Vapor-grown carbon fibers enhanced sulfur-multi walled carbon nanotubes composite cathode for lithium/sulfur batteries

Vapor-grown carbon fibers （VGCFs） were introduced as conductive additives for sulfur-multiwalled carbon nanotubes （S-MWCNTs） composite cathode of lithium-sulfur batteries. The performance of S-MWCNTs composite cathodes with carbon black and VGCFs as sole conductive additives was investigated using scanning electron microscopy （SEM）, galvanostatic charge-discharge tests and electrochemical impedance spectroscopy （EIS）. The results show that the S-MWCNTs composite cathode with VGCFs displays a network-like morphology and exhibits higher activity and better cycle durability compared with the composite cathode with carbon black, delivering an initial discharge capacity of 1254 mA＆#183;h/g and a capacity of 716 mA＆#183;h/g after 40 cycles at 335 mA/g. The interconnected VGCFs can provide a stable conductive network, suppress the aggregation of cathode materials and residual lithium sulfide and maintain the porosity of cathode, and therefore the electrochemical performance of S-MWCNTs composite cathode is enhanced.

Hierarchical nanostructured composite cathode with carbon nanotubes as conductive scaffold for lithium-sulfur batteries

Carbon nanotubes （CNTs） are excellent scaffolds for advanced electrode materials, resulting from their intrinsic sp2 carbon hybridization, interconnected electron pathway, large aspect ratio, hierarchical porous structures, and low cost at a large-scale production. How to make full utilization of the mass produced CNTs as building blocks for nanocomposite electrodes is not well understood yet. Herein, a composite cathode containing commercial agglomerated multi-walled CNTs and S for Li-S battery was fabricated by a facile melt-diffusion strategy. The hierarchical CNT@S coaxial nanocables exhibited a discharging capacity of 1020 and 740 mAh .g-1 at 0.5 and 2.0 C, respectively. A rapid capacity decay of 0.7% per cycle at the initial 10 cycles and a slow decay rate of 0.14% per cycle for the later 140 cycles were detected. Such hierarchical agglomerated CNT@ S cathodes show advantages in easy fabrication, environmentally benign, low cost, excellent scalability, and good Li ion storage performance, which are extraordinary composites for high performance Li-S battery.

Sulfur/carbon composites prepared with ordered porous carbon for Li-S battery cathode

Ordered porous cabon with a 2-D hexagonal structure,high specific surface area and large pore volume was synthesized through a twostep heating method using tri-block copolymer as template and phenolic resin as carbon precursor.The results indicated the electrochemical performance of the sulfur/carbon composites prepared with the ordered porous carbon was significantly affected by the pore structure of the carbon.Both the specific capacity and cycling stability of the sulfur/carbon composites were improved using the bimodal micro/meso-porous carbon frameworks with high surface area.Its initial discharge capacity can be as high as 1200 mAh·g-1 at a current density of 167.5 mA·g-1The improved capacity retention was obtained during the cell cycling as well.

Electrochemical performance of sulfur composite cathode materials for rechargeable lithium batteries

The structure and characteristic of carbon materials have a direct influence on the electrochemical performance of sulfur-carbon composite electrode materials for lithium-sulfur battery. In this paper, sulfur composite has been synthesized by heating a mixture of elemental sulfur and activated carbon, which is characterized as high specific surface area and microporous structure. The composite, contained 70% sulfur, as cathode in a lithium cell based on organic liquid electrolyte was tested at room temperature. It showed two reduction peaks at 2.05 V and 2.35 V, one oxidation peak at 2.4 V during cyclic voltammogram test. The initial discharge specific capacity was 1180.8 mAh g-1 and the utilization of electrochemically active sulfur was about 70.6% assuming a complete reaction to the product of Li2S. The specific capacity still kept as high as 720.4 mAh g^-1 after 60 cycles retaining 61% of the initial discharge capacity.

Facile synthesis and performance of polypyrrole-coated sulfur nanocomposite as cathode materials for lithium/sulfur batteries

In situ chemical oxidation polymerization of pyrrole on the surface of sulfur particles was carried out to synthesize a sulfur/polypyrrole （SIPPy） nanocomposite with core-shell structure. The composite was characterized by elemental analysis, X-ray diffraction, scanning/transmission electron microscopy, and electrochemical measurements. XRD and FTIR results showed that sulfur well dispersed in the core-shell structure and PPy structure was successfully obtained via in situ oxidative polymerization of pyrrole on the surface of sulfur particles. TEM observation revealed that PPy was formed and fixed to the surface of sulfur nanoparticle after polymerization, developing a well-defined core-shell structure and the thickness of PPy coating layer was in the range of 20-30 nm. In the composite, PPy worked as a conducting matrix as well as a coating agent, which confined the active materials within the electrode. Consequently, the as prepared SIPPy composite cathode exhibited good cycling and rate performances for rechargeable lithium/sulfur batteries. The resulting cell containing SIPPy composite cathode yields a discharge capacity of 1039 mAh·g^-1 at the initial cycle and retains 59% of this value over 50 cycles at 0.1 C rate. At 1 C rate, the SIPPy composite showed good cycle stability, and the discharge capacity was 475 mAh·g^-1 after 50 cycles.

Biomass-derived porous carbon with single-atomic cobalt toward high-performance aqueous zinc-sulfur batteries at room temperature

Aqueous zinc-sulfur batteries at room temperature hold great potential for next-generation energy storage technology due to their low cost,safety and high energy density.However,slow reaction kinetics and high activation energy at the sulfur cathode pose great challenges for the practical applications.Herein,biomass-derived carbon with single-atomic cobalt sites(MMPC-Co)is synthesized as the cathode in Zn-S batteries.The catalysis of single-atom Co sites greatly promotes the transform of cathode electrolyte interface(CEI)on the cathode surface,while offering accelerated charge transfer rate for high conversion reversibility and large electrochemical surface area(ECSA)for high electrocatalytic current.Furthermore,the rich pore structure not only physically limits sulfur loss,but also accelerates the transport of zinc ions.In addition,the large pore volume of MMPC-Co is able to relieve the stress effect caused by the volume expansion of Zn S during charge/discharge cycles,thereby maintaining the stability of electrode structure.Consequently,the sulfur cathode maintains a high specific capacity of 729.96 m A h g^(-1)after 500 cycles at4 A g^(-1),which is much better than most cathode materials reported in the literature.This work provides new insights into the design and development of room-temperature aqueous Zn-S batteries.

Atomic Layer Deposition-Assisted Construction of Binder-Free Ni@N-Doped Carbon Nanospheres Films as Advanced Host for Sulfur Cathode

Rational design of hybrid carbon host with high electrical conductivity and strong adsorption toward soluble lithium polysulfides is the main challenge for achieving high-performance lithium-sulfur batteries(LSBs).Herein,novel binder-free Ni@N-doped carbon nanospheres(N-CNSs)films as sulfur host are firstly synthesized via a facile combined hydrothermal-atomic layer deposition method.The cross-linked multilayer N-CNSs films can effectively enhance the electrical conductivity of electrode and provide physical blocking“dams”toward the soluble long-chain polysulfides.Moreover,the doped N heteroatoms and superficial NiO layer on Ni layer can work synergistically to suppress the shuttle of lithium polysulfides by effective chemical interaction/adsorption.In virtue of the unique composite architecture and reinforced dual physical and chemical adsorption to the soluble polysulfides,the obtained Ni@N-CNSs/S electrode is demonstrated with enhanced rate performance(816 mAh g?1 at 2 C)and excellent long cycling life(87%after 200 cycles at 0.1 C),much better than N-CNSs/S electrode and other carbon/S counterparts.Our proposed design strategy offers a promising prospect for construction of advanced sulfur cathodes for applications in LSBs and other energy storage systems.

Novel Nanosized Adsorbing Composite Cathode Materials for the Next Generational Lithium Battery

A novel carbon-sulfur nano-composite material was synthesized by heating sublimed sulfur and high surface area activated carbon （HSAAC） under certain conditions. The physical and chemical per- formances of the novel carbon-sulfur nano-composite were characterized by scanning electron microscopy （SEM）, Brunauer-Emmett-Teller （BET） and X-ray diffraction （XRD）. The electrochemical performances of nano-composite were characterized by charge-discharge characteristic, cyclic voltammetry and electrochemical impendence spectroscopy （EIS）. The experimental results indicate that the electrochemical capability of nano- composite material was superior to that of traditional S-containing composite material. The cathode made by carbon-sulfur nano-composite material shows a good cycle ability and a high specific charge-discharge capacity. The HSAAC shows a vital role in adsorbing sublimed sulfur and the polysulfides within the cathode and is an excellent electric conductor for a sulfur cathode and prevents the shuttle behavior of the lithium-sulfur battery.

Housing Sulfur in Polymer Composite Frameworks for Li–S Batteries

Extensive efforts have been devoted to the design of micro-, nano-, and/or molecular structures of sulfur hosts to address the challenges of lithium–sulfur(Li–S) batteries, yet comparatively little research has been carried out on the binders in Li–S batteries. Herein, we systematically review the polymer composite frameworks that confine the sulfur within the sulfur electrode, taking the roles of sulfur hosts and functions of binders into consideration. In particular, we investigate the binding mechanism between the binder and sulfur host(such as mechanical interlocking and interfacial interactions), the chemical interactions between the polymer binder and sulfur(such as covalent bonding, electrostatic bonding, etc.), as well as the beneficial functions that polymer binders can impart on Li–S cathodes, such as conductive binders, electrolyte intake, adhesion strength etc. This work could provide a more comprehensive strategy in designing sulfur electrodes for long-life, large-capacity and high-rate Li–S battery.

Dry electrode technology for scalable and flexible high-energy sulfur cathodes in all-solid-state lithium-sulfur batteries

All-solid-state lithium-sulfur batteries(ASSLSBs)employing sulfide solid electrolytes are one of the most promising next-generation energy storage systems due to their potential for higher energy density and safety.However,scalable fabrication of sheet-type sulfur cathodes with high sulfur loading and excellent performances remains challenging.In this work,sheet-type freestanding sulfur cathodes with high sulfur loading were fabricated by dry electrode technology.The unique fibrous morphologies of polytetrafluoroethylene(PTFE)binders in dry electrodes not only provides excellent mechanical properties but also uncompromised ionic/electronic conductance.Even employed with thickened dry cathodes with high sulfur loading of 2 mg cm^(-2),ASSLSBs still exhibit outstanding rate performance and cycle stability.Moreover,the all-solid-state lithium-sulfur monolayer pouch cells(9.2 m Ah)were also demonstrated and exhibited excellent safety under a harsh test situation.This work verifies the potential of dry electrode technology in the scalable fabrication of thickened sulfur cathodes and will promote the practical applications of ASSLSBs.

Carbon-based derivatives from metal-organic frameworks as cathode hosts for Li–S batteries

Lithium-sulfur batteries(Li–S batteries) are promising candidates for the next generation high-energy rechargeable Li batteries due to their high theoretical specific capacity(1672 m Ahg-1) and energy density(2500 Wh kg-1). The commercialization of Li–S batteries is impeded by several key challenges at cathode side, e.g. the insulating nature of sulfur and discharged products(Li2S 2 and Li2S), the solubility of long-chain polysulfides and volume variation of sulfur cathode upon cycling. Recently, the carbonbased derivatives from metal-organic frameworks(MOFs) has emerged talent in their utilization as cathode hosts for Li–S batteries. They are not only highly conductive and porous to enable the acceleration of Li +/e-transfer and accommodation of volumetric expansion of sulfur cathode during cycling, but also enriched by controllable chemical active sites to enable the adsorption of polysulfides and promotion of their conversion reaction kinetics. In this review, based on the types of MOFs(e.g. ZIF-8, ZIF-67, Prussian blue, Al-MOF, MOF-5, Cu-MOF, Ni-MOF), the synthetic methods, formation process and morphology, structural superiority of MOFs-derived carbon frameworks along with their electrochemical performance as cathode host in Li–S batteries are summarized and discussed.

Mechanical Properties of Composite SiNx/DLC Films Prepared by Filtered Cathodic Arc of Graphite Incorporated with RF Sputtering of Silicon Nitride

Composite SiNx/DLC films were deposited on Si substrate by RF magnetron sputtering of silicon nitride (Si3N4) target simultaneously with filtered cathode arc (FCA) of graphite. The RF power was fixed at 100 W whereas the arc currents of FCA were 20, 40, 60 and 80 A. The effects of arc current on the structure, surface roughness, density and mechanical properties of SiNx/DLC films were investigated. The results show that the arc current in the studied range has effect on the structure, surface roughness, density and mechanical properties of composite SiNx/DLC films. The composite SiNx/DLC films show the sp3 content between 53.5% and 66.7%, density between 2.54 and2.98 g/cm3, stress between 1.7 and 2.2 GPa, and hardness between 35 and 51 GPa. Furthermore, it was found that the density, stress and hardness correlate linearly with the sp3 content for composite SiNx/DLC films.

Core-shell meso/microporous carbon host for sulfur loading toward applications in lithium-sulfur batteries

Lithium-sulfur（Li-S） batteries belong to one of the promising technologies for high-energy-density rechargeable batteries.However,sulfur cathodes suffer from inherent problems of its poor electronic conductivity and the shuttling of highly dissoluble lithium polysulfides generated during the cycles.Loading sulfur into porous carbons has been proved to be an effective approach to alleviate these issues.Mesoporous and microporous carbons have been widely used for sulfur accommodation,but mesoporous carbons have poor sulfur confinement,whereas microporous carbons are impeded by low sulfur loading rates.Here,a core-shell carbon,combining both the merits of mesoporous carbon with large pore volume and microporous carbon with effective sulfur confinement,was prepared by coating the mesoporous CMK-3 with a microporous carbon（MPC） shell and served as the carbon host（CMK-3 @MPC） to accommodate sulfur.After sulfur infusion,the as-obtained S/（CMK-3@MPC） cathode delivered a high initial capacity of up to 1422 mAh·g-1 and sustained 654 mAh·g-1 reversible specific capacity after 36 cycles at 0.1 C.The good performance is ascribed to the unique core-shell structure of the CMK-3@MPC matrix,in which sulfur can be effectively confined within the meso/microporous carbon host,thus achieving simultaneously high electrochemical utilization.

Status and perspectives of hierarchical porous carbon materials in terms of high-performance lithium-sulfur batteries

Lithium-sulfur(Li-S)batteries,although a promising candidate of next-generation energy storage devices,are hindered by some bottlenecks in their roadmap toward commercialization.The key challenges include solving the issues such as low utilization of active materials,poor cyclic stability,poor rate performance,and unsatisfactory Coulombic efficiency due to the inherent poor electrical and ionic conductivity of sulfur and its discharged products(e.g.,Li2S2 and Li_(2)S),dissolution and migration of polysulfide ions in the electrolyte,unstable solid electrolyte interphase and dendritic growth on an odes,and volume change in both cathodes and anodes.Owing to the high specific surface area,pore volume,low density,good chemical stability,and particularly multimodal pore sizes,hierarchical porous carbon(HPC)mate rials have received considerable attention for circumventing the above pro blems in Li-S batteries.Herein,recent progress made in the synthetic methods and deployment of HPC materials for various components including sulfur cathodes,separators and interlayers,and lithium anodes in Li-S batteries is presented and summarized.More importantly,the correlation between the structures(pore volume,specific surface area,degree of pores,and heteroatom-doping)of HPC and the electrochemical performances of Li-S batteries is elaborated.Finally,a discussion on the challenges and future perspectives associated with HPCs for Li-S batteries is provided.

One dimensional carbon-based composites as cathodes for lithium-sulfur battery

Lithium-sulfur batteries(LSBs),owing to their much higher energy density compared to the traditional lithium-ion battery,are deemed as one of the most promising candidates for the energy storage system.However,several issues including shuttle effect,lithium dendrites,and volumetric expansion seriously impede the commercial applications of LSBs.One-dimensional carbon materials(1DCMs)have been widely used as the matrix material for LSBs due to their high surface area,superior conductivity,good flexibility,excellent mechanical stability,and functional modifiability.In this review,the recent progress in 1D carbon-based composites as cathode including metal compounds/1DCMs,MOFs/1DCMs,MXenes/1DCMs,and polymers/1DCMs were discussed.Different strategies for polysulfide confinement and analysis of the functions of various components in the composites were summarized detailly.In the end,the current challenges of LSBs were systematically summarized,and the future outlooks were proposed,aiming at providing a comprehensive insight into the design of new host materials for nextgeneration LSBs.

A high-loading and cycle-stable solid-phase conversion sulfur cathode using edible fungus slag-derived microporous carbon as sulfur host

Developing a high sulfur(S)-loading cathode with high capacity utilization and long term cyclability is a key challenge for commercial implementation of Li-S battery technology.To overcome this challenge,we propose a solid-phase conversion sulfur cathode by using an edible fungus slag-derived porous carbon(CFS)as sulfur host to fabricate the S/CFS composite and meanwhile,utilizing the vinyl carbonate(VC)as co-solvent of the ether-based electrolyte to in-situ form a protective layer on the S/CFS composite surface through its nucleophilic reaction with the freshly generated lithium polysulfides(LiPSs)at the very beginning of initial discharge,thus isolating the interior sulfur from the outer electrolyte and inhibiting the further generation of soluble LiPSs.Benefitting from the ultrahigh specific surface area of>3,000 m^(2)·g^(−1),ideal pore size of<4 nm,and large pore volume of>2.0 cm^(3)·g^(−1)of the CFS host matrix,the S/CFS cathode even with a high S-loading of 80 wt.%(based on the weight of S/CFS composite)can still operate in a solid-phase conversion manner in the VC-ether co-solvent electrolyte to exhibit a high reversible capacity of 1,557 mAh·g^(−1),a high rate capability with 50%remaining capacity at 2 A·g^(−1)and a high cycling efficiency of 99.9%over 500 cycles.The results presented in this work suggest that a combined action of solid-phase conversion electrochemistry and nanoarchitectured host structure may provide a new path for the design and development of practical lithium-sulfur batteries.

Polyaniline-coated selenium/carbon composites encapsulated in graphene as efficient cathodes for Li-Se batteries

In this work, we developed a polyaniline （PANI）-coated selenium/carbon nanocomposite encapsulated in graphene sheets （PANI@Se/C-G）, with excellent performance in Li-Se batteries. The PANI@Se/C-G nanostructure presents attractive properties as cathode of Li-Se batteries, with a high specific capacity of 588.7 mAh·g^-1 at a 0.2C （1C = 675 mA·g^-1） rate after 200 cycles. Even at a high rate of 2C, a high capacity of 528.6 mAh·g^-1 is obtained after 500 cycles. The excellent cycle stability and rate performance of the PANI@Se/C-G composite can be attributed to the synergistic combination of carbon black （as the conductive matrix for Se） and the double conductive layer comprising the uniform PANI shell and the graphene sheets, which effectively improves the utilization of selenium and significantly enhances the electronic conductivity of the whole electrode.

木质素基碳/硫纳米球复合材料作为高性能锂硫电池正极材料

锂硫二次电池因具有非常高的理论比容量(1675 mAh/g)和能量密度(2600 Wh/kg)而备受关注。然而,锂硫电池的正极材料单质硫因导电性差和在充放电过程中生成的多硫化物Li_(2)S_(n)(4≤n≤8)极易发生“穿梭效应”等问题,严重降低了对活性硫的利用效率,造成电极材料不可逆的容量损失。因此寻找成本低、可循环利用、热稳定性好的碳载体基质是提高锂硫电池电化学性能最有效的方法之一。在本研究中,以天然木质素作为碳源,首先经过萃取和碳化过程制备了多孔碳纳米球,再通过熔融过程,将单质硫成功地包裹进木质素基碳纳米球的孔隙中,制备得到多孔球状结构的碳/硫复合材料(LS-C/S)。当该复合材料用作锂硫电池正极材料时,在0.1 C电流密度下,硫含量为59.41%(质量分数)的电极材料的首次放/充电比容量分别为800.3 mAh/g和758.8 mAh/g,对应库仑效率为94.8%,在经过200次充放电循环后,其比容量稳定在647.4 mAh/g,容量保持率为84.3%,相当于每循环一圈容量平均损失为0.0785%。此外,在经过高倍率的充放电循环后,比容量仍能恢复并稳定在620 mAh/g,展现出良好的可逆倍率稳定性。这种木质素基碳纳米球具有的高比表面积和多孔结构,促进了锂离子和电子的传输,有效地抑制了中间产物多硫化锂的溶解扩散,提高了单质硫作为正极材料的利用效率,因此,复合材料表现出优异的循环稳定性和可逆倍率性能。

高载量锂硫电池正极设计优化

高载量硫正极是研发高能量密度锂硫电池的必要先决条件。然而,硫载量的提高不可避免地会引起正极导电性不良、多硫化物转化动力学缓慢,穿梭效应加剧等问题。本文从化学工程的角度出发,重点关注高载量硫正极中的传质和反应过程,综述了性能优良的高载量锂硫电池正极设计思路。具体而言,从增强电子传导、改善锂离子传质、优化反应动力学、抑制多硫化物穿梭这四种研究思路出发,对比了不同优化策略之间的优劣性,并提出下一代高硫载量硫正极设计的探索方向。分析表明,基于吸附-催化双重功能的三维高导电正极具有巨大发展前景。从应用层面考虑,本文还关注了高载量正极设计中常被忽视的安全性问题,探讨了削弱正极诱导并从源头降低热失效风险的可行性,旨在为研究人员优化高载量(≥4mg/cm^(2))正极设计方案时提供实用指导。

Synthesis of LiFePO_4/C Composite Cathode Materials Using High Surface Area Carbon as Carbon Sources

1 Results The pyrolyzed product of peanut shells was utilized as a carbon source to synthesize a LiFePO4/C composite.The advantages of using agricultural wastes such as peanut shells are low costs,easy processing,and environmentally benigness.Peanut shell was first treated with a porogenic agent to produce a precursor with high porosity and surface area (>2 000 m2·g-1).A small amount of precursor was mixed with LiFePO4 fine powders and heated.The optimum calcination process for synthesizing LiFePO4/C co...