Graphene-supported SnO2 nanoparticles prepared by a solvothermal approach for an enhanced electrochemical performance in lithium-ion batteries

SnO₂ nanoparticles were dispersed on graphene nanosheets through a solvothermal approach using ethylene glycol as the solvent. The uniform distribution of SnO₂ nanoparticles on graphene nanosheets has been confirmed by scanning electron microscopy and transmission electron microscopy. The particle size of SnO₂ was determined to be around 5 nm. The as-synthesized SnO₂/graphene nanocomposite exhibited an enhanced electrochemical performance in lithium-ion batteries, compared with bare graphene nanosheets and bare SnO₂ nanoparticles. The SnO₂/graphene nanocomposite electrode delivered a reversible lithium storage capacity of 830 mAh g⁻¹ and a stable cyclability up to 100 cycles. The excellent electrochemical properties of this graphene-supported nanocomposite could be attributed to the insertion of nanoparticles between graphene nanolayers and the optimized nanoparticles distribution on graphene nanosheets.     

Electrochemical properties of bare and Ta-substituted Nb2O5 nanostructures

In this work, bare and Ta-substituted Nb₂O₅ nanofibers are prepared by electrospinning followed by sintering at temperatures in the 800–1100 °C range for 1 h in air. Obtained bare and Ta-substituted Nb₂O₅ polymorphs are characterized by X-ray diffraction, scanning electron microscopy, density measurement, and Brunauer, Emmett and Teller surface area. Electrochemical properties are evaluated by cyclic voltammetry and galvanostatic techniques. Cycling performance of Nb₂O₅ structures prepared at temperature 800 °C, 900 °C, and 1100 °C shows following discharge capacity at the end of 10th cycle: 123, 140, and 164 (±3) mAh g⁻¹, respectively, in the voltage range 1.2–3.0 V and at current rate of 150 mA g⁻¹ (1.5 C rate). Heat treated composite electrode based on M-Nb₂O₅ (1100 °C) in argon atmosphere at 220 °C, shows an improved discharge capacity of 192 (±3) mAh g⁻¹ at the end of 10th cycle. The discharge capacity of Ta-substituted Nb₂O₅ prepared at 900 °C and 1100 °C showed a reversible capacity of 150, 202 (±3) mAh g⁻¹, respectively, in the voltage range 1.2–3.0 V and at current rate of 150 mA g⁻¹. Anodic electrochemical properties of M-Nb₂O₅ deliver a reversible capacity of 382 (±5) mAh g⁻¹ at the end of 25th cycle and Ta-substituted Nb₂O₅ prepared at 900 °C, 1000 °C and 1100 °C shows a reversible capacity of 205, 130 and 200 (±3) mAh g⁻¹ (at 25th cycle) in the range, 0.005–2.6 V, at current rate of 100 mA g⁻¹.     

The investigation on electrochemical reaction mechanism of CuF2 thin film with lithium

Crystalline CuF₂ thin films were prepared by pulsed laser deposition under room temperature. The physical and electrochemical properties of the as-deposited thin films have been investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), galvanostatic cycling and cyclic voltammetry (CV). Reversible capacity of 544 mAh g⁻¹ was achieved in the potential range of 1.0–4.0 V. A reversible couple of redox peaks at 3.0 V and 3.7 V was firstly observed. By using ex situ XRD and TEM techniques, an insertion process followed by a fully conversion reaction to Cu and LiF was revealed in the lithium electrochemical reaction of CuF₂ thin film electrode. The reversible insertion reaction above 2.8 V could provide a capacity of about 125 mAh g⁻¹, which makes CuF₂ a potential cathode material for rechargeable lithium batteries.     

High capacity ZnFe2O4 anode material for lithium ion batteries

A nanostructured ternary transition metal oxide, ZnFe₂O₄, is synthesized via the simple polymer pyrolysis method. The characteristics of the material are examined by thermogravimetry, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The electrochemical test results show that this method of ZnFe₂O₄ synthesis produces high specific capacities and good cycling performance, with an initial specific capacity as high as 1419.6 mAh g⁻¹ at first discharge that is maintained at over 800 mAh g⁻¹ even after 50 charge–discharge cycles. The electrode also presents a good rate capability, with a high rate of 4C (1C = 928 mA g⁻¹), a reversible specific capacity that can be as high as 400 mAh g⁻¹. ZnFe₂O₄ is a potential alternative to high-performance nanostructured anode material in lithium ion batteries.     

Enhanced cycling performance of Fe3O4-graphene nanocomposite as an anode material for lithium-ion batteries

Fe₃O₄-graphene nanocomposite was prepared by a gas/liquid interface reaction. The structure and morphology of the Fe₃O₄-graphene nanocomposite were characterized by X-ray diffraction, scanning electron microscopy and high-resolution transmission electron microscopy. The electrochemical performances were evaluated in coin-type cells. Electrochemical tests show that the Fe₃O₄-22.7 wt.% graphene nanocomposite exhibits much higher capacity retention with a large reversible specific capacity of 1048 mAh g⁻¹ (99% of the initial reversible specific capacity) at the 90th cycle in comparison with that of the bare Fe₃O₄ nanoparticles (only 226 mAh g⁻¹ at the 34th cycle). The enhanced cycling performance can be attributed to the facts that the graphene sheets distributed between the Fe₃O₄ nanoparticles can prevent the aggregation of the Fe₃O₄ nanoparticles, and the Fe₃O₄-graphene nanocomposite can provide buffering spaces against the volume changes of Fe₃O₄ nanoparticles during electrochemical cycling.     

SnO2–graphene–carbon nanotube mixture for anode material with improved rate capacities

SnO₂–graphene–carbon nanotube (SnO₂–G–CNT) mixture is synthesized using graphene oxide as precursor for application as anode material in rechargeable Li ion batteries. It is shown that the SnO₂ nanoparticles of 3–6 nm in diameter are not only attached onto the surface of graphene sheets by anchoring with surface functional groups, but they also are encapsulated in pore channels formed by entangled graphene sheets. The incorporation of carbon nanotubes reduces the charge transfer resistance of the anode made from the mixture through the formation of 3D electronic conductive networks. The SnO₂–G–CNT anodes deliver remarkable capacities of 345 and 635 mAh g⁻¹ at 1.5 and 0.25 A g⁻¹, respectively. Flexible electrodes consisting of highly-aligned SnO₂–G–CNT papers are also prepared using a simple vacuum filtration technique. They present a stable capacity of 387 mAh g⁻¹ at 0.1 A g⁻¹ after 50 cycles through the synergy of the high specific capacity of SnO₂ nanoparticles and the excellent cycleability of G–CNT paper.     

A nanocomposite of graphene/MnO2 nanoplatelets for high-capacity lithium storage

A nanocomposite of graphene/MnO₂ nanoplatelets was prepared by one-step chemistry route at room temperature. The microstructure was characterized by X-ray diffraction, N₂ absorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Both TEM and SEM images show that MnO₂ nanoplatelets are homogeneously distributed on the graphene nanosheets. The electrochemical properties were tested by cyclic voltammetry, galvanostatic charge–discharge experiments. The nanocomposite exhibited high lithium capacity (905?mAh?g^?1 at 100?mA?g^?1). The superior lithium storage capability can be attributed to the “open” structure: the large effective surface area and short diffusion paths.     

Electrochemistry of V2ON with lithium

V₂ON thin film has been successfully fabricated by reactive dc sputtering method and annealing process and was investigated for its electrochemistry with lithium. The reversible discharge capacities of V₂ON/Li cells cycled between 0.01 and 4.0 V were found in the range of 803–915 mAh g⁻¹ during the first 50 cycles. By using ex situ scanning electron microscopy, transmission electron microscopy, selected-area electron diffraction and X-ray photoelectron spectroscopy measurements, the reversible transformation between nanocrystalline V₂ON and well dispersed V, Li₂O, Li₃N nano-composites were revealed in the lithium electrochemical reaction. V₂ON thin film exhibits high reversible capacity and good cycle performance with remarkable lower polarization than VN thin film.     

Synthesis of mesoporous SnO2 spheres via self-assembly and superior lithium storage properties

This paper firstly reported a simple route to prepare SnO₂ mesoporous spheres for lithium ion battery. Mesoporous SnO₂ spheres in range of 100–300 nm were prepared by primary reaction at 353 K for 30 min, and calcination process at 773 K, which could be scaled up for manufacturing. The nano-size effect of the small particle and the 3D mesoporous structure promoted the electrolyte and lithium ion transfer and suppressed the volume changes, which greatly enhanced the cycle performances. As the anode material, it could deliver 761 mAh g⁻¹ capacity after 50 cycles at the current density of 200 mA g⁻¹. Even at 2 A g⁻¹, it retained 480 mAh g⁻¹ after 50 cycles. Furthermore, we suggested that the high stability of the structure was responsible for the improved cycle properties.     

Coaxial MnO/C nanotubes as anodes for lithium-ion batteries

Coaxial MnO/C nanotubes with an average diameter of about 450 nm, a wall thickness of about 150 nm, a length of 1–5 μm and a 10 nm thick carbon layer have been prepared using β-MnO₂ nanotubes as self-templates in acetylene at 600 °C. The microstructure of the product has been characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution transmission electron microscopy, and Raman spectroscopy. The electrochemical performance of the product has been evaluated by galvanostatic charge/discharge cycling. It is found that the product exhibits a reversible capacity of nearly 500 mAh g⁻¹ at a current density of 188.9 mA g⁻¹, and 83.9% of capacity retention, higher than bare MnO nanotubes (58.2%) and MnO nanoparticles (25.8%). The results reveal that coaxial MnO/C nanotubes would be a promising anode material for next-generation lithium-ion batteries.     

Lithium storage performance of carbon nanotubes prepared from polyaniline for lithium-ion batteries

Carbon nanotubes with large surface area and surface nitrogen and oxygen functional groups are prepared by carbonizing and activating of polyaniline nanotubes, which is synthesized by polymerization of aniline with the self-assembly method in aqueous media. The physicochemical properties of the carbon nanotubes are characterized by scanning electron microscope, transmission electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller, elemental analyses and X-ray photoelectron spectroscopy measurements. The surface area and pore diameter are 618.9 m² g⁻¹ and 3.10 nm. The electrochemical properties of the carbon nanotubes as anode materials in lithium ion batteries are evaluated. At a current density of 100 mA g⁻¹, the activated carbon nanotube shows an enormously first discharge capacity of about 1370 mAh g⁻¹ and a charge capacity of 907 mAh g⁻¹. After 20 cycling tests, the activated carbon nanotube retains a reversible capacity of 728 mAh g⁻¹. These indicate it may be a promising candidate for an anode material for lithium secondary batteries.     

Core–shell Ni0.5TiOPO4/C composites as anode materials in Li ion batteries

Pristine Ni_0.5TiOPO₄ was prepared via a traditional solid-state reaction, and then Ni_0.5TiOPO₄/C composites with core–shell nanostructures were synthesized by hydrothermally treating Ni_0.5TiOPO₄ in glucose solution. X-ray diffraction patterns indicate that Ni_0.5TiOPO₄/C crystallizes in monoclinic P2₁/c space group. Scanning electron microscopy and transmission electron microscopy show that the small particles with different sizes are coated with uniform carbon film of ∼3 nm in thickness. Raman spectroscopy also confirms the presence of carbon in the composites. Ni_0.5TiOPO₄/C composites presented a capacity of 276 mAh g⁻¹ after 30 cycles at the current density of 42.7 mA g⁻¹, much higher than that of pristine Ni_0.5TiOPO₄ (155 mAh g⁻¹). The improved electrochemical performances can be attributed to the existence of carbon shell.     

Synthesis of spindle-shaped nanoporous C–LiFePO4 composite and its application as a cathodes material in lithium ion batteries

In this work, LiFePO₄/C composites were prepared in hydrothermal system by using iron gluconate as iron source, and two feeding sequences during the preparation were comparatively studied. The morphology, crystal structure and charge–discharge performance of the prepared samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and galvanostatic charge–discharge testing. The results showed that the feeding sequences and iron gluconate seriously affected the microstructures and electrochemical properties of the resulting LiFePO₄ cathodes in lithium ion batteries. The spindle-shaped LiFePO₄ with hierarchical microporous structure self-assembled by nanoparticles has been successfully synthesized by synthesis route B. In addition, the cell performance of the synthesized LiFePO₄ by synthesis route B was better than that of LiFePO₄ by synthesis route A. Specially at high rates, the superior rate performance of the spindle-shaped LiFePO₄/C microstructure (LFP/C-B) was revealed. And special reversible capacities of ∼118 and ∼95 mAh g⁻¹ were obtained at rates of 2 C and 5 C, comparing to ∼96 and ∼68 mAh g⁻¹ for LFP/C-A.     

Enhanced high rate capability of dual-phase Li4Ti5O12–TiO2 induced by pseudocapacitive effect

The dual-phase Li₄Ti₅O₁₂–TiO₂ nanocomposite is successfully synthesized by a hydrothermal route with adding thiourea. The electrochemical performance of the dual-phase nanocomposite as anode for lithium-ion batteries is investigated by the galvanostatic method, cyclic voltammetry and electrochemical impedance spectra. It is demonstrated that the dual-phase Li₄Ti₅O₁₂–TiO₂ nanocomposite presents the improved electrochemical performance over individual single phase Li₄Ti₅O₁₂ and anatase TiO₂ samples. After 300 cycles at 1 C, the dual-phase Li₄Ti₅O₁₂–TiO₂ nanocomposite can still maintain the large discharge capacity of 116 mAh g⁻¹. It indicates that the as-prepared nanocomposite can endure great changes of various discharge current densities to retain a good stability. The large discharge capacity of 132 mAh g⁻¹ is also obtained at the large current density of 1600 mA g⁻¹ upon cycling. In particular, as verified by the cyclic voltammetry, the pseudocapacitive effect is induced due to the presence of abundant phase interfaces in the dual-phase Li₄Ti₅O₁₂–TiO₂ nanocomposite, which is beneficial to the enhanced high rate capability and good cycle stability.     

Electrochemical performance of single crystalline spinel LiMn2O4 nanowires in an aqueous LiNO3 solution

Single crystalline cubic spinel LiMn₂O₄ nanowires were synthesized by hydrothermal method and the precursor calcinations. The phase structures and morphologies were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and high-resolution transmission electron microscopy (HRTEM). Galvanostatic charging/discharging cycles of as-prepared LiMn₂O₄ nanowires were performed in an aqueous LiNO₃ solution. The initial discharge capacity of LiMn₂O₄ nanowires was 110 mAh g⁻¹, and the discharge capacity was still above 100 mAh g⁻¹ after 56 cycles at 10C-rate, and then 72 mAh g⁻¹ was registered after 130 cycles. This is the first report of a successful use of single crystalline spinel LiMn₂O₄ nanowire as cathode material for the aqueous rechargeable lithium battery (ARLB).     

Highly reversible Co3O4/graphene hybrid anode for lithium rechargeable batteries

A Co₃O₄/graphene hybrid material was fabricated using a simple in situ reduction process and demonstrated as a highly reversible anode for lithium rechargeable batteries. The hybrid is composed of 5 nm size Co₃O₄ particles uniformly dispersed on graphene, as observed by transmission electron microscopy, atomic force microscopy, Raman spectroscopy and X-ray diffraction analysis. The Co₃O₄/graphene anode can deliver a capacity of more than 800 mA h g⁻¹ reversibly at a 200 mA g⁻¹ rate in the voltage range between 3.0 and 0.001 V. The high reversible capacity is retained at elevated current densities. At a current rate as high as 1000 mA g⁻¹, the Co₃O₄/graphene anode can deliver more than 550 mA h g ⁻¹, which is significantly higher than the capacity of current commercial graphite anodes. The superior electrochemical performance of the Co₃O₄/graphene is attributed to its unique nanostructure, which intimately combines the conductive graphene network with uniformly dispersed nano Co₃O₄ particles.     

Synthesis and electrochemical characterization of LiCoxMn1−xPO4/C nanocomposites

LiCo_xMn_1−xPO₄/C nanocomposites (0 ≤ x ≤ 1.0) were prepared by a combination of spray pyrolysis at 300 °C and wet ball-milling followed by heat treatment at 500 °C for 4 h in 3% H₂ + N₂ atmosphere. X-ray diffraction analysis indicated that all samples had the single phase olivine structures indexed by orthorhombic Pmna. The lattice parameters linearly decreased with increasing cobalt content, which confirmed the existence of solid solutions. It was clearly seen from the scanning electron microscopy observation that the LiCo_xMn_1−xPO₄/C samples were agglomerates with approximately 100 nm primary particles. The LiCo_xMn_1−xPO₄/C nanocomposites were used as cathode materials for lithium batteries, and electrochemical performance was comparatively investigated with cyclic voltammetry and galvanostatic charge–discharge test using the Li?1 M LiPF₆ in EC:DMC = 1:1?LiCo_xMn_1−xPO₄/C cells at room temperature. The cells at 0.05 C charge–discharge rate delivered first discharge capacities of 165 mAh g⁻¹ (96% of theoretical capacity) at x = 0, 136 mAh g⁻¹ at x = 0.2, 132 mAh g⁻¹ at x = 0.5, 125 mAh g⁻¹ at x = 0.8 and 132 mAh g⁻¹ (79% of theoretical capacity) at x = 1.0, respectively. While the first discharge capacity increased with the cobalt content at high charge–discharge rates more than 0.5 C due to higher electronic conductivity of LiCoPO₄ in comparison with LiMnPO₄, the cycleability of cell became worse with increasing the amount of cobalt. The existence of Mn²⁺ seemed to enhance the cycleability of LiCo_xMn_1−xPO₄/C nanocomposite cathode.     

Synthesis and electrochemical performance of bismuth–vanadium oxyfluoride

Bismuth–vanadium oxyfluoride (Bi₂VO₅F) has been synthesized using a simple, solid-state reaction process at different sintering temperatures. The structure and performance of the samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and galvanostatic charge/discharge experiments. The results show that bismuth–vanadium oxyfluoride belongs to a tetragonal crystal system with space group I4mm. The sample that was synthesized at 550 °C (P550) exhibits relatively good electrochemical properties. Sample P550 shows a high, initial discharge capacity of 222 mAh g⁻¹ at a rate of 100 mA g⁻¹ between 1.4 and 3.5 V. Sample P550 also shows acceptable electrochemical cycling properties. After the first cycle, the discharge specific capacity remains between 106 and 155 mAh g⁻¹, which plateaus between 2.1 and 1.9 V during the first 15 cycles.     

Preparation and electrochemical characterization of MnOOH nanowire–graphene oxide

MnOOH nanowire–graphene oxide composites are prepared by hydrothermal reaction in distilled water or 5% ammonia aqueous solution at 130 °C with MnO₂–graphene oxide composites which are synthesized by a redox reaction between KMnO₄ and graphene oxide. Powder X-ray diffraction (XRD) analyses and energy dispersive X-ray analyses (EDAX) show MnO₂ is deoxidized to MnOOH on graphene oxide through hydrothermal reaction without any extra reductants. The electrochemical capacitance of MnOOH nanowire–graphene oxide composites prepared in 5% ammonia aqueous solution is 76 F g⁻¹ at current density of 0.1 A g⁻¹. Moreover, electrochemical impedance spectroscopy (EIS) suggests the electrochemical resistance of MnOOH nanowire–graphene oxide composites is reduced when hydrothermal reaction is conducted in ammonia aqueous solution. The relationship between the electrochemical capacitance and the structure of MnOOH nanowire–graphene oxide composites is characterized by cyclic voltammetry (CV) and field emission scanning electron microscopy (FESEM). The results indicate the electrochemical performance of MnOOH nanowire–graphene oxide composites strongly depends on their morphology.     

Hollow CuFe2O4 spheres encapsulated in carbon shells as an anode material for rechargeable lithium-ion batteries

We report here a polymer-templated hydrothermal growth method and subsequent calcination to achieve carbon coated hollow CuFe₂O₄ spheres (H–CuFe₂O₄@C). This material, when used as anode for Li-ion battery, retains a high specific capacity of 550 mAh g⁻¹ even after the 70th cycle, which is much higher than those of both CuFe₂O₄@C (∼300 mAh g⁻¹) and H–CuFe₂O₄ (∼120 mAh g⁻¹). And galvanostatic cycling at different current densities reveals that a capacity of 480 mAh g⁻¹, 91% recovery of the specific capacity cycling at 100 mA g⁻¹, can be obtained even after 50 cycles running from 100 to 1600 mA g⁻¹. The significantly enhanced electrochemical performances of H–CuFe₂O₄@C with regard to Li-ion storage are ascribed to the following factors: (1) the hollow void, which could mitigate the pulverization of electrode and facilitate the lithium-ion, electron and electrolyte transport; (2) the conductive carbon coating, which could enhance the conductivity, alleviate the agglomeration problem, prevent the formation of an overly thick SEI film and buffer the electrode. Such a structural motif of H–CuFe₂O₄@C is promising, for electrode materials of LIBs, and points out a general strategy for creating other hollow-shell electrode materials with improved electrochemical performances.