High-performance lithium-sulfur battery based on porous N-rich g-C_(3)N_(4) nan-otubes via a self-template method

The commercial development of lithium-sulfur batteries(Li-S)is severely limited by the shuttle effect of lithium polysulfides(LPSs)and the non-conductivity of sulfur.Herein,porous g-C_(3)N_(4) nanotubes(PCNNTs)are synthesized via a self-template method and utilized as an efficient sulfur host material.The one-dimensional PCNNTs have a high specific surface area(143.47 m^(2)·g^(-1))and an abundance of macro-/mesopores,which could achieve a high sulfur loading rate of 74.7wt%.A Li-S battery bearing the PCNNTs/S composite as a cathode displays a low capacity decay of 0.021% per cycle over 800 cycles at 0.5 C with an initial capacity of 704.8 mAh·g^(-1).PCNNTs with a tubular structure could alleviate the volume expansion caused by sulfur and lithium sulfide during charge/discharge cycling.High N contents could greatly enhance the adsorption capacity of the carbon nitride for LPSs.These synergistic effects contribute to the excellent cycling stability and rate performance of the PCNNTs/S composite electrode.

Preparation of CoO/SnO_(2)@NC/S composite as high-stability cathode material for lithium-sulfur batteries

To improve the sulfur loading capacity of lithium-sulfur batteries(Li-S batteries)cathode and avoid the inevitable“shuttle effect”,hollow N doped carbon coated CoO/SnO_(2)(CoO/SnO_(2)@NC)composite has been designed and prepared by a hydrothermal-calcination method.The specific surface area of CoO/SnO_(2)@NC composite is 85.464 m2·g^(-1),and the pore volume is 0.1189 cm3·g^(-1).The hollow core-shell structure as a carrier has a sulfur loading amount of 66.10%.The initial specific capacity of the assembled Li-S batteries is 395.7 mAh·g^(-1) at 0.2 C,which maintains 302.7 mAh·g^(-1) after 400 cycles.When the rate increases to 2.5 C,the specific capacity still has 221.2 mAh·g^(-1).The excellent lithium storage performance is attributed to the core-shell structure with high specific surface area and porosity.This structure effectively increases the sulfur loading,enhances the chemical adsorption of lithium polysulfides,and reduces direct contact between CoO/SnO_(2) and the electrolyte.

Fabricating titanium dioxide/N-doped carbon nanofibers as advanced interlayer for improving cycling reversibility of lithium-sulfur batteries

"Shuttle effect" is detrimental for maintaining the high capacity and cycling reversibility of lithium-sulfur batteries(LSBs).To inhibit polysulfide migration,N-doped carbon nanofibers(N-CNFs) membrane comprising TiO_(2)nanoparticles(TiO_(2)/N-CNFs) is fabricated using an electrospinning-calcination method and further applied as interlayer in LSBs.The TiO_(2)/N-CNFs interlayer helps the battery to deliver a high specific capacity of 1155.2 mA·h·g^(-1)at 0.2 C with high Coulombic efficiency,good rate capability and stability.When cycling at 0.5 C,a capacity retention rate of 62.4% is achieved over 300 cycles,which is higher than that of CNFs and TiO_(2)/CNFs counterparts.The excellent performance should mainly be attributed to the alleviated "shuttle effect" deriving from high polysulfide trapping ability of TiO_(2)nanoparticles and N heteroatoms in interwoven CNFs.

KOH-assisted aqueous synthesis of bimetallic metal-organic frameworks and their derived selenide composites for efficient lithium storage

To solve low efficiency,environmental pollution,and toxicity for synthesizing zeolitic imidazolate frameworks(ZIFs)in organic solvents,a KOH-assisted aqueous strategy is proposed to synthesize bimetallic ZIFs polyhedrons,which are used as precursors to prepare bimetallic selenide and N-doped carbon(NC)composites.Among them,Fe–Co–Se/NC retains the three-dimensional(3D)polyhedrons with mesoporous structure,and Fe–Co–Se nanoparticles are uniform in size and evenly distributed.When assessed as anode material for lithium-ion batteries,Fe–Co–Se/NC achieves an excellent initial specific capacity of 1165.9 m Ah·g^(-1)at 1.0 A·g^(-1),and the reversible capacity of Fe–Co–Se/NC anode is 1247.4 m Ah·g^(-1)after 550 cycles.It is attributed to that the uniform composite of bimetallic selenides and N-doped carbon can effectively tune redox active sites,the stable 3D structure of Fe–Co–Se/NCs guarantees the structural stability and wettability of the electrolyte,and the uniform distribution of Fe–Co–S nanoparticles in size esuppresses the volume expansion and accelerates the electrochemical reaction kinetics.

KOH-assisted aqueous synthesis of ZIF-67 with high-yield and its derived cobalt selenide/carbon composites for high-performance Li-ion batteries

To solve the environmental pollution and low yield during the sythesis of zeolitic imidazolate frameworks(ZIFs)and their derived materials,a KOH-assisted aqueous strategy is proposed to synthesize cobalt zeolitic imidazolate framework(ZIF-67)polyhedrons,which are used as precursors to prepare cobalt selenide/carbon composites with different crystal phases(Co_(0.85)Se,CoSe_2).When evaluated as anode material for lithium ion batteries,Co_(0.85)Se/C composites deliver a reversible capacity of 758.7 m A·h·g^(-1)with a capacity retention rate of 90.5%at 1.0 A·g^(-1)after 500 cycles,and the superior rate capability is 620 m A·h·g^(-1)at 2.0 A·g^(-1).The addition of KOH accelerates the production of ZIF-67 crystals by boosting deprotonation of dimethylimidazole,resulting in rapid growth and structures transition from two-dimensional to three-dimensional of ZIF-67 in aqueous solution,which greatly promotes the application of MOFs in the field of energy storage and conversion.

泵组浮筏隔振系统参数设计及性能分析

对浮筏隔振系统的动力参数进行研究设计,通过Matlab编程分析不同质量比和刚度比对系统动力特性的影响。分析表明:质量比的影响主要体现在系统的第2个共振频率之前,随着质量比的增大,力的传递率变小,系统的隔振性能逐渐提高;刚度比的影响较为复杂,刚度比越大,系统的振动衰减越快,但同时也会使系统的第1个共振频率变小,使其隔振频带减小。最后利用ANSYS有限元软件对所设计的浮筏隔振系统的隔振性能进行数值模拟研究,对所设计系统的隔振性能进行分析研究。

基于正交实验的库水位骤降边坡渗透稳定敏感性分析

为定量化研究库水位骤降下不同非饱和参数对边坡的渗流特性以及稳定性的影响,根据非饱和渗流及抗剪强度原理,利用Geostudio的Seep/w与Slope/w模块对某边坡库水位骤降不同非饱和参数下的渗透稳定性进行了数值模拟研究,并根据正交实验分析法进行了敏感性分析,计算结果表明:库水位骤降下不同监测点孔压呈现先减小后不变的趋势,上部监测点的孔压降幅较下部监测点要小,孔压降幅与参数a,k呈负相关,而与参数m呈正相关;库水位骤降情况下上部监测点与下部监测点存在两个变形阶段,即库水位骤降时间段内的位移快速上升阶段以及库水位骤降结束后的位移缓慢上升阶段,上部监测点的位移要大于下部监测点的位移;参数a与参数k变动对安全系数的变幅影响较大,参数m与参数n对安全系数的变幅影响较小,参数a,m,k与安全系数呈正相关,而参数n与安全系数呈负相关;对非饱和参数对边坡稳定性进行了正交实验敏感性分析,参数a,m,n,k的敏感性大小分别为参数a≥参数k≥参数m≥参数n.

Controllable fabrication of FeCoS_(4) nanoparticles/S-doped bowl-shaped hollow carbon as efficient lithium storage anode

To address the low conductivity and easy agglomeration of transition metal sulfide nanoparticles,FeCoS_(4) nanoparticles embedded in S-doped hollow carbon(FeCoS_(4)@S-HC)composites were successfully fabricated through a combination of hydrothermal processes and sulfidation treatment.The unique bowlshaped FeCoS_(4)/S-HC composites exhibit excellent structural stability with a high specific surface area of 303.7 m^(2)·g^(-1) and a pore volume of 0.93 cm^(3)·g^(-1).When applied as anode material for lithium-ion batteries,the FeCoS_(4)@S-HC anode exhibits efficient lithium storage with high reversible specific capacity(970.2 mA·h·g^(-1) at 100 mA·g^(-1))and enhanced cycling stability(574 mA·h·g^(-1) at 0.2 A·g^(-1) after 350 cycles,a capacity retention of 84%).The excellent lithium storage is attributed to the fact that the bimetallic FeCoS_(4) nanoparticles with abundant active sites can accelerate the electrochemical reaction kinetics,and the bowl-shaped S-HC structure can provide a stable mechanical structure to suppress volume expansion.

Zephyranthes-like Co2NiSe4 arrays grown on 3D porous carbon frame-work as electrodes for advanced supercapacitors and sodium-ion batteries

Developing suitable electrode materials for electrochemical energy storage devices by biomorph assisted design has become a fascinating topic due to the fantastic properties derived from bio-architectures.Herein,zephyranthes-like Co_(2)NiSe_(4)arrays grown on butterfly wings derived three-dimensional(3D)carbon framework(Z-Co_(2)NiSe_(4)/BWC)is fabricated via hydrothermal assembly and further conversion method.Benefiting from its unique structure and multi-components,the obtained Z-Co_(2)NiSe_(4)/BWC electrode for supercapacitor delivers an excellent specific capacitance of 2,280 F·g^(-1)at 1 A·g^(-1).Impressively,the constructed asymmetric supercapacitor using Co_(2)NiSe_(4)/BWC as positive electrode and activated butterfly wings carbon as negative electrode acquires a high energy density of 42.9 Wh·kg^(-1)at a power density of 800 W·kg^(-1)with robust stability of 94.6%capacitance retention at 10 A·g^(-1)after 5,000 cycles.Moreover,the Z-Co_(2)NiSe_(4)/BWC as anode for sodium-ion batteries exhibits a high specific capacity of 568 mAh·g^(-1)at 0.1 A·g^(-1)and high cycling stability(maintaining 80.1%of the second cycle after 100 cycles).The outstanding electrochemical performances are ascribed to that the synergistic effect of bimetallic selenides and N-doped carbon improves electrochemical activities and conductivity.One-dimensional(1D)nanoneedles grown on 3D porous framework increase the exposure of redox-active sites,endow adequate transmission channels of electrons/ions,and guarantee stability of the electrode during charge/discharge processes.This study will shed light on the avenue towards extending such nanohybrids to excellent energy storage applications.