Characterization of TiO2 thin films prepared by electrolytic deposition for lithium ion battery anodes

The electrolytic deposition of TiO₂ thin films on platinum for lithium batteries is carried out in TiCl₄ alcoholic solution and the films are subsequently annealed. The as-prepared films are amorphous TiO(OH)₂·H₂O, transformed into anatase TiO₂ at 350 °C, and then gradually into rutile TiO₂ at 500 °C. Cyclic voltammograms show oxidation and reduction peaks at 2.20 and 1.61 V, respectively, corresponding to charge and discharge plateaus at 1.98 and 1.75 V vs. Li⁺/Li. The specific capacity decreases with increasing current density for film of 128-nm thickness in the initial discharge. It is observed that the diffusion flux of Li⁺ insertion/extraction into/from TiO₂ controls the reaction rate at higher current densities. Consequently, at low film thickness, high discharge capacity (per weight) is found for the initial cycle at a current density of 10 μA cm^− 2. However, the capacity of prepared films in various thicknesses approach 103 ± 5 mAh g^− 1 after 50 cycles, since the formation of cracks for thicker films offers shorter diffusion paths for Li⁺. In addition, TiO₂ films show electrochromic properties during lithiation and delithiation.     

Fabrication of Cu2S on Cu film electrode and its application in lithium ion battery

Cu₂S film electrode direct growth on Cu foil is prepared by a simple hydrothermal approach. The electrochemical properties of the as-prepared Cu₂S electrode are investigated via conventional discharge and charge tests. When applying a current density of 0.1 mA cm^− 2, the as-prepared Cu₂S electrode exhibits discharge and charge capacity of 0.27, 0.32, 0.35, 0.34 and 0.34 mAh cm^− 2 at the 100th, 200th, 300th, 400th and 500th cycle, respectively. Such good performance of the as-prepared Cu₂S electrode is attributed to the fine electric contact between Cu₂S and Cu foil and the possible hollow structure of Cu₂S film.     

High performance LiFePO4/C cathode for lithium ion battery prepared under vacuum conditions

LiFePO₄/C with smaller particle size (0.3-0.6 μm) was synthesized via a two-step vacuum sintering method. X-ray diffraction and scanning electron microscopy were used to detect the phases presented in the composites and observe sample morphology. In addition, AC electrochemical impedance spectroscopy, cyclic voltammetry, along with constant current discharge/charge tests, were used to characterize the electrochemical properties of the composites. It was shown that LiFePO₄/C with a single olive crystal structure could deliver discharge capacity of 145.5 and 108.7 mAh g⁻¹ at 0.5 and 6C for the fist cycle, and kept reversible capacity of 147.5 and 117.1 mAh g⁻¹ after 100 cycles.     

Nanostructured ZnO network films deposited on Al2O3 substrates by chemical bath deposition

Nanostructured ZnO network films have been fabricated on Al₂O₃ substrates by the combination of chemical bath deposition and thermal decomposition process. Layered basic zinc nitrate (LBZN) network films were deposited on the Al₂O₃ substrates with LBZN crystal seeds in methanol solution of zinc nitrate hexahydrate and hexamethylenetetramine. The LBZN precursor films were then transformed into nanostructured ZnO films by heating at 260 °C in air. During the thermal decomposition process abnormal exothermic heat effect was observed at 200-210 °C and CH₃ groups were found in the as-deposited films. We propose that methanol molecules are integrated in the LBZN films forming LBZN-CH₃OH complex and that the heat effect comes from the exothermic release of the methanol.     

Chemical bath deposition of SnS films with different crystal structures

SnS (stannous sulfide) films were prepared by chemical bath deposition in which a novel chelating reagent ammonium citrate was used. The film has a zinc blende structure or orthorhombic structure which is determined by the pH value of the deposition solution (zinc blende structure at pH = 5 and orthorhombic structure at pH = 6). The reason for this result may be that SnS films prepared at different pH values have different deposition mechanisms, which results in different structures. The prepared SnS films are all smooth and well adhered. The optical bandgaps of the SnS films are determined to be 1.75 eV and 1.12 eV for zinc blende structure and orthorhombic structure, respectively.     

Aqueous bath process for deposition of Cu2ZnSnS4 photovoltaic absorbers

Chemical bath deposition and ion exchange were used to incorporate copper, zinc, tin and sulfur into a thin film precursor stack. The stack was then sulfurized to form the photovoltaic absorber material Cu₂ZnSnS₄ (CZTS). The morphology and elemental composition of the films at each process stage were analyzed by Auger electron spectroscopy and scanning electron microscopy, and the structural and optical properties of the sulfurized film were determined by a combination of X-ray diffraction, Raman scattering, and diffuse reflectance UV-Vis spectroscopy. Compositionally uniform microcrystalline CZTS with kesterite structure and a bandgap of 1.45 eV were observed. A preliminary solar cell device was produced exhibiting photovoltaic and rectifying behavior.     

In situ synthesis of SnO2/graphene nanocomposite and their application as anode material for lithium ion battery

SnO₂/graphene nanocomposite was prepared via an in situ chemical synthesis method. The nanocomposite was characterized by X-ray diffraction, filed emission scanning electron microscope and transmission electron microscope, which revealed that tiny SnO₂ nanoparticles could be homogeneously distributed on the graphene matrix. The electrochemical performance of the SnO₂/graphene nanocomposite as anode material was measured by galvanostatic charge/discharge cycling. The SnO₂/graphene nanocomposite showed a reversible capacity of 665 mAh/g after 50 cycles and an excellent cycling performance for lithium ion battery, which was ascribed to the three-dimensional architecture of SnO₂/graphene nanocomposite. These results suggest that SnO₂/graphene nanocomposite would be a promising anode material for lithium ion battery.     

Chemical bath deposition of CdS highly-textured, columnar films

Chemical bath deposition (CBD) is one of the most common techniques for depositing CdS films. While there have been many studies on these films, and considerable characterization of their morphologies, most of this characterization has been by either X-ray diffraction or plan-view electron microscopy. With the exception of epitaxial films deposited on single crystal substrates, there has been little characterization of the cross-sectional structure of CBD CdS films. We show how, using a CdSO₄ bath and ethylenediamine as complexant, dense, columnar films of predominantly cubic CdS can be very reproducibly obtained. The initial growth is disordered, but preferential growth perpendicular to the polar face results in highly textured growth. A similar, if somewhat less ordered, morphology is obtained from a commonly-used ammonia bath using CdCl₂ as the source of Cd. Although not explicitly recognized, chloride baths in the literature exhibited sharp X-ray diffraction peaks and this is now connected with the growth mode these baths have in common with ethylenediamine baths.     

Preparation and characterization of SnO2/carbon nanotube composite for lithium ion battery applications

SnO₂/multi-walled carbon nanotube (MWCNT) composite was prepared via a diffusion method. Firstly the MWCNT was sonicated in a filtrate which was derived from a tin dichloride solution mixed with AgNO₃ solution. Then the SnO₂/MWCNT composite was prepared whereby, after calcination in N₂ atmosphere, the salts inside the MWCNT decomposed to SnO₂. The resulting composite was characterized by transmission electron microscopy, Raman spectroscopy and X-ray diffraction, which indicated that SnO₂ had infiltrated into the MWCNT and filled the interior. The subsequent evaluation of the electrochemical performance in lithium ion batteries showed that the SnO₂/MWCNT composite had a reversible discharge capacity of 505.9 mAh?g^− 1 after 40 cycles, as compared to 126.4 mAh?g^− 1 for pure nano-SnO₂.     

Hydrothermal synthesis of Zn3(OH)2V2O7·nH2O nanosheets and its application in lithium ion battery

Well crystallized zinc vanadium oxide hydroxide hydrate (Zn₃(OH)₂V₂O₇·nH₂O) nanosheets have been successfully synthesized by a simple hydrothermal method. The products were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), and Raman spectrum. The composition of Zn₃(OH)₂V₂O₇·nH₂O has been studied by thermal analysis (TG, DTA). The results indicate that there are two water molecules in Zn₃(OH)₂V₂O₇·nH₂O molecular formula. Electrochemical properties of Zn₃(OH)₂V₂O₇·nH₂O nanosheets as negative electrode of lithium ion battery were studied by conventional charge/discharge test, which shows steady platform near 1.4 V, suggesting it as an ideal candidate of negative material for lithium ion battery.     

Electrochemical performance of the chalcopyrite CuFeS2 as cathode for lithium ion battery

Chalcopyrite CuFeS₂ was synthesized by solvothermal process. It was used as active species to prepare cathode of lithium ion batteries together with some conducting materials. Electrochemical performance of the assembled Li/CuFeS₂ batteries was characterized by cyclic voltammetry and discharging test. Our results proved that CuFeS₂ as a new cathode material showed room-temperature specific discharging capacity of 1100 mAh g⁻¹ at a current density of 14 mA g⁻¹, and that its specific discharging capacity was higher than 500 mAh g⁻¹ at a current density of 350 mA g⁻¹. Different from what reported by Eda et al., the discharging curves presented two apparent plateaus, which were related to different cathode reactions, in the whole measured temperature range.     

Effect of CdCl2 annealing treatment on thin CdS films prepared by chemical bath deposition

In order to study the CdS recrystallization mechanism, a comparative study was carried out on thin films prepared by chemical bath deposition. The CdS films were annealed in air with or without a CdCl₂ coating layer. In-situ Raman spectra obtained during the annealing showed that both the air- and the CdCl₂-annealing did not cause rearrangement of the neighboring atoms in the CdS clusters below ~ 300 °C. CdS thin film was partially oxidated to CdO and CdSO₄ on the cluster surface when annealed in air. The oxides and the sulfur stoichiometric deficiency prevented the clusters to coalesce at higher temperatures. Coating thin CdS film with a thin CdCl₂ layer protected it from oxidation during annealing in air and promoted formation of Cl_S and V_Cd point defects in CdS. The anti-oxidation was attributed to the incorporation of a significant amount of Cl into CdS to form the Cl_S, which prevented the oxygen in-diffusion and chemical bonding during the annealing. The anti-oxidation at the CdS nano-crystalline surface and the point defects formed in the CdS promoted coalescence of the neighboring clusters without the need of long-range redistribution of the atoms. Large CdS grains with good crystalline quality formed through recrystallization during the CdCl₂ heat treatment, which provided the solid basis for the subsequent CdTe growth and high efficient CdS/CdTe solar cell fabrication.     

Chemical bath deposition of different phases of copper selenide thin films by controlling bath parameters

In the preparation of copper selenide thin films using chemical bath deposition (CBD) technique, it is observed that the pH of the final reacting mixture is the major factor controlling the composition of the film. Thin films of cubic Cu_2−xSe and tetragonal Cu₃Se₂, of band gaps 2.20 and 2.83 eV, respectively, have been prepared using the CBD technique by adjusting the bath parameters like pH, temperature and the ratio between copper and selenium atoms in the reaction bath. X-ray diffraction analysis is used as the major tool for identification of these phases. The results have been confirmed using XPS, ICP and absorption studies.     

3DOM SnO2-SiO2锂离子电池负极材料的制备及电化学性能

针对SnO2锂离子电池负极材料长循环性能差的缺点,把非晶SiO2引入SnO2材料中,形成SnO2-SiO2纳米复合材料。采用聚苯乙烯(PS)胶晶作为模板,制备出三维有序大孔SnO2-SiO2纳米复合材料。研究结果表明,3DOM SnO2材料晶体结构和3DOM SnO2-SiO2材料相似,但是加入SiO2以后,3DOM SnO2-SiO2材料的长循环性能得到显著提高。在500 mAh/g的电流密度下循环100次,此时加0%Si的3DOM SnO2-SiO2材料的充电比容量急剧衰减为147 mAh/g,加5%Si的3DOM SnO2-SiO2材料的充电比容量达654 mAh/g,此外500次循环后加5%Si的3DOM SnO2-SiO2材料充电比容量增至728 mAh/g。这些结果表明SiO2能够改善3DOM SnO2材料长循环稳定性。     

Crystal habits of LiMn2O4 and their influence on the electrochemical performance

Crystal habits of LiMn₂O₄ prepared through a sol-gel method using different starting materials (metal acetates and metal nitrates) are studied using a crystal shape algorithm. Density functional theory (DFT) as implemented in VASP is employed to study the thermodynamic stabilities and the electronic structure of the different hkl planes of LiMn₂O₄, as identified by the crystal shape algorithm. The crystal habit of lithium manganate prepared through the metal acetate route, LiMn₂O₄ (A), seems to possess a higher thermodynamic stability compared to the metal nitrate route viz. LiMn₂O₄ (N). Electrochemical cycling measurements show that the capacity retention in LiMn₂O₄ (A) is better than LiMn₂O₄ (N) at low (C/10) as well as at higher (5C) rates.     

锂离子电池正极材料LiNi0.8Co0.15Al0.05O2的制备与性能

采用共沉淀法制备粒径10 μm左右的前驱体Ni_0.8Co_0.15Al_0.05（CO₃）_x（OH）_y,然后采用该前驱体和LiOH·H₂O成功制备了锂离子电池正极材料LiNi_0.8Co_0.15Al_0.05O₂（LiNCA）,并详细研究了煅烧氛围、煅烧温度和煅烧方式等条件对LiNCA电化学性能的影响。研究表明,在O₂中煅烧获得的LiNCA放电容量达到170 mAh·g^-1,50次循环后容量保持率达到95%,性能明显优于空气氛围中煅烧得到的LiNCA。在O₂氛围下,700~750℃温度范围煅烧得到的LiNCA性能最好,煅烧温度过高或过低,LiNCA性能均明显下降。将前驱体在O₂氛围中450℃条件预煅烧,然后与LiOH·H₂O在700~750℃混合煅烧的煅烧方式,得到的LiNCA放电容量明显提高,可达190 mAh·g^-1。     

Hydrothermal synthesis of Fe3O4 nanoparticles and its application in lithium ion battery

Well dispersed Fe₃O₄ nanoparticles with a mean diameter of about 160 nm were synthesized by a simple hydrothermal method in the presence of sodium sulfate. The products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Raman spectrum, and Fourier transform infrared spectra (FTIR). Electrochemical properties of the nanostructured Fe₃O₄ as cathode electrodes of lithium ion battery were studied by conventional charge/discharge tests, showing a high initial discharge capacity of 1267 mA h g^− 1 at a current density of 0.1 mA cm^− 2.     

Synthesis of V-doped TiO2 films by chemical bath deposition and the effect of post-annealing on their properties

Amorphous composite films, composed of a Ti_1 − xV_xO₂ solid-solution phase and a V₂O₅ phase, were produced by chemical bath deposition and subsequently air-annealed at various temperatures up to 550 °C. The microstructure and chemical composition of the as-prepared and annealed films were investigated by a combinatorial experimental approach using Scanning electron microscopy, X-ray powder diffraction and X-ray photoelectron spectroscopy. Ultraviolet-Visible Spectrometry was applied to determine the optical band gap of the as-prepared and annealed films. It followed that the incorporation of vanadium in the as-deposited films reduces the optical band gap of TiO₂ from about 3.8 eV to 3.2 eV. Annealing of the films up to 350 °C leads to slight increase of band gap, as attributed to a reduction of the defect density in the initially amorphous oxide films due to the gradual development of long-range order and a concurrent reduction of the V⁴⁺-dopant concentration in the Ti_1 − xV_xO₂ solid-solution phase. The films crystallized upon annealing in air at 550 °C, which resulted in drastic changes of the phase constitution, optical absorbance and surface morphology. Due to the lower solubility of V⁴⁺ in crystalline TiO₂, V⁴⁺ segregates out of the crystallizing Ti_1 − xV_xO₂ solid-solution phase, forming crystalline V₂O₅ at the film surface.     

Synthesis and electrochemical performance of a simple and low-cost sulfur/porous carbon composite cathode for rechargeable lithium sulfur battery

The sugar and phenolic resin were used as source materials to prepare porous carbons labeled as PC1 and PC2 respectively, which were activated by chemical methods with CaCO₃ as active agent. Sulfur/porous carbon composites were synthesized by thermally treating a mixture of sublimed sulfur and porous carbon. The morphology, structure, and electrochemical performance of the composite were investigated by scanning electron microscopy, Brunauer–Emmett–Teller, and a variety of electrochemical techniques. The electrochemical measurements show that the SPC2 electrode presents a more favorable electrochemical kinetics than the SPC1 electrode. In comparison with SPC1, it is shown that the rate of Li⁺ diffusion with SPC2 is significantly higher and the charge transfer resistance is much lower. The PC2 with high surface area (735.2 m² g⁻¹) and large pore volume (1.56 cm³ g⁻¹) not only increases the electronic conductivity of composites, but also facilitates transfer of the Li ion in the composite electrode.     

Polycrystalline SnO2 nanowires coated with amorphous carbon nanotube as anode material for lithium ion batteries

One-dimensional (1D) SnO₂ nanowires, coated by in situ formed amorphous carbon nanotubes (a-CNTs) with a mean diameter of ca. 60 nm, were synthesized by annealing the anodic alumina oxide (AAO) filled with a sol of SnO₂. X-ray diffraction (XRD) and selected area electron diffraction (SAED) patterns revealed that the prepared SnO₂ nanowires exist in polycrystalline rutile structure. The coating of carbon nanotubes has some defects on the wall after the internal SnO₂ nanoparticles were removed. The 1D SnO₂ nanowires present a reversible capacity of 441 mAh/g and an excellent cycling performance as an anode material for lithium ion batteries. This suggests that 1D nanostructured materials have great promise for practical application.