LiCoO<Subscript>2</Subscript> nanoplates with exposed (001) planes and high rate capability for lithium-ion batteries

We report the synthesis of near-uniform LiCoO₂ nanoplates by a two-step approach in which β-Co(OH)₂ nanoplates are synthesized by co-precipitation and then transformed into LiCoO₂ nanoplates by solid state reaction at 750 °C for 3 hours. Characterization by high-resolution transmission electron microscopy (HRTEM) and electron diffraction (ED) reveal that the as-prepared LiCoO₂ nanoplates are covered with many cracks and have exposed (001) planes. The electrochemical performance of the LiCoO₂ nanoplates was investigated by galvanostatic tests. The capacity of LiCoO₂ nanoplates stabilized at 123 mA·h/g at a rate of 100 mA/g and 113 mA·h/g at a rate of 1000 mA/g after 100 cycles. The excellent rate capability of the LiCoO₂ nanoplates results from cracks which are perpendicular to the (001) plane and favor fast Li+ transportation. In addition, compared with other methods of synthesis of LiCoO₂ the time of the solid reaction state is significantly shorter even at relatively low temperatures, which means the energy consumption in preparing LiCoO₂ is greatly decreased. The controllable synthesis of LiCoO₂ nanoplates with exposed (001) plane paves an effective way to develop layered cathode materials with high rate capabilities for use in Li-ion batteries.      

SnO<Subscript>2</Subscript>/graphene composite with high lithium storage capability for lithium rechargeable batteries

SnO₂/graphene nanocomposites have been fabricated by a simple chemical method. In the fabrication process, the control of surface charge causes echinoid-like SnO₂ nanoparticles to be formed and uniformly decorated on the graphene. The electrostatic attraction between a graphene nanosheet (GNS) and the echinoid-like SnO₂ particles under controlled pH creates a unique nanostructure in which extremely small SnO₂ particles are uniformly dispersed on the GNS. The SnO₂/graphene nanocomposite has been shown to perform as a high capacity anode with good cycling behavior in lithium rechargeable batteries. The anode retained a reversible capacity of 634 mA·h·g⁻¹ with a coulombic efficiency of 98% after 50 cycles. The high reversibility can be attributed to the mechanical buffering by the GNS against the large volume change of SnO₂ during delithiation/lithiation reactions. Furthermore, the power capability is significantly enhanced due to the nanostructure, which enables facile electron transport through the GNS and fast delithiation/lithiation reactions within the echinoid-like nano-SnO₂. The route suggested here for the fabrication of SnO₂/graphene hybrid materials is a simple economical route for the preparation of other graphene-based hybrid materials which can be employed in many different fields.     

MoS<Subscript>2</Subscript>/CoS<Subscript>2</Subscript> composites composed of CoS<Subscript>2</Subscript> octahedrons and MoS<Subscript>2</Subscript> nano-flowers for supercapacitor electrode materials

In pursuing excellent supercapacitor electrodes, we designed a series of MoS₂/CoS₂ composites consisting of flower-liked MoS₂ and octahedron-shaped CoS₂ through a facile one-step hydrothermal method and investigated the electrochemical performance of the samples with various hydrothermal time. Due to the coupling of two metal species and a big amount of well-developed CoS₂ and MoS₂, the results indicated that the MoS₂/CoS₂ composites electrodes exhibited the best electrochemical performance with a large specific capacitance of 490 F/g at 2 mV/s or 400 F/g at 10 A/g among all samples as the hydrothermal time reached 48 h (MCS₄₈). Furthermore, the retention of MCS₄₈ is 93.1% after 10000 cycles at 10 A/g, which manifests the excellent cycling stability. The outstanding electrochemical performance of MCS₄₈ indicates that it could be a very promising and novel energy storage material for supercapacitors in the future.     

MoS<Subscript>2</Subscript>-graphene in-plane contact for high interfacial thermal conduction

Recent studies have indicated that two-dimensional (2D) MoS₂ exhibits low in-plane and inter-plane thermal conductivities. This poses a significant challenge to heat management in MoS₂-based electronic devices. To address this challenge, we have designed MoS₂-graphene interfaces that fully utilize graphene, a 2D material that exhibits very high thermal conductivity. First, we performed ab initio atomistic simulations to understand bonding and structural stability at the interfaces. The interfaces that we designed, which were connected via strong covalent bonds between Mo and C atoms, were energetically stable. We then performed molecular dynamics simulations to investigate interfacial thermal conductance in these materials. Surprisingly, the interfacial thermal conductance was high and comparable to those of covalently bonded graphene-metal interfaces. Importantly, each interfacial Mo–C bond served as an independent thermal channel, enabling modulation of the interfacial thermal conductance by controlling the Mo vacancy concentration at the interface. The present work provides a viable heat management strategy for MoS₂-based electronic devices.

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MoS<Subscript>2</Subscript>/h-BN heterostructures: controlling MoS<Subscript>2</Subscript> crystal morphology by chemical vapor deposition

Tuning the properties of van der Waals heterostructures based on alternating layers of two-dimensional materials is an emerging field of research with implications for electronics and photonics. Hexagonal boron nitride (h-BN) is an attractive insulating substrate for two-dimensional materials as it may exert less influence on the layer’s properties than silica. In this work, MoS₂ layers were deposited by chemical vapor deposition (CVD) on thick h-BN flakes mechanically exfoliated deposited on Si/SiO₂ substrates. CVD affords the controllable, large-scale preparation of MoS₂ on h-BN alleviating shortcomings of manual mechanical assembly of such heterostructures. Electron microscopy revealed that in-plane and vertical to the substrate MoS₂ layers were grown at high yield, depending on the sample preparation conditions. Raman and photoluminescence spectroscopy were employed to assess the optical and electronic quality of MoS₂ grown on h-BN as well as the interactions between MoS₂ and the supporting substrate. Compared to silica, MoS₂ layers grown on h-BN are less prone to oxidation and are subjected to considerably weaker electronic perturbation.     

Responsivity to solar irradiation and the behavior of carrier transports for MoS<Subscript>2</Subscript>/Si and MoS<Subscript>2</Subscript>/Si nanowires/Si devices

The behavior of carrier transports and the responsivity to solar irradiation are studied for MoS₂/n-type Si (n-Si) and MoS₂/Si nanowires (SiNWs)/n-Si device. The MoS₂ thin films were prepared by the sol–gel method. The MoS₂/n-Si and MoS₂/SiNWs/n-Si devices exhibit reliable rectification behavior. The thermionic emission-diffusion model is the dominant process in these fabricated MoS₂/n-Si and MoS₂/SiNWs/n-Si devices. By applying the insertion of the SiNWs, the responsivity to solar irradiation can be effectively increased. Because of the low reflectance values for the MoS₂/SiNWs/n-Si sample, the increased photocurrent density for the MoS₂/SiNWs/n-Si device is due to high external light injection efficiency. MoS₂/SiNWs/n-Si devices benefit from the high surface to volume ratio for SiNWs leading to a high responsivity of the device. The photo-response results confirm that the decay in the photocurrent is due to the dominance of short-lifetime electron trapping in the MoS₂ thin film.     

Ultrathin MoS<Subscript>2</Subscript> with expanded interlayers supported on hierarchical polypyrrole-derived amorphous N-doped carbon tubular structures for high-performance Li/Na-ion batteries

Layered molybdenum disulfide (MoS₂) has received much attention as one of the most promising energy-storage and conversion materials for Li/Na ion batteries. Here, a simple and effective approach is proposed for the rational design and preparation of hierarchical three-d imensional (3D) amorphous N-doped carbon nanotube@MoS₂ nanosheets (3D-ANCNT@MoS₂) via a simple hydrothermal method, followed by an annealing process. With such a unique nanoarchitecture, ultrathin MoS₂ nanosheets grown on the external surfaces of polypyrrole-derived ANCNTs are assembled to form a hierarchical 3D nanoarchitecture, where the adopted ANCNTs serve not only as the template and continuous conductive matrix, but can also prevent MoS₂ from aggregating and restacking, and help to buffer the volumetric expansion of MoS₂ during cycling. More importantly, when evaluated as an anode material for lithium-ion batteries, the 3D-ANCNT@MoS₂ composite exhibits excellent cycling stability, superior rate performance, and reversible specific capacity as high as 893.4 mAh?g^-1 at 0.2 A?g^-1 after 200 cycles in a half battery, and 669.4 mAh?g^-1 at 0.2 A?g^-1 after 100 cycles in the 3D-ANCNT@MoS₂//LiCoO₂ full battery. With respect to sodium-ion batteries, the outstanding reversible capacity, excellent rate behavior, and good cycling performance of 3D-ANCNT@MoS₂ composites are also achieved.

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Enhanced electrochemical performance of Na<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>2</Subscript>F<Subscript>3</Subscript> for Na-ion batteries with nanostructure and carbon coating

Carbon-coating Na₃V₂(PO₄)₂F₃ nanoparticles (NVPF@C NP) were prepared by a hydrothermal assisted sol–gel method and applied as cathode materials for Na-ion batteries. The as-prepared nanocomposites were composed of Na₃V₂(PO₄)₂F₃ nanoparticles with a typical size of ~?100 nm and an amorphous carbon layer with the thickness of ~?5 nm. Cyclic voltammetry, rate and cycling, and electrochemical impedance spectroscopy tests were used to discuss the effect of carbon coating and nanostructure. Results display that the as-prepared NVPF@C NP demonstrates a higher rate capability and better long cycling performance compared with bare Na₃V₂(PO₄)₂F₃ bulk (72 mA h g^?1 at 10 C vs 39 mA h g^?1 at 10 and 1 C capacity retention of 95% vs 88% after 50 cycles). The remarking electrode performance was attributed to the combination of nanostructure and carbon coating, which can provide short Na-ion diffusion distance and rapid electron migration.     

A polyimide cathode with superior stability and rate capability for lithium-ion batteries

Organic-based electrode materials for lithium-ion batteries (LIBs) are promising due to their high theoretical capacity, structure versatility and environmental benignity. However, the poor intrinsic electric conductivity of most polymers results in slow reaction kinetics and hinders their application as electrode materials for LIBs. A binder-free self-supporting organic electrode with excellent redox kinetics is herein demonstrated via in situ polymerization of a uniform thin polyimide (PI) layer on a porous and highly conductive carbonized nanofiber (CNF) framework. The PI active material in the porous PI@CNF film has large physical contact area with both the CNF and the electrolyte thus obtains superior electronic and ionic conduction. As a result, the PI@CNF cathode exhibits a discharge capacity of 170 mAh·g⁻¹ at 1 C (175 mA·g⁻¹), remarkable rate-performance (70.5% of 0.5 C capacity can be obtained at a 100 C discharge rate), and superior cycling stability with 81.3% capacity retention after 1,000 cycles at 1 C. Last but not least, a four-electron transfer redox process of the PI polymer was realized for the first time thanks to the excellent redox kinetics of the PI@CNF electrode, showing a discharge capacity exceeding 300 mAh·g⁻¹ at a current of 175 mA·g⁻¹.

     

Ionic liquid-derived Co<Subscript>3</Subscript>O<Subscript>4</Subscript>/carbon nano-onions composite and its enhanced performance as anode for lithium-ion batteries

In this work, a novel composite of Co₃O₄ nanoparticle and carbon nano-onions (CNOs) is synthesized by using ionic liquid as carbon and nitrogen source through a facile carbothermic reduction followed by low-temperature oxidation method. The SEM and HRTEM images reveal that the Co₃O₄ particles are homogenously embedded in the CNOs. Due to the unique nano-structure, the electrolyte contacts well with the active materials, leading to a better transfer of lithium ions. Moreover, the unique nano-structure not only buffers the volume changes but also facilitates the shuttling of electrons during the cycling process. As a result, the electrode made up of Co₃O₄/CNOs composite delivers favorable cycling performance (676 mAh g^?1 after 200 cycles) and rate capability (557 mAh g^?1 at the current of 1 C), showing a promising prospect for lithium-ion batteries as anode materials.     

Tribological properties of MoS<Subscript>2</Subscript> and carbon fiber reinforced polyimide composites

The tribological properties of carbon fiber reinforced polyimide (PI) composites with different MoS₂ containing sliding against GCr15 steel were comparatively evaluated on an M-2000 model ring-on-block test rig. The wear mechanisms were also comparatively discussed, based on scanning electron microscopic examination of the worn surface of the PI composites and the transfer film formed on the counterpart. It was found that small incorporation of MoS₂ was harmful to the improvement of friction and wear behaviors of carbon fiber reinforced PI composites. However, it was found that the increasing filler of MoS₂ significantly improved the wear resistance and decreased the friction coefficient of carbon fiber reinforced PI composites. It was also found that the tribological properties of MoS₂ and short carbon fiber reinforced PI composites were closely related with the sliding condition such as sliding rate and applied load.     

Novel porous starfish-like Co<Subscript>3</Subscript>O<Subscript>4</Subscript>@nitrogen-doped carbon as an advanced anode for lithium-ion batteries

A Co-based metal-organic framework (Co-MOF) with a unique three-dimensional starfish-like nanostructure was successfully synthesized using a simple ultrasonic method.After subsequent carbonization and oxidation,a nanocomposite of nitrogen-doped carbon with a Co3O4 coating (Co3O4@N-C) with a porous starfish-like nanostructure was obtained.The final hybrid exhibited excellent lithium storage performance when evaluated as an anode material in a lithiumion battery.A remarkable and stable discharge capacity of 795 mAh·g-1 was maintained at 0.5 A·g-1 after 300 cycles.Excellent rate capability was also obtained.In addition,a full Co3O4@N-C/LiFePO4 battery displayed stable capacity retention of 95％ after 100 cycles.This excellent lithium storage performance is attributed to the unique porous starfish-like structure,which effectively buffers the volume expansion that occurs during Li+ insertion/deinsertion.Meanwhile,the nitrogendoped carbon coating enhances the electrical conductivity and provides a buffer layer to accommodate the volume change and accelerate the formation of a stable solid electrolyte interface layer.     

Synthesis of well-defined Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> nanorods/N-doped graphene for lithium-ion batteries

The geometric size and distribution of magnetic nanoparticles are critical to the morphology of graphene (GN) nanocomposites, and thus they can affect the capacity and cycling performance when these composites are used as anode materials in lithium-ion batteries (LiBs). In this work, Fe₃O₄ nanorods were deposited onto fully extended nitrogen-doped GN sheets from a binary precursor in two steps, a hydrothermal process and an annealing process. This route effectively tuned the Fe₃O₄ nanorod size distribution and prevented their aggregation. The transformation of the binary precursor was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). XPS analysis indicated the presence of N-doped GN sheets, and that the magnetic nanocrystals were anchored and uniformly distributed on the surface of the flattened N-doped GN sheets. As a high performance anode material, the structure was beneficial for electron transport and exchange, resulting in a large reversible capacity of 929 mA·h·g^–1, high-rate capability, improved cycling stability, and higher electrical conductivity. Not only does the result provide a strategy for extending GN composites for use as LiB anode materials, but it also offers a route for the preparation of other oxide nanorods from binary precursors.

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Rational synthesis of carbon shell coated polyaniline/MoS<Subscript>2</Subscript> monolayer composites for high-performance supercapacitors

Conducting polymers generally show high specific capacitance but suffer from poor rate capability and rapid capacitance decay, which greatly limits their practical applications in supercapacitor electrodes. To this end, many studies have focused on improving the overall capacitive performance by synthesizing nanostructured conducting polymers or by depositing a range of coatings to increase the active surface area exposed to the electrolyte and enhance the charge transport efficiency and structural stability. Despite this, simultaneously achieving high specific capacitance, good rate performance, and long cycle life remains a considerable challenge. Among the various two-dimensional (2D) layered materials, octahedral (1T) phase molybdenum disulfide (MoS₂) nanosheets have high electrical conductivity, large specific surface areas, and unique surface chemical characteristics, making them an interesting substrate for the controlled growth of nanostructured conducting polymers. This paper reports the rational synthesis of carbon shell-coated polyaniline (PANI) grown on 1T MoS₂ monolayers (MoS₂/PANI@C). The composite electrode comprised of MoS₂/PANI@C with a ~3 nm carbon shell exhibited a remarkable specific capacitance of up to 678 F·g^–1 (1 mV·s^–1), superior capacity retention of 80% after 10,000 cycles and good rate performance (81% at 10 mV·s^–1) due to the multiple synergic effects between the PANI nanostructure and 1T MoS₂ substrates as well as protection by the uniform thin carbon shell. These properties are comparable to the best overall capacitive performance achieved for conducting polymers-based supercapacitor electrodes reported thus far.

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Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>-nanoparticle-decorated TiO<Subscript>2</Subscript> nanofiber hierarchical heterostructures with improved lithium-ion battery performance over wide temperature range

A facile strategy was designed for the fabrication of Fe₃O₄-nanoparticle-decorated TiO₂ nanofiber hierarchical heterostructures (FTHs) by combining the versatility of the electrospinning technique and the hydrothermal growth method. The hierarchical architecture of Fe₃O₄ nanoparticles decorated on TiO₂ nanofibers enables the successful integration of the binary composite into batteries to address structural stability and low capacity. In the resulting unique architecture of FTHs, the 1D heterostructures relieve the strain caused by severe volume changes of Fe₃O₄ during numerous charge-discharge cycles, and thus suppress the degradation of the electrode material. As a result, FTHs show excellent performance including higher reversible capacity, excellent cycle life, and good rate performance over a wide temperature range owing to the synergistic effect of the binary composition of TiO₂ and Fe₃O₄ and the unique features of the hierarchical nanofibers.

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Size-controlled MoS<Subscript>2</Subscript> nanodots supported on reduced graphene oxide for hydrogen evolution reaction and sodium-ion batteries

Transition metal dichalcogenide nanodots (NDs) have received considerable interest.We report a facile bottom-up synthetic route for MoS2 NDs by using molybdenum pentachloride and L-cysteine as precursors in oleylamine.The synthesis of NDs with a narrow size distribution ranging from 2.2 to 5.3 nm,was tailored by controlling the reaction time.Because of its coating characteristics,oleyalmine leads to uniformity and monodispersity of the NDs.Moreover,the NDs synthesized have large specific surface areas providing active sites.Graphene possesses outstanding conductivity.Combining the advantages of the two materials,the 0D/2D material exhibits superior electrochemical performance because of the 2D permeable channels for ion adsorption,energy storage,and conversion.The as-prepared MoS2/rGO (～2.2 nm) showed a stable capacity of 220 mAh·g-1 after 10,000 cycles at the current density of 20 A·g-1.Furthermore,a reversible capacity ～140 mAh·g-1 was obtained at a much higher current density of 40 A·g-1.Additionally,this composite exhibited superior catalytic performance evidenced by a small overpotential (222 mV) to afford 10 mA·cm-2,and a small Tafel slope (59.8 mV·decade-1) with good acid-stability.The facile approach may pave the way for the preparation of NDs with these nanostructures for numerous applications.     

Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocrystal anode materials with improved cyclic stability for lithium ion batteries

The cyclic stability of Cr₂O₃ is very poor due to the large volume change during lithiation/delithiation. In this study, we have found that Cr₂O₃ nanocrystals synthesized by using a simple hydrothermal method can improve its cyclic stability. Sample calcined at 430 °C has uniform size, compact structure and high crystallization degree. These Cr₂O₃ nanocrystals exhibit a stable cyclic performance of 185 mAh g^?1 after 100 cycles at 100 mA g^?1. It is useful in real life, such as providing power consumption for minitype device, etc.     

Facile synthesis and electrochemical properties of layered Li[Ni<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>]O<Subscript>2</Subscript> as cathode materials for lithium-ion batteries

A layered oxide Li[Ni_1/3Mn_1/3Co_1/3]O₂ was synthesized by an oxalate co-precipitation method. The morphology, structural and composition of the as-papered samples synthesized at different calcination temperatures were investigated. The results indicate that calcination temperature of the sample at 850°C can improve the integrity of structural significantly. The effect of calcination temperature varying from 750°C to 950°C on the electrochemical performance of Li[Ni_1/3Mn_1/3Co_1/3]O₂, cathode material of lithiumion batteries, has been investigated. The results show that Li[Ni_1/3Mn_1/3Co_1/3]O₂ calcined at 850°C possesses a higher capacity retention and better rate capability than other samples. The reversible capacity is up to 178.6 mA?h?g^-1, and the discharge capacity still remains 176.3 mA?h?g^-1 after 30 cycles. Moreover, our strategy provides a simple and highly versatile route in fabricating cathode materials for lithium-ion batteries.     

Interlayer coupling in anisotropic/isotropic van der Waals heterostructures of ReS<Subscript>2</Subscript> and MoS<Subscript>2</Subscript> monolayers

In-plane symmetry is an important contributor to the physical properties of two-dimensional layered materials, as well as atomically thin heterojunctions. Here, we demonstrate anisotropic/isotropic van der Waals (vdW) heterostructures of ReS₂ and MoS₂ monolayers, where interlayer coupling interactions and charge separation were observed by in situ Raman-photoluminescence spectroscopy, electrical, and photoelectrical measurements. We believe that these results could be helpful for understanding the fundamental physics of atomically thin vdW heterostructures and creating novel electronic and optoelectronic devices.

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