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Abstract
Tailored design/construction of high-quality sulfur/carbon composite cathode is critical for development of advanced lithium-sulfur batteries. We report a powerful strategy for integrated fabrication of sulfur impregnated into three-dimensional (3D) multileveled carbon nanoflake-nanosphere networks (CNNNs) by means of sacrificial ZnO template plus glucose carbonization. The multileveled CNNNs are not only utilized as large-area host/backbone for sulfur forming an integrated S/CNNNs composite electrode, but also serve as multiple carbon blocking barriers (nanoflake infrastructure andnanosphere superstructure) to physically confine polysulfides at the cathode. The designedself-supported S/CNNNs composite cathodes exhibit superior electrochemical performances with high capacities (1395 mAh g⁻¹ at 0.1C, and 769 mAh g⁻¹ at 5.0C after 200 cycles) and noticeable cycling performance (81.6% retention after 200 cycles). Our results build a new bridge between sulfur and carbon networks with multiple blocking effects for polysulfides, and provide references for construction of other high-performance sulfur cathodes.
... 1.5 V [26][27][28][29]. However, crystalline FeS 2 suffers from drawbacks such as the "shuttle effect" of polysulfide dissolution, nanoiron agglomeration, and a huge volume expansion ratio of 170% [26,[30][31][32]. ...
Areal power density is one of the core indicators determining how large areas a microbattery need to occupy when integrated directly with microelectronic devices for the Internet of Things. Unfortunately, the low power density of microbatteries hinders their applications, because microelectronic devices only provide finite areas for integration. Herein, we show that sputtered iron oxysulfide (FeOxSy) thin films subjected to in situ plasma pretreatment display ultrahigh power density. This in situ plasma pretreatment can be regarded as a universal interface optimization strategy for suppressing mechanical degradation upon extended cycling. The synergistic effects of high structural integrity (robust interfacial adhesiveness and stress-relieving islands), perfect electrochemical reversibility, and near-surface charge exchanges (pseudocapacitive lithium storage mechanism) result in extremely high power density and stable cycling performance. The pretreated FeOxSy thin films can output an areal power density as high as 14.6 mW cm−2 and a considerable volumetric energy density of 291 µW h cm−2 µm−1. Such a highpower density constitutes a new state-of-the-art level for sputtered thin-film materials with comparative areal capacity. This work provides an efficient and simple pretreatment method for achieving ultrahigh-power and stable thin-film electrodes for microbatteries.
... Among the various alternative energy storage systems, the lithium-sulfur (Li-S) batteries are considered as one of the most promising candidates for next-generation energy storage devices, owing to the extremely high theoretical specific capacity (1672 mAh g −1 ) of sulfur [9,10]. Additionally, sulfur is a cheap, low-toxic and abundant resource, which makes Li-S batteries a particularly low-cost and attractive energy storage technology [11,12]. However, Li-S batteries still hindered by the following critical challenges [13][14][15]. ...
Improving the utilization efficiency of active materials and suppressing the dissolution of lithium polysulfides into the electrolyte are very critical for development of high-performance lithium-sulfur batteries. Herein, a novel strategy is proposed to construct a three-dimensional (3D) N-doped carbon nanotubes (CNTs) networks to support lithium polysulfides (3D-NCNT-Li2S6) as a binder-free cathode for high-performance lithium-sulfur batteries. The 3D N-doped CNTs networks not only provide a conductive porous 3D architecture for facilitating fast ion and electron transport but also create void spaces and porous channels for accommodating active sulfur. In addition, lithium polysulfides can be effectively confined among the networks through the chemical bond between Li and N. Owing to the synergetic effect of the physical and chemical confinement for the polysulfides dissolution, the 3D-NCNT-Li2S6 cathodes exhibit enhanced charge capacity and cyclic stability with lower polarization and faster redox reaction kinetics. With an initial discharge capacity of 924.8 mAh g−1 at 1 C, the discharge capacity can still maintain 525.1 mAh g−1 after 200 cycles, which is better than that of its counterparts.
... Recently, lithium-sulfur (Li-S) batteries have been considered as great deal of the most promising candidates for the nextgeneration electric vehicles because of its higher energy density (2600 Wh kg À1 ), specific capacity (1675 mAh g À1 , about 3-6 times higher than the conventional Li-ion batteries), natural abundance and low cost of sulfur (Ref [1][2][3][4][5]. Apart from these merits, numerous practical challenges of Li-S batteries are required to overcome for commercialization: (1) poor electronic conductivity of sulfur and its discharge products, which causes low utilization of active material; (2) large volume expansion (80%) of active material during lithiation/delithiation process resulting in structural destruction of electrode; (3) the high solubility of lithium polysulfides in organic electrolytes, which leads to low Coulombic efficiency during cycling (Ref [6][7][8][9][10][11][12][13][14][15]. ...
Herein, sulfur-/nitrogen-doped graphene (SNG) binary composite has been prepared by melt diffusion method and employed as cathode material for lithium-sulfur (Li-S) battery. The physical and electrochemical performances of prepared SNG binary composite were characterized using x-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscope, cyclic voltammetry and galvanostatic charge–discharge test.
The SNG cathode delivers a high initial discharge capacity of 1135 mAh g−1, and it sustains the capacity of 687 mAh g−1 over the 50th cycle at 0.1C rate. The good electrochemical performance of SNG cathode is accredited to N-doping in graphene, which provides faster charge transfer pathway and suppresses the shuttle effect of polysulfides. The present study determines that the prepared SNG composite is a suitable material for cathode in Li-S battery application.
... To further confirm the chemical feature of the composite, Raman spectrum of NMO/RGO/ S was collected (Fig. 2b). The peak located at 473 cm −1 can be attributed to sulfur [26]. The low peak broad band at 620 cm −1 can be attributed to the tensile vibration of the Mn-O bond [27]. ...
In this work, we fabricated a sulfur-infiltrated three-dimensional reduced graphene oxide wrapped Na4Mn9O18 nanorods microsphere (NMO/RGO/S) as efficient cathode material lithium/sulfur (Li/S) batteries. The NMO/RGO/S microsphere was developed by spray drying the NMO, GO, and S suspension followed by a hydrazine reduction process. The resulting hierarchical microsphere, constructed by cross-linked NMO nanorods and RGO sheet, shortens the electron/ion diffusion pathway. It also provides adequate void space to accommodate S and mitigate the volume variation during cycling. Additionally, the polar NMO nanorods offer strong chemical adsorption to lithium polysulfides, which was confirmed by adsorption experiment. Owing these features, the NMO/RGO/S electrode exhibited a high specific capacity and good cyclability as well. The initial discharge capacity is 952.8 mAh g−1 at 1 C, and after 500 cycles, a discharge capacity of 520 mAh g−1 is maintained, which corresponds to a capacity fading of 0.09% per cycle. The simple preparation method for the construction of NMO/RGO/S microsphere reported in the study advances the development of efficient cathode materials for Li/S battery.
Graphical abstract
... To cope with these notorious posers, conductive matrices with polyporous volume like conductive polymers [3e5] and carbon nanomaterials [6e9] have been developed for compositing with sulfur in current researches. In addition to reinforcing conductivity and accommodating volumetric change, the sulfur hosts with hollow nanostructure [3,6,10] or meso-/micropore [8,11,12] were also reported to physical restrict the sulfur species. Among them, carbon based nanomaterials like hollow carbon nanorods [13], porous carbon [14], graphene aerogels [15] and porous graphene frameworks [16,17] were the most extensively studied hosts for sulfur immobilization. ...
Employ of hollow nanostructure carbon materials as a host framework for sulfur cathode is a promising strategy to cope with the notorious posers in lithium-sulfur (Li–S) battery. However, the dissolution and diffusion of intermediate polysulfides in electrolytes still result in rapid capacity loss and poor rate performances, due to the weak interaction between polarized lithium polysulfides and non-polarized carbon host. To address this challenge, a bipolar material, zinc oxide embedded tetrapod-shaped carbon shell (TCS/ZnO) is designed for polysulfides immobilization in Li–S battery. The TCS/ZnO composites are synthesized through a CVD process using tetrapod shaped ZnO nanowhiskers as template, following by a partially hydrogen etching treatment. Attributed to the strong chemisorption of ZnO to polysulfides, high initial specific capacity of 1284 mAh g⁻¹sulfur, stable Coulombic efficiency of ∼99.5% and excellent cycling stability (815 mAh g⁻¹sulfur after 100 cycles at 0.2 C) are exhibited for S-TCS/ZnO cathode with optimized ratio of ZnO.
Room‐temperature sodium–sulfur (RT Na–S) batteries are arousing great interest in recent years. Their practical applications, however, are hindered by several intrinsic problems, such as the sluggish kinetic, shuttle effect, and the incomplete conversion of sodium polysulfides (NaPSs). Here a sulfur host material that is based on tungsten nanoparticles embedded in nitrogen‐doped graphene is reported. The incorporation of tungsten nanoparticles significantly accelerates the polysulfides conversion (especially the reduction of Na2S4 to Na2S, which contributes to 75% of the full capacity) and completely suppresses the shuttle effect, en route to a fully reversible reaction of NaPSs. With a host weight ratio of only 9.1% (about 3–6 times lower than that in recent reports), the cathode shows unprecedented electrochemical performances even at high sulfur mass loadings. The experimental findings, which are corroborated by the first‐principles calculations, highlight the so far unexplored role of tungsten nanoparticles in sulfur hosts, thus pointing to a viable route toward stable Na–S batteries at room temperatures.
Lithium–sulfur batteries (LSBs) are attracting much attention due to their high theoretical energy density and are considered to be the predominant competitors for next‐generation energy storage systems. The practical commercial application of LSBs is mainly hindered by the severe “shuttle effect” of the lithium polysulfides (LiPSs) and the serious damage of lithium dendrites. Various carbon materials with different characteristics have played an important role in overcoming the above‐mentioned problems. Carbon spheres (CSs) are extensively explored to enhance the performance of LSBs owing to their superior structures. The review presents the state‐of‐the‐art advances of CSs for advanced high‐energy LSBs, including their preparation strategies and applications in inhibiting the “shuttle effect” of the LiPSs and protecting lithium anodes. The unique restriction effect of CSs on LiPSs is explained from three working mechanisms: physical confinement, chemical interaction, and catalytic conversion. From the perspective of interfacial engineering and 3D structure designing, the protective effect of CSs on the lithium anode is also analyzed. Not only does this review article contain a summary of CSs in LSBs, but also future directions and prospects are discussed. The systematic discussions and suggested directions can enlighten thoughts in the reasonable design of CSs for LSBs in near future.
Owing to the inimitable properties of the 1D carbon nanofibers (CNFs) and 2D carbon nanosheets (CNSs), especially the nanoscale size and functionalized structures, CNFs and CNSs showed excellent application in electrochemistry, adsorption, electrochemical sensing, and energy storage. This review covers an opening introduction of CNFs and CNSs and pointed out the key points of fabrication methods of CNFs and CNSs, especially about the electrospun CNFs and biomass CNSs. In addition, the functional tailoring of CNFs and CNSs was detailed by constructing pores, doping heteroatoms (N, S, P), graphitizing and combining with metal/alloy, polymers, carbon nanomaterials, biomolecules, and so on. At the end, we summarized some of the most significant achievements attained by CNFs and CNSs and their nanocomposites, meanwhile addressing the future challenges in this area.
The massive and sustained realization of highly reactive [email protected] scaffold matrix may push forward the further development of next-generation alkaline battery systems. Herein, we put forward a scalable and applicable strategy to convert wasted bamboo products into porous carbon microfibers (CMFs) with Fe or Ni nanoparticles evenly inlaid, using a special and effective “colloid-assisted” approach. Such a smart/economical nano-engineering technique would enable the vast production of uniform “mosaic” hybrid configurations, endowing CMFs-based electrodes with desired superiorities like the ease of electrochemical activation, excellent electrical conductivity and great sustainability/feasibility in real applications. The as-built Fe and Ni [email protected] can serve as admirable negative and positive electrodes for Ni-Fe cells, respectively, with outstanding electrochemical performances including stable/high specific capacities and good capacity retention over 4000 cycles. The assembled full-cell batteries also demonstrate large specific charge capacity, excellent rate capability and long-lasting cyclic lifetime as well as high energy/power densities, holding a great promise in near-future low-cost energy-storage usage.
Tremendous demands for highly sensitive and selective nonenzymatic electrochemical biosensors have motivated intensive research on advanced electrode materials with high electrocatalytic activity. Herein, the 3D‐networked CuO@carbon nanowalls/diamond (C/D) architecture is rationally designed, and it demonstrates wide linear range (0.5 × 10⁻⁶–4 × 10⁻³ m), high sensitivity (1650 µA cm⁻² mm⁻¹), and low detection limit (0.5 × 10⁻⁶ m), together with high selectivity, great long‐term stability, and good reproducibility in glucose determination. The outstanding performance of the CuO@C/D electrode can be ascribed to the synergistic effect coming from high‐electrocatalytic‐activity CuO nanoparticles and 3D‐networked conductive C/D film. The C/D film is composed of carbon nanowalls and diamond nanoplatelets; and owing to the large surface area, accessible open surfaces, and high electrical conduction, it works as an excellent transducer, greatly accelerating the mass‐ and charge‐transport kinetics of electrocatalytic reaction on the CuO biorecognition element. Besides, the vertical aligned diamond nanoplatelet scaffolds could improve structural and mechanical stability of the designed electrode in long‐term performance. The excellent CuO@C/D electrode promises potential application in practical glucose detection, and the strategy proposed here can also be extended to construct other biorecognition elements on the 3D‐networked conductive C/D transducer for various high‐performance nonenzymatic electrochemical biosensors.
Rational design of modified separator is of great significance in effectively suppressing the shuttle of lithium polysulfides (LiPSs) and hence realizing fulfilling cycling performance of lithium-sulfur batteries (LSBs). In this paper, we developed a facile strategy to fabricate P-doped carbon coated CNT skeleton coupled with nickel phosphide (Ni 2 P) nanospheres ([email protected]), and then we employed the as-developed hybrid as a multifunctional modified interlayer onto PP separator (denoted as PCNPmPP) to face the challenge of LiPSs shuttling. The as-prepared hybrid provides abundant physical confinement and strong chemical adsorption for inhibiting polysulfides shuttling as well as efficient catalysis for accelerating LiPSs converting. As a result, the LSBs based on [email protected] modified PP separator have delivered a highly reversible cycling performance with high initial discharge capacity of 1067 mAh g ⁻¹ and low capacity decay rate of 0.077% per cycle within 500 cycles at 1 C. The promising results demonstrate that the [email protected] composite is capable of effectively inhibiting the diffusion and shuttle of LiPSs. This paper provides a novel thinking for the synthesis of multifunctional interlayer onto PP separator for advanced LSBs.
Discarded cigarette filters mainly composed of cellulose acetate (CA) are non-biodegradable and can cause severe environmental pollution hazard. In an effort to turn waste into wealth, herein, we explore a hierarchically porous carbon@graphene composites derived from cigarette filters as efficient cathode hosts for lithium-sulfur (Li-S) batteries. The hierarchical porous structure enables high sulfur loading and confines the dissolution of lithium polysulfides while the strongly coupled graphene provide electrically conductive network for electrons to transfer within the composites. Accordingly, the cigarette filters-derived porous carbon@graphene-based cathode containing 78 wt% sulfur could achieve a high capacity of 1010 mAh g-1 at 0.2 C after 200 cycles and even 722 mAh g-1 at 0.5 C over 1000 cycles with only ~0.04% capacity loss per cycle. The findings may pave a new trash-to-treasure avenue for the development of high-performance electrode materials in energy storage devices.
Lithium-sulfur batteries (LSBs) are deemed to be among the most prospective next-generation advanced high-energy batteries. Advanced cathode materials fabricated from biological carbon are becoming more popular due to their unique properties. Inspired by the fibrous structure of bamboo, herein we put forward a smart strategy to convert bamboo sticks for barbecue into uniform bamboo carbon fibers (BCF) via a simple hydrothermal treatment proceeded in alkaline solution. Then NiCl2 is used to etch the fibers through a heat treatment to achieve Ni-embedded porous graphitic carbon fibers (PGCF/Ni) for LSBs. The designed PGCF/Ni/S electrode exhibits improved electrochemical performances including high initial capacity (1198 mAh g1 at 0.2 C), prolonged cycling life (1030 mAh g1 at 0.2 C after 200 cycles), and improved rate capability. The excellent properties are attributed to the synergistic effect of 3D porous graphitic carbon fibers with highly conductive Ni nanoparticles embedded.
Lithium−sulfur batteries have been regarded as very promising energy storage devices due to their high energy density as well as low cost and toxicity of sulfur cathode. However, the practical applications of Li–S batteries have been impeded by short cycling life and low sulfur utilization, resulting from the dissolution of intermediate lithium polysulfides into electrolytes and the large volume variation of sulfur during cycling. Herein, we present a dual−confined strategy to efficiently entrap lithium polysulfides and alleviate the large volume change using N−doped tube−in−tube structured carbon tubes anchored on a 3D scaffold of graphene foam through the synergistic effect of spatial restriction and chemical interaction. The tube−in−tube carbon structures provide sufficient empty space to confine sulfur for high loading, accommodate large volume change during lithiation and de−lithiation, and facilitate better immobilization of polysulfides demonstrated by first-principles calculations. Therefore, enhanced capacities, ultralong−cycling stability, and improved rate capability even with a high sulfur loading (~5.6 mg cm−2) could be achieved.
Herein we report an effective way for construction of all-solid-state lithium-sulfur batteries (LSBs) with sulfur/reduced graphene oxide (rGO) and Li9.54Si1.74P1.44S11.7Cl0.3 solid electrolyte. In the composite cathode, the Li9.54Si1.74P1.44S11.7Cl0.3 powder is homogeneously mixed with the S/rGO composite to enhance the ionic conductivity. Coupled with metallic Li anode and solid electrolyte, the designed S/rGO-Li9.54Si1.74P1.44S11.7Cl0.3 composite cathode exhibits a high specific capacity and good cyclic stability. A high initial discharge capacity of 969 mAh g-1 is achieved at a current density of 80 mA g-1 at room temperature and the cell retains a reversible capacity over 827 mAh g-1 after 60 cycles. The enhanced performance is attributed to the intimate contact between the S/rGO and Li9.54Si1.74P1.44S11.7Cl0.3 electrolyte, and high electrical conductivity of rGO and high ionic conductivity of the solid electrolyte.
In this work, a microporous and high surface area carbon material with excellent electron conductivity is synthesized through carbonizing and activation processes using waste shaddock wadding. Because of the unique multi-hole, thin sheets cluster and irregular wrinkled surface coexisting structure, the shaddock wadding carbon-sulfur (SWD-S) composite can be used as a kind of cathode material for rechargeable lithium-sulfur batteries by loading element sulfur into the shaddock wadding activated carbon via simple heat treatments. Because of the high specific surface area of SWD (1637.3 m² g⁻¹), the SWD-S composite has a sulfur content about 73.7 wt%, and delivers a high initial discharge capacity of 1050 mAh g⁻¹ at a rate of 0.2C. Moreover, SWD-S composite exhibits a good rate capacity and excellent cycle ability. Over 200 cycles it achieves with a high columbic efficiency around 95%. After 200 cycles at 0.2C, it still remains a capacity of 599 mAh g⁻¹.
The rechargeable Lithium-Sulfur (Li-S) battery is an attractive platform for high-energy, low-cost electrochemical energy storage. Practical Li-S cells are limited by several fundamental issues, such as the low conductivity of sulfur and its reduction compounds with Li and the dissolution of long-chain lithium polysulfides (LiPS) into the electrolyte. We report on an approach that allows high-performance sulfur-carbon cathodes to be designed based on tethering polyethylenimine (PEI) polymers bearing a large amount of amine groups in every molecular unit to hydroxyl and carboxyl functionalized multi-wall carbon nanotubes. Significantly, for the first time we show by means of direct dissolution kinetics measurements that the incorporation of CNT-PEI hybrids in a sulfur cathode stabilizes the cathode by both kinetic and thermodynamic processes. Composite sulfur cathodes based the CNT-PEI hybrids display high capacity at both low and high current rates, with capacity retention rates exceeding 90%. The exceptional electrochemical performance of the materials is shown by means of DFT analysis to originate from the specific and strong interaction between sulfur species and amine groups in PEI; from interconnected conductive CNT substrate; and from the combination of physical and thermal sequestration of LiPS provided by the CNT-PEI composite.
Elemental sulfur cathodes for lithium/sulfur cells are still in the stage of intensive research due to their unsatisfactory capacity retention and cyclability. The undesired capacity degradation upon cycling originates from gradual diffusion of lithium polysulfides out of the cathode region. To prevent losses of certain intermediate soluble species and extend lifespan of cells, the effective encapsulation of sulfur plays a critical role. Here we report an applicable way, by using thin-layered nickel-based hydroxide as a feasible and effective encapsulation material. In addition to being a durable physical barrier, such hydroxide thin films can irreversibly react with lithium to generate protective layers that combine good ionic permeability and abundant functional polar/hydrophilic groups, leading to drastic improvements in cell behaviours (almost 100% coulombic efficiency and negligible capacity decay within total 500 cycles). Our present encapsulation strategy and understanding of hydroxide working mechanisms may advance progress on the development of lithium/sulfur cells for practical use.
Lithium-sulfur batteries attract much interest as energy storage devices for their low cost, high specific capacity, and energy density. However, the insulating properties of sulfur and high solubility of lithium polysulfides decrease the utilization of active materials by the battery resulting in poor cycling performance. Herein, we design a multifunctional carbon-nanotube paper/titanium-dioxide barrier which effectively reduces active material loss and suppresses the diffusion of lithium polysulfides to the anode, thereby improving the cycling stability of lithium-sulfur batteries. Using this barrier, an activated carbon/sulfur cathode with 70% sulfur content delivers stable cycling performance and high Coulombic efficiency (∼99%) over 250 cycles at a current rate of 0.5 C. The improved electrochemical performance is attributed to the synergistic effects of the carbon nanotube paper and titanium dioxide, involving the physical barrier, chemical adsorption from the binding formation of Ti-S and S-O, and other interactions unique to the titanium dioxide and sulfur species. [Figure not available: see fulltext.] © 2015, Tsinghua University Press and Springer-Verlag Berlin Heidelberg.
Elemental sulfur is one of the most attractive cathode active materials in lithium batteries because of its high theoretical specific capacity. Despite the positive aspect, lithium-sulfur batteries have suffered from severe capacity fading and limited rate capability. Here we report facile large-scale synthesis of a class of organosulfur compounds that could open a new chapter in designing cathode materials to advance lithium-sulfur battery technologies. Porous trithiocyanuric acid crystals are synthesized for use as a soft template, where the ring-opening polymerization of elemental sulfur takes place along the thiol surfaces to create three-dimensionally interconnected sulfur-rich phases. Our lithium-sulfur cells display discharge capacity of 945 mAh g(-1) after 100 cycles at 0.2 C with high-capacity retention of 92%, as well as lifetimes of 450 cycles. Particularly, the organized amine groups in the crystals increase Li(+)-ion transfer rate, affording a rate performance of 1210, mAh g(-1) at 0.1 C and 730 mAh g(-1) at 5 C.
Highly active electrode materials with judicious design in nanostructure are important for the construction of high-performance electrochemical energy storage devices. In this work, we have fabricated tubular TiC fibre cloth as an interesting type of stable supercapacitve materials. Hollow microfibres of TiC are synthesized by carbothermal treatment of commercial T-shirts cotton fibres. To demonstrate the rational of nanostructuring in energy storage, the hollow fibres are further covered by interwoven TiC nanotube branches, forming 3D tubular all-TiC hierarchical fibres with high electrical conductivity, high surface area, and high porosity. For energy storage functions, organic symmetric supercapacitors based on the hollow fibre-nanotube (HFNT) TiC cloth electrodes are assembled and thoroughly characterized. The TiC-based electrodes show very stable capacitance in long charge/discharge cycles and at different temperatures. In particular, the integrated TiC HFNT cloth electrodes show a reasonably high capacitance (185 F/g at 2 A/g), better cycling stability at high-rates (e.g., 97% retention at room temperature after 150,000 cycles, and 67% at 15 oC after 50,000 cycles) than other control electrodes (e.g., pure carbon fibre cloths). It is envisaged that these 3D tubular TiC fibres cloth is also useful for solar cells and electrocatalysis.
Prohibiting lithium polysulfides from being dissolved to electrolyte is the most critical challenge for pursuing high-performance Li/S batteries. Taking full advantage of interactions between polysulfides and functional groups of third-party additives has been proven to be an efficient strategy. In the present work, we selected DNA to decorate CMK-3/S cathodes. The –PO and N– sites of the constituent deoxyribonucleotides of DNA are demonstrated to be capable of anchoring polysulfides through our DFT calculations. The experimental results show that adding a small amount of DNA into the CMK-3/S composite significantly improved the cyclic performance. In particular, with a moderate DNA loading rate, the DNA post-loading procedure resulted in a discharge capacity of 771 mA h g−1 at 0.1 C after 200 cycles (70.7% retention of the initial), which yielded slightly improved performance as compared to the DNA pre-loading procedure. The proposed DNA decorating scheme may provide an applicable technical solution for developing high-performance Li/S batteries.
Being simple, inexpensive, scalable and environmentally friendly, microporous biomass biochars have been attracting enthusiastic attention for application in lithium-sulfur (Li−S) batteries. Herein, porous bamboo biochar is activated via a KOH/annealing process that creates a microporous structure, boosts surface area and enhances electronic conductivity. The treated sample is used to encapsulate sulfur to prepare microporous bamboo carbon-sulfur (BC-S) nanocomposite as the cathode for Li–S batteries for the first time. The BC-S nanocomposite with 50 wt% sulfur content delivers a high initial capacity of 1295 mAh/g at a low discharge rate of 160 mA/g and high capacity retention of 550 mAh/g after 150 cycles at a high discharge rate of 800 mA/g with excellent coulombic efficiency (≥95%). This suggests that the BC-S nanocomposite could be a promising cathode material for Li–S batteries.
A porous three-dimensional nitrogen-doped graphene (3D-NG) was introduced as an interconnected framework for sulfur in lithium–sulfur batteries. The 3D-NG-sulfur composite (3D-NGS) with a high sulfur content of 87.6 wt% was synthesized via a facile one-pot solution method and sulfur was well dispersed within it. The as-designed 3D-NGS composite exhibits excellent rate capability and cyclability. The discharge specific capacity is 792 mA h g−1 after 145 cycles at a current density of 600 mA g−1 and the capacity fading rate is 0.05% per cycle. Even at a high rate of 1500 mA g−1, the composite still shows a good cycle performance with a capacity of 671 mA h g−1 after 200 cycles. The outstanding electrochemical performance can be attributed to the flexible porous 3D structure and N-doping in graphene. The flexible 3D-NG can provide a conductive framework for electron transport and alleviate the volume effect during cycling. N-doping can facilitate the penetration of Li ions across the graphene and restrain sulfur due to the strong chemical bonding between S and the nearby N atoms.
In lithium-sulfur batteries, small S2–4 molecules show very different electrochemical responses from the traditional S8 material. Their exact lithiation/delitiation mechanism is not clear and how to select proper electrolytes for the S2–4 cathodes is also ambiguous. Here, S2–4 and S8/S2–4 composites with highly ordered microporous carbon as a confining matrix are fabricated and the electrode mechanism of the S2–4 cathode is investigated by comparing the electrochemical performances of the S2–4 and S2–4/S8 electrodes in various electrolytes combined with theoretical calculation. Experimental results show that the electrolyte and microstructure of carbon matrix play important roles in the electrochemical performance. If the micropores of carbon are small enough to prevent the penetration of the solvent molecules, the lithiation/delithiation for S2–4 occurs as a solid-solid process. The irreversible chemically reactions between the polysulfudes and carbonates, and the dissolution of the polysulfides into the ethers can be effectively avoided due to the steric hindrance. The confined S2–4 show high adaptability to the electrolytes. The sulfur cathode based on this strategy exhibits excellent rate capability and cycling stability.
Shot boundary detection (SBD) is a fundamental step in video retrieval and analysis. Although the existing methods have achieved a lot on this field, this problem has not been sufficiently resolved, especially for the gradual boundary. This paper proposed a new method for SBD using a three-stage approach based on the Multilevel Difference of Colour Histograms. In the first stage, we detect the cut candidate boundaries and gradual candidate boundaries using two self-adapted thresholds. In this stage, we transform the candidate gradual change to cut change so that the cut change and gradual change can be dealt in a same way. It helps to keep a high recall rate. The second stage detects the local maximum difference of the MDCH generated by shot boundaries to filter the noises incurred by object motion, flash and camera zoom. A voting mechanism is used to make a final detection in the third stage. The second and the third stage contribute to a high precision rate. We evaluated the proposed method on TRECVID datasets and compared it with other methods. Experiment results demonstrate that the proposed method achieves high detection accuracy with low computational cost.
Sulfur is an attractive active material for lithium batteries in terms of its high specific capacity and energy density. Despite main advantages, lithium sulfur (Li-S) batteries still suffer from great challenges with serious capacity decay and awful rate performance due to severe “shuttle effect” and mass loss of active materials. Herein we report a free-standing carbon-sulfur cathodes by anchoring sulfur into 3D carbon nanorods arrays. Binder-free and integrated characteristics are realized. Sulfur infuses into interspaces among arrays and trapped by the interconnected carbon arrays. The assembled cells exhibit initial discharge specific capacity of 1050 mAh g−1 at 0.2C and 892 mAh g−1 at 2.0C, companied by an outstanding coulombic efficiency of 98% after 200 cycles at 0.2C. The obtained S-C cathode also shows excellent rate capacity with low capacity fade. The proposed new S-C architecture may pave the way toward construction of novel S-Li batteries.
Tailored design/fabrication of hierarchical porous advanced electrodes is of great importance for developing high-performance power sources. Herein, we report a facile solvothermal method for fabrication of hierarchical porous MoS2/C flower-like microspheres. Interestingly, the obtained MoS2/C microspheres are composed of interconnected secondary thin nanoflakes and an amorphous carbon layer. As an anode material for lithium ion batteries, the resultant MoS2/C flower-like microspheres electrode delivers a high specific capacity of 1125.9 mAh g−1 and good cycle capability (916.6 mAh g−1 at 200 mA g−1 up to 400 cycles), as well as enhanced rate performance. The excellent electrochemical performance is attributed to the unique porous composite architecture with fast transportation of ion/electron and good strain accommodation during the lithiation/delithiation reaction. Our research may pave the way for construction of other high-performance metal sulfides electrodes for electrochemical energy storage.
Reduced graphene oxide (RGO) wrapped metal-organic frameworks (MOFs) derived cobalt doped porous carbon polyhedrons synthesized via a carbonization process, are for the first time used for sulfur immobilizers (RGO/C–Co-S) as cathodes for high performance lithium-sulfur (Li–S) batteries. The RGO/Co-C-S cathode exhibits greatly improved electrochemical performance, showing excellent specific capacity of 949 mAh g−1 at 300th cycle at a current density 0.3 A g−1, displaying enhanced rate capability with specific capacity of 772, 704 and 606 mAh g−1 at current density of 0.5, 1 and 2 A g−1, respectively. The synergetic effect of MOFs-derived porous carbon, homogeneously distributed Co nanoparticles and RGO nanosheets simultaneously contributes to the confinement of sulfur species. The presence of abundant mesopores and micropores is conducive to immobilize large amounts of S species. The homogenously inlaid ultrafine Co nanoparticles can further immobilize sulfur by chemical interactions between Co and S/polysulfides. The RGO nanosheets tightly wrapped on carbon hosts act as barrier layers to prevent polysulfides from diffusing out of the matrix, further suppressing shuttle effect. The porous structure and the RGO can effectively alleviate the volume changes resulted from charge–discharge process. This design strategy can be inspiring for MOF-derived materials in energy storage applications.
Chapter 2 gives a general method for analysis of the battery charge/discharge characteristics. An accurate battery model is required to simulate battery performance and state of charge estimation. The state of the art in battery modeling is presented, and the simulation accuracy and adaptation of three battery models for lithium-ion batteries are discussed. A new algorithm for battery pack modeling, including batteries in parallel and series, is developed.
Pyrolyzed porous spherical composites of polyacrylonitrile-Ketjenblack carbon and sulfur (pPAN-KB/S) with a high sulfur content (ca. 72%) and enhanced conductivity and porosity (pore volume: 1.42 cm3/g; BET surface area: 727 m2/g) were prepared by an aerosol-assisted process and applied as cathode for lithium-sulfur batteries. Electrochemical tests showed that the pPAN-KB/S composite exhibited a high capacity of 866 mAh/g (based on sulfur) after 100 cycles at 0.5C (1C = 1.68 A/g) and a good rate performance at high current density (431 mAh/g at 5C). In addition, a pPAN-KB/S composite electrode with high sulfur loading (ca. 4.4 mg-S/cm2) exhibited impressive electrochemical performance with a reversible capacity of 513 mAh/g and 576 mAh/cm3 (based on sulfur) and a coulombic efficiency >99% after 100 cycles at 0.5C.
Rechargeable lithium-sulfur (Li-S) batteries are attractive candidates for energy storage devices because they have five times the theoretical energy storage of state-of-the-art Li-ion batteries. The main problems plaguing Li-S batteries are poor cycle life and limited rate capability, caused by the insulating nature of S and the shuttle effect associated with the dissolution of intermediate lithium polysulfides. Here, we report the use of bio-cell-inspired polydopamine (PD) as a coating agent on both the cathode and separator to address these problems (the "systematic effects"). The PD-modified cathode and separator play key roles in facilitating ion diffusion and keeping the cathode structure stable, leading to uniform lithium deposition and a solid electrolyte interphase. As a result, an ultra-long cycle performance of more than 3000 cycles, with a capacity fade of only 0.018% per cycle, was achieved at 2 C. It is believed that the systematic modification of the cathode and separator for Li-S batteries is a new strategy for practical applications.
Boron doped hydrothermal carbon microspheres were synthesized by introducing boric acid into glucose precursor solution to obtain boron concentration from 0.1 to 1 wt. %. Following hydrothermal treatment, samples were thermally treated to 1000 °C. For obtained samples structural and surface characterization were performed. Characterization of obtained samples as material for carbon paste electrode was achieved by measurement of the Fe (CN)63-/4- redox couple and linuron determination. Catalytic effect of boric acid on hydrothermal reaction induced enlargement of particle size for boron doped samples. Significant reduction of specific surface area for samples with highest boron concentration was observed. Boron was substitutionally incorporated in the structure of doped samples and incorporation up to 0.6 wt. % in precursor solution generates structure ordering, which induces a reduction of surface active sites for oxygen adsorption in a greater extent. It was found that modified structural and surface characteristics are responsible for good electron transfer property of carbon paste electrode based on doped samples with nominal boron concentration range from 0.2 to 0.6 wt. %. However, it has been shown that sample with nominal boron concentration of 0.2 wt. % proved to be most promising candidate as a material for carbon paste electrode.
Tailored sulfur cathode is vital for the development of high performance lithium-sulfur (Li-S) battery. A surface modification on the sulfur/carbon composite would be an efficient strategy to enhance the cycling stability. Herein, we report a nickel hydroxide-modified sulfur/conductive carbon black composite (Ni(OH)2@S/CCB) as the cathode material for Li-S battery through thermal treatment and chemical precipitation method. In this composite, the sublimed sulfur is stored into the CCB, and followed by a surface modification of Ni(OH)2 nanoparticles with size of 1-2 nm. As a cathode for Li-S battery, the as-prepared Ni(OH)2@S/CCB electrode exhibits better cycle stability and higher rate discharge capacity, compared with the bare S/CCB electrode. The improved performance is largely due to the introduction of Ni(OH)2 surface modification, which can effectively suppress the "shuttle effect" of polysulfides, resulting in enhanced cycling life and higher capacity.
Based on material point method (MPM), two dimensional (2D) orthogonal chip model on titanium alloy is established. Unlike finite element method (FEM) with seriously distorted meshes during the simulation of large strains such as the formation of shear band, the MPM is especially suitable for the numerical simulation of large deformation and high strain rate of metal material at high temperature. The generalized interpolation material point (GIMP) contact algorithm, Johnson–Cook model and Hillerborg׳s fracture energy criterion are used to simulate the cutting process on Ti–6Al–4V alloy. The parameters option and simulation process are first discussed, then the corresponding chip force and temperature field etc. are analyzed and compared with experimental data available. A good agreement has been found between them. Finally, the evolution of the temperature and cutting force are studied, and the effects of cutting speed and cutting feed rate on the chip morphology and cutting force are also investigated. It was the first time to simulate the serrated and discontinuous chips with the MPM and obtain relatively satisfactory results. The transition from serrated to discontinuous chips has been well captured in this paper.
High energy density Li-S battery is a promising green battery chemistry, but the polysulfide shuttling and lithium anode degradation hinder the practical use of Li-S batteries. Tremendous efforts have been made including confining sulfur in a closed cathode porous matrix and stabilizing lithium-metal anode with additives; however, satisfactory confinement is challenging to achieve and electrolyte additives could be electrochemically unstable, deteriorating the long-term cyclability of Li-S batteries. Here, we demonstrate the control of polysulfide shuttling and stabilization of the lithium-metal anode with a fluorinated ether electrolyte without either cathode confinement or additives, which can be beneficial for both the efficient use of electrolyte and safe operation of Li-S batteries. Moreover, solid-electrolyte interphase (SEI) layer with a hierarchical chemical composition of LiF and sulfate/sulfite/sulfide was identified on lithium anode, which suppresses parasitic reactions and helps preserve the anode quality.
A novel type of one-dimensional ordered mesoporous carbon fiber has been prepared via the electrospinning technique by using resol as the carbon source and triblock copolymer Pluronic F127 as the template. Sulfur is then encapsulated in this ordered mesoporous carbon fibers by a simple thermal treatment. The interwoven fibrous nanostructure has favorably mechanical stability and can provide an effective conductive network for sulfur and polysulfides during cycling. The ordered mesopores can also restrain the diffusion of long-chain polysulfides. The resulting ordered mesoporous carbon fiber sulfur (OMCF-S) composite with 63% S exhibits high reversible capacity, good capacity retention and enhanced rate capacity when used as cathode in rechargeable lithium-sulfur batteries. The resulting OMCF-S electrode maintains a stable discharge capacity of 690 mAh/g at 0.3 C, even after 300 cycles.
Mesoporous carbon (MC) materials with large pore volume and high surface area have been synthesized as the conductive matrix in the sulfur cathode for the lithium sulfur (Li/S) batteries using a simultaneous templating and carbonization method. The magnesium citrate is used as the precursor of the carbon and provides nanometer sized MgO particles template. Wide-angle X-ray diffraction (WA-XRD), high-resolution transmission electron microscopy (HR-TEM) and N2 sorption analysis show that the resultant carbon material possesses mesopores structure (about 6.5 nm), high surface area (1432 m2 g−1), and large pore volumes (2.894 cm3 g−1) after pyrolysis (1000 °C). Elemental maps confirm that sulfur is homogeneously dispersed in the MC framework after encapsulation. Electrochemical measurements performed on this mesoporous carbon used as an electrode material for Li/S batteries show excellent discharge capacity (1083.6 mAh g−1) at current density 200 mA g−1. The mesopores with large volume and high surface area are crucial in loading insulated sulfur, which provide enough space and good conducting networks for active materials. Meanwhile, mesoporous structure with high adsorption capacity can both effectively accommodate the polysulfide anions and improve the electrochemical performance of Li/S batteries.
A self-assembly approach is used to fabricate a graphene-coated mesoporous carbon/sulfur composite. The graphene coating on the surface of the composite is 15-20 nm in thickness, and sulfur is well dispersed in the pores of mesoporous carbon and the interfaces between the mesoporous carbon and graphene sheets after a heat treatment at 300 degrees C. The graphene coating helps to increase the sulfur content and retard the diffusion of polysulfides. The galvanostatic charge-discharge tests show that the graphene-coated sulfur electrode presents good cycling stability. Specific discharge capacities up to 650 mAh g(-1) over 100 cycles at 0.1 C is achieved with enhanced coulombic efficiency, representing a promising cathode material for lithium-sulfur battery.
Nitrogen-doped porous carbon (NPC) and multi-wall carbon nanotube (MWCNT) have been frequently studied to immobilize sulfur in lithium–sulfur (Li–S) batteries. However, neither NPC nor MWCNT itself can effectively confine the soluble polysufides if cathode thickness e.g. sulfur loading is increased. In this work, NPC was combined with MWCNT to construct an integrated host structure to immobilize sulfur at a relevant scale. The function of doped nitrogen atoms was revisited and found to effectively attract sulfur radicals generated during the electrochemical process. The addition of MWCNT facilitated the uniform coating of sulfur nanocomposites to a practically usable thickness and homogenized the distribution of sulfur particles in the pristine electrodes, while NPC provided sufficient pore volume to trap dissolved species. More importantly, the wetting issue, the critical challenge for thick sulfur cathodes, is also mitigated after the adoption of MWCNT, leading to a high areal capacity of ca. 2.5 mA h/cm2 with capacity retention of 81.6% over 100 cycles.
While Li–S batteries are poised to be the next generation high-density energy storage devices, low sulfur utilization and slow rate performance have limited their practical applications. Here, we report the synthesis of monodispersed S8 nanoparticles (NPs) with different diameter and the nanosize dependent kinetic characteristics of the corresponding Li–S batteries. Most remarkably, 5 nm S NPs display the theoretical discharging/charging capacity of 1672 mAh g–1 at 0.1 C rate and a discharge capacity of 1089 mAh g–1 at 4 C.Keywords: Sulfur nanoparticle; theoretical specific capacity; Li−S battery; nanosize effect
The high performance of electrochemical energy-storage devices relies largely on scrupulous design of nanoarchitectures and smart hybridization of bespoke active materials. Carbon nanopsheres (CNSs) are widely used for energy storage and conversion devices. Here, the directional assembly of CNSs on a vertical-standing metal scaffold into a core/shell array structure is reported. The method uses a three-step all-solution synthesis strategy (chemical bath deposition, electrodeposition, and hydrothermal) and begins from ZnO microrod arrays as a sacrificial template. The self-assembly of CNSs can be correlated to a simultaneous etching effect to the ZnO accompanying the polymerization of glucose precursor. The Ni microtube/CNSs arrays are selected as an example for structural and electrochemical characterizations. The novel type of metal/CNSs arrays is demonstrated to be a highly stable electrode for supercapacitors. The electrodes of metal/CNSs arrays are assembled into symmetric supercapacitors and exhibit high capacitances of 227 F g−1 (at 2.5 A g−1) and an outstanding cycling stability with capacitance retention of 97% after 40 000 cycles.
Nitrogen-doped hierarchically porous coralloid carbon/sulfur composites (N-HPCC/S) served as attractive cathode materials for lithium-sulfur (Li-S) batteries were fabricated for the first time. The nitrogen-doped hierarchically porous coralloid carbon (N-HPCC) with an appropriate nitrogen content (1.29 wt%) was synthesized via a facile hydrothermal approach, combined with subsequent carbonization-activation. The N-HPCC/S composites prepared by a simple melt-diffusion method displayed an excellent electrochemical performance. With a high sulfur content (58 wt%) in the total electrode weight, the N-HPCC/S cathode delivered a high initial discharge capacity of 1626.8 mA h g−1 and remained high up to 1086.3 mA h g−1 after 50 cycles at 100 mA g−1, which is about 1.86 times as that of activated carbon. Particularly, the reversible discharge capacity still maintained 607.2 mA h g−1 after 200 cycles even at a higher rate of 800 mA g−1. The enhanced electrochemical performance was attributed to the synergetic effect between the intriguing hierarchically porous coralloid structure and appropriate nitrogen doping, which could effectively trap polysulfides, alleviate the volume expansion, enhance the electronic conductivity and improve the surface interaction between the carbon matrix and polysulfides.
Lightweight, flexible electrodes based on three-dimensional (3D) graphene have received increasing attention because of their application potential in electrochemical energy storage and conversion. Integrating 3D graphene networks with other active components endows electrodes with large capacity/capacitance, high energy and power densities, and ultrastable cycling at high rates. This review highlights the fabrication techniques for self-supported 3D porous graphene structures and their integrated electrodes with metal oxides/hydroxides for battery, supercapacitor, and oxygen reduction reaction applications. Merits and demerits of different preparation methods and the associated electrochemical properties are presented. General advantages of graphene-based integrated electrodes are discussed.
Batteries with high energy and power densities along with long cycle life and acceptable safety at an affordable cost are critical for large-scale applications such as electric vehicles and smart grids, but is challenging. Lithium–sulfur (Li-S) batteries are attractive in this regard due to their high energy density and the abundance of sulfur, but several hurdles such as poor cycle life and inferior sulfur utilization need to be overcome for them to be commercially viable. Li–S cells with high capacity and long cycle life with a dual-confined flexible cathode configuration by encapsulating sulfur in nitrogen-doped double-shelled hollow carbon spheres followed by graphene wrapping are presented here. Sulfur/polysulfides are effectively immobilized in the cathode through physical confinement by the hollow spheres with porous shells and graphene wrapping as well as chemical binding between heteronitrogen atoms and polysulfides. This rationally designed free-standing nanostructured sulfur cathode provides a well-built 3D carbon conductive network without requiring binders, enabling a high initial discharge capacity of 1360 mA h g−1 at a current rate of C/5, excellent rate capability of 600 mA h g−1 at 2 C rate, and sustainable cycling stability for 200 cycles with nearly 100% Coulombic efficiency, suggesting its great promise for advanced Li–S batteries.
A facile and unique layer-by-layer strategy for high-areal-capacity sulfur cathodes was reported, in which commercial sulfur powders are directly splinted between porous carbon nanofiber (PCNF) layers. The pristine carbon nanofiber (CNF) sheets were prepared via a vacuum-filtrate, peel-off, and punch-out process using commercial CNF powder as the starting material without any additional binder. During the CO2 activation process, part of the solid carbon is consumed to produce CO gas, thus leading to carbons with enhanced pore volume and specific surface area. To prepare the layer-by-layer cathodes, sulfur powder was first spread onto the carbon layers as uniform as possible to form sulfur-particle-spread carbon layers, which were used as the bottom layer or middle layers for the cathodes. Finally, the stacked layers were pressed slightly to ensure that the sulfur particles are embedded well in the carbon layers. After the first scan, all the CV curves display the typical two-step reactions in both the cathodic and anodic sweeps; the stable peak positions and currents demonstrate that the layer-by-layer cathodes are efficient in trapping the soluble polysulfides. Also, the sharp peaks imply that the active material has been confined with a highly ion/charge accessible environment successfully after the first discharge/charge processes.
The increasing demand for electric vehicles and large-scale smart grids has aroused great interest in developing high energy density storage devices. Lithium–sulfur (Li–S) battery has attracted much attention owing to its high theoretical energy density and abundance, but many challenges such as rapid capacity fade and low sulfur loading and utilization have impeded its practical use. Here, we present a free-standing TiO2 nanowire/graphene hybrid membrane for Li/dissolved polysulfide batteries with high capacity and long cycling life. Graphene membrane with high electrical conductivity is used as a current collector to effectively reduce the internal resistance in the sulfur cathode and physically immobilize the dissolved lithium polysulfides. The TiO2 nanowires introduced into the graphene membrane offer a hierarchical composite structure, in which the TiO2 nanowires not only have strong chemical binding with the lithium polysulfides, but also show a strong catalytic effect for polysulfide reduction and oxidation, promoting a fast redox reaction kinetics with high capacity and low voltage polarization. This hybrid electrode delivers a high specific capacity of 1327 mA h g−1 at 0.2 C rate, a Coulombic efficiency approaching 100%, high-rate performance of 850 mA h g−1 at 2 C rate, and long cyclic stability with a capacity of 1053 mA h g−1 at 0.2 C rate over 200 cycles, demonstrating great prospect for application in high energy Li–S batteries.
A novel gel polymer electrolyte (GPE) based on an electrospun polymer membrane of polyimide (PI) activating with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and further coating with nano-Al2O3 was prepared, and its performance for lithium-sulfur (Li-S) cell was investigated. It is found that the Li-S cell using the new GPE enabled achieving a stable discharge capacity of 820 mAh g−1 after more than 100 cycles. This new GPE system with activating with PVDF-HFP and further coating with nano-Al2O3 was capable of upholding the electrolyte solution and can suppress the dissolution of the intermediate products generated during the discharge process and thus improves the performance of Li-S cell.
S-doped mesoporous carbon fibres with an S content as high as 14.0 atom % (29.4 wt. %) are synthesized by carbonization of sucrose using MgSO4-containing porous whiskers as templates and S source. The ultrahigh S concentration is obtained at an optimized condition, including a calcination temperature of 600 °C, whisker templates with a smaller diameter and a relatively lower carbon source to template ratio (1:5). X-ray photoelectron spectroscopy demonstrates that the bonding configurations of S are mainly assigned to thiophene-S (C-S-C). Raman spectra demonstrate that the amount of defects rise with the increase of S content. As electrodes for supercapacitors, the specific capacitance of the S-doped mesoporous carbon fibres significantly increases as the S content increasing, reaching 221 F g−1 at the scan rate of 10 mV s−1 with an area-normalized capacitance of 38 μF cm−2. And the capacitance retention maintains 95% even after 500 cycles, exhibiting excellent cycling stability. Our results indicate that S-doped mesoporous carbons with ultrahigh S concentration can be potential candidates as high quality electrode materials for supercapacitors.
Hierarchical porous carbon (HPC, DUT-106) with tailored pore structure is synthesized using a versatile approach based on ZnO nanoparticles avoiding limitations present in conventional silica hard templating approaches. The benefit of the process presented here is the removal of all pore building components by pyrolysis of the ZnO/carbon composite without any need for either toxic/reactive gases or purification of the as-prepared hierarchical porous carbon. The carbothermal reduction process is accompanied by an advantageous growing of distinctive micropores within the thin carbon walls. The resulting materials show not only high internal porosity (total pore volume up to 3.9 cm3 g−1) but also a large number of electrochemical reaction sites due to their remarkably high specific surface area (up to 3060 m2 g−1), which renders them particularly suitable for the application as sulfur host material. Applied in the lithium-sulfur battery, the HPC/sulfur composite exhibits a capacity of >1200 mAh g−1-sulfur (>750 mAh g−1 electrode) at a high sulfur loading of ≥ 3 mg cm−2 as well as outstanding rate capability. In fact, this impressive performance is achieved even using a low amount of electrolyte (6.8 μl mg−1sulfur) allowing for further weight reduction and maintenance of high energy density on cell level.
A composite separator with a thin-film polysulfide trap is developed for lithium-sulfur batteries. A polyethylene glycol-supported microporous carbon coating (MPC/PEG coating) on a Celgard separator suppresses polysulfide diffusion through its physical and chemical polysulfide-trapping capabilities. The MPC/PEG-coated separator thus facilitates the use of pure sulfur cathodes that generally suffer from poor cyclability and low electrochemical utilization.
Traditional lithium-ion batteries that are based on layered Li intercalation electrode materials are limited by the intrinsically low theoretical capacities of both electrodes and cannot meet the increasing demand for energy. A facile route for the synthesis of a new type of composite nanofibers, namely carbon nanofibers decorated with molybdenum disulfide sheets (CNFs@MoS2), is now reported. A synergistic effect was observed for the two-component anode, triggering new electrochemical processes for lithium storage, with a persistent oxidation from Mo (or MoS2) to MoS3 in the repeated charge processes, leading to an ascending capacity upon cycling. The composite exhibits unprecedented electrochemical behavior with high specific capacity, good cycling stability, and superior high-rate capability, suggesting its potential application in high-energy lithium-ion batteries.
Traditional lithium-ion batteries that are based on layered Li intercalation electrode materials are limited by the intrinsically low theoretical capacities of both electrodes and cannot meet the increasing demand for energy. A facile route for the synthesis of a new type of composite nanofibers, namely carbon nanofibers decorated with molybdenum disulfide sheets (CNFs@MoS2), is now reported. A synergistic effect was observed for the two-component anode, triggering new electrochemical processes for lithium storage, with a persistent oxidation from Mo (or MoS2) to MoS3 in the repeated charge processes, leading to an ascending capacity upon cycling. The composite exhibits unprecedented electrochemical behavior with high specific capacity, good cycling stability, and superior high-rate capability, suggesting its potential application in high-energy lithium-ion batteries.
A mixed ionic–electronic conductor (MIEC) of polypyrrole (PPy) synthesized with poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAAMPSA), which is water-dispersible and is in the form of nanoparticles intertwined by the PAAMPSA, is explored as an additive in sulfur cathodes for rechargeable lithium–sulfur (Li–S) batteries. A S-MIEC composite containing a sulfur content of 75 wt % was synthesized by an in situ deposition of sulfur with MIEC. The sulfur retains an orthorhombic phase randomly mixed with MIEC nanoparticles, exhibiting a lower thermal decomposition temperature than the pristine sulfur. Cathodes containing the S-MIEC composite were prepared and evaluated in half cells by cyclic voltammetry and galvanostatic cycling. The S-MIEC composite cathode shows excellent electrochemical stability as the MIEC facilitates ion and electron transfer and capture intermediate polysulfides within the electrodes. The MIEC in the composite electrodes forms a porous, 3D heterostructure providing good electrochemical contact upon cycling as indicated by scanning electron microscopy and electrochemical impedance spectroscopy. The sulfur in the S-MIEC composite retains a capacity of >600 mA h g–1 at low rates and 500 mA h g–1 at 1C after 50 cycles.
As one important component of sulfur cathodes, the carbon host plays a key role in the electrochemical performance of lithium-sulfur (Li-S) batteries. In this paper, a mesoporous nitrogen-doped carbon (MPNC)-sulfur nanocomposite is reported as a novel cathode for advanced Li-S batteries. The nitrogen doping in the MPNC material can effectively promote chemical adsorption between sulfur atoms and oxygen functional groups on the carbon, as verified by X-ray absorption near edge structure spectroscopy, and the mechanism by which nitrogen enables the behavior is further revealed by density functional theory calculations. Based on the advantages of the porous structure and nitrogen doping, the MPNC-sulfur cathodes show excellent cycling stability (95% retention within 100 cycles) at a high current density of 0.7 mAh cm-2 with a high sulfur loading (4.2 mg S cm-2) and a sulfur content (70 wt%). A high areal capacity (≈3.3 mAh cm-2) is demonstrated by using the novel cathode, which is crucial for the practical application of Li-S batteries. It is believed that the important role of nitrogen doping promoted chemical adsorption can be extended for development of other high performance carbon-sulfur composite cathodes for Li-S batteries.
