Compact structured silicon/carbon composites as high-performance anodes for lithium ion batteries

Compact-structured silicon/carbon composites consisting of silicon, graphite, and coal tar pitch pyrolysis carbon are prepared via two heating procedures after liquid solidification. The first heating procedure plays a key role in the formation of compact-structured silicon/carbon composites, in which the coal tar pitch has a good fluidity at 180 °C above the softening temperature, and it is easy to form a uniform coating on the surface of materials. At the same time, the fluidic coal tar pitch could also fill the voids between particles to form compact-structured silicon/carbon composites. As-prepared silicon/carbon composites exhibit moderate reversible capacity of 602.4 mAh g^?1, high initial charge-discharge efficiency of 82.3%, and good cycling stability with the capacity retention of 93.4% at 0.1 A g^?1 after 50 cycles. It is noteworthy that the synthetic method is scalable which is suitable for mass production.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Chitosan: A N-doped carbon source of silicon-based anode material for lithium ion batteries

Silicon/graphite/carbon (Si/G/CTS-C) composite, based on nano-silicon, flake graphite, and chitosan-derived carbon (CTS-C), was prepared by spray drying and subsequent pyrolysis. The results of X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy illustrate that chitosan is a good dispersion agent and chitosan-derived carbon is N-doped. The results indicate that the initial charge capacity of Si/G/CTS-C composite is 613.9 mAh g^?1 at a current density of 100 mA g^?1 corresponding to an initial coulombic efficiency of 81.89%. Besides, the Si/G/CTS-C composite exhibits higher specific capacity, more superior rate capability, better cycling performance, and lower impedance than that of silicon/graphite/phenolic resin-derived carbon (Si/G/P-C) composite.     

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.     

Mesoporous Li<Subscript>2</Subscript>FeSiO<Subscript>4</Subscript>/C nanocomposites with enhanced performance synthesized from fumed nano silica

Mesoporous Li₂FeSiO₄/C nanocomposites (LFS-FNS and LFS-NS) were prepared from fumed nano silica (FNS) and nano silica (NS) through facile solid-state reactions, respectively. XRD analysis indicates that the crystalline structures of LFS-FNS and LFS-NS are indexed to monoclinic Li₂FeSiO₄ of P2₁. SEM results prove that the particle size of LFS-FNS and FNS (25~40 nm) is smaller than that of LFS-NS and NS, revealing the particle size of Li₂FeSiO₄/C nanocomposites can be tuned by choosing different silica. TEM further indicates Li₂FeSiO₄ nanoparticles are uniformly dispersed in the amorphous carbon networking of LFS-FNS. Pore structure analysis indicates the external surface areas of LFS-FNS as well as LFS-NS are 51.4 and 36.1 m² g^?1, indicating the pore properties of mesoporous Li₂FeSiO₄/C nanocomposites can be controlled by using different silica as silicon resource. The reduced particle size and high external surface area shorten the lithium-ion diffusion path and make LFS-FNS possess better electrochemical performance over LFS-NS. The discharge capacity of LFS-FNS is as high as 172 mA h g^?1 at 0.1 C.     

In Situ Synthesis and Characterization of Polypyrrole/Graphene Conductive Nanocomposites via Electrochemical Polymerization and Chemical Reduction

Polypyrrole/graphene sheets (PPy/GNs) nanocomposite electrodes were in- situ synthesized via electrochemical polymerization and chemical reduction from pyrrole (Py) and graphene oxide (GO). The surface morphologies of the nanocomposites were observed by scanning electron microscopy (SEM). The SEM results showed graphene sheets (GNs) scattered on the surface of the polypyrrole (PPy), and the morphologies of PPy/GNs nanocomposites manufactured by pulse current (PC-PPy/GNs) or direct current (DC-PPy/GNs) were smoother than that of PC-PPy. The electrochemical capacitance properties of the nanocomposite films were measured by cyclic voltammetry (CV), galvanostatic charge and discharge (GC), and electrochemical impedance spectroscopy (EIS) techniques in 3 mol·L^?1 KCl aqueous solutions. The results indicated that the specific capacitance of the DC-PPy/GNs nanocomposite was 13.5% higher than that of a PC-PPy electrode. Comparison of the electrochemical performance of the nanocomposites indicated that the PC-PPy/GNs nanocomposite had higher specific capacitance and better charging/discharging capability than that of the DC-PPy/GNs nanocomposite. The specific capacitance of the PC-PPy/GNs nanocomposite could reach to 280 F·g^?1 at a scanning rate of 100 mV·s^?1.     

Advanced LiTi<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>/C anode by incorporation of carbon nanotubes for aqueous lithium-ion batteries

Inferior rate capability is a big challenge for LiTi₂(PO₄)₃ anode for aqueous lithium-ion batteries. Herein, to address such issue, we synthesized a high-performance LiTi₂(PO₄)₃/carbon/carbon nanotube (LTP/C/CNT) composite by virtue of high-quality carbon coating and incorporation of good conductive network. The as-prepared LTP/C/CNT composite exhibits excellent rate performance with discharge capacity of 80.1 and 59.1 mAh g^?1 at 10 C and 20 C (based on the mass of anode, 1 C = 150 mA g^?1), much larger than that of the LTP/C composite (53.4 mAh g^?1 at 10 C, and 31.7 mAh g^?1 at 20 C). LTP/C/CNT also demonstrates outstanding cycling stability with capacity retention of 83.3 % after 1000 cycles at 5 C, superior to LTP/C without incorporation of CNTs (60.1 %). As verified, the excellent electrochemical performance of the LTP/C/CNT composite is attributed to the enhanced electrical conductivity, rapid charge transfer, and Li-ion diffusion because of the incorporation of CNTs.     

Vertically aligned α-MnO<Subscript>2</Subscript> nanosheets on carbon nanotubes as cathodic materials for aqueous rechargeable magnesium ion battery

In this work, vertically aligned α-MnO₂ nanosheets on carbon nanotubes are synthesized simply by a solution process and the electrochemical performance as host materials of magnesium ion is tested in aqueous solution. Cyclic voltammetry analysis confirms the enhanced electrochemical activity of carbon nanotube-supported samples. Moreover, carbon nanotubes skeleton could reduce the charge transfer resistant of the cathode materials, which is confirmed by electrochemical impedance spectroscopy. Furthermore, when tested as magnesium ion batteries cathodic electrode, the α-MnO₂/carbon nanotube sample registers a prominent discharge capacity of 144.6 mAh g^?1 at current density of 0.5 A g^?1, which is higher than the discharge capacity of α-MnO₂ (87.5 mAh g^?1) due to the synergistic effect of insertion/deinsertion reaction and physical adsorption/desorption process. After the 1000th cycle, a remarkable discharge capacity of 48.3 mAh g^?1 is collected for α-MnO₂/carbon nanotube at current density of 10 A g^?1, which is 85% of the original. It is found that the carbon skeleton not only improved the capacity but also enhanced the cycling performance of the α-MnO₂ electrode significantly. Therefore, α-MnO₂/carbon nanotube is a very promising candidate for further application in environmentally benign magnesium ion batteries.     

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.     

An improved solid-state reaction route to Mg2+-doped LiFePO4/C cathode material for Li-ion battery

An improved solid-state reaction route has been employed to synthesize Mg²⁺-doped LiFePO₄/C nanocomposite cathode by calcining the precursor obtained via evaporating the mixture of ascorbic acid, LiCH₃COO·2H₂O, Mg(CH₃COO)₂·4H₂O, and amorphous FePO₄ nanoparticles in anhydrous ethanol under continuous stirring. Ascorbic acid used here acted as both reducing agent and carbon source. The amorphous FePO₄ was pre-prepared via a simple and fast oxidic precipitation method. Electrochemical tests showed that the final product exhibited good rate and cycling performance, with discharge capacities of 145.2 mAh g^?1 at 0.2 C, 129.8 mAh g^?1 at 1 C, 107.6mAh g^?1 at 5 C, and 81.4 mAh g^?1 at 20 C, respectively. The Mg²⁺-doped LiFePO₄/C showed enhanced charge–discharge performance compared with undoped LiFePO₄/C, especially at high rates. The enhanced electrochemical performance of the composite could be attributed to a combination result of the fine particle size with narrow particle size distribution, homogeneous carbon coating on the surface of the particles, and magnesium ion doping.     

Plasma-assisted nitrogen doping of VACNTs for efficiently enhancing the supercapacitor performance

Nitrogen doping of vertically aligned carbon nanotubes (VACNTs) using plasma-enhanced chemical vapour deposition has been investigated to improve the supercapacitance performance of CNTs. Incorporating electrochemical measurements on the open-ended nitrogen-doped CNTs, showed the achievement of 6 times improvement in the capacitance value. For nitrogen-doped CNTs on silicon substrate, specific capacitance of 60 F g^?1 was obtained in 0.5 M KCl solution, with capacity retention ratio above 90 % after cycled at 0.1 A g^?1 for 5000 cycles. Using this sample, a symmetric supercapacitance was fabricated which showed the power density of 37.5 kW kg^?1. The facile fabrication approach and its excellent capacitance improvement, propose it as an efficient technique for enhancing the supercapacitance performance of the carbon-based electrodes.     

Double-walled core-shell structured Si@SiO2@C nanocomposite as anode for lithium-ion batteries

Double-walled core-shell structured Si@SiO₂@C nanocomposite has been prepared by calcination of silicon nanoparticles in air and subsequent carbon coating. The obtained Si@SiO₂@C nanocomposite demonstrates a reversible specific capacity of about 786 mAh g^?1 after 100 cycles at a current density of 100 mA g^?1 with a capacity fading of 0.13 % per cycle. The enhanced electrochemical performance can be due to that the double walls of carbon and SiO₂ improve the electronic conductivity and enhance the compatibility of electrode materials and electrolyte as a result of accommodating the significant volumetric change during cycles. The interlayer SiO₂ may release the mechanical strain and enhance the interfacial adhesion between carbon shell and silicon core.