Synthesis of hollow silica-sulfur composite nanospheres towards stable lithium-sulfur battery

Herein, porous hollow silica nanospheres were prepared via a facile sol-gel process in an inverse microemulsion, using self-assemblies of chiral amphiphile as a soft template and fine water droplets as a hard template. The shells of the hollow silica nanospheres are composed of flake-like nanoparticles with dense big holes on the surface. After covering a layer of sulfur on the silica nanospheres, followed by hydrothermal treatment in a D-glucose aqueous solution, silica-sulfur and silica-sulfur-carbon nanospheres were successfully fabricated. The silica-sulfur composites exhibit a stable capacity of 454 mAh g^?1 at current density of 335 mA g^?1 after 100 cycles with capacity retention of 85%, demonstrating a promising cathode material for rechargeable lithium-sulfur batteries. We believe that the approach for synthesis of porous hollow silica nanospheres and its carbon spheroidal shell can also be applicable for designing other electrode materials for energy storage.     

Synthesis and electrochemical performance of micro-mesoporous carbon-sulfur composite cathode for Li–S batteries

Even though significant improvement has been made in the Li–S battery technology, the poor cycling and rate performance have always limited the further growth. Thus, the development of cost-effective and high performing electrodes is considered to be an important technology for the practical aspect. It is quite logical that the porous electrode systems can improve the electrochemical performance of a given battery system. Here, this study benchmarks a new class of electrodes based on double (micro and meso)porous carbon spheres (MMPCs) prepared by a facile soft template method followed by wet chemical etching. The particle size analysis, performed by scanning electron microscopy, shows that the templating agents, such as sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide(CTAB), have a distinct effect on the size distribution of carbon particles. Different electrochemical characterizations have been carried out to understand the effect of SDS and CTAB on the electrochemical performance of carbon-sulfur nanocomposite electrode. BET analysis shows that the pore size distribution of the carbon spheres prepared by only the soft template method (MPCs) is mainly in the micropore range, which limits the storage and the dispersive capacity. However, the etched samples (MMPCs) showed better electrochemical performance, such as high initial discharge capacity of 921 mAh g^?1(sulfur loading ～77.2%) with 82.7% capacity retention at the end of 150 cycles at 200 mA g^?1 and an impressive rate capability of 1086 mAh g^?1 at a current density of 100 mA g^?1.This improved performance could be attributed to the double porous structure of MMPCs. Such a feasible and facile architecture provides a good strategy to prepare other different materials that require better material dispersion and electrode/electrolyte interactions.     

Facile synthesis of three-dimensional porous carbon networks for highly stable sodium storage

Novel three-dimensional porous carbon network (3D-PC) anode was developed by a facile in situ NaCl-template method utilizing citric acid as carbon source. The synthesis process involves the dissolution of NaCl and citric acid in deionized water, citric acid coated on NaCl template during freeze-drying process, carbonization of the composites, and removal of the template with water. The resultant 3D-PC presents high electrical conductivity, large specific surface area, sufficient active sites, large interlayer distance, and high mechanical flexibility, which are contributed to the efficient Na-storage. Therefore, the 3D-PC anode displays enhanced rate performance of 101 mAh g^?1 at 1000 mA g^?1 and extremely long cycle life of 138 mAh g^?1 after 2000 cycles at 200 mA g^?1. The unique synthesis strategy coupled with the excellent Na-storage performance ensures 3D-PC a promising anode material for low-cost sodium-ion batteries.     

Enhanced lithium storage performance of a self-assembled hierarchical porous Co<Subscript>3</Subscript>O<Subscript>4</Subscript>/VGCF hybrid high-capacity anode material for lithium-ion batteries

A Co₃O₄/vapor-grown carbon fiber (VGCF) hybrid material is prepared by a facile approach, namely, via liquid-phase carbonate precipitation followed by thermal decomposition of the precipitate at 380 °C for 2 h in argon gas flow. The material is characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller specific surface area analysis, and carbon elemental analysis. The Co₃O₄ in the hybrid material exhibits the morphology of porous submicron secondary particles which are self assembled from enormous cubic-phase crystalline Co₃O₄ nanograins. The electrochemical performance of the hybrid as a high-capacity conversion-type anode material for lithium-ion batteries is investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic discharge/charge methods. The hybrid material demonstrates high specific capacity, good rate capability, and good long-term cyclability, which are far superior to those of the pristine Co₃O₄ material prepared under similar conditions. For example, the reversible charge capacities of the hybrid can reach 1100–1150 mAh g^?1 at a lower current density of 0.1 or 0.2 A g^?1 and remain 600 mAh g^?1 at the high current density of 5 A g^?1. After 300 cycles at 0.5 A g^?1, a high charge capacity of 850 mAh g^?1 is retained. The enhanced electrochemical performance is attributed to the incorporated VGCFs as well as the porous structure and the smaller nanograins of the Co₃O₄ active material.     

Promising nitrogen-doped porous nanosheets carbon derived from pomegranate husk as advanced electrode materials for supercapacitors

Nitrogen-doped porous activated carbons (N-PHACs) have been successfully synthesized using pomegranate husk as carbon precursor via ZnCl₂-activation carbonization and subsequent urea-assisted hydrothermal nitrogen-doping method. The obtained N-PHACs possesses abundant mesoporous structure, high specific surface area (up to 1754.8 m² g^?1), pore volume (1.05 cm³ g^?1), and nitrogen-doping content (4.51 wt%). Besides, the N-PHACs-based material showed a high specific capacitance of 254 F g^?1 at a current density of 0.5 A g^?1 and excellent rate performance (73% capacitance retention ratio even at 20 A g^?1) in 2 M KOH aqueous electrolyte, which is attributed to the contribution of double-layer capacitance and pseudocapacitance. The assembled N-PHACs-based symmetric capacitor with a wide operating voltage range of 0–1.8 V exhibits a maximum energy density of 15.3 Wh kg^?1 at a power density of 225 W kg^?1 and superior cycle stability (only 6% loss after 5000 cycles) in 0.5 M Na₂SO₄ aqueous electrolyte. These exciting results suggest that the novel N-doping porous carbon material prepared by a green and low-cost design strategy has a potential application as high-performance electrode materials for supercapacitors.     

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.     

Shape-controlled porous carbon from calcium citrate precursor and their intriguing application in lithium-ion batteries

Porous carbon nanosheets (PCNSs), porous carbon nanofibers (PCNFs), and flowerlike porous carbon microspheres (FPCMs) were successfully synthesized through a carbonization method combined with a simple acid pickling treatment using calcium citrate as the precursor. The as-prepared products show uniform morphologies, in which the FPCMs are self-assembled from PCNSs. As anodes of lithium-ion (Li-ion) batteries, these carbon materials deliver a stable reversible capacity above 515 mAh g^?1 after 50 cycles at 100 mA g^?1. Compared with PCNSs and PCNFs, FPCMs demonstrate preferable rate capability (378 mAh g^?1 at 1 A g^?1) and cyclability (643 mAh g^?1 at 100 mA g^?1). These results suggest that an appropriate select of morphology and structure will significantly improve the lithium storage capacity. The study also indicates that the novel shape-controlled porous carbon materials have potential applications as electrode materials in electronic devices.     

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.     

Synthesis of selenium/EDTA-derived porous carbon composite as a Li–Se battery cathode

The carbon substrate with unique 3D macroporous structure has been prepared through the immediate carbonization of ethylenediaminetetraacetic acid (EDTA) and KOH mixture. The porous carbon composed of micro- and small mesoporous (2–5 nm) structure has a BET specific surface area of 1824.8 m² g^?1. The amorphous and nanosized Se is uniformly encapsulated into the porous structure of porous carbon using melting diffusion route, and the weight content of Se in target Se/C composite can be as high as ~50 %. As an Li–Se battery cathode, the Se/C composite delivers a reversible (2nd) discharge capacity of 597.4 mAh g^?1 at 0.24C and retains a discharge capacity of 538.4 mAh g^?1 at 0.24C after 100 cycles. Furthermore, the composite also has a stable capacity of 291.0 mAh g^?1 at a high current of 4.8C. The high specific area and good porous size of EDTA-derived carbon substrate may a be responsibility for the excellent electrochemical performances of Se/C composite.     

Nanoporous carbon microspheres as anode material for enhanced capacity of lithium ion batteries

Nanoporous carbon microspheres (NCMs) are prepared by a one-step carbonizing and activating resorcinol?formaldehyde polymer spheres (RFs) in inert and CO₂ atmosphere for anode materials of lithium-ion batteries (LIBs). Compared with RFs carbon microspheres (RF-C), after activating with hot CO₂, the NCMs with porous structure and high BET surface area of 2798.8 m² g^?1, which provides abundant lithium-ion storage site as well as stable lithium-ion transport channel. When RF-C and NCM are used to anode material for LIBs, at the same current density of 210 mA g^?1, the initial specific discharge capacity are 482.4 and 2575.992 mA h g^?1, respectively; after 50 cycles, the maintain capacity are 429.379 and 926.654 mA h g^?1, respectively. The porous spherical structure of NCM possesses noticeably lithium-ion storage capability, which exhibits high discharge capacity and excellent cycling stability at different current density. The CO₂ activating carbonaceous materials used in anode materials can tremendously enhance the capacity storage, which provides a promising modification strategy to improve the storage capacity and cyclic stability of carbonaceous anode materials for LIBs.     

Red phosphorus encapsulated in porous carbon derived from cigarette filter solid waste as a promising anode material for lithium-ion batteries

Red phosphorus (RP) is considered to be one of the promising anode materials for lithium-ion batteries (LIBs) on account of its high theoretical capacity (2596 mAh g^?1), abundant resources, and environmental friendliness. However, the intrinsic insulating nature and large volume change during lithium insertion/extraction process lead to drastic capacity loss upon cycling. Recently, great attention has been devoted to constructing P-based composites via mixing with carbon materials. Here, a novel P/C composite, in which red P nanoparticles were homogeneously distributed in cigarette filter-derived porous carbon (CPC), was fabricated by vaporization-condensation method. Due to the unique characteristics of porous carbon, including high specific area, good conductivity, and rich internal porous structure, CPC obtained by means of heat treatment that serves as conductive matrix to load red P could be of great benefits, which can not only improve the overall electrical conductivity but also mitigate the volume expansion issues. As a result, the RP/CPC composite as an anode material for LIBs delivers a good cycling stability (500 mAh g^?1 at 100 mA g^?1 with a high Coulombic efficiency above 99% after 50 cycles) and rate capability (355 mAh g^?1 even at 1000 mA g^?1).     

Electrochemical synthesis and lithium storage properties of three-dimensional porous Sn–Co alloy/CNT composite

Three-dimensional (3-D) porous copper with stable pore structure is prepared by electroless plating. 3-D porous Sn–Co alloy/carbon nanotube (CNT) composite is synthesized by electrodeposition using 3-D porous copper as the substrate. The scanning electron microscope results indicate that 3-D porous Sn–Co alloy/CNT composite contains a large amount of interconnected pores with the diameter size of ~3 μm. Upon cycling, the pore structure gradually disappears, but no serious exfoliation appears due to porous structure and reinforcement by CNT. The charge/discharge results demonstrate that the 3-D porous Sn–Co alloy/CNT composite electrode delivers high first reversible specific capacity of 490 mAh g^?1, and remains 441 mAh g^?1 after 60 cycles tested at different current densities. Even at the current density of 3,200 mA g^?1, the reversible specific capacity remains 319 mAh g^?1, which is 65 % of the first specific capacity cycled at the current density of 100 mA g^?1.     

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.     

Hydrothermal synthesis of carbon- and reduced graphene oxide-supported CoMoO4 nanorods for supercapacitor

Hybrid CoMoO₄ nanorods with carbon (C) and graphene oxide (rGO) are successfully synthesized via one-step hydrothermal process. Hybrid α-CoMoO₄ nanorods have shown excellent electrochemical performances compared to pristine CoMoO₄ in alkaline electrolyte. Specifically, CoMoO₄/C nanorod exhibits a maximum specific capacitance of 451.6 F g^?1 at the current density of 1 A g^?1, whereas CoMoO₄/rGO shows high specific capacitance of 336.1 F g^?1 at the same current density. Both the hybrid nanorods show good rate capability even at high current density of 20 A g^?1 and long-term cyclic stability. The observed electrochemical features of the hybrid CoMoO₄ nanostructure could be attributed to the presence of highly conductive carbonaceous material on unique one-dimensional nanorod microstructure which enhances the electrical conductivity of the nanorods thereby allowing faster electrolyte ion diffusion during the redox process.     

Porous NiO hollow quasi-nanospheres derived from a new metal-organic framework template as high-performance anode materials for lithium ion batteries

Porous hollow metal oxides derived from nanoscaled metal-organic framework (MOF) have drawn tremendous attention due to their high electrochemical performance in advanced Li-ion batteries (LIBs). In this work, porous NiO hollow quasi-nanospheres were fabricated by an ordinary refluxing reaction combination of a thermal decomposition of new nanostructured Ni-MOF, i.e., {Ni₃(HCOO)₆·DMF}_n. When evaluated as an anode material for lithium ion batteries, the MOF derived NiO electrode exhibits high capacity, good cycling stability and rate performance (760 mAh g^?1 at 200 mA g^?1 after 100 cycles, 392 mAh g^?1 at 3200 mA g^?1). This superior lithium storage performance is mainly attributed to the unique hollow and porous nanostructure of the as-synthesized NiO, which offer enough space to accommodate the dramstic volume change and alleviate the pulverization problem during the repeated lithiation/delithiation processes, and provide more electro-active sites for fast electrochemical reactions as well as promote lithium ions and electrons transfer at the electrolyte/electrode interface.     

Hierarchical porous ZnMn<Subscript>2</Subscript>O<Subscript>4</Subscript> synthesized by the sucrose-assisted combustion method for high-rate supercapacitors

A simple sucrose-assisted combustion and subsequent high-temperature calcination route have been employed to prepare hierarchical porous ZnMn₂O₄ nanostructure. When used as an electrode for supercapacitor, the ZnMn₂O₄ electrode displays a high specific capacitance of 411.75 F g^?1 at a current density of 1 A g^?1, remarkable capacitance retention rate of 64.28 % at current density of 32 A g^?1 compared with 1 A g^?1, as well as excellent cycle stability (reversible capacity retention of 88.32 % after 4000 cycles). The outstanding electrochemical performances are mainly attributed to its hierarchical porous architecture, which provides large reaction surface area, fast ion and electron transfer, and good structure stability. All these impressive results demonstrate that ZnMn₂O₄ shows promise for its application in supercapacitors.     

A microporous carbon derived from phenol–melamine–formaldehyde resin by K2CO3 activation for lithium ion batteries

A microporous carbon material with large surface area was prepared by carbonizing and activating of phenol–melamine–formaldehyde resin, using K₂CO₃ as activation reagent. The textural characteristics of the carbon materials were characterized by scanning electron microscope, X-ray diffraction, Raman spectra, Brunauer–Emmett–Teller, elemental analyses, respectively. Results showed that the surface area and pore diameter of the activated carbon were 1,610 m² g^?1 and less than 2 nm. Electrochemical lithium insertion properties were also investigated. At a current density of 100 mA g^?1, the activated carbon showed an enormous first-discharge capacity of 2,610 mAh g^?1 and the first charge capacity of 992 mAh g^?1. From the second cycle, the coulombic efficiency went up rapidly to above 95 %. The results indicated it may be a promising candidate as an anode material for lithium secondary batteries.     

Construction of 3D polypyrrole/CoS/graphene composite electrode with enhanced pseudocapacitive performance

Herein, 3D graphene/nickel foam (GE/NF) composite matrix was successfully fabricated by using NF as template through a self-catalytic thermal chemical vapor deposition process. By using the prepared GE/NF as substrate, CoS nanosheets were deposited via a facial one-step electrochemical deposition method. Owing to the advantage of GE in boosting the electrical contact between the electroactive host material and current collector, the as-prepared 3D CoS/GE/NF electrode demonstrated a superior capacitance value of 2308 F g^?1 at 1 A g^?1 and a high rate capability of 70.49% at 20 A g^?1. After depositing the polypyrrole (PPY) film on 3D CoS/GE/NF electrode, the electrochemical performance of CoS was further greatly improved and delivered an extremely high capacitance value of 3450 F g^?1 at 1 A g^?1, with good rate capability (62.61% at 20 A g^?1) and improved cycling stability. The enhanced electrochemical performance of PPY/CoS/GE/NF electrode is closely related to the advantage of PPY film in increasing the electrical conductivity and reinforcing the integrity of electrode.     

Distinctive slit-shaped porous carbon encapsulating phosphorus as a promising anode material for lithium batteries

A distinctive structure of carbon materials for Li-ion batteries is proposed for the preparation of red phosphorus-carbon composites. The slit-shaped porous carbon is observed with aggregation of plate-like particles, whose isotherm belongs to the H3 of type IV. The density functional theory (DFT) method reveals the presence of micro-mesopores in the 0.5–5 nm size range. The unique size distribution plays an important role in adsorbing phosphorus and electrochemical performance. The phosphorus-slit-shaped porous carbon composite shows initial capacity of 2588 mAh g^?1, reversible capacity of 1359 mAh g^?1 at a current density of 100 mA g^?1. It shows an excellent coulombic efficiency of ～99 % after 50 cycles.     

Synthesis of nanofiber-composed dandelion-like CoNiAl triple hydroxide as an electrode material for high-performance supercapacitor

In this work, CoNiAl triple hydroxide with nanofiber-composed dandelion-like morphology was synthesized on nickel foam by a hydrothermal route. This delicate nanostructure was initiated from the rolling up of hydroxide nanosheets. The hierarchical nanostructure and optimized molar ratio of Co, Ni, and Al guarantees the high electrochemical performance of obtained samples. The maximum specific capacitance of 2,791 F g^?1 for the as-prepared CoNiAl hydroxides was achieved at scan rate of 5 mV s^?1 in 3 M KOH aqueous solution. The capacitance of material still remained 85 % after 2,000 charge–discharge cycles. These results demonstrated that the as-prepared CoNiAl triple hydroxide can be applied as a high-performance electrode material for supercapacitor.