Electrodeposition of iron oxide nanorods on carbon nanofiber scaffolds as an anode material for lithium-ion batteries

Iron oxide film with spaced radial nanorods is formed on the VGCF (vapor-grown carbon nanofiber) scaffolds by means of anodic electrodeposition. X-ray diffraction, scanning electron microscopy, and transmission electron microscopy show that the iron oxide film deposited on the VGCF surface is α-Fe₂O₃ and consists of spaced radial nanorods having 16-21 nm in diameter after annealing at 400 °C. Galvanostatic charge/discharge results indicate that the α-Fe₂O₃/VGCF anode (970 mAh g⁻¹) has higher capacity than bare α-Fe₂O₃ anode (680 mAh g⁻¹) at 10 C current discharge. VGCF scaffolds fabricated by electrophoretic deposition favor the electron conduction, and the spaced radial nanorods on VGCFs facilitate the migration of lithium ion from the electrolyte. Electrochemical reactions between α-Fe₂O₃ and lithium ion are therefore improved significantly by this tailored architecture.     

Preparation and characterization of carbon films prepared from poly(vinyl alcohol) containing metal oxide and nano fibers with iodine pretreatment

This research focused on the combination of catalyst effect of metal oxide, thermal conductive effect of carbon nano fibers and iodine pretreatment during carbonization of polymer precursor in order to prepare tough carbon films. Poly(vinyl alcohol) (PVA) composites containing metal oxide (Fe₃O₄) and vapor-grown carbon fibers (VGCFs) were prepared by gelation/crystallization method with the freezing/thawing technique. The dry gel films as precursor were pretreated in the atmosphere of vapor iodine, and then heat-treated at 600-1200 °C. The combined effect of iodine, Fe₃O₄ and VGCF on the carbonization of PVA was analyzed with thermo-gravimetric analysis, X-ray diffraction, and scanning electron microscope in details. Iodine pretreatment for 24 h significantly promoted the dehydration of PVA, and resulted the carbon film with a high crystallinity. Fe₃O₄ as catalyst facilitated the carbonization of PVA at a low temperature of 800-900 °C. The addition of VGCFs was found to play an important role to prepare tough films by mild carbonization due to its high thermal conductivity. The degree of graphitization in the carbon film depended on the filler contents, pretreatment conditions and carbonization conditions. The graphitization degrees for G- and T-components in the film were investigated on the basis of X-ray diffraction intensity distribution from the (0 0 2) plane.     

Origin of Capacity Fading in Nano-Sized Co3O4 Electrodes: Electrochemical Impedance Spectroscopy Study

Transition metal oxides have been suggested as innovative, high-energy electrode materials for lithium-ion batteries because their electrochemical conversion reactions can transfer two to six electrons. However, nano-sized transition metal oxides, especially Co₃O₄, exhibit drastic capacity decay during discharge/charge cycling, which hinders their practical use in lithium-ion batteries. Herein, we prepared nano-sized Co₃O₄ with high crystallinity using a simple citrate-gel method and used electrochemical impedance spectroscopy method to examine the origin for the drastic capacity fading observed in the nano-sized Co₃O₄ anode system. During cycling, AC impedance responses were collected at the first discharged state and at every subsequent tenth discharged state until the 100th cycle. By examining the separable relaxation time of each electrochemical reaction and the goodness-of-fit results, a direct relation between the charge transfer process and cycling performance was clearly observed.     

Microwave-hydrothermal synthesis of Fe-based materials for lithium-ion batteries and supercapacitors

Fe-based materials, Fe₂O₃, Fe₃O₄, and FeOOH, were synthesized by the microwave–hydrothermal process in the temperature range of 100–200 °C and under very short reaction times of 15 min to 2 h. Under microwave-controlled hydrolysis and redox reactions, cube-like Fe₂O₃ was crystallized using FeCl₃, Fe₃O₄ particles were crystallized from FeCl₂ and FeOOH nanorods were crystallized using FeCl₃. The Fe-based materials were fabricated to make anodes and cathodes of lithium-ion battery and supercapacitor electrode materials to study their potential electrochemical applications. The electrochemical results showed that FeOOH had better anode capacity as lithium-ion batteries than those of Fe₂O₃ and Fe₃O₄. The present results suggest that the microwave–hydrothermally synthesized Fe-based materials are promising lithium-ion battery anode materials.     

Uniform α-Fe2O3 nanoparticles with narrow gap immobilized on CNTs through N-doped carbon as high-performance lithium-ion batteries anode

Fe₂O₃ with high theoretical capacity, low cost, and environmental friendliness has been attracted great attention in lithium-ion batteries (LIBs), which however is limited by low rate capability and fast capacity fading owing to low electronic conductivity, self-aggregation, and sever volume expansion. CNTs with excellent conductivity and unique 3D interconnected network are ideal matrices for composite electrochemical materials, but it is difficult to meet the demand of high capacity. Here, uniform α-Fe₂O₃ nanoparticles with narrow gap (~1.4 nm) were immobilized on CNTs through N-doped carbon (α-Fe₂O₃/CNTs-NC) that can address these issues. As an advanced LIBs anode, the electrode displays unprecedented specific capacity (1173 mAh/g at 0.2 A/g) and outstanding rate behavior (716.4 mAh/g at 5.0 A/g after 1200 cycles), which are even superior to the theoretical capacity (1007 mAh/g) and the performance of most reported Fe₂O₃-based anodes. Homogeneous nano-sized α-Fe₂O₃ with a narrow gap highly shortens the diffusion path for Li⁺ transport, exposes quite sufficient active sites, and prevents the volume change. Moreover, the 3D backbone of CNTs with a more homogeneously distributed electric field can enhance conductivity, and tightly contact with α-Fe₂O₃ by NC, then obtain robust structural stability, which boosts LIBs in storage capacity, rate capability, and cycling stability.     

Nanocomposite Fe2O3-Se as a new lithium storage material

The electrochemical properties of nanocomposite Fe₂O₃-Se thin film prepared by pulsed laser deposition (PLD) method have been investigated by cyclic voltammetry and charge/discharge measurements. A large reversible capacity of nanocomposite Fe₂O₃-Se thin film was found to be around 650 mAh g⁻¹. A new couple of reduction and oxidation peaks at 1.4 and 1.8 V were observed from cyclic voltammogram for the first time. Our data demonstrated that nanocomposite Fe₂O₃-Se exhibit larger capacity and better cycle performance than pure Fe₂O₃. The electrochemical reaction mechanisms of Fe₂O₃-Se with lithium were examined by X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) and selected-area electron diffraction (SAED). The reversible conversions reaction of nanosized metal Fe with Li₂Se and Li₂O formed after initial discharge process into FeSe and Fe₂O₃ respectively were revealed.     

Enhancing glass anode performance for lithium-ion batteries via crystallization

We investigate the thermal and electrochemical properties of xFe₂O₃-(100-x) P₂O₅ glass (x = 20, 30, 40, and 50 mol%) and 50Fe₂O₃-50P₂O₅ (50FeP) glass-ceramics as anodes for lithium-ion batteries (LiBs). The results show that both the glass transition temperature and the energy bandgap monotonically decrease with the increasing Fe₂O₃ while a critical Fe₂O₃ content of 30 mol% is found to give glass the highest thermal stability, the largest capacity at 1 Ag^-1, and the lowest charge-transfer resistance before cycling. Moreover, Fe₃(P₂O₇)₂ crystals formed during heat treatment in 50FeP glass effectively enhances the electrochemical properties. The optimum heat treatment condition for 50FeP glass is found at 1033 K for 4 h, that is, 1033 K-4 h sample enables a reversible capacity of 237 mA h g⁻¹ at the end of 1000 cycles at 1 Ag^-1, which is more than 1.5 times higher than that of the 50FeP glass-based anode. These findings suggest that the Fe₂O₃-P₂O₅ glass-ceramics hold significant potential for the effective development of new types of glass anodes for future advanced LiBs.     

Li2ZnTi3O8@α-Fe2O3 composite anode material for Li-ion batteries

Li₂ZnTi₃O₈@α-Fe₂O₃ composites have been successfully prepared by a facile hydrothermal process. Li₂ZnTi₃O₈/α-Fe₂O₃ composites show similar irregular spherical morphologies like Li₂ZnTi₃O₈ and relatively smaller particle sizes than pristine Li₂ZnTi₃O₈. Among all Li₂ZnTi₃O₈/α-Fe₂O₃ composites, Li₂ZnTi₃O₈/α-Fe₂O₃ composite (5 wt%) exhibits the best electrochemical properties. Li₂ZnTi₃O₈/α-Fe₂O₃ composite (5 wt%) delivers a reversible charge capacity of 184.8 mAh g^?1 even at 1000 mA g^?1 after 500 cycles, while pristine Li₂ZnTi₃O₈ only delivers a reversible charge capacity of 110.7 mAh g^?1. The strong covalent bonds between Li₂ZnTi₃O₈ and α-Fe₂O₃ will be formed, which is beneficial for the reduction of interfacial energy and thus helpful for the stabilization of the composite. Because of the special synergistic effect of the multi-phase interface, Li₂ZnTi₃O₈/α-Fe₂O₃ composites not only possess the advantages of single components but also show novel and attractive performances, such as the enhanced ionic conductivity, reduced interfacial charge transfer impedance, improved migration rate of lithium ions, and the enhancement of the rate performance and reversible capacity. The as-prepared Li₂ZnTi₃O₈/α-Fe₂O₃ composites reveal important potentials as anode materials for next-generation rechargeable Li-ion batteries, and this work also offers an effective strategy to design high performance lithium storage materials for advanced lithium-ion batteries.     

Grafting of vinyl polymers onto VGCF surface and the electric properties of the polymer-grafted VGCF

The graft polymerization of vinyl monomers onto vapor grown carbon fibers (VGCF) initiated by the system consisting of molybdenum hexacarbonyl (Mo(CO)₆) and trichloroacetyl (COCCl₃) groups introduced onto the surface was investigated. The introduction of trichloroacetyl groups onto VGCF surface was successfully achieved by the reaction of carboxyl groups on VGCF surface with trichloroacetyl isocyanate. It was found that the radical graft polymerization of vinyl monomers, such as methyl methacrylate (MMA), styrene, and glycidyl methacrylate (GMA) is successfully initiated by the system consisting of Mo(CO)₆ and COCCl₃ groups introduced onto the surfaces. In the polymerization, the corresponding vinyl polymers were effectively grafted onto the VGCF surface, based on the propagation of polymer from surface radicals formed by the interaction of trichloroacetyl groups and Mo(CO)₆: the percentage of PMMA grafting reached 40%. Polymer-grafted VGCF gave a stable colloidal dispersion in good solvents for grafted polymer. The electric resistance of composite prepared from the polymer-grafted VGCF suddenly increased in organic solvent vapor over 10³ times, and returned to initial resistance when it was transferred into dry air. These results indicate that such composites can be used as novel gas sensors.     

Co2SnO4–multiwalled carbon nanotubes composite as a highly reversible anode material for lithium-ion batteries

We report a facile strategy to synthesize the composite of Co₂SnO₄ nanoparticles and multiwalled carbon nanotubes (MWCNTs) as a highly reversible anode material for high-performance lithium-ion batteries. Galvanostatic charge/discharge, cyclic voltammograms(CVs) and electrochemical impedance spectra (EIS) testing results indicate that the Co₂SnO₄–MWCNTs composite display large reversible capacity, excellent cyclic performance and good rate performance, highlighting the importance of the added MWCNTs for maximum utilization of electrochemically active Co₂SnO₄ nanoparticles for energy storage applications in high-performance lithium-ion batteries.     

The role of phosphorus in the growth of vapour-grown carbon fibres obtained by catalytic decomposition of hydrocarbons

Production of VGCF fibres from the decomposition of a methane-hydrogen mixture over metal particles is influenced by the support on which the particles have been laid. It was found that different as-received commercial graphite supports, according to their impurity content, could promote or inhibit the VGCF growth.Good yields of vapour-grown carbon fibres with a length up to 6 cm have been fabricated by catalytic decomposition of methane over particles obtained from Fe₃(CO)₁₂. Addition to the substrate of small amounts of phosphorus from a solution of H₃PO₄ in ethanol, followed by impregnation with Fe₃(CO)₁₂, was found to be effective in promoting the growth of VGCFs and increasing the yield. But increasing the amount of phosphorus over P/Fe ∼0.25 had an inhibiting effect on the growth of VGCFs. So the yield of VGCFs was optimized for a given phosphorus concentration.These phenomena are interpreted by the formation of Fe-P compounds which, depending on their formulae, lower or increase the melting point of the catalyst particles. According to the VLS theory, catalytic growth up to a macroscopic scale results from the liquid state of the catalyst.     

High lithium storage of Co3O4 enabled by integrating hollow and porous carbon scaffolds

The Co₃O₄, as a potential anode of lithium-ion batteries, has gained considerable attention because of high theoretical capacity. However, the Co₃O₄ is suffering from serious structure deterioration and rapid capacity fading due to its bulky volume change during cyclic charge/discharge process. Herein, to stabilize the lithium storage performance of the Co₃O₄ nanoparticles, a characteristic carbon scaffold (HPC) integrating hollow and porous structures has been fabricated by a well-designed method for the first time. The ultrafine Co₃O₄ nanoparticles are cleverly anchored on the HPC (HPC@Co₃O₄) and hence achieve significantly improved electrochemical properties including high capacity, improved reaction kinetics and outstanding cycle stability, showing high capacity of 1084.7 mAh g^-1 after 200 cycles at 200 mA g^-1 as well as 681.4 mAh g^-1 after 300 cycles at 1000 mA g^-1. The HPC@Co₃O₄ therefore shows good promising for application in advanced lithium-ion battery anodes. The results of the systematically material and electrochemical characterizations indicate that the synergistic effects of ultrafine Co₃O₄ nanoparticles and well-designed HPC scaffolds are responsible for the outstand performance of the HPC@Co₃O₄ anode. Moreover, this work can enrich the understanding and development of stable and high-performance metal oxide-based lithium-ion battery anodes for advanced lithium storage.     

Microwave-assisted one-pot synthesis of SnC2O4/graphene composite anode material for lithium-ion batteries

Currently, SnC₂O₄ is considered as one of the most promising anode materials for high-energy lithium-ion batteries (LIBs) because its charge capacity is higher than that of metal oxides. Herein, a facile microwave-assisted solvothermal method was employed to obtain SnC₂O₄/GO composites within only 30?min, which is time-efficient. The amount of SnC₂O₄ was increased to 95.3?wt% to improve the capacity of the composite. Pure SnC₂O₄ with a high specific surface area of 19.6?m² g^?1 without any other tin compound was used for fabrication. The SnC₂O₄/GO composite exhibited excellent electrochemical performance, with reversible discharge/charge capacity of 657/659?mA?h?g^?1 after 100 cycles at 0.2?A?g^?1. Furthermore, at high current densities of 1.0 and 2.0?A?g^?1, the SnC₂O₄/GO composite anode exhibited high reversible discharge/charge capacities of 553/552 and 418/414?mA?h?g^?1, respectively, after 200 cycles at room temperature. These improvements were likely obtained because SnC₂O₄ was well composited with graphene, which not only offered rapid electron transfer but also released the tension produced by the volumetric effect during repeated lithiation/delithiation. Cyclic voltammetry (CV) was also performed to further study the electrochemical reactions of SnC₂O₄/GO. The facile microwave-assisted solvothermal method used herein is considered as a highly efficient method to fabricate metal oxalate/graphene composites for use as anode materials in LIBs.     

Preparation and electrochemical performance of composite oxide of alpha manganese dioxide and Li-Mn-O spinel

Nano-sized composite powder which consisted of two manganese-based oxides, alpha manganese dioxide (α-MnO₂) and spinel Li-Mn-O, was successfully formed by intergrowth of the spinel phase inside α-MnO₂. This composite oxide was synthesized by precipitation and heat treatment in air; α-manganese dioxide powder was firstly prepared by oxidative precipitation of Mn(II) with K₂S₂O₈ in an aqueous solution, and then a mixture of the obtained manganese oxide powder and LiOH methanol solution was heat-treated in air. Electron microscopy and diffraction observations confirmed that the manganese oxide composite consisted of nano-sized grains of the spinel LiMn₂O₄ and α-MnO₂ phases. It was found that this α-MnO₂/spinel LiMn₂O₄ composite electrode exhibited highly reversible lithium insertion compared to the pristine α-MnO₂ and conventional LiMn₂O₄, that is, the composite demonstrated high discharge capacity of 148 mAh g⁻¹ as a cathode material of lithium cells in the potential range of 2.5-4.3 V with no significant capacity fading. It was thought that the intimately mixing of two oxides on a nanometer scale helped to maintain structural integrity on charge-discharge cycling, which leads to excellent capacity retention for both of the spinel and alpha-type manganese oxide.     

Formation and electrochemical performance of copper/carbon composite nanofibers

Copper-loaded carbon nanofibers are fabricated by thermally treating electrospun Cu(CH₃COO)₂/polyacrylonitrile nanofibers and utilized as an energy-storage material for rechargeable lithium-ion batteries. These composite nanofibers deliver more than 400 mA g⁻¹ reversible capacities at 50 and 100 mA g⁻¹ current densities and also maintain clear fibrous morphology and good structural integrity after 50 charge/discharge cycles. The relatively high capacity and good cycling performance of these composite nanofibers, stemmed from the integrated combination of metallic copper and disordered carbon as well as their unique textures and surface properties, make them a promising electrode candidate for next-generation lithium-ion batteries.     

Effect of ball-milling on the rate and cycle-life performance of graphite as negative electrodes in lithium-ion capacitors

A commercial graphite is ball-milled and the pristine and ball-milled graphites are characterised for use as negative electrodes in lithium-ion capacitors (LICs). Ball milling graphite results in a decrease in discharge capacity when the charge rate is relatively slow, whereas, it leads to an increase in discharge capacity when the charge rate is high. When charged at 0.1 C, the discharge capacities of pristine, 3 h, 10 h and 30 h-milled materials at 6 C are 75, 69, 67 and 66% of theoretical capacity, respectively; however, when charged at 60 C, the discharge capacities of pristine, 3 h, 10 h and 30 h-milled materials, at 60 C, fall to 0.9, 13, 23 and 24% of theoretical capacity, respectively (theoretical capacity: 372 mAh g⁻¹, for LiC₆ stoichiometry). This difference in the discharge rate capability behaviour of the pristine and ball-milled graphites with charge rate is attributed to the interplay of two different charge storage mechanisms: Li-ion intercalation and Li-ion adsorption that co-exist; but the later becomes more significant for milled samples. In terms of cycle-life performance, pristine and ball-milled graphites follow similar trends observed for their rate capability behaviour.     

Simple fabrication of a Fe2O3/carbon composite for use in a high-performance lithium ion battery

A simple approach was developed for the fabrication of a Fe₂O₃/carbon composite by impregnating activated carbon with a ferric nitrate solution and calcinating it. The composite contains graphitic layers and 10 wt.% Fe₂O₃ particles of 20–50 nm in diameter. The composite has a high specific surface area of ∼828 m² g⁻¹ and when used as the anode in a lithium ion battery (LIB), it showed a reversible capacity of 623 mAh g⁻¹ for the first 100 cycles at 50 mA g⁻¹. A discharge capacity higher than 450 mAh g⁻¹ at 1000 mA g⁻¹ was recorded in rate performance testing. This highly improved reversible capacity and rate performance is attributed to the combination of (i) the formation of graphitic layers in the composite, which possibly improves the matrix electrical conductivity, (ii) the interconnected porous channels whose diameters ranges from the macro- to meso- pore, which increases lithium-ion mobility, and (iii) the Fe₂O₃ nanoparticles that facilitate the transport of electrons and shorten the distance for Li⁺ diffusion. This study provides a cost-effective, highly efficient means to fabricate materials which combine conducting carbon with nanoparticles of metal or metal oxide for the development of a high-performance LIB.     

Spray-drying assisted synthesis of a Li4Ti5O12/C composite for high rate performance lithium ion batteries

Spinel crystalline lithium titanium oxide (Li₄Ti₅O₁₂ or LTO) has gained attention as a possible alternative material to graphite for use as anodes in lithium-ion rechargeable batteries due to its low volume expansion and dendrite-free long-term stability. However, the rate capability of LTO is limited by its low electronic conductivity, which results in a large polarization resistance between electrodes. In this study, we demonstrate a spray-drying-assisted carbon coating approach to synthesize LTO/C composites for enhanced lithium-insertion capacity and facilitated charge-discharge reaction kinetics. The thin carbon layer of LTO/C composite contributes to suppressing particle growth by forming passivating carbon layers. In addition to the decrease in particle size for short lithium-diffusion pathways, the highly conductive carbon layers reduce the interfacial resistance between the electrode and electrolyte by enhanced electrical conductivity. The electrochemical performances of the spray-drying-prepared LTO/C composite such as the specific capacity, cycle and rate capabilities, and impedance are compared with pristine LTO and carbon-coated LTO synthesized without spray-drying. The LTO/C prepared from glucose exhibits a 11.15% enhancement in rate characteristics of pristine LTO at 0.5 C after 100 cycles. These results indicate that the carbon coating layer promotes charge transfer and ion diffusion as well as provides a buffering effect for improved rate and cyclic capabilities.     

Fabrication of three-dimensional porous structured Co3O4 and its application in lithium-ion batteries

A novel three-dimensional (3D) porous structured Co₃O₄ was prepared by electrodeposition combined with thermal-treatment method. The electrochemical properties of as-prepared 3D porous Co₃O₄ were closely related to its morphology and structure which can be modified by various thermal-treatment temperatures. The 3D porous Co₃O₄ prepared at 300 °C exhibited smaller crystallite size and higher capacity compared to 400 °C as well as 500 °C. As used in lithium-ion batteries, the porous Co₃O₄ anodes delivered a high reversible capacity of about 1100 mAh g⁻¹ with no obvious capacity fading up to 50 cycles and exhibited higher rate capability compared with Co₃O₄ foil anodes. The enhanced electrochemical performances of 3D porous Co₃O₄ anodes are attributed to its unique 3D porous structure which can offer a large materials/electrolyte contact area and accommodate the strain induced by the volume change during cycling.     

Nanorod-like Fe2O3/graphene composite as a high-performance anode material for lithium ion batteries

In this study, a nanorod-like Fe₂O₃/graphene nanocomposite is synthesized by a facile template-free hydrothermal method and a following calcination in air at 300 °C for 2 h. The Fe₂O₃ nanorods with diameter of 15–30 nm and length of 120–300 nm are homogenous distributed on both sides of graphene. The morphologies of intermediates at different hydrothermal reaction times are investigated by transmission electron microscopy (TEM) characterization, and a possible growth mechanism of this one-dimensional structure is proposed. It is shown that the α-FeOOH rodlike precursors are formed through a rolling-broken-growth (RBG) model, then the α-FeOOH is transformed into α-Fe₂O₃ nanorods during calcinations, preserving the same rodlike morphology. Electrochemical characterizations demonstrate that the Fe₂O₃ nanorod/graphene composites exhibit a very large reversible capacity of 1063.2 mAh/g at the charge/discharge rate of 0.1 C.