Porous carbon nanotubes improved sulfur composite cathode for lithium-sulfur battery

Porous multi-walled carbon nanotubes (PCNTs) with multiple mesopores structure are synthesized through activation of multi-walled carbon nanotubes (MWCNTs) by potassium hydroxide. The potassium hydroxide activation process results in a significantly enhanced specific surface area with numerous small pores. The as-obtained PCNTs are employed as the conductive matrix for sulfur in the sulfur cathode. Compared with the composite sulfur cathode based on the original MWCNTs, the sulfur-PCNTs cathode shows a significantly improved cycle performance and columbic efficiency. The reversible capacity is 530 mAh?g^?1 and columbic efficiency is 90 % after 100 cycles at a current density of 100 mA?g^?1. The improvement in the electrochemical performance for S-PCNT is mainly attributed to the enlarged surface area and the porous structure of the unique mesopores carbon nanotube host, which cannot only facilitate transport of electrons and Li⁺ ions, but also trap polysulfides, retard the shuttle effect during charge/discharge process.     

Self-assembled reduced graphene oxide/sulfur composite encapsulated by polyaniline for enhanced electrochemistry performance

Reduced graphene oxide/sulfur/polyaniline (referred to RGO/S/PANI) composite was self-assembled through in situ synthesis and used to investigate the electrochemical properties of lithium/sulfur cells. The RGO/S/PANI composite possessed 809.3/801.9 mAh g^?1 of initial charge/discharge capacities, higher than 588.3/588.2 mAh g^?1 for reduced graphene oxide/sulfur (referred to RGO/S) and 681.4/669.9 mAh g^?1 for sulfur/polyaniline (referred to S/PANI) at similar conditions. The RGO/S/PANI composite obtained 400 mAh g^?1 at 2 C and good reversible capacities of 605.5 and 600.8 mAh g^?1 at 100th charge/discharge cycle at 0.1 C, in comparison with low electrochemical performance of RGO/S and S/PANI. The improved properties could be attributed to the collaboration of RGO and PANI. Co-generation of RGO and sulfur acted as seeds for their depositions, stimulated their uniform distributions, and restricted the agglomeration of sulfur particles in situ synthesis. Polyaniline coated RGO/S and stabilized the nanostructure of RGO/S/PANI in repeated charge/discharge cycles. In addition, RGO and PANI provided many electron channels to enhance sulfur conductivity and sufficient void space for sulfur swelling during charge/discharge cycles.     

Mesoporous TiO<Subscript>2</Subscript> nanosheet with a large amount of exposed {001} facets as sulfur host for high-performance lithium–sulfur batteries

Li–S battery is an attractive electrochemical energy storage system because of its high energy density. However, its commercialization has been greatly affected by the poor cycle life and low rate performance, which is attributed to the dissolution of polysulfides and their shuttle effects. In this study, titanium dioxide particles with a large amount of exposed {001} facets (TDPEF) were prepared by alcohol-thermal method. The as-prepared TDPEF achieved a relatively high specific surface area of 92 m² g^?1 and a pore volume of 0.27 cm g^?1. Sulfur was mixed with the TDPEF to form TDPEF/S composite by a melt diffusion process. The TDPEF/S composite exhibits much excellent discharge capacity retention of 80 % after 100 cycles compared with pure sulfur at a high current rate of 0.5 C, and it still has a discharge capacity as high as 530 mAh g^?1 even at the current rate of 4 C.     

Preparation of NiO/multiwalled carbon nanotube nanocomposite for use as the oxygen cathode catalyst in rechargeable Li–O2 batteries

NiO/multiwalled carbon nanotube (NiO/MWCNT) nanocomposites have been prepared and used for a Li–O₂ battery cathode catalyst. Electrochemical measurements demonstrate that the batteries with NiO/MWCNT catalyst have a discharge capacity of 2,500 mAh g^?1, a charge capacity of 2,100 mAh g^?1, and a rechargeable ability performing better than Ketjenblack (KB) and MWCNTs. KB has the largest discharge capacity (2,700 mAh g^?1) due to the highest surface area and pore volume but the worst charging behavior due to poor mass transport in the small-width pore (2.48 nm). MWCNTs have a much better charging performance owing to a larger pore width (8.93 nm) than carbon black. NiO/MWCNTs have the largest charge capacity because of the facilitated mass transport in the comparatively large pores (7.68 nm) and the increased catalytic ability produced by the NiO nanoparticles. These improvements are also responsible for the best cycle and rate performances of the nanocomposites among the three catalysts.     

Synthesis and electrochemical performance of sulfur–carbon composite cathode for lithium–sulfur batteries

In this paper, porous carbon was synthesized by an activation method, with phenolic resin as carbon source and nanometer calcium carbonate as activating agent. Sulfur–porous carbon composite material was prepared by thermally treating a mixture of sublimed sulfur and porous carbon. Morphology and electrochemical performance of the carbon and sulfur–carbon composite cathode were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectra (EIS), and galvanostatic charge–discharge test. The composite containing 39 wt.% sulfur obtained an initial discharge capacity of about 1,130 mA?h g^?1 under the current density of 80 mA?g^?1 and presented a long electrochemical stability up to 100 cycles.     

Hybrids of MnO<Subscript>2</Subscript> nanoparticles anchored on graphene sheets as efficient sulfur hosts for high-performance lithium sulfur batteries

Lithium–sulfur (Li–S) battery is considered as a promising option for electrochemical energy storage applications because of its low-cost and high theoretical capacity. However, the practical application of Li–S battery is still hindered due to the poor electrical conductivity of S cathode and the high dissolution/shuttling of polysulfides in electrolyte. Herein, we report a novel physical and chemical entrapment strategy to address these two problems by designing a sulfur–MnO₂@graphene (S–MnO₂@GN) ternary hybrid material structure. The MnO₂ particles with size of ~ 10 nm are anchored tightly on the wrinkled and twisted GN sheets to form a highly efficient sulfur host. Benefiting from the synergistic effects of GN and MnO₂ in both improving the electronic conductivity and hindering polysulfides by physical and chemical adsorptions, this unique S–MnO₂@GN composite exhibits excellent electrochemical performances. Reversible specific capacities of 1416, 1114, and 421 mA h g^?1 are achieved at rates of 0.1, 0.2, and 3.2 C, respectively. After a 100 cycle stability test, S–MnO₂@GN composite cathode could still maintain a reversible capacity of 825 mA h g^?1.     

The short-term cycling properties of Na/PVdF/S battery at ambient temperature

The Na/PVdF/S cells were composed of solid sodium, sulfur, and polyvinylidene fluoride–hexafluoropropene (PVdF) gel polymer electrolyte. The PVdF polymer electrolyte was prepared form tetraglyme plasticizer and NaCF₃SO₃ salt, and its electrochemical properties were studied using CV and impedance analysis. The interfacial resistance between sodium and polymer electrolyte increase with storage time, which might be associated with passivation layer. Solid-state sodium/sulfur cell using a PVdF gel polymer electrolyte has been tested. The Na/PVdF/S cell with 0.288 mA cm^?2 shows a high discharge capacity of 392 mAh g^?1 and 36 mAh g^?1 after 20 cycles. The cycle performance of Na/GPE/S cell operating at 25 °C is worse than Na/S cell at a high temperature.     

Activated carbon aerogels with high bimodal porosity for lithium/sulfur batteries

Activated carbon aerogels (ACAs) with high bimodal porosity were obtained for lithium/sulfur batteries by potassium hydroxide (KOH) activation. Then sulfur–activated carbon aerogels (S–ACAs) composites were synthesized by chemical deposition strategy. The S–ACAs composites were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy, and N₂ adsorption/desorption measurements. It is found that the activated carbon aerogels treated by KOH activation presents a porous structure, and sulfur is embedded into the pores of the ACAs network-like matrix after a chemical deposition process. The Li/S–ACAs (with 69.1 wt% active material) composite cathode exhibits discharge capacities of 1,493 mAh g^?1 in the first cycle and 528 mAh g^?1 after 100 cycles at a higher rate of C/5 (335 mA g^?1). The S–ACAs composite cathode exhibits better electrochemical reversibility, higher active material utilization, and less severe polysulfide shuttle than S–CAs composite cathode because of high bimodal porosity structure of the ACAs matrix.     

Novel multi-sorbent for sampling and determination of trace volatile organic sulfur compounds in ambient air

Novel adsorbent APSG-MW (average particle size 215?µm and specific surface 98 m²?g^?1) bonding multi-walled carbon nanotubes (MWCNTs) on silica gel are obtained. Then the sampling tubes filled with Tenax TA and APSG-MW are prepared and the adsorptive capacity of Tenax TA/APSG-MW for volatile organic sulfur compounds (VOSCs) is studied. The data show that the adsorption and desorption recoveries of multi-sorbent for VOSCs are satisfactory (>85%), and the breakthrough values are large (>16?L?g^?1) enough to absorb VOSCs in ambient air. The sampling precision of the sorbent tubes meets TO-17 criteria. The sampling tubes are successfully used to concentrate and analyze a sample of landfill air, and the major S compounds are identified.     

Sulfur‐Impregnated Core–Shell Hierarchical Porous Carbon for Lithium–Sulfur Batteries

Core–shell hierarchical porous carbon spheres (HPCs) were synthesized by a facile hydrothermal method and used as host to incorporate sulfur. The microstructure, morphology, and specific surface areas of the resultant samples have been systematically characterized. The results indicate that most of sulfur is well dispersed over the core area of HPCs after the impregnation of sulfur. Meanwhile, the shell of HPCs with void pores is serving as a retard against the dissolution of lithium polysulfides. This structure can enhance the transport of electron and lithium ions as well as alleviate the stress caused by volume change during the charge–discharge process. The as‐prepared HPC‐sulfur (HPC‐S) composite with 65.3 wt % sulfur delivers a high specific capacity of 1397.9 mA h g^?1 at a current density of 335 mA g^?1 (0.2 C) as a cathode material for lithium–sulfur (Li‐S) batteries, and the discharge capacity of the electrode could still reach 753.2 mA h g^?1 at 6700 mA g^?1 (4 C). Moreover, the composite electrode exhibited an excellent cycling capacity of 830.5 mA h g^?1 after 200 cycles.     

A Facile Synthesis of High‐Surface‐Area Sulfur–Carbon Composites for Li/S Batteries

Small‐grained elemental sulfur is precipitated from sodium thiosulfate (Na₂S₂O₃) in a carbon‐containing oxalic acid (HOOC?COOH) solution through a novel spray precipitation method. Surface area analysis, elemental mapping, and transmission electron micrographs revealed that the spray‐precipitated sulfur particles feature 11 times higher surface area compared to conventional precipitated sulfur, with homogeneous distribution in the carbon. Moreover, the scanning electron micrographs show that these high‐surface‐area sulfur particles are firmly adhered to and covered by carbon. This precipitated S–C composite exhibits high discharge capacity with about 75 % capacity retention. The initial discharge capacity was further improved to 1444 mA h g^?1 by inserting a free‐standing single‐walled carbon nanotube layer in between the cathode and the separator. Moreover, with the help of the fixed capacity charging technique, 91.6 % capacity retention was achieved.     

Nanofibers of V<Subscript>2</Subscript>O<Subscript>5</Subscript>/C@MWCNTs as the cathode material for lithium-ion batteries

Vanadium pentoxide (V₂O₅) nanofibers (NFs) with a thin carbon layer of 3–5 nm, which wrapped on V₂O₅ nanoparticles, and integrated multiwalled carbon nanotubes (MWCNTs) have been fabricated via simple electrospinning followed by carbonization process and post-sintering treatment. The obtained composite displays a NF structure with V₂O₅ nanoparticles connected to each other, and good electrochemical performance: delivering initial capacity of 320 mAh g^?1 (between 2.0 and 4.0 V vs. Li/Li⁺), good cycling stability (223 mAh g^?1 after 50 cycles), and good rate performance (~?150 mAh g^?1 at 2 A g^?1). This can attribute to the carbon wrapped on the V₂O₅ nanoparticles which can not only enhance the electric conductivity to decrease the impendence of the cathode materials but also maintain the structural stability to protect the nanostructure from the corruption of electrolyte and the strain stress due to the Li-ion intercalation/deintercalation during the charge/discharge process. And, the added MWCNTs play the role of framework of the unique V₂O₅ coated by carbon layer and composited with MWCNT NFs (V₂O₅/C@MWCNT NFs) to ensure the material is more stable.     

Sucrose assisted hydrothermal synthesis of SnO2/graphene nanocomposites with improved lithium storage properties

SnO₂/graphene nanocomposites are synthesized by a new hydrothermal treatment strategy under the assistance of sucrose. From the images of the scanning electron microscope (SEM) and transmission electron microscope (TEM), it can be observed that SnO₂ nanoparticles with the size of 4~5 nm uniformly distribute on the graphene nanosheets. The result demonstrates that sucrose can effectively prevent graphene nanosheets from restacking during hydrothermal treatment and subsequently treatment. The charging/discharging test result indicates that the SnO₂/graphene nanocomposites exhibit high specific capacity and excellent cycleability. The first reversible specific capacity is 729 mAh.g^?1 at the current density of 50 mA.g^?1, and remains 646 mAh.g^?1 after 30 cycles at the current density of 100 mA.g^?1, 30 cycles at the current density of 200 mA.g^?1, 30 cycles at the current density of 400 mA.g^?1, 30 cycles at the current density of 800 mA.g^?1, and 30 cycles at the current density of 50 mA.g^?1.     

Dual‐Confined Sulfur Nanoparticles Encapsulated in Hollow TiO2 Spheres Wrapped with Graphene for Lithium–Sulfur Batteries

Lithium–sulfur (Li?S) batteries are attractive owing to their higher energy density and lower cost compared with the universally used lithium‐ion batteries (LIBs), but there are some problems that stop their practical use, such as low utilization and rapid capacity‐fading of the sulfur cathode, which is mainly caused by the shuttle effect, and the uncontrollable deposition of lithium sulfide species. Herein, we report the design and fabrication of dual‐confined sulfur nanoparticles that were encapsulated inside hollow TiO₂ spheres; the encapsulated nanoparticles were prepared by a facile hydrolysis process combined with acid etching, followed by “wrapping” with graphene (G?TiO₂@S). In this unique composite architecture, the hollow TiO₂ spheres acted as effective sulfur carriers by confining the polysulfides and buffering volume changes during the charge‐discharge processes by means of physical force from the hollow spheres and chemical binding between TiO₂ and the polysulfides. Moreover, the graphene‐wrapped skin provided an effective 3D conductive network to improve the electronic conductivity of the sulfur cathode and, at the same time, to further suppress the dissolution of the polysulfides. As results, the G?TiO₂@S hybrids exhibited a high and stable discharge capacity of up to 853.4 mA h g^?1 over 200 cycles at 0.5 C (1 C=1675 mA g^?1) and an excellent rate capability of 675 mA h g^?1 at a current rate of 2 C; thus, G?TiO₂@S holds great promise as a cathode material for Li?S batteries.     

Mesoporous carbon/sulfur composite with N-doping and tunable pore size for high-performance Li-S batteries

Mesoporous carbons (MCs) were used as the matrixes to load sulfur for lithium sulfur (Li-S) batteries, and pore sizes were tuned by heat treatment at different high temperatures. The cathode material shows the highest discharge capacity of 1158.2 mAh g^?1 at the pore size of 4.1 nm among as-prepared nitrogen-free materials with different sizes. Meanwhile, the nitrogen doping of mesoporous carbon helps to inhibit the diffusion of polysulfide species via an enhanced surface adsorption. The carbon/sulfur containing N (4.56%) shows a high initial discharge capacity of 1315.8 mAh g^?1 and retains about 939 mAh g^?1 after 100 cycles at 0.2 C. The improved electrochemical performance is ascribed to the proper pore size, surface chemical property, and conductivity of the N-doped carbon material.     

Porous Si coated with S-doped carbon as anode material for lithium ion batteries

A novel porous Si/S-doped carbon composite was prepared by a magnesiothermic reaction of mesoporous SiO₂, subsequently coating with a sulfur-containing polymer-poly(3,4-ethylene dioxythiophene), and a post-carbonization process. The as-prepared Si composite was homogeneously coated with disordered S-doped carbon with 2.6 wt.%?S in the composite and retained a high surface area of 58.8 m²?g^?1. The Si/S-doped carbon composite exhibited superior electrochemical performance and long cycle life as an anode material in lithium ion cells, showing a stable reversible capacity of 450 mAh g^?1 even at a high current rate of 6,000 mA?g^?1.     

Facile synthesis of multiwalled carbon nanotube–V2O5 nanocomposites as cathode materials for Li-ion batteries

Multiwalled carbon nanotube (MWCNT)–vanadium pentoxide (V₂O₅) nanocomposites have been fabricated using a facile and environmental friendly hydrothermal method without any pretreatment, surfactants, or chelate agents added. The as-annealed nanocomposites are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), and the results indicate that V₂O₅ nanoparticles grew on MWCNTs. As a cathode material for lithium batteries, it exhibits superior electrochemical performance compare to the pure V₂O₅ powders. A high specific discharge capacity of 253 mA h g^?1 can be obtained for the 15 % MWCNT–V₂O₅ nanocomposite electrodes, which retains 209 mA h g^?1 after 50 cycles. However, the pure V₂O₅ powder electrodes only possess a specific discharge capacity of 157 mA h g^?1 with a capacity retention of 127 mA h g^?1 after 50 cycles. Moreover, the MWCNT–V₂O₅ nanocomposite electrodes show an excellent rate capability with a specific discharge capacity of 180 mA h g^?1 at the current rate of 4 C. The enhanced electrochemical performance of the nanocomposites is attributed to the formation of conductive networks by MWCNTs, and large surface areas of V₂O₅ nanoparticles grew on MWCNTs which stabilizes these nanoparticles against agglomeration.     

Electrochemical performance of LiVPO4F synthesized by ball-milling assisted sol-gel method

Lithium vanadium fluorophosphate, a cathode material for lithium-ion batteries, was synthesized by a ball-milling assisted sol-gel method. The micro structure, surface morphology and electrochemical performance of LiVPO₄F were investigated by X-ray diffraction (XRD), scanning electronic microscopy (SEM) and electrochemical tests. The results show that the sample synthesized at 550°C for 4 h was pure phase, possessed good crystallinity and uniform particle size distribution. At 0.1 C rate, the LiVPO₄F sample demonstrated charge and discharge capacity of about 153.2 and 125.7 mA h g^?1 at the first cycle respectively, the coulombic efficiency was 82%. The initial discharge capacity was 121.9 mA h g^?1 at the rate of 0.3 C, and it became 118.7 mA h g^?1 after 50 cycles.     

Nickel foam as interlayer to improve the performance of lithium–sulfur battery

In this report, a porous, electronically conductive nickel foam foil (NFF), which is rolled for smooth surface, is introduced as an interlayer placed between the sulfur electrode and the separator to suppress the loss of active material and self-discharge behavior in lithium–sulfur (Li–S) systems. The electrodes are characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge–discharge test. The cell with the rolled NFF interlayer shows superior performance in terms of capacity utilization, reversibility, and enhanced rate capability. It exhibits reversible discharge capacity of 604 mAh g^?1 after 80 cycles at 0.2 C, which is much higher than that of pristine sulfur without NFF (424 mAh g^?1). The improvement on electrochemical performance is attributed to the 3D architecture of nickel foam foil as lithium–sulfur batteries interlayer, which can provide a good conductive network with structural stability and the porous architecture accommodating the migrating polysulfide to reduce the shuttling phenomenon during the charge–discharge processes.     

A comparison of sulfur loading method on the electrochemical performance of porous carbon/sulfur cathode material for lithium–sulfur battery

To get a high sulfur loaded porous carbon/sulfur cathode material with an excellent performance, we investigated four different sulfur loading treatments. The samples were analyzed by the Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD) patterns, thermal gravimetric analysis (TGA), and scanning electron microscopy (SEM). We proved that it is more effective to introduce the sulfur into the pores of porous carbon at 300 °C than at 155 °C. Especially, the porous carbon/sulfur composite heated in a sealed reactor at 300 °C for 8 h presents a fine sulfur load with sulfur content of 78 wt.% and exhibits an excellent electrochemical performance. The discharge capacity is 760, 727, 744, 713, and 575 mAh g^?1 of sulfur at a current density of 80, 160, 320, 800, and 1,600 mA g^?1 based on the sulfur/carbon composite, respectively. What is more, there is almost no decay at the current density of 800 mA g^?1 for 50 cycles and coulombic efficiency remains over 95 %.