二硫苏糖醇/多壁碳纳米管阻隔层抑制锂硫电池的穿梭效应

二硫苏糖醇(DTT)作为剪切剂,对高阶多硫化物进行剪切阻止其溶解,抑制穿梭效应的产生。以二硫苏糖醇(DTT)和多壁碳纳米管(MWCNTs)复合薄膜作为锂硫电池正极片与隔膜之间的阻隔层,抑制多硫化物的溶解和扩散,阻止穿梭效应,减小活性物质的损失,提高锂硫电池的容量和循环性能。利用透射电子显微镜(TEM)和扫描电镜(SEM)等进行结构和性能的表征。电化学测试结果表明,含DTT/MWCNTs阻隔层的锂硫电池在0.2 C倍率首次放电比容量达到1 674 mAh/g,活性物质的利用率达到99.9%。在1 C充放电300次循环后,容量依然保持在780 mAh/g,是首次放电容量1 094 mAh/g的71.3%,且库伦效率保持在95.3%以上。在5 C和10 C倍率下充放电,电池比容量分别达到597和214 mAh/g。     

利用二硫苏糖醇夹层抑制锂硫电池的穿梭效应

为了抑制锂硫电池的穿梭效应,改善锂硫电池的电化学性能,尝试以二硫苏糖醇(DTT)为剪切剂,对高阶多硫化物进行剪切以阻止其溶解。将二硫苏糖醇(DTT)掺入多壁碳纳米管(MWCNTs)纸中,制得DTT夹层,将该DTT夹层置于锂硫扣式半电池正极片和隔膜之间,正极片的载硫面密度约为2 mg/cm2。SEM观察结果证实DTT均匀分散在MWCNTs纸的表面和空隙中。电化学测试结果表明引入DTT夹层结构的锂硫电池在0.05C倍率首次放电比容量达到1 288 mAh/g,首次库伦效率接近100%,在0.5C、2C、4C倍率下充放电时的比容量分别达到650mAh/g、600mAh/g、410mAh/g。DTT夹层结构的引入可有效剪切高阶多硫化物并阻止其迁移到锂负极,从而抑制穿梭效应,改善锂硫电池的循环稳定性和库伦效率。     

多壁碳纳米管纸作正极集流体的锂硫电池性能

为了改善锂硫电池的循环性能,以纸纤维为基体,多壁碳纳米管(MWCNTs)为导电剂,采用真空抽滤法制得MWCNTs导电纸,并将MWCNTs导电纸作为正极集流体代替铝箔应用于锂硫电池。对MWCNTs导电纸进行了形貌结构表征和电化学性能测试,并对循环后的MWCNTs导电纸电极进行EDS检测。结果显示,MWCNTs均匀地附着在纸纤维基体上,多空隙的MWCNTs导电纸三维结构明显。采用MWCNTs导电纸作集流体的锂硫电池在0.05C和1C倍率充放电下循环30次,比容量分别保持615mAh/g、496mAh/g,库伦效率达97.5%以上,且电荷转移电阻在循环后降低。EDS元素分析结果证实MWCNTs导电纸对多硫化锂有吸附作用,从而一定程度抑制了锂硫电池的穿梭效应。因此,以MWCNTs导电纸作为集流体能有效增加活性物质硫的负载量和接触面积,使锂硫电池具有良好的循环稳定性和库伦效率性能。     

三维多孔碳纳米片PC/CNT夹层高性能锂硫电池

为了抑制多硫化物的溶解与扩散,改善锂硫电池的电化学性能,利用多孔碳纳米片(PC)与多壁碳纳米管(MWCNTs)复合形成新型三维多孔碳纳米片(PC/CNT)夹层来捕获可溶性多硫化物。其中,MWCNTs提供高效的导电通道并维持电极结构完整性;一维碳纳米管和二维多孔碳纳米片形成三维互联结构,有利于电/离子快速传输。利用透射电子显微镜(TEM)和扫描电镜(SEM)等进行结构和性能的表征。电化学测试结果表明,PC/CNT夹层高性能锂硫电池在0.05C倍率下首次放电比容量达到1 311 m Ah/g,活性物质的利用率高达78.8%。在2C倍率下循环5次后,放电比容量仍然达到941 m Ah/g,是首次比容量的71.8%,且库伦效率仍然保持在96%,显示出良好的倍率和循环性能。     

碳纳米管改性锰酸锂电化学性能的研究

以多壁碳纳米管(Multi-walled carbon nanotubes,MWCNTs)为主要添加相,协同超导乙炔炭黑(SP),对锰酸锂进行电化学改性。对MWCNTs进行预处理,采用扫描电子显微镜观察MWCNTs的微观形貌。掺杂不同质量比的导电剂,制成电池并以恒流充放电方法测试其电化学性能。结果表明,碳包覆后电池的初始充放电比容量都有所下降,掺入1%(质量分数,下同)MWCNTs后的LiMn2O4的首次充放电效率为96.51%,不可逆容量最小,初始放电比容量为116.42mAh/g,经20次循环后容量保持率仍达96.2%,使用复合碳源掺杂时,当m(MWCNTs)∶m(SP)=1∶2时,首次充放电效率达96.67%,不可逆容量最小,初始放电比容量为119.37 mAh/g,且掺杂2%MWCNTs的效果要略好于掺入2%SP。     

花瓣状纳米硫和球状纳米硫的制备及性能

锂硫电池因能量密度高、环境友好,被认为是最有希望的新一代能源储存装置。但是,多硫化物穿梭效应和体积膨胀等问题是锂硫电池目前所面临的巨大挑战。通过化学合成法制备了不同形貌且具有稳定规则结构的纳米硫,为电池在充放电过程中提供更多的活性位点,有效减少正极活性物质的损失,使电池的电化学性能得到提升。结果表明,花瓣状纳米硫材料在0.1C的电流密度下有740.72 mAh/g的初始容量,100次循环后容量保持在362.07 mAh/g;球状纳米硫材料在0.1C的电流密度下初始容量为825.30 mAh/g,100次循环后容量保持在418.06 mAh/g,每圈的容量衰减率仅为0.493%。     

氧化炭黑/Ni_3S_2-S正极材料在Li-S电池中的应用研究

制备了氧化炭黑与Ni_3S_2复合材料作为导电客体的硫正极材料,并研究了基于此硫正极的锂硫电池的电化学性能。研究结果证明,Ni_3S_2作为共同导电客体材料可以使锂硫电池具有更好的倍率性能和循环稳定性。在1C的充放电倍率下,锂硫电池在300次循环后可逆容量为595mAh/g;其中,首次放电比容量达到1163mAh/g。     

多硫化物阻隔层在锂硫电池中的应用研究进展

锂硫电池具有远高于锂离子电池的理论放电比容量(1 675 mAh/g)和能量密度(2 600 Wh/kg),被认为是很具应用潜力的电池体系,因此被广泛的研究和关注。然而硫的导电性能差、利用率低以及多硫化物的穿梭效应等问题使得锂硫电池的循环性能不稳定。为了克服穿梭效应的影响,近年来发展了多种新型的多硫化物阻隔层设计和制备方法来提高电池循环稳定性,本文分别从碳质材料阻隔层、金属氧化物阻隔层以及导电聚合物阻隔层三方面综述了最新的研究进展,并指出免集流体正极材料、阻隔层以及隔膜实现一体化设计将成为锂硫电池研究的发展方向。     

三维结构石墨烯与硫的复合正极材料研究

在蔗糖辅助下以一步水热法制备了具有三维网络结构的石墨烯材料,以其作为与硫复合的载体实现了硫在石墨烯中的均匀分布,将此复合材料(3DGNS/S)应用于锂硫电池中表现出了优异的电化学性能:该材料在285mA/g下,首次放电比容量为1396mAh/g。2142mA/g下,首次放电比容量为713mAh/g,循环100周后,仍具有681mAh/g的放电比容量,平均每周的容量衰减率为0.04%,表现出优秀的循环性能。     

二硫化钼对锂硫电池正极材料性能的影响机理

炭黑具有良好的导电性、价格较低、来源稳定、可大量制备等优点,可有效提高硫正极材料的导电性,改善电极的动力学性能。二维层状结构的二硫化钼(MoS_2)因其含有的金属-硫键可以与多硫化物通过静电作用或化学键作用结合,从而可以有效地抑制锂硫电池存在的穿梭效应,提高锂硫电池的倍率性能。本文采用球磨法和水热法制备了硫/炭黑复合材料以及类石榴状硫/炭黑/层状MoS_2复合正极材料,并研究了该复合正极材料的性能。研究结果表明,硫/炭黑/层状MoS_2复合正极材料有效提高了电池的比容量,改善了电池的倍率性能和循环稳定性。在0.2 A/g倍率下,初始放电容量可达767.9 mAh/g。     

Three-dimensionally ordered,ultrathin graphitic-carbon frameworks with cage-like mesoporosity for highly stable Li-S batteries

Mesoporous carbons have been widely utilized as the sulfur host for lithium-sulfur (Li-S) batteries.The ability to engineer the porosity,wall thickness,and graphitization degree of the carbon host is essential for addressing issues that hamper commercialization of Li-S batteries,such as fast capacity decay and poor high-rate performance.In this work,highly ordered,ultrathin mesoporous graphitic-carbon frameworks (MGFs) having unique cage-like mesoporosity,derived from self-assembled Fe3O4 nanoparticle superlattices,are demonstrated to be an excellent host for encapsulating sulfur.The resulting S@MGFs exhibit high specific capacity (1,446 mAh·g-1 at 0.15 C),good rate capability (430 mAh.g-1 at 6 C),and exceptional cycling stability (～0.049％ capacity decay per cycle at 1 C) when used as Li-S cathodes.The superior electrochemical performance of the S@MGFs is attributed to the many unique and advantageous structural features of MGFs.In addition to the interconnected,ultrathin graphitic-carbon framework that ensures rapid electron and lithium-ion transport,the microporous openings between adjacent mesopores efficiently suppress the diffusion of polysulfides,leading to improved capacity retention even at high current densities.     

Modulating d-Band Electronic Structures of Molybdenum Disulfide via p/n Doping to Boost Polysulfide Conversion in Lithium-Sulfur Batteries

Polysulfide shuttle effect and sluggish sulfur reaction kinetics severely impede the cycling stability and sulfur utilization of lithium-sulfur (Li-S) batteries. Modulating d-band electronic structures of molybdenum disulfide electrocatalysts via p/n doping is promising to boost polysulfide conversion and suppress polysulfide migration in lithium-sulfur batteries. Herein, p-type V-doped MoS₂ (V-MoS₂) and n-type Mn-doped MoS₂ (Mn-MoS₂) catalysts are well-designed. Experimental results and theoretical analyses reveal that both of them significantly increase the binding energy of polysulfides on the catalysts’ surface and accelerate the sluggish conversion kinetics of sulfur species. Particularly, the p-type V-MoS₂ catalyst exhibits a more obvious bidirectional catalytic effect. Electronic structure analysis further demonstrates that the superior anchoring and electrocatalytic activities are originated from the upward shift of the d-band center and the optimized electronic structure induced by duplex metal coupling. As a result, the Li-S batteries with V-MoS₂ modified separator exhibit a high initial capacity of 1607.2 mAh g⁻¹ at 0.2 C and excellent rate and cycling performance. Moreover, even at a high sulfur loading of 6.84 mg cm⁻², a favorable initial areal capacity of 8.98 mAh cm⁻² is achieved at 0.1 C. This work may bring widespread attention to atomic engineering in catalyst design for high-performance Li-S batteries.     

Nickel embedded porous macrocellular carbon derived from popcorn as sulfur host for high-performance lithium-sulfur batteries

Due to the demands for high performance and ecological and economical alternatives to conventional lithium-ion batteries (LiBs),the development of lithium-sulfur (Li-S) batteries with remarkably higher theoretical capacity (1675 mA h g-1) has become one of the extensive research focus directions world-wide.However,poor conductivity of sulfur,critical cyclability problems due to shuttle of polysulfides as intermediate products of the cathodic reaction,and large volume variation of the sulfur composite cathode upon operation are the major bottlenecks impeding the implementation of the next-generation Li-S batteries.In this work,a unique three-dimensional (3D) interconnected macrocellular porous carbon (PC) architecture decorated with metal Ni nanopatticles was synthesized by a simple and facile strategy.The as-fabricated Ni/PC composite combines the merits of conducting carbon skeleton and highly adsorptive abilities of Ni,which resulted in efficient trapping of lithium polysulfides (LiPSs) and their fast conversion in the electrochemical process.Owing to these synergistic advantageous features,the composite exhibited good cycling stability (512.3 mA h g-1 after 1000 cycles at 1 C with an extremely low capacity fading rate 0.03 ％ per cycle),and superior rate capability (747.5 mAh g-1 at 2 C).Accordingly,such Ni nanoparticles embedded in a renewable puffed corn-derived carbon prepared via a simple and effective route represent a promising active type of sulfur host matrix to fabricate high-performance Li-S batteries.     

Dealloying-derived nanoporous deficient titanium oxide as high-performance bifunctional sulfur host-catalysis material in lithium-sulfur battery

In this work,we report a facile dealloying strategy to tailor the surface state of nanoporous TiO2 towards high-efficiency sulfur host material for lithium-sulfur(Li-S)batteries.When used as a sulfur cathode material,the oxygen-deficient TiO2-x exhibits enhanced lithium polysulfides(LiPS)adsorption and con-version kinetics that effectively tackle the shuttle effect in lithium-sulfur batteries.The excellent ability of the oxygen vacancy sites on TiO2-x surface to trap LiPS is proved by experimental observations and density functional theory(DFT)calculations.Meanwhile,it also promotes conversion kinetics of lithium polysul-fides,as verified by the asymmetric cell experiment.Accordingly,compared with the S/TiO2 cathode,the oxygen-deficient S/TiO2-x electrode exhibits preeminent rate and cycling performance in lithium-sulfur batteries:it delivers an ultra-low capacity decay of0.039％per cycle after 1000 cycles at 1 C.Tunning the surface state of metal oxides by dealloying method offers a new facile strategy to design efficient sulfur cathode materials for lithium-sulfur batteries.     

切割方向对桦木衍生的取向微通道生物质炭锂硫电池隔膜性能的影响

生物源材料由于来源丰富、可循环使用、无污染, 并且能够实现多功能化而引起了广泛关注。本研究利用大自然中广泛分布的桦木树干为原料, 通过不同取向切割、去木质素和碳化等过程得到具有相应取向的微孔道结构的生物质炭, 并用作锂硫电池的隔层。生物质炭的比表面积为267.7 m ²/g, 有大量的微孔及介孔。测试结果表明: 沿与电极平面呈45°方向切割所得的生物质炭的电化学性能最好。在0.2C(1C=1650 mA/g)下该生物质炭隔层制备的锂硫电池初始比容量为979.4 mAh/g, 200次循环后保留有625.4 mAh/g, 每圈容量损失率仅为0.18%。该生物质炭隔层可以有效地吸附和阻挡多硫化锂, 减小充放电过程中产生的穿梭效应, 并且桦木的微通道结构和类蒸腾特性可以有效地提高电池的比容量、循环稳定性, 有利于锂硫电池的商业化应用。     

Ni Single Atoms on MoS2 Nanosheets Enabling Enhanced Kinetics of Li-S Batteries

The practical application of Li-S batteries is seriously hindered due to its shuttle effect and sluggish redox reaction, which requires a better functional separator to solve the problems. Herein, polypropylene separators modified by MoS₂ nanosheets with atomically dispersed nickel (Ni-MoS₂) are prepared to prevent the shuttle effect and facilitate the redox kinetics for Li-S batteries. Compared with pristine MoS₂ nanosheets, Ni-MoS₂ nanosheets exhibit both excellent adsorption and catalysis performance for overcoming the shuttle effect. Assembled with this novel separator, the Li-S batteries exhibit an admirable cycling stability at 2 C over 400 cycles with 0.01% per cycle decaying. In addition, even with a high sulfur loading of 7.5 mg cm⁻², the battery still provides an initial capacity of 6.9 mAh cm⁻² and remains 5.9 mAh cm⁻² after 50 cycles because of the fast convention of polysulfides catalyzed by Ni-MoS₂ nanosheets, which is further confirmed by the density functional theory (DFT) calculations. Therefore, the proposed strategy is expected to offer a new thought for single atom catalyst applying in Li-S batteries.     

A dual-functional poly(vinyl alcohol)/poly(lithium acrylate)composite nanofiber separator for ionic shielding of polysulfides enables high-rate and ultra-stable Li-S batteries

Despite the high theoretical specific capacity,the main challenges of rechargeable lithium-sulfur(Li-S)batteries,including the unceasing shuttle of soluble lithium polysulfides(LiPSs)and severe Li corrosion,seriously hinder their commercial and practical applications.Herein,a bifunctional polyvinyl alcohol/poly(lithium acrylate)(C-PVA/PAA-Li)composite nanofiber separator is developed to address the main challenges in Li-S batteries by simultaneously allowing rapid lithium ion transport and ionic shielding of polysulfides.The C-PVA/PAA-Li composite nanofiber membrane is prepared via the facile electrospinning strategy,followed by thermal crosslinking and in-situ lithiation processes.Differing from the conventional Celgard-based coating methods accompanied by impaired lithium ion transport efficiency,the C-PVA/PAA-Li composite nanofiber membrane possesses well-developed porous structures and high ionic conductivity,thus synergistically reducing the charge transfer resistance and inhibiting the growth of lithium dendrites.The resulting Li-S batteries exhibit an ultra-low fading rate of 0.08%per cycle after 400 cycles at 0.2 C,and a capacity of 633 mAhg?1 at a high current density of 3 C.This study presents an inspiring and promising strategy to fabricate emerging dual-functional separators,which paves the pathway for the practical implementation of ultra-stable and reliable Li-S battery systems.     

S,N-codoped carbon capsules with microsized entrance: Highly stable S reservoir for Li-S batteries

Nanostructured carbon materials are extensively applied as host materials to improve the utilization rate and reversibility of elemental sulfur in lithium sulfur (Li-S) batteries. Here, S, N-codoped carbon capsules (SNCCs) with microporous walls, prepared by a self-assembly process, are used as the sulfur host material in Li-S batteries. The SNCCs provide plenty of micron-sized cavities to accommodate a high S loading, which are sealed by thick walls with microsized entrance to efficently suppress the shuttle effect of lithium polysulfides. As the cathode in Li-S battery, the SNCCs/sulfur composite with a sulfur mass loading of 70 wt% exhibits a high average reversible capacity of 1220 and 1116 mA h g^?1 at 0.5C and 1C, respectively, superior rate performance (905 and 605 mAh g^?1 at 5C and 10C, respectively) and excellent cycling stability (capacity fading rate of 0.03% per cycle in 500 cycles). Even at a high sulfur areal loading of 7.3 mg/cm², the SNCCs/0.7S electrode still deliver a high initial discharge capacity of 838 mAh g^?1 and keeps at 730 mAh g^?1 after 100 cycles, corresponding to an extraordinary capacity retention of 87.1%, showing an excellent cyclic stability. The outstanding electrochemical performance is associated with the unique capsule structure with abundant volume, microsized entrance and high conductivity. Our results provides a new strategy to prepare highly stable sulfur-carbon composites for the application in Li-S batteries.     

磷掺杂石墨相氮化碳的制备及其在锂硫电池中的应用

通过热缩聚合成法,采用尿素为原料,制备石墨相氮化碳(g-C₃N₄),以磷酸氢二胺作为磷源,制备不同磷含量的磷掺杂g-C₃N₄ (xP-CN),研究磷掺杂对xP-CN的微观结构、形貌及xP-CN/S复合材料作为锂硫电池正极材料电化学性能的影响。研究表明,磷掺杂后xP-CN的层间距增大,导电性提高,比表面积变大,10% P-CN的比表面积最大达到101.741 m2·g?1。10% P-CN/S复合材料在0.05 C (1 C=1675 mA·h·g?1)下首次放电比容量达到1383.8 mA·h·g?1,在0.2 C下循环100次后可逆比容量为860.0 mA·h·g?1,而g-C₃N₄/S复合材料比容量仅为178.3 mA·h·g?1;10% P-CN/S复合材料经过倍率测试后比容量可以回复到0.2 C时的93.6%,表现出良好的循环性能和倍率性能。