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.     

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.     

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.     

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.     

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.     

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).     

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.     

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 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.     

Self-breathing ternary nanocomposite based on nitrogen-doped graphene aerogel/polyaniline/sulfur as a cathode material for lithium-sulfur (Li-S) batteries

Li-S batteries are one of exciting new technologies in high energy density storage devices. But, their widespread commercialization has been limited by several obstacles. Elemental sulfur is not conductive electrically and electrochemical conversion during cycles causes intense change in volume. In this work, a sulfur/polyaniline/nitrogen-doped graphene aerogel (S@PANi-NGA) nanocomposite synthesized through a facile chemical procedure. Nitrogen-doped amino functionalized graphene aerogel (NGA) used as cross-linker for polyaniline to improve the stability of the entire cathode framework. Also, NGA possesses porous structure, high surface area, and enhances electronic conductance due to the nitrogen atoms doped into graphene sheets. As a result, S@PANi-NGA delivered an initial discharge capacity of 1332 mAh g^?1 at a scan rate of 0.2 C and 872 mAh g^?1 of the capacity retained after 100 cycles. The performance was clearly superior to the sulfur/PANi binary composite, in which pure polyaniline used as accommodator.     

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.     

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.     

A facile synthesis of heteroatom-doped carbon framework anchored with TiO<Subscript>2</Subscript> nanoparticles for high performance lithium ion battery anodes

Titanium dioxide (TiO₂)-based materials have been well studied because of the high safety and excellent cycling performance when employed as anode materials for lithium ion batteries (LIBs), whereas, the relatively low theoretical capacity (only 335 mAh g^?1) and serious kinetic problems such as poor electrical conductivity (~?10^?13S cm^?1) and low lithium diffusion coefficient (~?10^?9 to 10^?13 cm² s^?1) hinder the development of the TiO₂-based anode materials. To overcome these drawbacks, we present a facile strategy to synthesize N/S dual-doping carbon framework anchored with TiO₂ nanoparticles (NSC@TiO₂) as LIBs anode. Typically, TiO₂ nanoparticles are anchored into the porous graphene-based sheets with N, S dual doping feature, which is produced by carbonization and KOH activation process. The as-obtained NSC@TiO₂ electrode exhibits a high specific capacity of 250 mAh g^?1 with a coulombic efficiency of 99% after 500 cycles at 200 mA g^?1 and excellent rate performance, indicating its promising as anode material for LIBs.     

Hard carbon derived from corn straw piths as anode materials for sodium ion batteries

Hard carbon is considered as the most promising anode material for practical sodium ion batteries. Herein, we report biomass-derived hard carbon made from corn straw piths through a simple carbonization process. X-ray diffraction patterns and Raman spectra elucidated highly disordered structures, and high-resolution transmission electron microscopy confirmed that the hard carbons have many local ordered structures containing turbostratic nanodomains and more nanovoids surround the turbostratic nanodomains. The electrochemical performances of the hard carbons were systematically investigated in sodium ion batteries. By optimizing the carbonization temperature, the sample carbonized at 1400 °C (HC1400) exhibited high reversible capacity of 310 mAh g^?1 and good cycling stability; the capacity can still retain 274 mAh g^?1 after 100 cycles. More importantly, HC1400 can deliver reversible capacity of 206 mAh g^?1 with 79% retention rate after 700 cycles measured at a current density of 200 mA g^?1, which is much better than those in most previous reports. This study provides a way to develop inexpensive, renewable, and recyclable materials from biomasses towards next-generation energy storage applications.     

Cobalt imidazoledicarboxylate coordination complex microspheres: stable intercalation materials for lithium and sodium-ion batteries

A simple and versatile method for preparation of cobalt 4,5-imidazoledicarboxylate microspheres is developed. The cobalt 4,5-imidazoledicarboxylate complex is a kind of stable intercalation materials for lithium- and sodium-ion batteries. When tested as an anode material for lithium-ion batteries, the coordination complex microspheres based composite electrode delivers a second discharge capacity of 595.4 mAh g^?1 at a current density of 1 Ah g^?1. A reversible capacity of 416.1 mAh g^?1 remained after 143 cycles, while a reversible capacity of 259.9 mAh g^?1 remained after 500 cycles at a current density of 1.5 A g^?1. In addition, it can also serve as stable anode materials for sodium-ion batteries. Research based on the topics would shed some light on the discovery of new alternative intercalation materials to graphite.     

Nitrogen-doped carbon nanofiber decorated LiFePO<Subscript>4</Subscript> composites with superior performance for lithium-ion batteries

Nitrogen-doped carbon nanofiber (NCNF) decorated LiFePO₄ (LFP) composites are synthesized via an in situ hydrothermal growth method. Electrochemical performance results show that the embedded NCNF can improve electron and ion transfer, thereby resulting in excellent cycling performance. The as-prepared LFP and NCNF composites exhibit excellent electrochemical properties with discharge capacities of 188.9 mAh g^?1 (at 0.2 C) maintained at 167.9 mAh g^?1 even after 200 charge/discharge cycles. The electrode also presents a good rate capability of 10 C and a reversible specific capacity as high as 95.7 mAh g^?1. LFP composites are a potential alternative high-performing anode material for lithium ion batteries.     

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.     

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.     

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.     

Preparation and comparative structural properties of porous SnO2 microrods and submicrorods

A facile two-step approach has been used for the synthesis of porous SnO₂ rods: the initial room-temperature precipitation of precursor SnC₂O₄ and its subsequent thermal decomposition at 550 °C. Both the as-obtained porous SnO₂ microrods (length ～10.0?±?3.5 μm, diameter ～1.1?±?0.4 μm) and submicrorods (length ～5.8?±?1.9 μm, diameter ～0.4?±?0.1 μm) are the crystalline mixtures of major tetragonal and minor orthorhombic crystal phases, showing a tetragonal fraction of 84.7 and 87.0 %, respectively. When applied as a lithium-ion battery anode, the porous submicrorods (specific surface area ～13.6 m² g^?1) can deliver an initial discharge capacity of 1,730.7 mAh g^?1 with a high coulombic efficiency of 61.6 % and show the 50th discharge capacity of 662.8 mAh g^?1 at 160 mA g^?1 within a narrow potential range of 10.0 mV to 2.0 V. Similarly, even the anode of porous microrods (specific surface area ～11.8 m² g^?1) can still exhibit an initial discharge capacity of 1,661.1 mAh g^?1 at 160 mA g^?1 with a coulombic efficiency of 60.9 %. Regardless of the polymorphic nature, the acquired porosity may only alleviate the huge volume change of anodes for the first cycle; thus, the structural parameters of average size and specific surface area can be feasibly associated with the enhanced lithium storage capability. Anyway, these indicate a facile oxalate precursor method for the controlling synthesis and high performance of rodlike SnO₂ for lithium-ion batteries.