Flocculant-assisted synthesis of Fe2O3/carbon composites for superior lithium rechargeable batteries

High-performance iron oxide/carbon (Fe₂O₃/C) composites for lithium-ion batteries are synthesized by the combination of flocculant-assisted process and thermo-chemical treatment. Carboxymethylcellulose is used simultaneously as the flocculant and carbon source. This facile and scalable method lends itself to the fabrication of other metal oxide/carbon composites based on the flocculation mechanism. The lithium storage mechanism and cycling performance of Fe₂O₃/C composites are investigated by cyclic voltammetry and charge–discharge tests. As the rates increase from 50 to 1000 mA g^?1, the composites display high charge capacities of 834 mAh g^?1 for the first cycle at 50 mA g^?1 and 497 mAh g^?1 at 1000 mA g^?1 over 100 cycles. Excellent rate capability and cyclability are ascribed presumablely to the isolation and buffer functions of the conductive carbon matrix against particle aggregation and large volume variety upon cycling.     

Effect of carbon content and calcination temperature on the electrochemical performance of lithium iron phosphate/carbon composites as cathode materials for lithium-ion batteries

Lithium iron phosphate/carbon (LiFePO₄/C) composites were prepared by a convenient method with water-soluble phenol-formaldehyde resin as the carbon precursor. The morphology, crystalline structure, thermal stability, and composition of as-prepared LiFePO₄/C composites were investigated by scanning electron microscopy, X-ray diffraction, thermogravimetric analysis, and Raman spectrometry. Their electrochemical performance was examined based on cyclic voltammogram with a LAND battery testing system while the effect of carbon content and calcination temperature was highlighted. Results show that carbon content and calcination temperature dramatically influence the discharge capacities and rate performance of LiFePO₄/C composites. The optimal calcination temperature is 700 °C, and the optimal carbon content (mass fraction) is 8.7%. The LiFePO₄/C composite prepared under the optimal conditions exhibits an initial room temperature discharge capacity of 150.2 mA h g^?1 at a 0.2 C rate and a constant discharge capacity of about 105.7 mA h g^?1 at a 20.0 C rate after 50 cycles, showing promising potential as a novel cathode material for lithium ion batteries.     

Binder-free graphene/carbon nanotube/silicon hybrid grid as freestanding anode for high capacity lithium ion batteries

Light-weight graphene/Si (G/Si) hybrid binder-free electrode is deemed a high energy density anode contender for lithium ion batteries (LIBs). However, paper-like G/Si electrodes tend to show an increased migration distance for Li⁺ through the fast interlayer channel with the increment of electrode size, in addition to an intrinsically slow diffusion kinetics; thereby encumbering their commercial realisation in high energy density and long life LIBs. To address these problems, herein, sandwich-structured graphene/carbon nanotube/silicon (G/CNT/Si, Si: 56 wt.%, ∼500 nm) hybrid grid is designed, cognizant of its uniform and shorter Li⁺ migration distance. Cyclic voltammograms indicate G/CNT/Si paper and grid anode to exhibit good electrochemical activity at both low and high temperatures. Noteworthy is that the Li⁺ diffusion coefficient ratio between G/CNT/Si grid and paper anodes are 1.82, 1.64, 1.43, 1.36 and 1.53 at a temperature of −5, 10, 25, 40 and 55 °C, respectively. The initial coulombic efficiencies of both paper and grid anode are as high as ∼82%. After 60 cycles at 420 mA g⁻¹, the charge capacity of G/CNT/Si grid is retained at 808 mA h g⁻¹, which by far surpasses that of paper anode (i.e., 490 mA h g⁻¹). The attained lithium ion storage performance at both high and low temperatures, underpins the G/CNT/Si sandwiched grid as effective to realise the practical deployment of paper-like graphene electrodes for high energy density and long life LIBs.     

Preparation and electrochemical characterization of lithium cobalt oxide nanoparticles by modified sol–gel method

Uniformly distributed nanoparticles of LiCoO₂ have been synthesized through the simple sol–gel method in presence of neutral surfactant (Tween-80). The powders were characterized by X-ray diffractometry, transmission electron microscopy and electrochemical method including charge–discharge cycling performance. The powder calcined at a temperature of 900 °C for 5 h shows pure phase layered LiCoO₂. The results show that the particle size is reduced in presence of surfactant as compared to normal sol–gel method. Also, the sample prepared in presence of surfactant and calcined at 900 °C for 5 h shows the highest initial discharge capacity (106 mAh g^?1) with good cycling stability as compared to the sample prepared without surfactant which shows the specific discharge capacity of 50 mAh g^?1.     

Cluster structure of SnO2/SnCo composites as anodes for lithium ion batteries

SnO₂/CoSn composites have been prepared by hydrolysis accompanied by carbothermal reduction. With the addition of cobalt, SnO₂/CoSn nanoparticles self-assemble to form nano-micro-structure cluster even microparticles. The nano-micro-structure cluster not only shortens lithium-ion diffusion and electron transportation route, but also cohere together to form compact defense. This preserves the integrity of the structure and the capacity from fading during cycling. It exhibits the improved charge capacity of 627.3 mA h/g in the first cycle and 421.9 mA h/g after 50 cycles at 100 mA/g. It paves the way for practical applications of tin-based anodes.     

Morphology dependent electrochemical performance of sputter deposited Sn thin films

This study deals with tailoring of the surface morphology, microstructure, and electrochemical properties of Sn thin films deposited by magnetron sputtering with different deposition rates. Scanning electron microscopy and atomic force microscopy are used to characterize the film surface morphology. Electrochemical properties of Sn thin film are measured and compared by cyclic voltammetry and charge–discharge cycle data at a constant current density. Sn thin film fabricated with a higher deposition rate exhibited an initial discharge capacity of 798 mAh g^?1 but reduced to 94 mAh g^?1 at 30th cycle. Film deposited with lower deposition rate delivered 770 mAh g^?1 during 1st cycle with improved capacity retention of 521 mAh g^?1 on 30th cycle. Comparison of electrochemical performances of these films has revealed important distinctions, which are associated with the surface morphology and hence on rate of deposition.     

Sodium gluconate-assisted hydrothermal synthesis,characterization and electrochemical performance of LiFePO4 powders

Nano- and micro-sized LiFePO₄ powders were synthesized by a sodium gluconate (C₆H₁₁NaO₇)-assisted hydrothermal synthesis method at 220 °C for 10 h with pH = 2–7. The resulting powders were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray spectrometer (EDS). The obtained data showed that the pH of synthesis solution played a key role in the formation of the LiFePO₄ powders with different morphologies, such as ball-like microspheres, irregular microspheres with the agglomerated rods and particles, sphere-like nanoparticles and nano-ellipsoids. The results from electrochemical performance measurements revealed that the charge–discharge cycling characteristics of the samples were strongly dependent on their morphologies. In particular, the ellipsoidal LiFePO₄ nanoparticles with the average size of 70–90 nm showed the highest initial discharge capacity of 150 mA h g⁻¹ at 0.1 C rate, and cycling stability of the ellipsoidal LiFePO₄ nanoparticles was optimum among all the samples prepared due to their dual advantages of high tap density and good diffusion property. The present study offers a simple morphology-controllable route, without carbon coating or doping with supervalent cations, to synthesize and to design high performance cathode materials for lithium-ion batteries.     

Nb2O5 hollow nanospheres as anode material for enhanced performance in lithium ion batteries

Nb₂O₅ hollow nanospheres of average diameter ca. ～29 nm and hollow cavity size ca. 17 nm were synthesized using polymeric micelles with core–shell–corona architecture under mild conditions. The hollow particles were thoroughly characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), infrared spectroscopy (FTIR), thermal (TG/DTA) and nitrogen adsorption analyses. Thus obtained Nb₂O₅ hollow nanospheres were investigated as anode materials for lithium ion rechargeable batteries for the first time. The nanostructured electrode delivers high capacity of 172 mAh g^?1 after 250 cycles of charge/discharge at a rate of 0.5 C. More importantly, the hollow particles based electrodes maintains the structural integrity and excellent cycling stability even after exposing to high current density 6.25 A g^?1. The enhanced electrochemical behavior is ascribed to hollow cavity coupled with nanosized Nb₂O₅ shell domain that facilitates fast lithium intercalation/deintercalation kinetics.     

An activated microporous carbon prepared from phenol-melamine-formaldehyde resin for lithium ion battery anode

Microporous carbon anode materials were prepared from phenol-melamine-formaldehyde resin by ZnCl₂ and KOH activation. The physicochemical properties of the obtained carbon materials were characterized by scanning electron microscope, X-ray diffraction, Brunauer–Emmett–Teller, and elemental analysis. The electrochemical properties of the microporous carbon as anode materials in lithium ion secondary batteries were evaluated. At a current density of 100 mA g^?1, the carbon without activation shows a first discharge capacity of 515 mAh g^?1. After activation, the capacity improved obviously. The first discharge capacity of the carbon prepared by ZnCl₂ and KOH activation was 1010 and 2085 mAh g^?1, respectively. The reversible capacity of the carbon prepared by KOH activation was still as high as 717 mAh g^?1 after 20 cycles, which was much better than that activated by ZnCl₂. These results demonstrated that it may be a promising candidate as an anode material for lithium ion secondary batteries.     

Electrochemical properties of lithium polymer batteries with doped polyaniline as cathode material

Polyaniline (PANI) was doped with different lithium salts such as LiPF₆ and LiClO₄ and evaluated as cathode-active material for application in room-temperature lithium batteries. The doped PANI was characterized by FTIR and XPS measurements. In the FTIR spectra, the characteristic peaks of PANI are shifted to lower bands as a consequence of doping, and it is more shifted in the case of PANI doped with LiPF₆. The cathodes prepared using PANI doped with LiPF₆ and LiClO₄ delivered initial discharge capacities of 125 mAh g^?1 and 112 mAh g^?1 and stable reversible capacities of 114 mAh g^?1 and 81 mAh g^?1, respectively, after 10 charge–discharge cycles. The cells were also tested using polymer electrolyte, which delivered highest discharge capacities of 142.6 mAh g^?1 and 140 mAh g^?1 and stable reversible capacities of 117 mAh g^?1 and 122 mAh g^?1 for PANI-LiPF₆ and PANI-LiClO₄, respectively, after 10 cycles. The cathode prepared with LiPF₆ doped PANI shows better cycling performance and stability as compared to the cathode prepared with LiClO₄ doped PANI using both liquid and polymer electrolytes.     

Synthesis and electrochemical performance of Li1+xNi0.5Mn0.3Co0.2O2+δ (0 ≤ x ≤ 0.15) cathode materials for lithium-ion batteries

In this work, layered lithium-excess materials Li_1+xNi_0.5Mn_0.3Co_0.2O_2+δ (x = 0, 0.05, 0.10 and 0.15), of spherical morphology with primary nanoparticles assembled in secondary microspheres, were synthesized by a coprecipitation method. The effects of lithium content on the structure and electrochemical performance of these materials were evaluated by employing X-ray diffraction (XRD), inductive coupled plasma (ICP), scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) and galvanostatic charge/discharge tests. It is found that Li_1.10Ni_0.5Mn_0.3Co_0.2O_2+δ, i.e., Li[(Ni_0.5Mn_0.3Co_0.2)_0.95Li_0.05]O₂ showed the best electrochemical performance due to the highly ordered layered structure, reduced cation mixing and the lowest charge transfer resistance. Li_1.10Ni_0.5Mn_0.3Co_0.2O_2+δ delivered a discharge capacity of 145 mA h g^?1 at 125 mA g^?1 in the cut-off voltage of 2.5–4.3 V, and had a capacity retention of 100% after 50 cycles at room temperature.     

Template-directed preparation of two-layer porous NiO film via hydrothermal synthesis for lithium ion batteries

A two-layer porous NiO film is prepared by hydrothermal synthesis method through self-assembled monolayer polystyrene spheres template. The substructure of the NiO film is composed of ordered close-packed hollow-sphere array and the superstructure is made up of randomly NiO nanoflakes. The electrochemical properties are measured by galvanostatic charge/discharge tests and cyclic voltammetric analysis (CV). As anode material for lithium ion batteries, the two-layer porous NiO film exhibits high initial coulombic efficiency of 75%, high reversible capacity and rather good cycling performance. The discharge capacity of the two-layer porous NiO film is 501 mAh g^?1 at 0.5 C after 50 cycles. The two-layer porous architecture is responsible for the enhancement of electrochemical properties.     

One-step preparation of six-armed Fe3O4 dendrites with carbon coating applicable for anode material of lithium-ion battery

Six-armed Fe₃O₄ dendrites with carbon coating were synthesized by a simple one-step reaction between ferrocene and urea at 550 °C. Electron microscopy examinations indicate the formation of large numbers of Fe₃O₄ dendrites with mutually vertical arms and uniform carbon shells. Electrochemical measurement demonstrates that the dendrites using as anode materials for lithium-ion battery exhibit an initial capacity of 658 mAh g^? 1 and a reversible capacity of 473 mAh g^? 1 after 100 cycles at a rate of C/10, as well as a high cycling efficiency of 97% after the forth cycle. The formation mechanism of the six-armed dendrites was also discussed.     

Molten-salt decomposition synthesis of SnO2 nanoparticles as anode materials for lithium ion batteries

SnO₂ nanoparticles were synthesized by a simple, easily scaled-up molten-salt decomposition method with SnSO₄ as the molten salt and the reactive phase. During the synthesis process, the undecomposed molten SnSO₄ makes it possible to obtain SnO₂ nanoparticles by serving as the dispersion medium and keeping the particles from aggregation. The as-prepared SnO₂ had a tetragonal rutile structure with an average particle size of 50 nm. When used as anode materials for lithium ion battery, SnO₂ nanoparticles retained the charge capacity still as high as 402 mAh g^? 1 at a current density of 156 mA g^? 1 after 40 cycles. Moreover, cyclic voltammograms tests showed the formation/deformation of Li₂O was partially reversible.     

An innovative process to fabricate copper/diamond composite films for thermal management applications

Diamond dispersed copper matrix (Cu/D) composite films with strong interfacial bonding were produced by tape casting and hot pressing without carbide forming additives. The tape casting process offers an original solution to obtain laminated materials with accurate thickness control, smooth surface finish, material net-shaping, scalability, and low cost. This study presents an innovative process of copper submicronic particles deposition onto diamond reinforcements prior to densification by hot pressing. Copper particles act as chemical bonding agents between the copper matrix and the diamond reinforcements during hot pressing, thus offering an alternative solution to traditionnal carbide-forming materials in order to get efficient interfacial bonding and heat-transfer in Cu/D composites. It allows high thermal performances with low content of diamond, thus enhancing the cost-effectiveness of the materials. Microstructural study of composites by scanning electron microscopy (SEM) was correlated with thermal conductivity and thermal expansion coefficient measurements. The as-fabricated films exhibit a thermal conductivity of 455 W m^?1 K^?1 associated to a coefficient of thermal expansion of 12 × 10^?6 °C^?1 and a density of 6.6 g cm^?3 with a diamond volume fraction of 40%, which represents a strong enhancement relative to pure copper properties (λ_Cu = 400 W m^?1 K^?1, α_Cu = 17 × 10^?6 °C^?1, ρ_Cu = 8.95 g cm^?3). The as-fabricated composite films might be useful as heat-spreading layers for thermal management of power electronic modules.     

Synthesis of LiFePO4/C doped with Mg2+ by reactive extrusion method

Reactive extrusion method is used to synthesizing LiMg_xFe_1−xPO₄/C, using LiOH⋅H₂O, FeC₂O₄⋅2H₂O, P₂O₅ and nano-MgO as raw materials and glucose as carbon source. Samples are investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), TG–DTA analysis and electrochemical performance test. Results show that amorphous product can be achieved after the reactive extrusion process. The particle size increases with the increase of magnesium content. Appropriately Mg²⁺ doping can reduce the electrode polarization effectively without seriously effect on material structure and morphology. LiMg_0.04Fe_0.96PO₄/C, showing the best electrochemical performances, has an initial discharge capacity of 155, 148, 140 and 137 mA h g⁻¹ at 0.2 C, 0.5 C, 1 C and 2 C rate, respectively. The discharge capacities remain above 99% after 20 cycles.     

Quinary icosahedral quasicrystalline Ti–V–Ni–Mn–Cr alloy: A novel anode material for Ni-MH rechargeable batteries

The substitution of manganese and chromium for 6 at.% nickel in Ti_1.6V_0.4Ni leads the rapid quenching synthesis of quinary icosahedral phase (i-phase) evidenced by the observations of 2-, 3- and 5-fold symmetries. As negative electrode in Ni-MH battery, the quinary Ti–V–Ni–Mn–Cr i-phase can deliver a maximum discharge capacity of 278 mAh g^?1 at 30 mA g^?1, larger than that of Ti_1.6V_0.4Ni master alloy anode owing to Mn and/or Cr doping. After a preliminary test of 30 consecutive cycles the cycling capacity retention rate (CR%) is 80%. The strong chemisorption of hydrogen shown in cyclic voltammetric (CV) response indicates that the electrocatalytic activity improvement for the i-phase negative electrode is highly demanded.     

Kinetics of thermal gradient chemical vapor infiltration of large-size carbon/carbon composites with vaporized kerosene

Large-size samples of carbon/carbon composites were prepared using thermal gradient chemical vapor infiltration with kerosene precursor at 950, 1020, 1100, 1180 and 1250 °C. The temperature gradient, kinetics and density distribution of these samples were studied and the microstructure of pyrolytic carbon was examined by polarized light microscopy. The results show that the initial infiltration rate increased from 5.81 to 21.32 g min^?1 by increasing deposition temperature from 950 to 1250 °C. The densification kinetics relied on deposition temperature and competition between reaction and diffusion, and the diffusion mechanism transformed from bulk to Knudsen diffusion regime. The calculated apparent activation energy is about 68.2 kJ mol^?1. The temperature range 1020–1100 °C is appropriate for fabricating composites with high final bulk density due to high degree of pore filling and the density of sample S3 infiltrated at 1100 °C is the highest among all investigated samples.     

Ion-exchange synthesis of Co-functionalized titanate nanotubes and their application in electrochemical capacitors

Co-functionalized titanate nanotubes (Co-Ti-NTs) were successfully synthesized by means of an ion-exchange reaction. In contrast to the pristine titanate nanotubes (Ti-NTs), Co-Ti-NTs retained rich porous channels and owned even larger specific surface area and better electronic conductivity, which rendered electrons and OH^? ions easily contact the Co species uniformly distributed on their surfaces for energy storage at high rates. The Co-Ti-NTs delivered a specific capacitance (SC) of 124 F g^?1 at 0.4 A g^?1, and a SC degradation of ca. 7% after 1500 continuous cycling at 3 A g^?1, indicating that the Co-Ti-NTs were good candidates and/or even good supports for other electroactive materials for supercapacitors application.     

The AMWCNTs supported porous nanocarbon composites for high-performance supercapacitor

The porous nanocarbons supported by acid-treated multiwall carbon nanotubes (PC@ACNTs) were prepared by the combination of the hydrothermal polymerization of glucose on ACNTs, carbonization under N₂ protection and final activation with ZnCl₂. The materials were characterized by transmission electron microscopy, X-ray powder diffraction and Raman spectra. The results indicated that the ACNTs distributed uniformly into the framework of the porous carbon. The composites showed the high BET specific surface area up to 1712 m² g⁻¹ and good conductivity. The electrochemical measurements indicated that the composites processed good performances for electrochemical energy storage (210 F g⁻¹ at 0.5 A g⁻¹), and high stability (>99.9%), much higher than the corresponding ACNTs, porous carbons and the samples prepared by using raw MWCNTs as source. The good performance of PC@ACNTs composites was relative with the synergy of good conductivity of ACNTs and large specific surface areas of PC.