Synthesis and modification mechanism of vanadium oxide coated LiFePO4cathode materials with excellent electrochemical performance.

In an era of rapid industrial development, such that the demand for energy is increasing daily, lithium-ion batteries are playing a dominant role in energy storage devices due to their high safety and low cost. However, it is still a challenge for the preparation of advanced cathodes, which can determine the battery performance, with stable structures and fast diffusion of Li+. This is especially the case for lithium iron phosphate (LFP), a cathode material with severe limitations due to its low conductive efficiency. To improve its conductivity, LFP was compounded with defect-modified V2O5to prepare LFP/V/C materials with excellent electrochemical properties, which exhibited an initial capacity of 138.85 mAh g-1and 95% retention after 500 charge/discharge cycles at a current density of 5 C. Also, the effect of defects on ionic diffusion was discussed in detail by means of density function theor (DFT) calculations, confirming that the improvement of electrochemical performance is closely related to the introduction of hybrid conductive layers of surface cladding.

High-Performance Alkali Metal Ion Storage in Bi2Se3 Enabled by Suppression of Polyselenide Shuttling Through Intrinsic Sb-Substitution Engineering.

Bismuth selenide holds great promise as a kind of conversion-alloying-type anode material for alkali metal ion storage because of its layered structure with large interlayer spacing and high theoretical specific capacity. Nonetheless, its commercial development has been significantly hammered by the poor kinetics, severe pulverization, and polyselenide shuttle during the charge/discharge process. Herein, Sb-substitution and carbon encapsulation strategies are simultaneously employed to synthesize SbxBi2-xSe3 nanoparticles decorated on Ti3C2Tx MXene with encapsulation of N-doped carbon (SbxBi2-xSe3/MX⊂NC) as anodes for alkali metal ion storage. The superb electrochemical performances could be assigned to the cationic displacement of Sb3+ that effectively inhibits the shuttling effect of soluble polyselenides and the confinement engineering that alleviates the volume change during the sodiation/desodiation process. When used as anodes for sodium- and lithium-ion batteries, the Sb0.4Bi1.6Se3/MX⊂NC composite exhibits superior electrochemical performances. This work offers valuable guidance to suppress the shuttling of polyselenides/polysulfides in high-performance alkali metal ion batteries with conversion/alloying-type transition metal sulfide/selenide anode materials.

Fe-doped V2O5layered nanowire cathode material with high lithium storage performance.

As a lithium-ion battery cathode material with high theoretical capacity, the application of V2O5is limited by its unstable structure and low intrinsic conductivity. In this paper, we report a Fe doped V2O5nanowire with a layered structure of 200-300 nm diameter prepared by electrostatic spinning technique. The 3Fe-V2O5electrode exhibited a superb capacity of 436.9 mAh g-1in the first cycle when tested in the voltage range of 2.0-4.0 V at current density of 100 mA g-1, far exceeding its theoretical capacity (294 mAh g-1), and the high capacity of 312 mAh g-1was still maintained after 50 cycles. The superb performance is mainly attributed to its unique layered nanowire structure and the enhanced electrical conductivity as well as optimized structure brought by Fe-doping. This work made the homogeneous doping and nanosizing of the material easily achieved through electrostatic spinning technology, leading to an increase in the initial capacity of the V2O5cathode material and the cycling stability compared to the pure V2O5, which is an extremely meaningful exploration.

Ultrathin-Walled Bi2 S3 Nanoroll/MXene Composite toward High Capacity and Fast Lithium Storage.

It is extremely important to develop a high energy density power source with rapid charge-discharge rate to meet people's growing needs. Hence, the development of advanced electrode materials is the top priority. Herein, a simple yet elaborate vacuum-assisted room-temperature phase transfer method is reported to transform MXene nanosheets from water into organic solution. Subsequently, an in-situ growth strategy is employed to deposit ultrathin-walled bismuth sulfide (Bi2 S3 ) nanorolls on MXene surface to prepare Bi2 S3 /MXene composite as an efficient and high-performance anode material for lithium-ion batteries. Attributed to the unique nanoroll-like structure and the strong synergistic effect, the Bi2 S3 /MXene-10 composite can deliver the high discharge capacities of 849 and 541 mAh g-1 at 0.1 and 5 A g-1 , respectively. The Bi2 S3 /MXene-10 electrode can deliver a high specific capacity of 541 mAh g-1 even after 600 cycles at a large current density of 1 A g-1 , proving the superb cycling stability of the Bi2 S3 /MXene-10 composite. Additionally, the simple vacuum-assisted room-temperature phase transfer strategy can enlighten researchers to expand the potential application of MXene. Furthermore, the formation mechanism of Bi2 S3 nanorolls is also proposed, which may open a new avenue to design and fabricate other nanoroll-like structures.

Versatile Interfacial Self-Assembly of Ti3C2Tx MXene Based Composites with Enhanced Kinetics for Superior Lithium and Sodium Storage.

Exploring nanostructured transition-metal sulfide anode materials with excellent electrical conductivity is the key point for high-performance alkali metal ion storage devices. Herein, we propose a powerful bottom-up strategy for the construction of a series of sandwich-structured materials by a rapid interfacial self-assembly approach. Oleylamine could act as a functional reagent to guarantee that the nanomaterials self-assemble with MXene. Benefiting from the small size of Co-NiS nanorods, excellent conductivity of MXene, and sandwiched structure of the composite, the Co-NiS/MXene composite could deliver a high discharge capacity of 911 mAh g-1 at 0.1 A g-1 for lithium-ion storage. After 200 cycles at 0.1 A g-1, a high specific capacity of 1120 mAh g-1 could be still remaining, indicating excellent cycling stability. For sodium-ion storage, the composite exhibits high specific capacity of 541 mAh g-1 at 0.1 A g-1 and excellent rate capability (263 mAh g-1 at 5 A g-1). This work offers a straightforward strategy to design and construct MXene-based anode nanomaterials with sandwiched structure for high-performance alkali metal ion storage and even in other fields.

Positive and negative photoconductivity characteristics in CsPbBr3/graphene heterojunction.

Broadband response photodetectors have received great research interest in optical sensing field. Usually, materials with positive photoconductivity (PPC) are general and the lack of negative photoconductivity (NPC) materials limits the application of photoelectric effect, especially in the broadband photodetecting field. Therefore, the finding of NPC materials is very important. Integrating PPC and NPC response into a single device is extremely meaningful to the development of broadband photodetector. In this work, we fabricated CsPbBr3 nanocrystals (NCs)-multilayered graphene heterojunction, which achieved persistent NPC response to ultra violet (300-390 nm) and PPC response to visible light (420-510 nm). The persistent NPC relies on the desorption of H2O vapor, and varies its intensity with the power intensity of laser. The PPC relies on the holes transmission from NCs to graphene. The recombination of NPC and PPC effect provides background knowledge for the development of broadband photodetector.

High-Tap-Density Fe-Doped Nickel Hydroxide with Enhanced Lithium Storage Performance.

Nickel hydroxide has attracted much attention as an anode material for lithium-ion batteries (LIBs) due to its high specific capacity, low cost, and easy preparation. However, the poor cycling stability greatly hampers its application. Herein, Fe-doped nickel hydroxide powders with a high tap density (2.16 g cm-3) are synthesized by a simple chemical co-precipitation method. Compared to undoped nickel hydroxide, this Fe-doped nickel hydroxide exhibits better lithium storage activity, enhanced cycling stability and rate capability, and improved electrochemical reaction kinetics. As an anode material for LIBs, the Fe-doped nickel hydroxide delivers a specific discharge capacity of 1080 mA h g-1 at 200 mA g-1 after 30 cycles, which is almost twice that (519 mA h g-1) of undoped nickel hydroxide; at a high current density of 2000 mA g-1, Fe-doped nickel hydroxide shows a specific capacity of 661 mA h g-1, significantly higher than that (182 mA h g-1) of undoped nickel hydroxide. Kinetic analysis reveals that Fe doping decreases the electrochemical reaction resistance and improves the lithium ion diffusivity in a nickel hydroxide electrode.

Graphene Aerogel Broken to Fragments for a Piezoresistive Pressure Sensor with a Higher Sensitivity.

The porous and elastic reduced graphene aerogel (rGA) is a promising active material for piezoresistive pressure sensors (PRSs) to realize an electronic skin. Due to the specific working mechanism and the limitation of the rGA's monolithic conductive network, the PRSs based on rGA suffer from a limited change of resistance with mechanical deformation, so they show poor sensitivity and cannot detect low pressures. Here we aim to improve the sensitivity of the PRS and make it suitable for a low-pressure system (0.5-8 kPa) through an effective method. The monolithic rGA is broken into small pieces by cutting (named as CGA). The sensitivity of the PRS based on CGA can be improved by 10 times that of the uncut rGA (named as UCGA). The resistance variation ratio of CGA (0.96) is 1.45 times of the resistance variation ratio of the UCGA (0.66). By using a package of elastic polypropylene thin films (PP), the cycle stability performance of CGA remains stable after 4200 cycles. The CGA can detect the pulse of a human being with sensitivity higher than the UCGA and the ordinary sensors. This method is simple, effective, and universal to improve the sensitivity of PRS based on porous and elastic materials.

Space-Confined Effect One-Pot Synthesis of γ-AlO(OH)/MgAl-LDH Heterostructures with Excellent Adsorption Performance.

Herein, γ-AlO(OH) as an inorganic was successfully inserted into MgAl-LDH layer by a one-pot synthesis, the composite as an adsorbent for removing methyl orange (MO) from wastewater. The structure and adsorption performance of γ-AlO(OH)/MgAl-LDH were characterized. The research shows that the expansion (003) plane and the hydroxyl active site of γ-AlO(OH)/MgAl-LDH can promote adsorption capacity and adsorption kinetics, respectively. Therefore, γ-AlO(OH)/MgAl-LDH exhibits a super adsorption performance, which completely adsorbs MO at the concentration of 1000 mg g-1. In addition, the maximum adsorption capacity of MO was 4681.40 mg g-1 according to the Langmuir model. These results indicate that γ-AlO(OH)/MgAl-LDH is a potential adsorbent for the removal of organic dyes in water.

Effect of La Doping on the Structure and Lithium Storage Performance of V2O5.

La-doped vanadium pentoxide (V2O5) was prepared by sol-gel method and subsequent heat treatment in air at 400 °C. The influence of La-doping on the crystalline structure, surface morphology, and lithium storage performance of V2O5 were investigated by XRD, SEM, CV, EIS, and discharge-charge tests. The results demonstrated that La doping did not change the phase structure of orthorhombic V2O5, but significantly refined the crystal grain of V2O5; La doping obviously improved the cycling stability and rate capability of V2O5 due to the decreased electrode polarization, smaller electron-transfer resistance, and enhanced lithium diffusivity. For example, the La-doped V2O5 delivered a reversible capacity of 131 mAh/g after 50 cycles at a current density of 200 mA/g, while the pure V2O5 showed a reversible capacity of only 63 mAh/g under the same condition. At the high rate of 500 mA/g, the La-doped V2O5 still displayed a reversible capacity of 106 mAh/g, which is two times higher than that (45 mAh/g) of pure V2O5 sample.

Facile synthesis of few-layer MoS2 in MgAl-LDH layers for enhanced visible-light photocatalytic activity.

A new photocatalyst, few-layer MoS2 grown in MgAl-LDH interlayers (MoS2/MgAl-LDH), was prepared by a facile two-step hydrothermal synthesis. The structural and photocatalytic properties of the obtained material were characterized by several techniques including powder X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL) and UV-vis absorption spectroscopy. The MoS2/MgAl-LDH composite showed excellent photocatalytic performance for methyl orange (MO) degradation at low concentrations (50 mg L-1 and 100 mg L-1). Furthermore, even for a MO solution concentration as high as 200 mg L-1, this composite also presented high degradation efficiency (>84%) and mineralization efficiency (>73%) at 120 min. The results show that the MoS2/MgAl-LDH composite has great potential for application in wastewater treatment.

A highly flexible and sensitive piezoresistive sensor based on MXene with greatly changed interlayer distances.

Since the successful synthesis of the first MXenes, application developments of this new family of two-dimensional materials on energy storage, electromagnetic interference shielding, transparent conductive electrodes and field-effect transistors, and other applications have been widely reported. However, no one has found or used the basic characteristics of greatly changed interlayer distances of MXene under an external pressure for a real application. Here we report a highly flexible and sensitive piezoresistive sensor based on this essential characteristics. An in situ transmission electron microscopy study directly illustrates the characteristics of greatly changed interlayer distances under an external pressure, supplying the basic working mechanism for the piezoresistive sensor. The resultant device also shows high sensitivity (Gauge Factor ~ 180.1), fast response (<30 ms) and extraordinarily reversible compressibility. The MXene-based piezoresistive sensor can detect human being's subtle bending-release activities and other weak pressure.

In situ controlled rapid growth of novel high activity TiB2/(TiB2-TiN) hierarchical/heterostructured nanocomposites.

In this work, a reaction coupling self-propagating high-temperature synthesis (RC-SHS) method was developed for the in situ controlled synthesis of novel, high activity TiB2/(TiB2-TiN) hierarchical/heterostructured nanocomposites using TiO2, Mg, B2O3, KBH4 and NH4NO3 as raw materials. The as-synthesized samples were characterized using X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray energy dispersive spectroscopy (EDX), transition electron microscopy (TEM), high-resolution TEM (HRTEM) and selected-area electron diffraction (SAED). The obtained TiB2/TiN hierarchical/heterostructured nanocomposites demonstrated an average particle size of 100-500 nm, and every particle surface was covered by many multibranched, tapered nanorods with diameters in the range of 10-40 nm and lengths of 50-200 nm. In addition, the tapered nanorod presents a rough surface with abundant exposed atoms. The internal and external components of the nanorods were TiB2 and TiN, respectively. Additionally, a thermogravimetric and differential scanning calorimetry analyzer (TG-DSC) comparison analysis indicated that the as-synthesized samples presented better chemical activity than that of commercial TiB2 powders. Finally, the possible chemical reactions as well as the proposed growth mechanism of the TiB2/(TiB2-TiN) hierarchical/heterostructured nanocomposites were further discussed.

Highly Stretchable and Self-Healable Supercapacitor with Reduced Graphene Oxide Based Fiber Springs.

In large-scale applications of portable and wearable electronic devices, high-performance supercapacitors are important energy supply sources. However, since the reliability and stability of supercapacitors are generally destroyed by mechanical deformation and damage during practical applications, the stretchability and self-healability must be exploited for the supercapacitors. Preparing the highly stretchable and self-healable electrodes is still a challenge. Here, we report reduced graphene oxide fiber based springs as electrodes for stretchable and self-healable supercapacitors. The fiber springs (diameters of 295 µm) are thick enough to reconnect the broken electrodes accurately by visual inspection. By wrapping fiber springs with a self-healing polymer outer shell, a stretchable and self-healable supercapacitor is successfully realized. The supercapacitor has 82.4% capacitance retention after a large stretch (100%), and 54.2% capacitance retention after the third healing. This work gave an essential strategy for designing and fabricating stretchable and self-healable supercapacitors in next-generation multifunctional electronic devices.

A Flexible Integrated System Containing a Microsupercapacitor, a Photodetector, and a Wireless Charging Coil.

Nowadays, the integrated systems on a plane substrate containing energy harvesting, energy storing, and working units are strongly desired with the fast development of wearable and portable devices. Here, a simple, low cost, and scalable strategy involving ink printing and electrochemical deposition is proposed to fabricate a flexible integrated system on a plane substrate containing an all-solid-state asymmetric microsupercapacitor (MSC), a photoconduct-type photodetector of perovskite nanowires (NWs), and a wireless charging coil. In the asymmetric MSCs, MnO2-PPy and V2O5-PANI composites are used as positive and negative electrodes, respectively. Typical values of energy density in the range of 15-20 mWh cm-3 at power densities of 0.3-2.5 W cm-3 with an operation potential window of 1.6 V are achieved. In the system, the wireless charging coil receives energy from a wireless power transmitter, which then can be stored in the MSC to drive the photoconductive detector of perovskite NWs in sequence. The designed integrated system exhibits a stable photocurrent response comparable with the detector driven by an external power source. This research provides an important routine to fabricate integrated systems.

Enhancing light emission in flexible AC electroluminescent devices by tetrapod-like zinc oxide whiskers.

Flexible alternating current electroluminescent devices (ACEL) are more and more popular and widely used in liquid-crystal display back-lighting, large-scale architectural and decorative lighting due to their uniform light emission, low power consumption and high resolution. However, presently how to acquire high brightness under a certain voltage are confronted with challenges. Here, we demonstrate an electroluminescence (EL) enhancing strategy that tetrapod-like ZnO whiskers (T-ZnOw) are added into the bottom electrode of carbon nanotubes (CNTs) instead of phosphor layer in flexible ACEL devices emitting blue, green and orange lights, and the brightness is greatly enhanced due to the coupling between the T-ZnOw and ZnS phosphor dispersed in the flexible polydimethylsiloxane (PDMS) layer. This strategy provides a new routine for the development of high performance, flexible and large-area ACEL devices.

Piezoresistive Sensor with High Elasticity Based on 3D Hybrid Network of Sponge@CNTs@Ag NPs.

Pressure sensors with high elasticity are in great demand for the realization of intelligent sensing, but there is a need to develope a simple, inexpensive, and scalable method for the manufacture of the sensors. Here, we reported an efficient, simple, facile, and repeatable "dipping and coating" process to manufacture a piezoresistive sensor with high elasticity, based on homogeneous 3D hybrid network of carbon nanotubes@silver nanoparticles (CNTs@Ag NPs) anchored on a skeleton sponge. Highly elastic, sensitive, and wearable sensors are obtained using the porous structure of sponge and the synergy effect of CNTs/Ag NPs. Our sensor was also tested for over 2000 compression-release cycles, exhibiting excellent elasticity and cycling stability. Sensors with high performance and a simple fabrication process are promising devices for commercial production in various electronic devices, for example, sport performance monitoring and man-machine interfaces.