Synthesis of SnO2/Mg2SnO4 nanoparticles and their electrochemical performance for use in Li-ion battery electrodes

Uniform crystalline MgSn(OH)₆ nanocubes were synthesized by a hydrothermal method. The influences of reaction conditions were investigated and the results showed that the solvent constituents significantly affected the shape and size of MgSn(OH)₆·SnO₂/Mg₂SnO₄ has been obtained by thermal treatment at 850 °C for 8 h under a nitrogen atmosphere using MgSn(OH)₆ as the precursor. The electrochemical tests of SnO₂/Mg₂SnO₄ revealed that SnO₂/Mg₂SnO₄ has a higher capacity and better cyclability compared to pure SnO₂ or Mg₂SnO₄. The electrochemical performance of SnO₂/Mg₂SnO₄ was sensitive to the size of the nanoparticles. The lithium-driven structural and morphological changes of the electrode after cycling were also studied by the ex-situ XRD pattern and TEM tests. This work indicates that SnO₂/Mg₂SnO₄ is a promising anode material candidate for application in Li-ion batteries.     

Preparation of Ti/SnO2-Sb2O4 photoanode by electrodeposition and dip coating for PEC oxidations

Thin films of antimony-doped SnO₂ on titanium substrate with a doping range of 1.5-8 mol% were prepared by an electrodeposition and dip coating method. The prepared Ti/SnO₂-Sb₂O₄ thin films were tested as a photoanode in the photoelectrocatalytic(PEC) experiments to degrade phenol in aqueous solution in order to evaluate their PEC performance. The photocatalytic (PC), electrocatalytic (EC) and PEC activity of Ti/SnO₂-Sb₂O₄ thin films was compared in the degradation processes. And the effect of annealing temperature on their PEC activity was also investigated. The experimental results confirmed that the Sb-doped Ti/SnO₂ thin films enhanced the phenol degradation and the Ti/SnO₂-Sb₂O₄ film containing 6 mol% of Sb calcinated at 450 °C achieved the best performance for phenol degradation. The degradation experiments also demonstrated that the Ti/SnO₂-Sb₂O₄ film achieved faster degradation of phenol in the PEC process than in the PC and EC processes. Compared with Ti/TiO₂ and Ti/SnO₂ photoanodes, the Ti/SnO₂-Sb₂O₄ photoanode showed higher activity.     

Correlation between AlPO4 nanoparticle coating thickness on LiCoO2 cathode and thermal stability

The thickness of an AlPO₄ coating significantly affects the thermal stability of a LiCoO₂ cathode. Increasing the coating thickness leads to not only a decrease in the exothermic reaction between the cathode and the electrolyte but also to an improvement in the cycling performance. A 1 C rate overcharge experiment up to 12 V is a good example of the thermal stability of the cathode in the Li-ion cell. Furthermore, increasing the AlPO₄ coating thickness results in the lowest cell surface temperature, which is indicative of the degree of heat generation.     

Electrochemical properties of SnO2/carbon composite materials as anode material for lithium-ion batteries

SnO₂/carbon composite anode materials were synthesized from SnCl₄·5H₂O and sucrose via a hydrothermal route and a post heat-treatment. The synthesized spherical SnO₂/carbon powders show a cauliflower-like micro-sized structure. High annealing temperature results in partial reduction of SnO₂. Metallic Sn starts to emerge at 500 °C. High Sn content in SnO₂/carbon composite is favorable for the increase of initial coulombic efficiency but not for the cycling stability. The SnO₂/carbon annealed at 500 °C exhibits high specific capacity (∼400 mAh g⁻¹), stable cycling performance and good rate capability. The generation of Li₂O in the first lithiation process can prevent the aggregation of active Sn, while the carbon component can buffer the big volume change caused by lithiation/delithiation of active Sn. Both of them make contribution to the better cycle stability.     

Control of AlPO4-nanoparticle coating on LiCoO2 by using water or ethanol

The electrochemical properties of AlPO₄-coated LiCoO₂ cathodes prepared in a water or ethanol solvent were characterized with the view of stabilizing LiCoO₂ at charge-cutoff voltages of 4.6 and 4.8 V. Under the influence of the AlPO₄ crystallinity, the coated LiCoO₂ prepared in ethanol had better capacity retention than those prepared in water. This enhancement also correlated with the improved suppression of Li-diffusivity decay in the coated cathode from the ethanol compared to that from water. In addition, the differential scanning calorimetry (DSC) results of the AlPO₄ nanoparticle-coated LiCoO₂ with ethanol showed an enhanced thermal stability.     

Synthesis of nanocrystalline SnO2 powder from SnCl4 by mechanochemical processing

The rapid synthesis of nanocrystalline SnO₂ powder using a mechanochemical reaction of SnCl₄ (instead of the widely used tin (II) compounds) with (NH₄)₂CO₃ and the subsequent annealing of the product in air and under an H₂O/NH₃ atmosphere has been investigated using X-ray powder diffraction, TG and TEM. The reaction was complete within 5 min. Additional milling of the product at a higher milling intensity for 120 min led to the crystallisation of tetragonal SnO₂. The NH₄Cl salt matrix was removed by annealing at 300 °C. The average crystallite size of tetragonal SnO₂ was in the range of 2-48 nm and it can be controlled by variation heating temperatures and annealing atmospheres in the range of 300-700 °C.     

Enhanced electrochemical and thermal stability of surface-modified LiCoO2 cathode by CeO2 coating

CeO₂-coated LiCoO₂ particles were successfully synthesized by a sol-gel coating of CeO₂ on the surface of the LiCoO₂ powder and subsequent heat treatment at 700 °C for 5 h. The surface-modified and pristine LiCoO₂ powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Auger electron spectroscopy (AES), slow rate cyclic voltammogram (CV), and differential scanning calorimetry (DSC). Cyclic voltammetry curves suggested that the CeO₂ coating suppressed the phase transitions. Unlike pristine LiCoO₂, the CeO₂-coated LiCoO₂ cathode exhibited better capacity retention than the pristine LiCoO₂ electrode in the higher cutoff voltage. Differential scanning calorimetric data revealed the higher thermal stability of the CeO₂-coated LiCoO₂ electrode.     

Enhanced cycling stability of LiMn2O4 cathode by amorphous FePO4 coating

The cycling performance of LiMn₂O₄ at room and elevated temperatures is improved by FePO₄ modification through chemical deposition method. The pristine and FePO₄-coated LiMn₂O₄ materials are characterized by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and transmission electron microscopy. Their cycling performances are thoroughly investigated and compared. The 3 wt.% FePO₄-coated LiMn₂O₄ exhibits capacity losses of only 32% and 34% at room temperature and 55 °C, respectively, after 80 cycles, much better than those of the pristine material, 55% and 72%. The cyclic voltammograms at 55 °C reveal that the improvement in the cycling performance of FePO₄-coated LiMn₂O₄ electrodes can be attributed to the stabilization of spinel structures. The separation of FePO₄ between active materials and electrolyte and its interaction with SEI (solid electrolyte interphase) film are believed to account for the improved performances.     

Microwave-assisted synthesis of SnS2/SnO2 composites by l-cysteine and their electrochemical performances when used as anode materials of Li-ion batteries

SnS₂/SnO₂ composites were prepared in a microwave-assisted reaction of a mixture solution of SnCl₄ and l-cysteine and were characterised by XRD, TEM, SEM and EDX. The influence of the mole ratio of SnCl₄ to l-cysteine (l-cys) on the sample was investigated. It was found that using a microwave method, SnS₂/SnO₂ composites were formed, and SnS₂/SnO₂ nanoparticles were obtained when the mole ratio of SnCl₄ to l-cysteine was 1:2. With higher contents of l-cys, when the mole ratio of SnCl₄ to l-cys was 1:4, the products were nanosheets instead of nanoparticles. Electrochemical tests demonstrated that the SnS₂/SnO₂ composites with layer structure exhibited high reversible capacities and good cycling performances when used as anode materials of Li-ion batteries. When the mole ratio of SnCl₄ to l-cys was 1:6, the initial reversible capacity of products was 593 mAh/g, and the retention capacity that was maintained was over 88%. Besides, the retention capacity of products was still excellent at high current charge/discharge.     

Electrocatalytic activity of IrO2-RuO2 supported on Sb-doped SnO2 nanoparticles

Electrocatalytic IrO₂-RuO₂ supported on Sb-doped SnO₂ (ATO) nanoparticles is very active towards the oxygen evolution reaction. The IrO₂-RuO₂ material is XRD amorphous and exists as clusters on the surface of the ATO. Systematic changes to the surface chemical composition of the ATO as a function of the IrO₂:RuO₂ ratio suggests an interaction between the IrO₂-RuO₂ and ATO. Cyclic voltammetry indicates that the electrochemically active surface area of IrO₂-RuO₂ clusters is maximised when the composition is 75 mol% IrO₂-25 mol% RuO₂. Decreasing the loading of IrO₂-RuO₂ on ATO reduces the electrochemically active surface area, although there is evidence to support a decrease in the clusters size with decreased loading. Tafel slope analysis shows that if the clusters are too small, the kinetics of the oxygen evolution reaction are reduced. Overall, clusters of IrO₂-RuO₂ on ATO have similar or better performance for the oxygen evolution reaction than many previously reported materials, despite the low quantity of noble metals used in the electrocatalysts. This suggests that these oxides may be of economic advantage if used as PEM water electrolysis anodes.     

Microwave dielectric properties of SnO2-doped CaSiO3 ceramics

SnO₂-doped CaSiO₃ ceramics were successfully synthesized by a solid-state method. Effects of different SnO₂ additions on the sintering behavior, microstructure and dielectric properties of Ca(Sn_1−xSi_x)O₃ (x=0.5–1.0) ceramics have been investigated. SnO₂ improved the densification process and expanded the sintering temperature range effectively. Moreover, Sn⁴⁺ substituting for Si⁴⁺ sites leads to the emergence of Ca₃SnSi₂O₉ phase, which has a positive effect on the dielectric properties of CaO–SiO₂–SnO₂ materials, especially the Qf value. The Ca(Sn_0.1Si_0.9)O₃ ceramics sintered at 1375 °C possessed good microwave dielectric properties: ε_r =7.92, Qf =58,000 GHz and τ_f=−42 ppm/°C. The Ca(Sn_0.4Si_0.6)O₃ ceramics sintered at 1450 °C also exhibited good microwave dielectric properties of ε_r=9.27, Qf=63,000 GHz, and τ_f=−52 ppm/°C. Thus, they are promising candidate materials for millimeter-wave devices.     

AC transport properties of nanocrystalline SnO2 semiconductor

Nanocrystalline SnO₂ materials were prepared by the chemical co-precipitation route by adding ammonia solution to 0.1 M solution of SnCl₄·5H₂O. The resulting precipitate after thorough washing with distilled water and calcination at 600 °C for 10 h was investigated by XRD for phase identification and crystallite size determination. The materials have been found to be polycrystalline SnO₂, possessing tetragonal rutile crystal structure and nanocrystalline in grain size of approximately 30 nm. The TEM micrograph shows agglomerated particles (cluster of primary crystallites) with an average size of 37.4 nm. A corresponding selected area electron diffraction pattern reveals the different Debye rings of SnO₂, as analyzed in XRD.The complex dielectric constant ?^* has been found to vary with frequency which is attributed to the multi-relaxation time constants of the energy states responsible for conduction mechanism. At any particular frequency, ?^* has been found to increase with temperature. The frequency dependence of loss tangent tan δ has been explained with the help of the equivalent circuit model. The observed frequency dependence of ac conductivity has been found to obey the power law: σ_ac ∝ ω^S, where variation of S with temperature indicates multi-hopping conduction mechanism in nanocrystalline SnO₂ samples. The complex impedance plots of Z′ versus Z″ at different temperatures have been found to be single semicircular arcs with a non-zero intersection with the real axis in the high frequency region and have their centres lying below the real axis at a particular angle of depression, indicating multirelaxation processes in the material.     

Al2O3-coated SnO2/TiO2 composite electrode for the dye-sensitized solar cell

A novel Al₂O₃-coated SnO₂/TiO₂ composite electrode has been applied to the dye-sensitized solar cell. In such an electrode, two kinds of energy barriers (SnO₂/TiO₂ and TiO₂/Al₂O₃) were designed to suppress the recombination processes of the photo-generated electrons and holes. After the SnO₂ was modified by colloid TiO₂, the photoelectric conversion efficiency of the SnO₂/TiO₂ composite cell increased to 2.08% by a factor of 2.8 comparing with that of the SnO₂ cell. The Al₂O₃ layer on the SnO₂/TiO₂ composite electrode further suppressed the generation of the dark current, resulting in 37% improvement in device performance comparing with the SnO₂/TiO₂ cell.     

Comparison of AlPO4- and Co3(PO4)2-coated LiNi0.8Co0.2O2 cathode materials for Li-ion battery

Electrochemical and thermal properties of Co₃(PO₄)₂- and AlPO₄-coated LiNi_0.8Co_0.2O₂ cathode materials were compared. AlPO₄-coated LiNi_0.8Co_0.2O₂ cathodes exhibited an original specific capacity of 170.8 mAh g⁻¹ and had a capacity retention (89.1% of its initial capacity) between 4.35 and 3.0 V after 60 cycles at 150 mA g⁻¹. Co₃(PO₄)₂-coated LiNi_0.8Co_0.2O₂ cathodes exhibited an original specific capacity of 177.6 mAh g⁻¹ and excellent capacity retention (91.8% of its initial capacity), which was attributed to a lithium-reactive Co₃(PO₄)₂ coating. The Co₃(PO₄)₂ coating material could react with LiOH and Li₂CO₃ impurities during annealing to form an olivine Li_xCoPO₄ phase on the bulk surface, which minimized any side reactions with electrolytes and the dissolution of Ni⁴⁺ ions compared to the AlPO₄-coated cathode. Differential scanning calorimetry results showed Co₃(PO₄)₂-coated LiNi_0.8Co_0.2O₂ cathode material had a much improved onset temperature of the oxygen evolution of about 218 °C, and a much lower amount of exothermic-heat release compared to the AlPO₄-coated sample.     

High reversible capacity of SnO2/graphene nanocomposite as an anode material for lithium-ion batteries

A gas–liquid interfacial synthesis approach has been developed to prepare SnO₂/graphene nanocomposite. The as-prepared nanocomposite was characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, and Brunauer–Emmett–Teller measurements. Field emission scanning electron microscopy and transmission electron microscopy observation revealed the homogeneous distribution of SnO₂ nanoparticles (2–6 nm in size) on graphene matrix. The electrochemical performances were evaluated by using coin-type cells versus metallic lithium. The SnO₂/graphene nanocomposite prepared by the gas–liquid interface reaction exhibits a high reversible specific capacity of 1304 mAh g⁻¹ at a current density of 100 mA g⁻¹ and excellent rate capability, even at a high current density of 1000 mA g⁻¹, the reversible capacity was still as high as 748 mAh g⁻¹. The electrochemical test results show that the SnO₂/graphene nanocomposite prepared by the gas–liquid interfacial synthesis approach is a promising anode material for lithium-ion batteries.     

Synthesis of Zn2SnO4 anode material by using supercritical water in a batch reactor

Zn₂SnO₄ anode powders were successfully synthesized using supercritical water (SCW) and metal salt solutions with 10 min reaction time. Effect of NaOH concentration, Zn to Sn ratio, and synthesis temperature were studied with a SCW batch reactor. X-ray diffraction (XRD), scanning electron microscopy (SEM), and charge/discharge cycling tests were employed to characterize the physical properties and electrochemical performance of the as-prepared samples. Alkaline solution concentration and synthesis temperature played a key role in the production of single-phase Zn₂SnO₄ powders. At a solution concentration of 0.3 M NaOH and a molar ratio of Zn:Sn = 2:1 at 400 °C and 30 MPa, the average size range of the pure Zn₂SnO₄ powders was 0.5-1.0 μm, and the morphology was nearly uniform and cubic-like in shape. The initial specific discharge capacity of the Zn₂SnO₄ powders prepared at this condition was 1526 mAh/g at a current density of 0.75 mA/cm² in 0.05-3.0 V, and their irreversible capacity loss was 433 mAh/g. The discharge capacities of the Zn₂SnO₄ powders decreased with cycling and remained at 856 mAh/g after 50 cycles, which was 56% of the initial capacity.     

Properties of sol-gel SnO2/TiO2 electrodes and their photoelectrocatalytic activities under UV and visible light illumination

A visible light active binary SnO₂-TiO₂ composite was successfully prepared by a sol-gel method and deposited on Ti sheet as a photoanode to degrade orange II dye. Titanium and SnO₂ can promote the development of rutile phase of TiO₂ and inhibit the formation of anatase phase of TiO₂. Formation of SnO₂ crystalline is insignificant even when the calcination temperature increases to 700 °C. Heterogenized interface between SnO₂ and TiO₂ inhibits growth of TiO₂ linkage and leads to the particle-filled surface morphology of SnO₂-containing films. The carbonaceous, Ti-O-C bonds and Ti³⁺ species are likely to account for the photoabsorption and photoelectrocatalytic (PEC) activity under visible light illumination. The electrode with 30% SnO₂ exhibits higher photocurrent when compared with those in the region of 0-50%. The 600 °C-calcined SnO₂-TiO₂ electrode indicates higher activity when compared with those at 400, 500, 700 and 800 °C. PEC degradation of orange II follows the Langmuir-Hinshelwood model and takes place much effectively in a solution of pH 3.0 than those in pH 7.0 and pH 11.0.     

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.     

Nonaqueous and template-free synthesis of Sb doped SnO2 microspheres and their application to lithium-ion battery anode

Antimony doped SnO₂ (ATO) microspheres composed of ATO nanoparticles were prepared by using a hydrothermal process in a nonaqueous and template-free solution from the inorganic precursors (SnCl₄ and Sb(OC₂H₅)₃). The physical properties of the as-synthesized samples were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption-desorption isotherms, and X-ray photoelectron spectrum (XPS). The resulting particles were highly crystalline ATO microspheres in the diameter range of 3-10 μm and with many pores. The as-prepared samples were used as negative materials for lithium-ion battery, whose charge-discharge properties, cyclic voltammetry, and cycle performance were examined. The results showed that a high initial discharge capacity of 1981 mAh g⁻¹ and a charge capacity of 957 mAh g⁻¹ in a potential range of 0.005-3.0 V was achieved, which suggests that tin oxide-based materials work as high capacity anodes for lithium-ion rechargeable batteries. The cycle performance is improved because the conducting ATO nanoparticles can also perform as a better matrix for lithium-ion battery anode.