Three-dimensional nitrogen-doped graphene/sulfur composite for lithium-sulfur battery

A three-dimensional nitrogen-doped graphene/sulfur composite (NGS3) was synthesized by a simple hydrothermal method using urea as the nitrogen source and subsequent thermal treatment. The structure and electrochemical performance of the prepared nitrogen-doped graphene/sulfur composite (NGS3) were confirmed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), Energy dispersive spectroscopy mapping (EDS), and galvanostatic charge/discharge measurements. SEM and EDS mapping show that NGS3 exhibits a porous structure with uniform distribution of sulfur. Compared with the graphene/sulfur composite (NGS1), NGS3 delivers an outstanding rate capability with 1501, 1278, 1136, and 1024 mAh g^?1 at 200, 400, 800, and 1000 mA g^?1, respectively, and the cycle stability of NGS3 is also wonderful, a reversible discharge capacity of 1330 mAh g^?1 is obtained after 80 cycles under the current rate of 200 mA g^?1. The wonderful electrochemical performance could be attributed to the special three-dimensional conductive structure with the help of nitrogen atom.     

Sulfur/microporous carbon composites for Li-S battery

A commercial carbon black with microporous framework is used as carbon matrix to prepare sulfur/microporous carbon (S/MC) composites for the cathode of lithium sulfur (Li-S) battery. The S/MC composites with 50, 60, and 72 wt.% sulfur loading are prepared by a facile heat treatment method. Electrochemical performance of the as-prepared S/MC composites are measured by galvanostatic charge/discharge tests, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS), with carbonate-based electrolyte of 1.0 M LiPF₆/(PC-EC-DEC). The composite with 50 wt.% sulfur presents the optimized electrochemical performance, including the utilization of active sulfur, discharge capacity, and cycling stability. At the current density of 50 mA g^?1, it can demonstrate a high initial discharge capacity of 1624.5 mAh g^?1. Even at the current density of 800 mA g^?1, the initial capacity of 1288.6 mAh g^?1 can be obtained, and the capacity can still maintain at 522.8 mAh g^?1 after 180 cycles. The remarkably improved electrochemical performance of the S/MC composite with 50 wt.% sulfur are attributed to the carbon matrix with microporous structure, which can effectively enhance the electrical conductivity of the sulfur cathode, suppress the loss of active material during charge/discharge processes, and restrain the migration of polysulfide ions to the lithium anode.     

N-doped graphene/Bi nanocomposite with excellent electrochemical properties for lithium–ion batteries

N-doped graphene/Bi nanocomposite was prepared via a two-step method, combining the gas/liquid interface reaction with the rapid heat treatment method. The as-prepared sample was characterized by X-ray diffraction (XRD), field-emission scanning electron microscope (FESEM), X-ray photoelectron spectroscopy (XPS), and elemental analyzer. The XRD, FESEM, XPS, and elemental analysis results confirm the successful synthesis of N-doped graphene/Bi nanocomposite. As a result, the prepared N-doped graphene/Bi nanocomposite as an anode material for lithium-ion batteries delivers excellent electrochemical performance. A high lithium storage capacity of about 522 mAh g^?1 in the voltage range of 0.01–3.5 V is obtained. After 50 cycles at different current densities from 50 to 1000 mA g^?1, the specific capacity can still remain 386 mAh g^?1. Even at the high current density of 1000 mA g^?1, the N-doped graphene/Bi nanocomposite can still deliver a specific capacity of 218 mAh g^?1. The excellent electrochemical performance of the N-doped graphene/Bi nanocomposite is supposed to benefit from the high electronic conductivity of nitrogen-doped graphene and the synergistic effect of bismuth nanoparticles and nitrogen-doped graphene.     

Flower-like MoS<Subscript>2</Subscript> supported on three-dimensional graphene aerogels as high-performance anode materials for sodium-ion batteries

Flower-like MoS₂ supported on three-dimensional graphene aerogel (MoS₂/GA) composite has been prepared by a facile hydrothermal method followed by subsequent heat-treatment process. Each of MoS₂ microflowers is surrounded by the three-dimensional graphene nanosheets. The MoS₂/GA composite is applied as an anode material of sodium-ion batteries (SIBs) and it exhibits high initial discharge/charge capacities of 562.7 and 460 mAh g^?1 at a current density of 0.1 A g^?1 and good cycling performance (348.6 mAh g^?1 after 30 cycles at 0.1 A g^?1). The good Na⁺ storage properties of the MoS₂/GA composite could be attributed to the unique structure which flower-like MoS₂ are homogeneously and tightly decorated on the surface of three-dimensional graphene aerogel. Our results demonstrate that as-prepared MoS₂/GA composite has a great potential prospect as anodes for SIBs.     

Nanoporous carbon microspheres as matrix of sulfur to prepare sulfur/carbon cathode material for lithium–sulfur battery

A high specific surface area (2798.8 m² g^?1) of nanoporous carbon microsphere (NPCM) is prepared by activated carbon microsphere in hot CO₂ atmosphere, which is used as matrix material of sulfur to prepare NPCM/sulfur composite cathode material by a melt-diffusion method. The NPCM/sulfur composite cathode material with the sulfur content of 53.5% shows high discharge capacity; the initial discharge capacity is 1274 mAh g^?1 which maintains as high as 776.4 mAh g^?1 after 50 cycles at 0.1 C current. At high current density of 1 C, the NPCM/sulfur cathode material still shows initial discharge capacity of 830.3 mAh g^?1, and the reversible capacity retention is 78% after 50 cycles. To study the influence of different sulfur content of NPCM/sulfur cathode material to the performance of Li–S battery, the different sulfur content of NPCM/sulfur composite cathode materials is prepared by changing the thermal diffusion time and the ratio of sulfur powder to NPCM. The performance of NPCM/sulfur cathode material with different sulfur content is studied at a current of 0.1 C, which will be very important to the preparation of high-performance sulfur/carbon cathode material with appropriate sulfur content.     

Three-dimensional carbon fiber as current collector for lithium/sulfur batteries

Ni foam and carbon fiber cloth were tested as three-dimensional (3D) current collectors for a sulfur/polypyrrole composite cathode in lithium batteries. The cell with the carbon fiber current collector has exhibited remarkably enhanced electrochemical performance compared with its Ni foam counterpart, delivering a high initial capacity of 1,278 mAh g^?1 and maintaining a discharge capacity at 810 mAh g^?1 after 40 cycles at 0.06 C. Furthermore, the carbon fiber-based cell demonstrated a better rate capability and delivered a highly reversible discharge capacity of 397 mAh g^?1 after 50 cycles at 0.5 C, representing an increase of 194 mAh g^?1 compared to the Ni foam counterpart. The electrochemical property investigations along with scanning electron microscope studies have revealed that the carbon fiber current collector possesses a three-dimensional network structure, provides an effective electron conduction path, and minimizes the loss of electrical contact within the deposited cathode material during cycling. These results indicate that the carbon fiber cloth can be used as a promising, effective, and inexpensive current collector for Li/S batteries.     

ZnO nanoparticles anchored on nitrogen and sulfur co-doped graphene sheets for lithium-ion batteries applications

Herein, we demonstrate a facile one-step hydrothermal synthesis route to anchor ZnO nanoparticles on nitrogen and sulfur co-doped graphene sheets. The detailed material and electrochemical characterization have been carried out to demonstrate the potential of novel ZnO/NSG nanocomposite in Li-ion battery (LIBs) applications. The structure and morphology of nanocomposite were assessed by X-ray diffraction (XRD), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The as-synthesized ZnO/NSG nanocomposite has been studied as anode material in LIBs and delivered a high initial discharge capacity of 1723 mAh g^?1, at the current density of 200 mA g^?1. After 100 cycles, the ZnO/NSG nanocomposites demonstrated a high reversible capacity of 720 mAh g^?1 and coulombic efficiency of 99.8%, which can be attributed to the porous three-dimensional network, constructed by ZnO nanoparticles and nitrogen and sulfur co-doped graphene. Moreover, the designed nanocomposite has shown excellent rate capability and lower charge transfer resistance. These results are promising and encourage further research in the area of ZnO-based anodes for next-generation LIBs.     

Graphene and polydopamine double-wrapped porous carbon-sulfur cathode materials for lithium-sulfur batteries with high capacity and cycling stability

Rechargeable lithium-sulfur batteries are deemed to be a promising energy supply to next-generation high energy power system, yet dissolution of lithium polysulfides in the electrolyte leads to poor cycling performance. Here, we report an approach to assemble graphene and polydopamine double-wrapped porous carbon/sulfur (GN-PD-PC-S) for lithium-sulfur batteries. Remarkably, the double-wrapping graphene and polydopamine further help confine the sulfur and polysulfides inside the mesopores and micropores of porous carbon. Moreover, the hierarchical porous structures provide a conductive network for electron transfer and facilitate the effective accommodation of the volume change of sulfur. The GN-PD-PC-S cathode presents an excellent cycling stability of 821 mAh g^?1 after 100 cycles, with a favorable high-rate capability of 496 mAh g^?1 at a current density of 2 A g^?1. Our results indicate the importance of chemically synergistic effect of polymer and carbon in the electrode system for achieving high-performance electrodes in rechargeable lithium-sulfur batteries.     

Electrochemical properties of modified acetylene black/sulfur composite cathode material for lithium/sulfur batteries

Lithium/sulfur (Li/S) batteries have a high theoretical specific capacity of 1672 mAh g^?1. However, the insulation of the elemental sulfur and polysulfides dissolution could result in poor cycling performance of Li/S batteries, thus restricting the industrialization process. Here, we prepared sulfur-based composite by thermal treatment. The modified acetylene black (H-AB) was used as a carrier to fix sulfur. The H-AB could interact with polysulfides and reduce the dissolution of polysulfides in the electrolyte. Nonetheless, the conductivity of H-AB relatively reduced. So the conductivity of the sulfur electrode would be improved by the addition of the conductive agent (AB). In this paper, the different content of conductive agent (AB) in the sulfur electrode was studied. The electrochemical tests indicate that the discharge capacity of the sulfur electrode can be increased by increasing the conductive agent (AB) content. The H-AB@S composite electrode with 30 wt.% conductive agent has the best cycle property. The discharge capacity still remains at 563 mAh g^?1 after 100 cycles at 0.1 C, which is 71% retention of the highest discharge capacity.     

Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> quantum dots on 3D-framed graphene aerogel as an advanced anode material in lithium-ion batteries

Three-dimensional fabricated Fe₃O₄ quantum dots/graphene aerogel materials (Fe₃O₄ QDs/GA) were obtained from a facile hydrothermal strategy, followed by a subsequently heat treatment process. The Fe₃O₄ QDs (2–5 nm) are anchored tightly and dispersed uniformly on the surface of three-dimensional GA. The as-prepared anode materials exhibit a high reversible capacity of 1078 mAh g^?1 at a current density of 100 mA g^?1 after 70 cycles in lithium-ion batteries (LIBs) system. Moreover, the rate capacity still remains 536 mAh g^?1 at 1000 mA g^?1. The enhanced electrochemical performance is attributed to that the GA not only acts as a three-dimensional electronic conductive matrix for the fast transportation of Li⁺ and electrons, but also provides with double protection against the aggregation and pulverization of Fe₃O₄ QDs during cycling. Apparently, the synergistic effects of the three-dimensional GA and the quantum dots are fully utilized. Therefore, the Fe₃O₄ QDs/GA composites are promising materials as advanced anode materials for LIBs.     

Si/polyaniline-based porous carbon composites with an enhanced electrochemical performance as anode materials for Li-ion batteries

Silicon/polyaniline-based porous carbon (Si/PANI-AC) composites have been prepared by a three-step method: coating polyaniline on Si particles using in situ polymerization, carbonizing, and further activating by steam. The morphology and structure of Si/PANI-AC composites have been characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman spectra, respectively. The content and pore structure of the carbon coating layer in Si/PANI-AC have been measured by thermogravimetric analysis and N₂ adsorption-desorption isotherm, respectively. The results indicate some micropores about 1~2 nm in the carbon layer appear during activation and that crystal structure and morphology of Si particles can be retained during preparation. Si/PANI-AC composites exhibit high discharge capacity about 1000 mAh g^?1 at 1.5 A g^?1; moreover, when the current density returns to 0.2 A g^?1, the discharge capacity is still 1692 mAh g^?1 and remains 1453 mAh g^?1 after 70 cycles. The results indicate that the porous carbon coating layer in composites plays an important role in the improvement of the electrochemical performance of pure Si.     

Facile synthesis of a sulfur/multiwalled carbon nanotube nanocomposite cathode with core–shell structure for lithium rechargeable batteries

A novel sulfur/multiwalled carbon nanotube nanocomposite (S/MWCNT) was prepared by a facile quasi-emulsion template method in an O/W system. Transmission and scanning electronic microscopy show the formation of a highly developed core–shell tubular structure consisting of S/MWCNT composite with uniform sulfur coating on its surface. The homogenous dispersion and integration of MWCNT in the S/MWCNT composite create a highly conductive and mechanically flexible framework, enhancing the electronic conductivity and consequently the rate capability of the material. The S/MWCNT composite cathode could deliver a stable discharge (the fifth cycle) capacity of about 903 mAh g^?1 at 0.1 C, 751 mAh g^?1 at 0.5 C, and 631 mAh g^?1 at 1 C.     

Self-assembled 3D Co3O4-graphene frameworks with high lithium storage performance

Three-dimensional Co₃O₄-graphene frameworks (3D-CGFs) are prepared with a one-pot hydrothermal method. Co₃O₄ particles are in situ anchored on graphene sheets, and the resulting composite self-assembles into 3D architecture during the hydrothermal treatment. Scanning electron microscope, transmission electron microscope, powder X-ray powder diffraction, and Raman spectroscopy are employed to characterize the sample. When tested as anode materials for lithium-ion batteries, 3D-CGFs demonstrate remarkable electrochemical lithium storage properties, such as large and stable reversible capacity (>530 mAh g^?1 at 500 mA g^?1 over 300 cycles), good capacity retention (88 % retention after 300 cycles at 500 mA g^?1 compared with the 4th cycle), excellent high-rate performance (515 mAh g^?1 at 1 A g^?1), making it a promising candidate for high-performance anode materials, especially for high-rate lithium-ion batteries.     

Facial synthesis of carbon-coated ZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/graphene and their enhanced lithium storage properties

Carbon-coated ZnFe₂O₄ spheres with sizes of ~110–180 nm anchored on graphene nanosheets (ZF@C/G) are successfully prepared and applied as anode materials for lithium ion batteries (LIBs). The obtained ZF@C/G presents an initial discharge capacity of 1235 mAh g^?1 and maintains a reversible capacity of 775 mAh g^?1 after 150 cycles at a current density of 500 mA g^?1. After being tested at 2 A g^?1 for 700 cycles, the capacity still retains 617 mAh g^?1. The enhanced electrochemical performances can be attributed to the synergetic role of graphene and uniform carbon coating (~3–6 nm), which can inhibit the volume expansion, prevent the pulverization/aggregation upon prolonged cycling, and facilitate the electron transfer between carbon-coated ZnFe₂O₄ spheres. The electrochemical results suggest that the synthesized ZF@C/G nanostructures are promising electrode materials for high-performance lithium ion batteries.

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Development of monodispersed MnCO<Subscript>3</Subscript>/graphene nanosheet composite as anode for lithium-ion battery by hydrothermal synthesis

A unique monodispersed MnCO₃/graphene nanosheet composite is synthesized by a simple one-step hydrothermal method and used as anode of lithium-ion battery. X-ray diffraction patterns show the typical rhombohedral structure of MnCO₃. A transmission electron micrograph reveals that MnCO₃ is evenly distributed on the graphene nanosheet surface with a uniform diameter of 100 nm. Electrochemical performance results show that the specific discharge capacities of MnCO₃/graphene nanosheet composite remain above 1015.9 mAh g^?1 at a rate of 0.2 C after 85 cycles in the potential window of 0.01–2.0 V and even at a high rate of 1.0 C this parameter remains at 683.5 mAh g^?1 after 100 cycles. Thus, the composite also exhibits favorable rate performance. The excellent reversible capacities are attributed to the highly dispersed and large nanosheet structure of the composite, which may not only facilitate the fast transport of Li⁺ ions between the electrode and electrolyte but also provide enough surfaces to accommodate extra Li⁺ ions that contribute to partial interfacial storage capacities. Additionally, graphene nanosheet can effectively improve electrical conductivity of the composite. Therefore, MnCO₃/graphene nanosheet composite can be a great potential anode material for lithium-ion batteries.     

The centrifugally constructed and thermally activated three-dimensional graphene toward a binder-free highly performed anode of the lithium-ion battery

A binder-free three-dimensional porous interconnected graphene (a-3DrGO@NF) was centrifugally constructed and KOH-activated at 800 °C, leading a mechanically strong and pore-developed anode candidate for lithium ion batteries (LIBs). The unique approach of the integration of the mechanical construction and thermal activation demonstrated favorable frameworks to facilitate the stable and fast migrations of both ion and electron during the galvanostatic charge/discharge process, thus significantly improving its durability and electrochemical performance compared to those without the activated and thermal treatment. The a-3DrGO@NF LIBs showed a highly reversible capacity of 1250 mAh g^?1 at a current density of 0.1 A g^?1 after 50 cycles without degradation relative to the first cycle. More importantly, the a-3DrGO@NF LIBs exhibited excellent large current discharge property and cyclic stability of 965 mAh g^?1 in its first cycle and 545 mAh g^?1 after 150 cycles at a current density of 4 A g^?1. Furthermore, it can be quickly charged and discharged in a very short time of 92 s together with high-rate capability of 256 mAh g^?1 after 200 cycles at 10 A g^?1. At both lower and higher its current density as to 10 A g^?1, the coulombic efficiency was close to 100% and showed the reliability of a-3DrGO@NF LIBs.     

Tin oxide nano-flower-anchored graphene composites as high-performance anode materials for lithium-ion batteries

The SnO₂ nano-flower/graphene (SnO₂-NF/GN) composites were synthesized by using graphene (GN) and SnO₂ nano-flower (SnO₂-NF). Among them, the SnO₂-NFs were prefabricated by using sodium hydroxide and stannic chloride pentahydrate (SnCl₄·5H₂O) as raw materials. The results of SEM show that the SnO₂-NFs are uniformly dispersed on the surface of GN. Furthermore, compared with the pure SnO₂, the as-prepared SnO₂-NF/GN composites displayed superior cycle performace and high rate capability. The SnO₂-NF/GN composite delivers a specific capacity of 650 mAh g^?1 after 60 cycles and an excellent rate capability of 480 mAh g^?1 at 2000 mA g^?1.     

Simple microwave synthesis and improved electrochemical performance of Nb-doped MnO<Subscript>2</Subscript>/reduced graphene oxide composite as anode material for lithium-ion batteries

Niobium-doped MnO₂/reduced graphene oxide (Nb-MnO₂/RGO) composite has been successfully synthesized via a simple microwave radiation method. The samples were systematically studied by X-ray diffraction (XRD), thermogravimetric analysis (TG), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM), and electrochemical measurements. As the anode material for lithium-ion batteries, the Nb-MnO₂/RGO (molar ratio of Mn/Nb?=?50:1) (NMG50) showed an outstanding reversible discharge capacity of 556.6 mAh g^?1 after 50 cycles with a capacity retention of 77% at a charge-discharge rate of 0.1 A g^?1 and the reversible discharge capacity can still retain 223.3 mAh g^?1 at a current of 1 A g^?1, which is much higher than those for Nb-MnO₂/RGO (molar ratio of Mn/Nb?=?10:1) (NMG10) and undoped MnO₂/RGO (MG). The improved electrochemical performance could be attributed to the proper amount of Nb doping, which could enhance both the conductivity and the structure stability of MnO₂.     

Effect of pyrolytic polyacrylonitrile on electrochemical performance of Si/graphite composite anode for lithium-ion batteries

The silicon/graphite (Si/G) composite was prepared using pyrolytic polyacrylonitrile (PAN) as carbon precursor, which is a nitrogen-doped carbon that provides efficient pathway for electron transfer. The combination of flake graphite and pyrolytic carbon layer accommodates the large volume expansion of Si during discharge-charge process. The Si/G composite was synthesized via cost-effective liquid solidification followed by carbonization process. The effect of PAN content on electrochemical performance of composites was investigated. The composite containing 40 wt% PAN exhibits a relatively better rate capability and cycle performance than others. It exhibits initial reversible specific capacity of 793.6 mAh g^?1 at a current density of 100 mA g^?1. High capacity of 661 mAh g^?1 can be reached after 50 cycles at current density of 500 mA g^?1.     

Sulfur/mesoporous carbon composites combined with γ-MnS as cathode materials for lithium/sulfur batteries

With the aim to develop high-performance sulfur electrode, manganese sulfide (MnS) was combined with sulfur/porous carbon composite electrode by a simple precipitation method. Both X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) results show that as-prepared MnS corresponds to Rambergite phase with a hexagonal structure (γ-MnS). MnS could be uniformly dispersed in the carbon matrix when the content was less than 20 wt%. When the content of MnS increased, γ-MnS particles aggregated on both outside of the mesoporous carbon channels and the surface of carbon particles. The CV curves of MnS/MC in the first cycle were similar to elemental sulfur, indicating partially decomposed MnS at the surface of mesoporous carbon. Charge/discharge tests indicated that the initial discharge-specific capacity of S/MnS/MC was 1412.5 mAh g^?1 and remained a reversible capacity of 727.4 mAh g^?1 after 50 cycles at a current of 100 mA g^?1, which is superior to that of sulfur composite electrode without MnS.