P2-Type Moisture-Stable and High-Voltage-Tolerable Cathodes for High-Energy and Long-Life Sodium-Ion Batteries.

P2-Na0.67Ni0.33Mn0.67O2 represents a promising cathode for Na-ion batteries, but it suffers from severe structural degradation upon storing in a humid atmosphere and cycling at a high cutoff voltage. Here we propose an in situ construction to achieve simultaneous material synthesis and Mg/Sn cosubstitution of Na0.67Ni0.33Mn0.67O2 via one-pot solid-state sintering. The materials exhibit superior structural reversibility and moisture insensitivity. In-operando XRD reveals an essential correlation between cycling stability and phase reversibility, whereas Mg substitution suppressed the P2-O2 phase transition by forming a new Z phase, and Mg/Sn cosubstitution enhanced the P2-Z transition reversibility benefiting from strong Sn-O bonds. DFT calculations disclosed high chemical tolerance to moisture, as the adsorption energy to H2O was lower than that of the pure Na0.67Ni0.33Mn0.67O2. A representative Na0.67Ni0.23Mg0.1Mn0.65Sn0.02O2 cathode exhibits high reversible capacities of 123 mAh g-1 (10 mA g-1), 110 mAh g-1 (200 mA g-1), and 100 mAh g-1 (500 mA g-1) and a high capacity retention of 80% (500 mA g-1, 500 cycles).

Ultrafast Charge-Discharge Capable and Long-Life Na3.9 Mn0.95 Zr0.05 V(PO4 )3 /C Cathode Material for Advanced Sodium-Ion Batteries.

Na4 MnV(PO4 )3 /C (NMVP) has been considered an attractive cathode for sodium-ion batteries with higher working voltage and lower cost than Na3 V2 (PO4 )3 /C. However, the poor intrinsic electronic conductivity and Jahn-Teller distortion caused by Mn3+ inhibit its practical application. In this work, the remarkable effects of Zr-substitution on prompting electronic and Na-ion conductivity and also structural stabilization are reported. The optimized Na3.9 Mn0.95 Zr0.05 V(PO4 )3 /C sample shows ultrafast charge-discharge capability with discharge capacities of 108.8, 103.1, 99.1, and 88.0 mAh g-1 at 0.2, 1, 20, and 50 C, respectively, which is the best result for cation substituted NMVP samples reported so far. This sample also shows excellent cycling stability with a capacity retention of 81.2% at 1 C after 500 cycles. XRD analyses confirm the introduction of Zr into the lattice structure which expands the lattice volume and facilitates the Na+ diffusion. First-principle calculation indicates that Zr modification reduces the band gap energy and leads to increased electronic conductivity. In situ XRD analyses confirm the same structure evolution mechanism of the Zr-modified sample as pristine NMVP, however the strong ZrO bond obviously stabilizes the structure framework that ensures long-term cycling stability.

Single-Handed Double Helix and Spiral Platelet Formed by Racemate of Dissymmetric Cages.

Spontaneous deracemization has been used to separate homochiral domains from the racemic system. However, homochirality can only be referred to when the scales of these domains and systems are specified. To clarify this, we report self-assembly of racemates of dissymmetric cages DC-1 with a cone-shape propeller geometry, forming a centrosymmetric columnar crystalline phase (racemic at crystallographic level). Owing to their anisotropic geometry, the two enantiomers are packed in a frustrated fashion in this crystalline phase; single-handed double helices are observed (single-handedness at supramolecular level). The frustrated packing (layer continuity break-up) in turn facilitates screw dislocation during the crystal growth, forming left- or right-handed spiral platelets (symmetry-breaking at morphological level), although each platelet is composed of DC-1 racemates. The symmetry correlation between DC-1 molecules, the crystalline phase and spiral platelets, all exhibit C3 symmetry.

Improved Cycling Performance of P2-Na0.67Ni0.33Mn0.67O2 Based on Sn Substitution Combined with Polypyrrole Coating.

P2-Na0.67Ni0.33Mn0.67O2 presents high working voltage with a theoretical capacity of 173 mAh g-1. However, the lattice oxygen on the particle surface participates in the redox reactions when the material is charged over 4.22 V. The resulting oxidized oxygen aggravates the electrolyte decomposition and transition metal dissolution, which cause severe capacity decay. The commonly reported cation substitution methods enhance the cycle stability by suppressing the high voltage plateau but lead to lower average working voltage and reduced capacity. Herein, we stabilized the lattice oxygen by a small amount of Sn substitution based on the strong Sn-O bond without sacrificing the high voltage performance and further protected the particle surface by polypyrrole (PPy) coating. The obtained Na0.67Ni0.33Mn0.63Sn0.04O2@PPy (3.3 wt %) composite showed excellent cycling stability with a reversible capacity of 137.6 (10) and 120.0 mAh g-1 (100 mA g-1) with a capacity retention of 95% (10 mA g-1, 50 cycles) and 82.5% (100 mA g-1, 100 cycles), respectively. The present work indicates that slight Sn substitution combined with PPy coating could be an effective approach to achieving superior cycling stability for high-voltage layered transition metal oxides.

Suppressing H2 evolution by using a hydrogel for reversible Na storage in Na3V2(PO4)3.

We report a low-cost hydrogel electrolyte by adding 3 wt% poly(acrylate sodium) (PAAS) into 1 M Na2SO4 aqueous electrolyte, which achieves a widened electrochemical stability window (ESW) of 2.45 V on stainless steel current collector from 2.12 V in 1 M Na2SO4 aqueous electrolytes (AE). Moreover, the H2 evolution potential reaches -1.75 V vs. Ag/AgCl on titanium current collector. The results reveal that the polymer network structure of PAAS has the ability to interact with water molecules and thus the hydrogen evolution reaction can be limited effectively, which broadens the ESW of aqueous electrolyte and allows the reversible Na-ion intercalation/deintercalation of Na3V2(PO4)3 as an anode material in aqueous electrolyte reported for the first time.

Multifunctional optical sensing probes based on organic-inorganic hybrid composites.

Several hybrid sensing materials, which are prepared by the covalent grafting of organic fluorescent molecules onto inorganic supports, have emerged as a novel and promising class of hybrid sensing probes and have attracted tremendous interest. In comparison to the organic fluorescent sensors, the hybrid sensing probes incorporate the beneficial chemical/physical properties of the organic molecules and inorganic materials, which accelerate the development of hybrid materials for ion recognition and removal. Hence, the novel hybrid sensing materials can selectively monitor and efficiently remove specific analytes, which can provide a novel opportunity to synthesize multifunctional hybrid materials. Considerable efforts have been devoted to developing effective and innovative approaches for the design and synthesis of hybrid sensing materials that can display highly desirable performance for ion detection and removal. This tutorial review firstly presents a brief description of the hybrid materials and mesoporous silica materials and then classifies the hybrid sensing materials into several categories, including mesoporous silica based hybrid sensors, magnetic core-shell particle based hybrid sensors, magnetic nanoparticle based hybrid sensors, polymer based hybrid sensors, surface-grafted composite based hybrid sensors, and host-guest interaction based hybrid sensors, followed by a detailed summary of the design and synthesis of hybrid sensing materials and their applications in environmental and biological fields. Hopefully, this review will provide perspectives and guidelines for the development and further research of hybrid sensing materials.

Preparation and characterization of OSA/CS core-shell microgel: in vitro drug release and degradation properties.

Cationic polymers have been widely used as drug delivery systems. Herein, an oxidized sodium alginate/chitosan (OSA/CS) core-shell microgel was prepared via water-in-oil emulsion method. Morphological properties of the resulting microgel were determined by transmission electron microscopy, hydrodynamic diameter of the microgel was characterized by dynamic light scattering. The objective of this work was to achieve the colon-specific delivery of an antiulcerative colitis drug using a fully nontoxic carrier. 5-aminosalicylic acid (5-ASA) was chosen as a model drug, which is rapidly absorbed before entering the colon, thus it is necessary to develop a colon-specific delivery system for it. The in vitro drug release profile was established in buffer solutions with 0.1 M HCl/NaCl (pH 1.2) and 0.1 M phosphate buffered saline (pH 7.4) at 37 °C. The results indicated that this OSA/CS core-shell microgel inhibited the release of 5-ASA in stomach to a certain extent and is degradable in physiological conditions. Due to the excellent biocompatible nature of CS and OSA, this core-shell microgel has good biocompatibility and may have potential applications in oral controlled drug delivery systems.

A convenient way to synthesize comb-shaped chitosan-graft-poly (N-isopropylacrylamide) copolymer.

Comb-shaped copolymers comprised of hydrophobic and hydrophilic blocks are self-assembled in aqueous solution, which results that they are suitable for delivery of hydrophobic drug molecules. Chitosan (CS) is an important biomaterial used widely in medical applications. Herein, a comb-shaped cationic copolymer composed of long biocompatible CS main chains and short PNIPAAm side chains was prepared via atom transfer radical polymerization (ATRP) by attaching an ATRP initiating group to N-phthaloyl chitosan. By subsequent removal of the protective groups on N-phthaloyl chitosan-graft-poly(N-isopropylacrylamide) (PHCS-g-PNIPAAm) copolymer with N(2)H(4)·H(2)O lead to the polymer pendant amino groups, this study attempted to synthesize a pH/temperature multi-responsive material. This chitosan-graft-poly(N-isopropylacrylamide) (CS-g-PNIPAAm) copolymer is self-assembled in aqueous solution into stimuli-responsive core-shell micelles with hydrodynamic diameters of about 170 nm. Structural organization and solution behavior were then investigated utilizing (1)H NMR spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering (DLS).