A densely packed air-stable free-standing film with FeP nanoparticles@C@P-doped reduced graphene oxide for sodium-ion batteries.

Developing a facile strategy which enhances the structural stability and air/moisture stability of transition metal phosphides for practical applications is important but challenging. Herein, we designed a densely packed free-standing film consisting of carbon-coated FeP nanoparticles anchored on P-doped graphene (FeP@C@PG film) through solventless thermal decomposition and the roll-press method. Phytic acid serves a multifunctional role as both a phosphorus source to prepare ultrafine FeP nanoparticles and a protective layer to improve air stability along with hydrophobic graphene and maximize the utilization of phosphide. This structure can enhance electron/ion transport kinetics, allowing for full utilization of active materials, and buffer large volume expansions while preventing pulverization/aggregation during cycling. Noticeably, the densely packed structure can greatly enhance oxidation resistance by effectively blocking the penetration of air/moisture. Therefore, the FeP@C@PG film delivers a stable reversible capacity of 536.6 mA h g-1 after 1000 cycles at 1 A g-1 with good capacity retention, an excellent rate capability of 440.7 mA h g-1 at 5 A g-1, and excellent oxidation stability at 80 °C in air. Furthermore, a pouch-type full-cell exhibits excellent rate/cycling performance and bendability. This study provides a new direction for the rational design and practical applications of advanced P-based materials used in alkali metal-ion batteries.

An expanded sandwich-like heterostructure with thin FeP nanosheets@graphene via charge-driven self-assembly as high-performance anodes for sodium ion battery.

In this work, we simply fabricate a novel expanded sandwich-like heterostructure of iron-phosphide nanosheets in between reduced graphene oxide (expanded FeP NSs@rGO) with a high ratio of FeP/Fe-POx and an expanded structure via a charge-driven self-assembly method by exploiting polystyrene beads (PSBs) as a sacrificial template. In such a design, even after the decomposition of PSBs during the annealing process, the PSBs successfully provide ample space between the nanosheets, enabling a structure with long-term stability and high ionic conductivity. Importantly, the PSBs are decomposed and simultaneously reacted with oxidized iron-phosphide (Fe-POx) on the surface of the nanosheets to reduce into FeP. As a result, the expanded FeP NSs@rGO results in a high content of FeP (52.3%) and remarkable electrochemical performances when it is used for sodium-ion battery anodes. The expanded FeP NSs@rGO exhibits a high capacity of 916.1 mA h g-1 at 0.1 A g-1, a superior rate capability of 440.9 mA h g-1 at 5 A g-1, and a long-term cycling stability of 85.4% capacity retention after 1000 cycles at 1 A g-1. In addition, the full cell also exhibits excellent capacity, rate capability, and cycling stability. This study clearly demonstrates that an increase in FeP proportion is directly related to an increase in capacity. This facile method of synthesizing rationally designed heterostructures is expected to provide a novel strategy to create nanostructures for advanced energy storage applications.

Design and synthesis of amorphous SiOx structures generated by Sn quantum dots: growth mechanism and luminescent origin.

SiOx structures with different diameters of a few hundreds of nanometers and/or a few micrometers are prepared using applied thermal evaporation. Subsequently, Sn quantum dot-based SiOx architectures are synthesized via the continuous steps of the carbothermal reduction of SnO2, substitution of Sn(4+) for In(3+), thermal oxidation of Si, Sn sublimation, interfacial reaction, and diffusion reaction consistent with corresponding phase equilibriums. Several crystalline and spherical-shaped Sn quantum dots with diameters between 2 and 7 nm are observed in the amorphous SiOx structures. The morphological evolution, including hollow Sn (or SnOx) sphere and wire-like, worm-like, tube-like, and flower-like SiOx, occurs stepwise on the Si substrate upon increasing the given process energies. The optical characteristics based on confocal measurements reveal the as-synthesized SiOx structures, irrespective of whether crystallinity is formed, which all have visible-range emissions originating from the numerous different-sized and -shaped Sn quantum dots permeating into the SiOx matrix. In addition, photoluminescence emissions ranging between ultraviolet and red regions are in agreement with confocal measurements. The origins of the morphology- and luminescence-controlled amorphous SiOx with Sn quantum dots are also discussed.

Growth Mechanism and Luminescent Properties of Amorphous SiOx Structures via Phase Equilibrium in Binary System.

Balloon whisk-like and flower-like SiOx tubes with well-dispersed Sn and joining countless SiOx loops together induce intense luminescence characteristics in substrate materials. Our synthetic technique called "direct substrate growth" is based on pre-contamination of the surroundings without the intended catalyst and source powders. The kind of supporting material and pressure of the inlet gases determine a series of differently functionalized tube loops, i.e., the number, length, thickness, and cylindrical profile. SiOx tube loops commonly twist and split to best suppress the total energy. Photoluminescence and confocal laser measurements based on quantum confinement effect of the embedded Sn nanoparticles in the SiOx tube found substantially intense emissions throughout the visible range. These new concepts related to the synthetic approach, pre-pollution, transitional morphology, and permeable nanoparticles should facilitate progress in nanoscience with regard to tuning the dimensions of micro-/nanostructure preparations and the functionalization of customized applications.