有机硫化合物在锂硫电池中的应用

锂硫电池具有理论能量密度高、环境友好和成本低等优点,有望成为替代锂离子电池的新一代储能系统。然而,锂硫电池充放电产物的绝缘性、可溶性多硫化锂的穿梭效应、硫正极体积膨胀及锂枝晶的不可控生长,严重影响了锂硫电池的实际容量发挥和循环稳定性。为解决上述问题,采用有机硫化合物来替代单质硫作为正极材料是有前途的策略。调控有机硫化合物的硫链、碳链及其相互作用,可改变其电化学反应过程,提高离子/电子电导,抑制穿梭效应。有机硫化合物作为电解液添加剂,可调控硫正极的反应过程并保护金属锂负极,作为聚合物电解质的改性链段可加速锂离子传导。本综述对有机硫化合物在锂硫电池的正极、电解液添加剂和固态电解质中的应用研究进展进行详细的阐述。将有机硫化合物的结构、反应机理和电化学性质联系起来,为解决锂硫电池存在的问题提供见解。最后,提出高性能有机硫化合物的设计合成和机理研究思路,以期实现可实用化的锂硫电池。

Carbon nanotube-hyperbranched polymer core-shell nanowires with highly accessible redox-active sites for fast-charge organic lithium batteries

Organic electrode materials are promising for lithium-ion batteries(LIBs) because of their environmental friendliness and structural diversity.However,they always suffer from limited capacity,poor cycling stability,and rate performance.Herein,hexaazatrinaphthalene-based azo-linked hyperbranched polymer(HAHP) is designed and synthesized as a cathode for LIBs.However,the densely stacked morphology lowers the chance of the active sites participating in the redox reaction.To address this issue,the singlewalled carbon nanotube(SWCNT) template is used to induce the growth of nanosized HAHP on the surface of SWCNTs.The HAHP@SWCNT nanocomposites have porous structures and highly accessible active sites.Moreover,the strong π-π interaction between HAHP and highly conductive SWCNTs effectively endows the HAHP@SWCNT nanocomposites with improved cycling stability and fast charge-discharge rates.As a result,the HAHP@SWCNT nanocomposite cathode shows a high specific capacity(320.4 mA h g^(-1)at 100 mA g^(-1)),excellent cycling stability(800 cycles;290 mA h g^(-1)at 100 mA g^(-1),capacity retained 91%) and outstanding rate performance(235 mA h g^(-1)at 2000 mA g^(-1),76% capacity retention versus 50 mA g^(-1)).This work provides a strategy to combine the macromolecular structural design and micromorphology control of electrode materials for obtaining organic polymer cathodes for high-performance LIBs.

Porous V_2O_5-SnO_2 /CNTs composites as high performance cathode materials for lithium-ion batteries

Vanadium pentoxide （V205） exhibits high theoretical capacities when used as a cathode in lithium ion batteries （LIBs）, but its application is limited by its structural instability as well as its low lithium and electronic conductivities. A porous composite of V2Os-SnO2/carbon nanotubes （CNTs） was prepared by a hydrothermal method and followed by thermal treatment. The small particles of V205, their porous structure and the coexistence of SnO2 and CNTs can all facilitate the diffusion rates of the electrons and lithium ions. Electrochemical impedance spectra indicated higher ionic and electric conductivities, as compared to commercial V205. The VzOs-SnOz/CNTs composite gave a reversible discharge capacity of 198 mAh.g- 1 at the voltage range of 2.05-4.0 V, measured at a current rate of 200 mA.g-1, while that of the commercial V205 was only 88 mAh.g-1, demonstrating that the porous V2Os-SnOz/CNTs composite is a promising candidate for high-performance lithium secondary batteries.

Single-atom catalysts for metal-sulfur batteries:Current progress and future perspectives

Metal-sulfur batteries are recognized as a promising candidate for next generation electrochemical energy storage systems owing to their high theoretical energy density,low cost and environmental friendliness.However,sluggish redox kinetics of sulfur species and the shuttle effect lead to large polarization and severe capacity decay.Numerous approaches from physical barrier,chemical adsorption strategies to electrocatalysts have been tried to solve these issues and pushed the rate and cycle performance of sulfur electrodes to higher levels.Most recently,single-atom catalysts(SACs)with high catalytic efficiency have been introduced into metal-sulfur systems to achieve fast redox kinetics of sulfur conversion.In this review,we systematically summarize the current progress on SACs for sulfur electrodes from aspects of synthesis,characterization and electrochemical performance.Challenges and potential solutions for designing SACs for high-performance sulfur electrodes are discussed.

Research and Prospect of Mulberry (Morus alba L.)

Mulberry(Morus alba L.)is not only rich in nutrients,but also has medicinal value.As a drug and food,it is widely planted all over the country,with considerable yield and economic value.In recent years,it has attracted many scholars and been widely reported,and in-depth research has already been conducted.Through reviewing the literatures on mulberry,this paper summarized the chemical composition,pharmacological effects and quality evaluation of mulberry,providing some reference for the further development and utilization of mulberry.

Efficient polysulfide blocker from conductive niobium nitride@graphene for Li-S batteries

Lithium sulfur batteries are one of the most promising alternative electrochemical systems,but their practical applications are largely hindered by the serious shuttling problems and sluggish redox kinetics.Here,the conductive and polar niobium nitride(NbN)is in-situ introduced onto graphene with ultrasmall size and high dispersion,and their composite is used to construct an efficient lithium polysulfide blocking layer.The graphene helps to construct highly conductive pathways,and niobium nitride serves as the sulfiphilic sites to chemically adsorb the migrating lithium polysulfides and catalyze their redox conversion.Hence,the cells with the Nb N/G interlayers exhibit a long cycle life with a lower capacity decay of 0.096%/cycle at 1 C for 300 cycles and high rate capability of 937 m Ah g^-1 at 2 C.Further coupling with a sulfur/carbon nanofiber electrode,the cell with an ultra-high sulfur loading of 10.8 mg cm^-2 delivers an areal capacity of 12.5 m Ah cm^-2 at 0.1 C.

Different environmental factors drive tree species diversity along elevation gradients in three climatic zones in Yunnan,southern China

Elevational patterns of tree diversity are well studied worldwide.However,few studies have examined how seedlings respond to elevational gradients and whether their responses vary across climatic zones.In this study,we established three elevational transects in tropical,subtropical and subalpine mountain forests in Yunnan Province,southern China,to examine the responses of tree species and their seedlings to elevational gradients.Within each transect,we calculated species diversity indices and composition of both adult trees and seedlings at different elevations.For both adult trees and seedlings,we found that species diversity decreased with increasing elevation in both tropical and subalpine transects.Species composition showed significant elevational separation within all three transects.Many species had specific elevational preferences,but abundant tree species that occurred at specific elevations tended to have very limited recruitment in the understory.Our results highlight that the major factors that determine elevational distributions of tree species vary across climatic zones.Specifically,we found that the contribution of air temperature to tree species composition increased from tropical to subalpine transects,whereas the contribution of soil moisture decreased across these transects.

Boosting nitrogen electrocatalytic fixation by three-dimensional TiO_(2-δ)N_δnanowire arrays

Owing to the environmental and inherent advantages,nitrogen reduction reaction(NRR)by electrocatalysts attracts global attention.The surface engineering is widely employed to enhance the electrocatalytic activity by atomic defects and heterostructure effects.A three-dimensional(3D)free-standing integrated electrode was fabricated by numerous nearly-single-crystal TiO_(2-δ)N_δnanowire arrays.Based on the high electronic conductivity network,it exposes numerous active sites as well to facilitate the selective nitrogen adsorption and*H adsorption suppression.The synergistic effects between Ti^(3+)and oxygen vacancy(O_v)boost the intrinsic catalytic activity,in which Ti^(3+)acquired electrons via Ovcan effectively activate the N≡N bond and make it easy to bind with protons.The energy barrier of primary protonation process(*N_(2)+H^(+)+e^(-)→*NNH)can be dramatically decreased.The highest ammonia yield rate(14.33μg h^(-1)mgcat^(-1))emerges at-0.2 V,while the optimal ammonia Faradaic efficiency(9.17%)is acquired at-0.1 V.Density functional theory(DFT)calculation reveals that the Ti^(3+)can be served as the active sites for nitrogen adsorption and activation,while ammonia synthesis is accomplished by the distal pathway.The high electronic conductivity integrated network and synergistic effects can significantly facilitate nitrogen absorption and accelerate electrocatalytic reaction kinetic,which are responsible for the excellent NRR performance at room temperature.

Electrochemical process of sulfur in carbon materials from electrode thickness to interlayer

Lots of efforts have been done on different porous carbon materials as cathode for Lithium–sulfur(Li–S)battery. However, seldom researches have been done on the relationship between cathode thickness and electrochemical performance. Our work investigates the relation between electrochemical performance and cathode thickness with typical porous carbon materials. We explain the phenomenon that only a modest cathode thickness can have the most adequate electrochemical reaction trend through the aspect of thermodynamics(chemical potential) so that the best electrochemical performance can be obtained.Besides, interlayer can remit the shuttle effect but hinder the lithium ion diffusion process simultaneously. And we verify the effect of interlayer thickness on the shuttle effect and lithium ion diffusion process.

Role of Catalytic Materials on Conversion of Sulfur Species for Room Temperature Sodium–Sulfur Battery

Room temperature sodium–sulfur(RT Na-S)battery with high theoretical energy density and low cost has spurred tremendous interest,which is recognized as an ideal candidate for large-scale energy storage applications.However,serious sodium polysulfide shutting and sluggish reaction kinetics lead to rapid capacity decay and poor Coulombic efficiency.Recently,catalytic materials capable of adsorbing and catalyzing the conversion of polysulfides are profiled as a promising method to improve electrochemical performance.In this review,the research progress is summarized that the application of catalytic materials in RT Na-S battery.For the role of catalyst on the conversion of sulfur species,specific attention is focused on the influence factors of reaction rate during different redox processes.Various catalytic materials based on lightweight and high conductive carbon materials,including heteroatom-doped carbon,metals and metal compounds,single-atom and heterostructure,promote the reaction kinetic via lowered energy barrier and accelerated charge transfer.Additionally,the adsorption capacity of the catalytic materials is the key to the catalytic effect.Particular attention to the interaction between polysulfides and sulfur host materials is necessary for the exploration of catalytic mechanism.Lastly,the challenges and outlooks toward the desired design of efficient catalytic materials for RT Na-S battery are discussed.

Functional trait space and redundancy of plant communities decrease toward cold temperature at high altitudes in Southwest China

Plant communities in mountainous areas shift gradually as climatic conditions change with altitude. How trait structure in multivariate space adapts to these varying climates in natural forest stands is unclear. Studying the multivariate functional trait structure and redundancy of tree communities along altitude gradients is crucial to understanding how temperature change affects natural forest stands. In this study, the leaf area, specific leaf area, leaf carbon, nitrogen, and phosphorous content from 1,590 trees were collected and used to construct the functional trait space of 12 plant communities at altitudes ranging from 800 m to 3,800 m across three mountains. Hypervolume overlap was calculated to quantify species trait redundancy per community. First,hypervolumes of species exclusion and full species set were calculated, respectively. Second, the overlap between these two volumes was calculated to obtain hypervolume overlap. Results showed that the functional trait space significantly increased with mean annual temperature toward lower altitudes within and across three mountains, whereas species trait redundancy had different patterns between mountains. Thus, warming can widen functional trait space and alter the redundancy in plant communities. The inconsistent patterns of redundancy between mountains suggest that warming exerts varying influences on different ecosystems. Identification of climate-vulnerable ecosystems is important in the face of global warming.

LX-92树脂对硫酸体系低浓度镓离子的动态吸附

研究了粉煤灰模拟硫酸浸出液中的镓在聚苯乙烯树脂(LX-92)上吸附分离的可能性,采用固定床吸附装置考察了树脂动态吸附-脱附镓的行为,利用Thomas, Yoon-Nelson和Adam-Bohart经验模型对动态吸附过程进行了分析和预测。结果表明,降低流速(F)、增加床层高度(Z)、减小镓(III)初始浓度(C0)有助于提高固定床吸附效率和平衡吸附容量;在C0为260 mg/L, Fad为5.0m L/min、吸附温度为55℃的条件下,树脂的最大动态平衡吸附容量为56.65 mg/g;用3.0 mol/L H_(2)SO4在1.0 m L/min流速的最佳洗脱条件下,洗脱率达到94.40%;树脂在硫酸体系中对低浓度镓离子的吸附-脱附具有良好的循环使用性,经过吸附-脱附镓离子可富集10倍以上;树脂吸附镓的动态行为满足Yoon-Nelson动态吸附模型,建立了动态吸附速率常数KYN和半穿透时间τ值常数与初始离子浓度、流速、床层高度的对应方程,为低浓度镓离子的吸附法提取工程化提供了理论基础。

A Novel Ion-exchange Method for the Synthesis of Nano-SnO/micro-C Hybrid Structure as High Capacity Anode Material in Lithium Ion Batteries

A novel and simple ion-exchange method was developed for the synthesis of nano-SnO/micro-C hybrid structure. The structure of the as prepared nano-SnO/micro-C was directly revealed by scanning electron microscopy （SEM） and transmission electron microscopy （TEM）. SnO particles with the size about 25 nm were well confined in amorphous carbon microparticles. Carbon matrix in micrometer scale not only acts as a protective buffer for the SnO nanoparticles during the battery cycling processes, but also avoids the shortcomings of nanostructures, such as low tap density and potential safety threats. Electrochemical behaviors of the nano-SnO/micro-C were tested as anode material in lithium ion batteries. The initial reversible capacity is 508 mA h g^-1, and the reversible capacity after 60 cycles is 511 mA h g^-1, indicating good capacity retention ability.

Environmental and spatial contributions to seedling and adult tree assembly across tropical,subtropical and subalpine elevational gradients

Aims Quantifying the relative importance of the mechanisms that drive community assembly in forests is a crucial issue in community ecol-ogy.The present study aims to understand the ways in which niche-based and spatially based processes influence community assembly in areas in different climatic conditions and how these processes change during the transition from seedling to adult.Methods In this study,we investigated how taxonomic and phylogenetic beta diversity in seedling and adult stages of forest trees change across three elevational transects in tropical,subtropical and subalpine for-ests in Southwest China,and the relationships of these changes to the environment and inter-site distances.We quantified the relative contribution of environmental conditions and spatial distribution to taxonomic and phylogenetic beta diversity of both seedling and adult life stages along each elevational transect.We also quantified the taxonomic and phylogenetic similarity between seedlings and adult trees along elevations.Important Findings Taxonomic and phylogenetic beta diversity of both seedlings and adult trees increased with an increase in both environmental distance and spatial distance in all three transects.On both taxonomic and phylo-genetic levels,the effects of environmental filtering and spatial dispos-ition varied between life stages and among forest types.Phylogenetic similarity between seedlings and adult trees increased with elevation,although the taxonomic similarity did not show clear elevational pat-terns.Our results suggest that the relative contribution of niche-based and space-based processes to taxonomic and phylogenetic assem-blages varies across major plant life stages and among forest types.Our findings also highlight the importance of ontogenetic stages for fully understanding community assembly of long-lived tree species.

Intrinsic emission and tunable phosphorescence of perfluorosulfonate ionomers with evolved ionic clusters

Intrinsic emission from unorthodox luminogens without traditional conjugated building blocks is drawing increasing attention.However,the emission mechanism is still controversial.Herein,we demonstrate the intriguing emission from perfluorosulfonate ionomers(PFSIs),which can be explained by the clustering triggered emission(CTE)mechanism.Despite being free of any conventional chromophores,PFSIs exhibit bright emission and multi-color phosphorescence(77 K)in concentrated solutions,powders and membranes with obvious aggregation-induced emission(AIE)characteristics.Clustered sulfonic acids are responsible for the light emission,and their connection and evolution are deeply explored via X-ray diffraction(XRD)and small angel X-ray scattering(SAXS),in which the electron overlap determined by the clustered status results in the extended conjugation and simultaneously rigidified conformations.These results demonstrate that it is feasible to use fluorescence analysis to explore the ionic cluster structure and evolution of PFSI,and it can be applied in the pure organic luminescent field as well.