Search

In this study, three types of biomass with different structures were selected to synthesize carbon matrix in a cathode of Li-S battery. The influence of the structure of raw biomass on microstructure, sulfur-loading amount, and electrochemical performance was investigated in detail. The results demonstrated that the catkin-derived porous carbon (CPC) inherited the 1D-structured morphology and exhibited the highest specific surface area (2033.09 m2/g), the largest sulfur loading (53.72%), and the highest initial discharge specific capacity (1369.52 mA h g−1) under 0.1 C. Comparatively speaking, the wrinkled cloth-like sakura petal–derived porous carbon showed a better capacity (1218.14 mA h g−1) but poor cycling performance. And the 3D network structure of bamboo-derived porous carbon (BPC) exhibited a relatively high capacity retention. These results demonstrated that the structural feature of biomass raw materials plays an important role in the microstructure and electrochemical performance of the carbon products.

The sulfonic acid group exhibits considerable ion affinity. The present work therefore synthesizes, a core-shell composite material having a sulfonated polyaniline shell, and a bamboo-derived porous carbon core loaded with sulfur. The thin, homogeneous shell has a thickness of approximately 20 nm. This composite is employed as a cathode material in Li-S batteries and the electrochemical properties of these devices are systematically investigated. This cathode (containing 64.0 wt% S) exhibits a higher initial discharge capacity (1484 mAh g−1 at 0.1 C), improved cycling stability (853 mAh g−1 after 100 cycles at 0.1 C), and remarkable rate performance (810.2, 682.7 and 353.0 mAh g−1 at 2, 3 and 5 C, respectively). These values are superior to those obtained using a polyaniline shell. Electrochemical impedance spectroscopy and density functional theory calculations are used to elucidate the internal mechanisms of the sulfonated polyaniline shell during cycling. The calculated results demonstrate that the shell possesses extremely high electron and Li ion conductivities, and so enhances the redox reaction kinetics during long-term cycling. It also physically confines and chemically anchors polysulfides, thus limiting the shuttle effect. This cathode design is expected to assist in the future commercialization of Li-S batteries.

Lithium-sulfur (Li-S) battery with high theoretical capacity (1675 mAh g−1) and energy density (2600 Wh kg−1) is principally considered as an attractive alternative for state of art Li-ion batteries. In this study, a series of ternary composites were synthesized with bamboo-derived hierarchical carbon (BDC) to load S and flexible polyaniline (PANI) as a coating layer. The BDC/S composite was encapsulated by different weight percentage of PANI. The ternary PANI@BDC/S composites were characterized detailly by structural and electrochemical analysis and the results revealed that the PANI@BDC/S-20% electrode presented a thin and uniform PANI coating. As a cathode material for Li-S battery, the PANI@BDC/S-20% electrode exhibited the highest initial capacity (1463 mAh g−1 at 0.1C), outstanding long-life performance (366 mAh g−1 at 0.5C after 500 cycles), excellent rate property (527 mAh g−1 at 2C). The incremented gains were mainly because thin PANI coating was polymerized along with the porous carbon walls of BDC substrate, leaving an excellent hierarchical porous microstructure. The specific structure showed great physical confinement for polysulfides, meantime, the polysulfide migration could be restricted by heteroatom (N atom) doped on the PANI backbone. The soft and stable PANI shell reduce volume expansion during cycles, providing an integrated conductive framework for enhancing the electrochemical contact between S particles and carbon substrate. More important, the modified polar interface contributed to stable SEI formation. Such a novel design of cathode material demonstrated great potential for practical applications in Li-S batteries.

Palladium thin films have been grown by thermal atomic layer (ALD) process using Palladium (II) hexafluoroacetylacetonate (Pd(hfac)2) and O3 as the precursors without molecular hydrogen or formalin in a temperature range of 180–220 °C. The palladium films were deposited on sapphire (α-Al2O3, (0001)), silicon (Si, (111)) and silica (SiO2, (100)) substrates at a constant growth rate of about 0.25 Å per cycle. The metallic palladium films produced were highly uniform without fluorine contamination. The surface roughness was only 0.2 nm. The resistivity of the metallic palladium film at ∼25 nm in thickness deposited at 200 °C was around 63 μΩ cm. The morphology of Pd thin films on sapphire, silicon and silica surfaces revealed the island growth and these islands finally coalesced after applying 800 cycles. Thickness-controllable palladium films were obtained with shortened pulse time of both reactants (Pd(hfac)2 and ozone). Our work provides important guidelines for fabrication of metals by adjusting reaction parameters in thermal ALD process. Agency for Science, Technology and Research (A*STAR) The authors would like to acknowledge funding support from the Agency for Science, Technology and Research (A*STAR), AME Individual Research Grant (IRG) for this project. The Program of Huxiang Young Talents (2018RS3099). Natural Science Foundation of Hunan Province (2019JJ50097).

Lithium-sulfur (Li-S) battery processes high theoretical capacity (1675 mA h g−1) and energy density (2600 Wh kg−1), which was widely accepted as one of the most promising candidates for energy storage devices. In this presented study, bamboo-derived hierarchical porous carbon (BDPC) was adopted as a conducting substrate for containing S. Soft polystyrene (PS) and polyaniline (PANI), were prepared as coating layers. The main purpose is to figure out the specific roles that the polymer shells and the heteroatoms doped on polymer backbone play during cycles. The ternary products were characterized by structural analysis and electrochemical testing. The results indicate that, as compared to BDPC/S, the PS@BDPC/S electrode displays higher capacity retention during long-term cycles, especially at the high current rate. It is attributed to the integrated coating shell, which provides physical confinement and reserves spaces for restraining volume expansion. It is noted that the PANI@BDPC/S electrode presents a higher initial capacity, remarkable long-life performance, and excellent rate property. The outstanding performances are closely related to the nitrogen atom doped on PANI backbone, they provide not just abundant polar conducting sites for fast electron/Li-ion transport but strong chemical anchoring for restricting the migration of polysulfides. Therefore, our study poses a clearer understanding of the functionalized polymers used in Li-S battery.

Undoped and Fe-doped Zinc Oxide (ZnO) nanofibers were prepared by electrospinning method to investigate the effect of transition metal ion doping on the photocatalytic performance of ZnO. A variety of techniques were employed to characterize various properties of the fabricated nanofibers. It was realized that the crystallization of ZnO fibers was significantly improved by optimizing the sintering conditions. The results revealed that Fe-doping greatly improved the photocatalytic activity of ZnO owing to modified nanofibers morphology and the reduced optical bandgap. The ZnO nanofibers showed the optimum photocatalytic activity for 1.5% Fe-doping percentage which was attributed to the presence of maximum dopant ions in the ZnO matrix. The enhanced photocatalytic performance of ZnO could increase its scope of industrial and commercial applications.

Nitrogen and sulfur dual-doped graphene (NSG) synthesized by a simple and low-cost one-pot microwave assisted method is applied to immobilize sulfur by the mean of an in situ sulfur deposition approach. Images of scanning electron microscope (SEM) and transmission electron microscope (TEM) show that nano-sulfur (2–20 nm) is wrapped by the transparent NSG nanosheets with wrinkled and folded features. The application of X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirmed the structure and composition of the obtained nitrogen and sulfur dual-doped graphene/sulfur (NSG/S) composites as well. The heteroatom doping content was controlled by adjusting the amount of thiourea. The XPS analysis results indicate that pyridinic-N and pyrrolic-N are dominant among the product, thereby improving the cycle life of the lithium sulfur batteries. The NSG-4/S composites with sulfur loading of 68 wt% exhibits a remarkably higher reversible specific capacity of 1583 mAh g−1, impressive rate capability, splendid specific discharge capacity of 819 mAh g−1 at 0.1 C after 100 cycles and long cycle stability of 640 mAh g−1 after 200 cycles at 1 C.

In this work, graphene quantum dots/sulfur (GQDs/S) composite was prepared as cathode material for lithium sulfur (Li-S) batteries by a feasible chemical method. Multiple polar functional groups in GQDs can provide more active absorption sites to significantly strengthen the chemical absorption with polysulfides, suppressing the ‘shuttle effect’. In addition, the highly dispersed GQDs particles in the solution served as nucleation sites, the dissolved sulfur are reprecipitated around the GQDs, forming a dendritic interlaced network structure to prevent the aggregation of the sulfur, and further enhance the utilization of active substances. A high initial discharge capacity of 1125 mA h g−1 at 0.1C has been obtained in the GQDs/S cell, which is much higher than the initial discharge capacity of 658 mA h g−1 of GQDs/SR prepared by physical melting method. The superior performance of GQDs/S is attributed to the unique dendritic interlaced framework and multiple polar functional groups. The strong chemical effects between polar functional groups and polysulfides have been confirmed by the absorption experiment and DFT calculation. This work develops a new strategy in cathode material design for Li-S batteries.

Here, the hydroxyl content of reduced graphene oxide (rGO) is controlled by adjusting reduction time with l -ascorbic acid as reduction agent to study the effect on cathode performance of lithium sulfur batteries (LSBs). The results indicate that the hydroxyl content decreases from 35.8% to 17.9% with prolonging reduction time from 6 h to 48 h, and the C/O ratio increases. More importantly, it is demonstrated that the rGO with relatively low hydroxyl content within 36 h of reduction is more beneficial to enhance both the initial capacity and capacity retention as well as rate performance of LSBs, which is ascribed to the higher conductivity, stronger adsorption and relatively few reaction by-products with the decrease of hydroxyl content. However, when the reduction time is further prolonged to 48 h, the cathode performance deteriorates. As a result, rGO-36h/S electrode with the optimum hydroxyl content (19.2%) achieves an initial discharge capacity of 1340.9 mAh g−1, which still maintains 707.8 mAh g−1 over 100 cycles at 0.1C. This work may provide a guide for reducing GO when used as sulfur host material or matrix material of LSBs.

The presence of O during the chemical vapour deposition (CVD) of B-doped diamond results in the suppression of B incorporation into the diamond film. In this study, we demonstrate that the amount o ...