies occurred on gold nanodot surfaces. The gold nanodot array with an diameter of 175 nm and a thickness of 20 nm was fabricated on a glass wafer using thermal nanoimprint lithography. The human interleukin (hIL) 5 antibody was immobilized on the gold nanodot, followed by binding of hIL 5 to the anti-hIL 5.

The fabrication scheme of a high resolution and high aspect ratio UV-nanoimprint mold.

We propose a new scheme of fabricating molds for UV-nanoimprint lithography (UV-NIL) that is both high resolution and has a high aspect ratio. The scheme involves the utilization of a hydrogen silsesquioxane (HSQ) electron beam resist for high resolution patterning and the sputter-deposited alpha-Si layer that defines the high-aspect-ratio mold pattern obtained from the high etch selectivity between the HSQ and the alpha-Si. We obtained high resolution line patterns and dot patterns with feature sizes of 40 nm and 25 nm, respectively.