Adaptive Force Field Parameter Optimization for Expanding Reaction Simulations within Wide-Ranged Temperature.

Large-scale and long-term simulation of chemical reactions are key research topics in computational chemistry. However, there are still difficulties in simulating high-temperature reactions, such as polymer thermal decomposition. Herein, we introduce an adaptive potential parameter optimization framework designed to automatically fine-tune parameters, and the application of it to optimize ReaxFF parameters enhances the accuracy of chemical reaction simulations conducted at experimental temperatures. To achieve this, we leverage the power of Random Forests and interpretable machine learning techniques that enable the identification and selection of parameters that exert a substantial influence on the target attribute. By training deep neural network (NN) models, we established optimized parameter associations with reference properties. We train deep neural network (NN) models to establish the relationship between the optimized parameters and reference properties. We employ a Genetic Algorithm (GA) to utilize the surrogate NN model and the quantum mechanical targets to speed up the search for the optimal parameters. Our simulation results of resin pyrolysis show that the adaptive optimized ReaxFF can predict the peak temperature more accurately and obtain reasonable product composition under conditions that more closely resemble experimental scenarios. This work facilitates advances in force field parameter optimization for more accurate and universal reaction simulations.

Sandwich Structured Metal oxide/Reduced Graphene Oxide/Metal Oxide-Based Polymer Electrolyte Enables Continuous Inorganic-Organic Interphase for Fast Lithium-Ion Transportation.

Introducing inorganic fillers into organic poly(ethylene oxide)(PEO)-based electrolyte has attracted substantial attention to enhance its ionic conductivity and mechanical strength, but limited inorganic-organic interphases are always caused by isolated particles agglomeration. Herein, a variety of sandwich structured metal oxide/reduced graphene oxide(rGO)/metal oxide nanocomposites to optimize lithium-ion conduction by interconnected amorphous organic-inorganic interphases in lithium metal batteries, are proposed. With the support of high surface area rGO, the agglomeration of metal oxide particles is precluded, forming continuous amorphous organic-inorganic interphases with stacked layer-by-layer structure, thus creating 3D interconnected lithium-ion transportation channels vertically and laterally. Besides, metal oxide nanoparticles with hydroxyls possess high affinity toward bis(tri-fluoromethanesulfonyl)imide anions by hydrogen bindings between hydroxyls and fluorine and metal-oxygen bonds, releasing more free lithium ions. Consequently, PEO-ZnO/rGO/ZnO electrolyte delivers superior ionic conductivity of 1.02 × 10-4 S cm-1 at 25 °C and lithium-ion transference number of 0.38 at 60 °C. Furthermore, ZnO/rGO/ZnO insertion promotes the formation of LiF-rich stable solid electrolyte interface, endowing Li symmetric cells with long-term cycling stability over 900 hours. The corresponding LiFePO4 cathode possesses a high reversible specific capacity of 130 mAh g-1 at 0.5C after cycling 300 cycles with a poor capacity fading of 0.05% per cycle.

Colloidal Synthesis of Silicon-Carbon Composite Material for Lithium-Ion Batteries.

We report colloidal routes to synthesize silicon@carbon composites for the first time. Surface-functionalized Si nanoparticles (SiNPs) dissolved in styrene and hexadecane are used as the dispersed phase in oil-in-water emulsions, from which yolk-shell and dual-shell hollow SiNPs@C composites are produced via polymerization and subsequent carbonization. As anode materials for Li-ion batteries, the SiNPs@C composites demonstrate excellent cycling stability and rate performance, which is ascribed to the uniform distribution of SiNPs within the carbon hosts. The Li-ion anodes composed of 46 wt % of dual-shell SiNPs@C, 46 wt % of graphite, 5 wt % of acetylene black, and 3 wt % of carboxymethyl cellulose with an areal loading higher than 3 mg cm-2 achieve an overall specific capacity higher than 600 mAh g-1 , which is an improvement of more than 100 % compared to the pure graphite anode. These new colloidal routes present a promising general method to produce viable Si-C composites for Li-ion batteries.

Zn-Cu-In-Se Quantum Dot Solar Cells with a Certified Power Conversion Efficiency of 11.6%.

The enhancement of power conversion efficiency (PCE) and the development of toxic Cd-, Pb-free quantum dots (QDs) are critical for the prosperity of QD-based solar cells. It is known that the properties (such as light harvesting range, band gap alignment, density of trap state defects, etc.) of QD light harvesters play a crucial effect on the photovoltaic performance of QD based solar cells. Herein, high quality ∼4 nm Cd-, Pb-free Zn-Cu-In-Se alloyed QDs with an absorption onset extending to ∼1000 nm were developed as effective light harvesters to construct quantum dot sensitized solar cells (QDSCs). Due to the small particle size, the developed QD sensitizer can be efficiently immobilized on TiO2 film electrode in less than 0.5 h. An average PCE of 11.66% and a certified PCE of 11.61% have been demonstrated in the QDSCs based on these Zn-Cu-In-Se QDs. The remarkably improved photovoltaic performance for Zn-Cu-In-Se QDSCs vs Cu-In-Se QDSCs (11.66% vs 9.54% in PCE) is mainly derived from the higher conduction band edge, which favors the photogenerated electron extraction and results in higher photocurrent, and the alloyed structure of Zn-Cu-In-Se QD light harvester, which benefits the suppression of charge recombination at photoanode/electrolyte interfaces and thus improves the photovoltage.

Ultrahigh-strength silicone aerogels reinforced by an armor-like epoxy framework via a temperature-controlled sequential reaction strategy.

Aerogels with low density and high porosity are extremely attractive for high-performance insulation, but their brittleness, complicated fabrication, and poor mechanical properties greatly limit their practical applications. Herein, we report an ultrahigh-strength silicone aerogel with an armor-like epoxy framework via a temperature-controlled sequential reaction strategy. The key to this synthesis is forming a Si-O-Si framework via the polycondensation of silanes at 100 °C, followed by in-situ armoring an epoxy framework via an intermolecular cyclization at an elevated temperature of 150 °C. Owing to the enhanced framework, the resulting aerogel could withstand capillary tension in the drying process, enabling it to be dried at ambient pressure without shrinkage. The obtained aerogel possesses a tunable density of 0.17-0.45 g/cm3 and ultrahigh-strength with compressive modulus up to 37.8-244.3 MPa, which surpasses other polymer-reinforced silicone aerogels by a factor of five in mechanical properties. It also demonstrates outstanding thermal insulation, with an extremely low thermal conductivity from 0.025 to 0.051 W m-1 K-1 at room temperature, and maintains thermal characteristics across a temperature range of -20 to 300 °C. Furthermore, the aerogel composites prepared by the reinforcement of low-density fiber mats have tunable densities of 0.36-0.87 g/cm3, much enhanced tensile strengths of 15.9-72.3 MPa, and low thermal conductivities at room temperature of 0.042-0.078 W m-1 K-1. This study presents a cost-effective method for enhancing the production of silicone aerogel materials, offering considerable opportunities for their application in insulation, energy transport, and the aerospace sector.

Enhanced Electron Delocalization within Coherent Nano-Heterocrystal Ensembles for Optimizing Polysulfide Conversion in High-Energy-Density Li-S Batteries.

Commercialization of high energy density Lithium-Sulfur (Li-S) batteries is impeded by challenges such as polysulfide shuttling, sluggish reaction kinetics, and limited Li+ transport. Herein, a jigsaw-inspired catalyst design strategy that involves in situ assembly of coherent nano-heterocrystal ensembles (CNEs) to stabilize high-activity crystal facets, enhance electron delocalization, and reduce associated energy barriers is proposed. On the catalyst surface, the stabilized high-activity facets induce polysulfide aggregation. Simultaneously, the surrounded surface facets with enhanced activity promote Li2S deposition and Li+ diffusion, synergistically facilitating continuous and efficient sulfur redox. Experimental and DFT computations results reveal that the dual-component hetero-facet design alters the coordination of Nb atoms, enabling the redistribution of 3D orbital electrons at the Nb center and promoting d-p hybridization with sulfur. The CNE, based on energy level gradient and lattice matching, endows maximum electron transfer to catalysts and establishes smooth pathways for ion diffusion. Encouragingly, the NbN-NbC-based pouch battery delivers a Weight energy density of 357 Wh kg-1, thereby demonstrating the practical application value of CNEs. This work unveils a novel paradigm for designing high-performance catalysts, which has the potential to shape future research on electrocatalysts for energy storage applications.

Designing electrolytes with high solubility of sulfides/disulfides for high-energy-density and low-cost K-Na/S batteries.

Alkaline metal sulfur (AMS) batteries offer a promising solution for grid-level energy storage due to their low cost and long cycle life. However, the formation of solid compounds such as M2S2 and M2S (M = Na, K) during cycling limits their performance. Here we unveil intermediate-temperature K-Na/S batteries utilizing advanced electrolytes that dissolve all polysulfides and sulfides (K2Sx, x = 1-8), significantly enhancing reaction kinetics, specific capacity, and energy density. These batteries achieve near-theoretical capacity (1655 mAh g-1 sulfur) at 75 °C with a 1 M sulfur concentration. At a 4 M sulfur concentration, they deliver 830 mAh g-1 at 2 mA cm-2, retaining 71% capacity after 1000 cycles. This new K-Na/S battery with specific energy of 150-250 Wh kg-1 only employs earth-abundant elements, making it attractive for long-duration energy storage.

Carbon dioxide capture using polyethylenimine-loaded mesoporous carbons.

A high efficiency sorbent for CO2 capture was developed by loading polyethylenimine (PEI) on mesoporous carbons which possessed well-developed mesoporous structures and large pore volume. The physicochemical properties of the sorbent were characterized by N2 adsorption/desorption, scanning electron microscopy (SEM), thermal gravimetric analysis (TG) and Fourier transform infrared spectroscopy (FT-IR) techniques followed by testing for CO2 capture. Factors that affected the sorption capacity of the sorbent were studied. The sorbent exhibited extraordinary capture capacity with CO2 concentration ranging from 5% to 80%. The optimal PEI loading was determined to be 65 wt.% with a CO2 sorption capacity of 4.82 mmol-CO2/g-sorbent in 15% CO2/N2 at 75 degrees C, owing to low mass-transfer resistance and a high utilization ratio of the amine compound (63%). Moisture had a promoting effect on the sorption separation of CO2. In addition, the developed sorbent could be regenerated easily at 100 degrees C, and it exhibited excellent regenerability and stability. These results indicate that this PEI-loaded mesoporous carbon sorbent should have a good potential for CO2 capture in the future.

Tensile Failure Behaviors of Adhesively Bonded Structure Based on In Situ X-ray CT and FEA.

Adhesive bonding plays a pivotal role in structural connections, yet the bonding strength is notably affected by the presence of pore defects. However, the invisibility of interior pores severely poses a challenge to understanding their influence on tensile failure behaviors under loading. In this study, we present a pioneering investigation into the real-time micro-failure mechanisms of adhesively bonded structures using in situ X-ray micro-CT. Moreover, the high-precision finite element analysis (FEA) of stress distribution is realized by establishing the real adhesive layer model based on micro-CT slices. The findings unveil that pores induce stress concentration within the adhesive layer during the tensile process, with stress levels significantly contingent upon pore sizes rather than their specific shapes. Consequently, larger pores initiate and propagate cracks along their paths, ultimately culminating in the failure of adhesively bonded structures. These outcomes serve as a significant stride in elucidating how pore defects affect the bonding performance of adhesively bonded structures, offering invaluable insights into their mechanisms.

Ultrafine Vacancy-Rich Nb2O5 Semiconductors Confined in Carbon Nanosheets Boost Dielectric Polarization for High-Attenuation Microwave Absorption.

The integration of nano-semiconductors into electromagnetic wave absorption materials is a highly desirable strategy for intensifying dielectric polarization loss; achieving high-attenuation microwave absorption and realizing in-depth comprehension of dielectric loss mechanisms remain challenges. Herein, ultrafine oxygen vacancy-rich Nb2O5 semiconductors are confined in carbon nanosheets (ov-Nb2O5/CNS) to boost dielectric polarization and achieve high attenuation. The polarization relaxation, electromagnetic response, and impedance matching of the ov-Nb2O5/CNS are significantly facilitated by the Nb2O5 semiconductors with rich oxygen vacancies, which consequently realizes an extremely high attenuation performance of - 80.8 dB (> 99.999999% wave absorption) at 2.76 mm. As a dielectric polarization center, abundant Nb2O5-carbon heterointerfaces can intensify interfacial polarization loss to strengthen dielectric polarization, and the presence of oxygen vacancies endows Nb2O5 semiconductors with abundant charge separation sites to reinforce electric dipole polarization. Moreover, the three-dimensional reconstruction of the absorber using microcomputer tomography technology provides insight into the intensification of the unique lamellar morphology regarding multiple reflection and scattering dissipation characteristics. Additionally, ov-Nb2O5/CNS demonstrates excellent application potential by curing into a microwave-absorbing, machinable, and heat-dissipating plate. This work provides insight into the dielectric polarization loss mechanisms of nano-semiconductor/carbon composites and inspires the design of high-performance microwave absorption materials.

Atomic Oxygen-Induced Surface Erosion Behavior and Mechanical Degradation of Polyether Ether Ketone via Reactive Molecular Dynamics Simulations.

Atomic oxygen (AO) collision is one of the most serious threats to polymeric materials exposed to the space environment, yet understanding the structural changes and degradation of materials caused by AO impact remains a tremendous issue. Herein, we systematically evaluate the erosion collision and mechanical degradation of polyether ether ketone (PEEK) resin under hypervelocity AO impact using reactive molecular dynamics simulations. The interaction process and local evolution mechanism between high-speed AO and PEEK are investigated for the first time, suggesting that AO will either be scattered or adsorbed by PEEK, which is strongly correlated with the main degraded species evolution including O2, OH, CO, and CO2. Different AO fluxes and AO incidence angle simulations indicate that high-energy AO collision on the surface transfers kinetic energy to PEEK's thermal energy, thus inducing mass loss and surface penetration mechanisms. Vertically impacted AO causes less erosion on the PEEK matrix, rather than obliquely. Furthermore, PEEK chains modified with functional side groups are comprehensively investigated by 200 AO impact and high strain rate (1010 s-1) tensile simulations, demonstrating that the spatial configuration and stable benzene functionality of phenyl side groups can significantly improve the AO resistance and mechanical properties of PEEK at 300 and 800 K. This work revealed useful insights into the interaction mechanisms between AO and PEEK at the atomic scale and may provide a protocol for screening and designing new polymers of high AO tolerance.

Surface positive-charged modification of inorganic fillers to optimize lithium ion conductive pathways in composite polymer electrolytes for lithium-metal batteries.

The incorporation of inorganic fillers into composite polymer electrolytes (CPEs) is a common strategy to improve ionic conductivity. However, the high surface energy of inorganic fillers typically aggravates poor interfacial contact with polymer chains. Herein, we develop a surface positive-charge modification strategy for enhancing the intermolecular interaction of poly(ethylene oxide) (PEO) electrolytes with inorganic fillers and optimizing lithium ion (Li+) conductive pathways in CPEs. The SiO2 nanoparticles are coated with a polydopamine adhesive layer and then functionalized with a branched polyethyleneimine positively charged functional layer. Such surface modification not only effectively induces more amorphous structure into the PEO matrix but also promotes the dissociation of lithium salts and activates more free Li+ in the PEO to accelerate Li+ transport. The CPEs achieved a superior ionic conductivity of 6.12 × 10-5 S cm-1 at 30 °C. In addition, the modified fillers could induce the formation of a lithium fluoride (LiF)-rich solid-state interphase and correspondingly achieve excellent compatibility with Li metal. The Li symmetric battery using the as-prepared CPEs delivered stable Li plating/stripping performances over 3960 h under 0.2 mA cm-2. The resulting LiFePO4|Li battery has an excellent capacity retention of 92.8 % after 260 cycles at 0.5C and 60 °C.

Ultrahigh-strength carbon aerogels for high temperature thermal insulation.

Carbon aerogels with nanoporous structure are attractive for thermal insulation under extreme conditions, but their practical applications are usually plagued by the inherent brittleness and easy-oxidation characteristic at high temperature. Herein, silica-modified carbon aerogels (SCAs) with extraordinarily high strength are prepared via a facile sol-gel polymerization of phenolic resin and siloxane, followed by ambient pressure drying and carbonization. The resulting SCAs possess medium-high density of ∼0.5 g·cm-3 and mesoporous structure with the mean pore size of 33 nm. During carbonization process, the siloxane could be gradually transformed into the amorphous SiO2 particles and crystalline SiC particles, which are coated on the surface of carbon nanoparticle and consequently improve the oxidation-resistance of carbon aerogels. Due to the density-porosity trade-off, the SCAs have high compressive strength of 10.0 MPa and satisfied thermal conductivities of 0.118 W·m-1·K-1 at 25 °C and 0.263 W·m-1·K-1 at 1000 °C. Furthermore, needled carbon fiber-reinforced SCAs (CF-SCAs) with ultrahigh compressive strength of 210.5 MPa are prepared, which exhibit good thermal conductivities of 0.207 W·m-1·K-1 at 25 °C and 0.407 W·m-1·K-1 at 1000 °C. The ultrahigh mechanical strength, good oxidation-resistance, good thermal insulation as well as the facile preparation make the SACs great promising in high-temperature insulations especially under harsh conditions.

Thermo-catalytic conversion of waste plastics into surrogate fuels over spherical activated carbon of long-life durability.

Recovery of value-added fuels or chemicals from waste plastics by pyrolysis is a promising way to eliminate the waste plastics accumulation and alleviate the energy crisis, while developing efficient catalysts of high durability remains a challenge. Herein, activated carbon spheres of various surface chemistry were fabricated and subsequently used in ex-situ catalytic pyrolysis of low-density polyethylene to produce jet fuel and gasoline-ranged hydrocarbons. Experiment results indicate that with the increase of activation time and temperature, the acidity of activated carbon increased slightly owning to the oxygen-containing functional groups increased, and the specific surface area reached the maximum value (707 m2/g) at the activation condition of 800℃ for 60 min. The enlarged specific surface area promotes the C-C bond cleavage that releases more small gases at the expense of liquid yield, and the increase in density of oxygen-containing functional groups and acidity boosts the formation of aromatic hydrocarbons in liquid. When the activated carbon spheres were activated at 800℃ for 80 min, 100% of the hydrocarbons in the liquid belonged to jet fuel and gasoline, and their selectivity was 81.70 area.% and 96.25 area.%, respectively. More importantly, the catalyst exhibits excellent catalytic activity after four reactivation cycles, where the quality of the liquid product is similar to or even better than that achieved by the fresh catalyst. Furthermore, the catalyst still showed excellent performance in the catalytic pyrolysis of waste plastic mixture.

Monolithic carbon aerogels within foam framework for high-temperature thermal insulation and organics absorption.

Carbon aerogels exhibit high porosity, good electrical conductivity, and low thermal conductivity, but their practical applications are greatly hindered by their tedious preparation and inherent structure brittleness. Herein, monolithic carbon aerogels (MCAs) with low density and large size are prepared via a facile sol-gel polymerization of phenolic resin within melamine foam (MF), followed by ambient pressure drying and co-carbonization. During ambient pressure drying process, the MF matrix can deliver supporting force to counteract against the solvent evaporation surface tension, thus inhibiting volume shrinkage and shape deformation. Upon co-carbonization process, the MF matrix and organic aerogel could pyrolyze and shrink cooperatively, which could effectively prevent the brittle fracture of monolith. Therefore, large-sized MCAs (up to 250 × 250 × 20 mm) with low densities of 0.12-0.22 g·cm-3 are obtained. The as-obtained MCAs possess high compressive strength (2.50 MPa), ultra-low thermal conductivity (0.051 W·m-1·K-1 at 25 °C and 0.111 W·m-1·K-1 at 800 °C), and high-volume organic absorption capability (77.3-88.0%, V/V). This facile and low-cost method for the fabrication of large-sized monolithic carbon aerogels with excellent properties could envision enormous potential for high-temperature thermal insulation and organics absorption.

General synthesis of ultrafine metal oxide/reduced graphene oxide nanocomposites for ultrahigh-flux nanofiltration membrane.

Graphene-based membranes have great potential to revolutionize nanofiltration technology, but achieving high solute rejections at high water flux remains extremely challenging. Herein, a family of ultrafine metal oxide/reduced graphene oxide (rGO) nanocomposites are synthesized through a heterogenous nucleation and diffusion-controlled growth process for dye nanofiltration. The synthesis is based on the utilization of oxygen functional groups on GO surface as preferential active sites for heterogeneous nucleation, leading to the formation of sub-3 nm size, monodispersing as well as high-density loading of metal oxide nanoparticles. The anchored ultrafine nanoparticles could inhibit the wrinkling of the rGO nanosheet, forming highly stable colloidal solutions for the solution processing fabrication of nanofiltration membranes. By functioning as pillars, the nanoparticles remarkably increase both vertical interlayer spacing and lateral tortuous paths of the rGO membranes, offering a water permeability of 225 L m-2 h-1 bar-1 and selectivity up to 98% in the size-exclusion separation of methyl blue.

Homogenously dispersed ultrasmall niobium(V) oxide nanoparticles enabling improved ionic conductivity and interfacial compatibility of composite polymer electrolyte.

Composite polymer electrolytes (CPEs) decorated with ceramic fillers have emerged as appealing structures that exhibit coalesced merits of both inorganic and polymer solid electrolytes, but are currently challenged by the particle agglomeration that weakens ionic conductivity and electrochemical performances. Herein, a facile solvothermal method is proposed to fabricate the ultrasmall niobium(V) oxide (Nb2O5) nanoparticle of average size being less than 3 nm, enabling the composite polymer electrolyte with homogenous dispersity (nano-CPE). Owning to the superior dispersity of ultrasmall Nb2O5 nanoparticles, the polymer chains can be effectively disordered to enhance the local segmental motion through the physical interruption. Moreover, strong Lewis acid-based interactions between Nb2O5 nanoparticles and lithium salts are formed, resulting in accelerating the dissociation of lithium salt and releasing more free charge carriers. Therefore, the 3D connected Li+ fast pathways along the amorphous region between the Nb2O5 nanoparticles and polymer chains are constructed, ensuring the improved ionic conductivity. In addition, the homogenous Li deposition can also be simultaneously achieved through the intimate interfacial contact, which can efficiently suppress the growth of lithium dendrite in the metal anode. The fabricated nano-CPE presents a high ionic conductivity of 6.6 × 10-5 S/cm at room temperature and wide anti-oxidative potential of 5.1 V. The lithium symmetric battery using nano-CPE delivers a decent lithium plating/stripping performance for 200 h at 0.5 mA/cm2. The solid-sate LiFePO4 battery achieves long stable cycling performances (151mAh/g and 140 mAh/g after 230 cycles at 0.5C and 1.0C, respectively). This work may offer a facile and efficient synthesized method of highly dispersed ultrasmall nanoparticles for advancing the CPE with improved ionic conductivity, interfacial contact and cell performances.

Pt-NbC Composite as a Bifunctional Catalyst for Redox Transformation of Polysulfides in High-Rate-Performing Lithium-Sulfur Batteries.

Accelerating the redox reaction of polysulfides via catalysis is an effective way to suppress the shuttling effect in lithium-sulfur (Li-S) cells. However, recent studies have mainly focused on the singular function of the catalyst, i.e., either oxidation or reduction of polysulfides. As such, the goal of rapid cycling of sulfur species remains to be highly desired. Herein, a Pt-carbide composite as a bifunctional catalyst was developed to simultaneously accelerate both the reduction of soluble polysulfides and the oxidation of insoluble Li2S/Li2S2. Typically, a Pt-NbC composite was synthesized by growing Pt nanoparticles on the surface of NbC, and the resultant intimate interface in the hybrid is a key component for the bifunctional catalysis. During the reduction process, polysulfides could be grabbed on the surface of NbC via strong adsorption, and then these trapped polysulfides could be catalytically converted by Pt nanoparticles. During the oxidation process, both NbC and Pt exhibited catalytic activities for the dissolution of Li2S. This process could lead to the renewal of the surface of the catalyst. By combining the sulfur cathode with a Pt-NbC-CNT (Pt-NbC anchored on a carbon nanotube)-coated separator, the cell was able to demonstrate a high initial capacity of 1382 mAh g-1 at a current density of 0.2C. Furthermore, the cell was able to achieve an exceptional rate capability of 795 mAh g-1 at 5C, and it was also able to show significantly inhibited self-discharge behavior. Thus, this work explores the catalyst design and the mechanism of a bifunctional catalyst for the performance enhancement in Li-S cells.

In Situ Formed Lithiophilic LixNbyO in a Carbon Nanofiber Network for Dendrite-Free Li-Metal Anodes.

Lithium metal is considered as a strongly attractive anode candidate for the high-energy-storage field, but its dreadful dendrite growth has haunted its commercialization progress. Herein, we develop a lithiophilic Nb2O5-embedded three-dimensional (3D) carbon nanofiber network (Nb2O5-CNF) as a scaffold to preload molten Li for the fabrication of dendrite-free composite anode. The in situ lithiation reaction between molten Li and Nb2O5 nanocrystals results in the formation of nanosize LixNbyO nanoparticles, which can serve as preferred sites that regulate nucleation/growth behavior of Li during the plating process. Besides, due to its high structural stability and abundant internal inner space, the 3D CNF network can function as a reservoir to confine the dimensional expansion of "hostless Li". The resulting Li composite anodes exhibit enlarged active areas and reduced interfacial energy barriers, delivering a prolonged cycling of 1000 h with an ultralow hysteresis of 52 mV and dendrite-free morphology in a symmetric cell (1.0 mA cm-2). Coupled with the LiFePO4 cathode, the Li@Nb2O5-CNF anode sustains a reversible capacity of 163 mAh g-1 with an excellent capacity retention of 93.0% after 370 cycles at 0.5C. This all-around strategy of lithiophilic sites coupled with a 3D conductive nanofiber matrix may shed light on promising applications of high-capacity and dendrite-free Li-metal batteries.

Preparation of nitrogen-doped graphene sheets by a combined chemical and hydrothermal reduction of graphene oxide.

Nitrogen-doped graphene sheets were prepared through a hydrothermal reduction of colloidal dispersions of graphite oxide in the presence of hydrazine and ammonia at pH of 10. The effect of hydrothermal temperature on the structure, morphology, and surface chemistry of as-prepared graphene sheets were investigated though XRD, N(2) adsorption, solid-state (13)C NMR, SEM, TEM, and XPS characterizations. Oxygen reduction and nitrogen doping were achieved simultaneously under the hydrothermal reaction. Up to 5% nitrogen-doped graphene sheets with slightly wrinkled and folded feature were obtained at the relative low hydrothermal temperature. With the increase of hydrothermal temperature, the nitrogen content decreased slightly and more pyridinic N incorporated into the graphene network. Meanwhile, a jellyfish-like graphene structure was formed by self-organization of graphene sheets at the hydrothermal temperature of 160 °C. Further increase of the temperature to 200 °C, graphene sheets could self-aggregate into agglomerate particles but still contained doping level of 4 wt % N. The unique hydrothermal environment should play an important role in the nitrogen doping and the jellyfish-like graphene formation. This simple hydrothermal method could provide the synthesis of nitrogen-doped graphene sheets in large scale for various practical applications.