Design criteria for nanostructured Li-ion batteries

Extensive experimental research has indicated that active/inactive nanocomposites are promising electrode materials for rechargeable Li-ion batteries. Nanocomposite anode materials allow for capacities between 900 and 4000 mAh g⁻¹ whereas graphitic anodes, which are currently being used by industry, allow for a much lower capacity of 372 mAh g⁻¹. By treating the active sites (which may be comprised of Si, Sn, Al, or Bi) as nanospheres embedded in an inert matrix, linear elastic fracture mechanics are employed in order to develop design criteria for these alternative battery systems, with respect to fracture that results from the large volume expansions that the active sites undergo upon Li-insertion. In particular, the present study: (i) predicts that smaller active site volume fractions are more stable; (ii) Griffith's criterion is used to estimate the crack radius at which cracking will stop; (iii) based on the ultimate tensile strength of the inactive matrix the critical crack length at which the electrode will fracture is calculated; (iv) a theoretical estimation is made for the size of the active sites that will not allow cracks to develop and hence fracture of the electrode will be prevented. Based on the above analysis, Si active sites allow for a greater anode lifetime and therefore are preferred over Sn, furthermore the formulation can be applied to determine the most appropriate matrix materials.     

Characteristics of Sn/Li2O multilayer composite anode for thin film microbattery

Sputtering growth of a Sn/Li₂O multilayer composite thin film is conducted to produce an anode thin film with less capacity fading than that of a pure SnO₂ film for a thin-film battery. The structural properties of the Sn/Li₂O multilayer are examined. In addition, the electrochemical characteristics of the Sn/Li₂O and pure SnO₂ thin films are compared. X-ray diffraction and transmission electron microscopy measurements reveal a Sn crystalline peak only and a Sn–Li₂O multilayer structure, respectively, in the Sn/Li₂O thin film. A SnO₂ thin film with a polycrystalline phase shows an irreversible side-reaction at 0.8 V versus Li/Li⁺, an initial charge retention of about 29%, and poor cycleability in the cut-off voltage range from 1.2 to 0 V versus Li/Li⁺. By contrast, no irreversible side-reaction is found in the Sn/Li₂O multilayer composite thin film while there is an initial charge retention of 49% and better cycleability (more than twice) than that of pure SnO₂ film after about 150 cycles. These results indicate that the Sn/Li₂O multilayer composite thin film can be used for tin-based, thin-film, microbatteries and provide motivation to pursue fabrication of Sn–Li₂O anode powder for bulk type batteries.     

Electrochemical behavior of Sn/SnO2 mixtures for use as anode in lithium rechargeable batteries

Anodes derived from oxides of tin have, of late, been of considerable interest because, in principle, they can store over twice as much lithium as graphite. A nanometric matrix of Li₂O generated in situ by the electrochemical reduction of SnO₂ can provide a facile environment for the reversible alloying of lithium with tin to a maximum stoichiometry of Li_4.4Sn. However, the generation of the matrix leads to a high first-cycle irreversible capacity. With a view to increasing the reversible capacity as well as to reduce the irreversible capacity and capacity fade upon cycling, tin–tin oxide mixtures were investigated. SnO₂, synthesized by a chemical precipitation method, was mixed with tin powder at two compositions, viz., 1:2 and 2:1, ball-milled and subjected to cycling studies. A mixture of composition Sn:SnO₂ = 1:2 exhibited a specific capacity of 549 mAh g⁻¹ (13% higher than that for SnO₂) with an irreversible capacity, which was 7% lower than that for SnO₂ and a capacity fade of 1.4 mAh g⁻¹ cycle⁻¹. Electrodes with this composition also exhibited a coulombic efficiency of 99% in the 40 cycles. It appears that a matrix in which tin can be distributed without aggregation is essential for realizing tin oxide anodes with high cyclability.     

Carbon-supported PdSn–SnO2 catalyst for ethanol electro-oxidation in alkaline media

Carbon-supported PdSn–SnO₂ with high electrical catalytic activity for ethanol oxidation in alkaline solution was synthesized using an impregnation reduction method. XRD analysis of the as-prepared PdSn–SnO₂/C revealed that the Pd diffraction peaks shifted to lower 2θ values with respect to the corresponding peaks of the Pd/C catalyst, indicating that Sn doping could shrink the Pd crystalline lattice. XPS measurements confirmed the existence of Sn and SnO₂ in the PdSn–SnO₂/C catalysts. The prepared PdSn–SnO₂/C catalysts presented a remarkably higher electrocatalytic activity than that of the Pd–Sn/C and Pd/C catalysts. This was mainly because the easy adsorption-dissociation of OH_ads over the SnO₂ surface changed the electronic effect and accelerated the adsorption of ethanol on the surface of Pd, thus enhancing the overall ethanol oxidation kinetics and contributing to a significant improvement in the catalytic activity.     

An empirical model to evaluate the contribution of alloyed and non-alloyed tin to the ethanol oxidation reaction on Pt-Sn/C catalysts based on the presence of SnO2 and a Pt(1−x)Snx solid solution: Application to DEFC performance

An empirical model is proposed to evaluate the contribution of alloyed and non-alloyed tin in Pt_z-Sn/C catalysts to the performance of direct ethanol fuel cells (DEFCs). The model is based on the presence of SnO₂ and a Pt_(1−x)S_x solid solution in the bimetallic catalysts. The model predicts the dependence of the performance of a single DEFC on the total Sn content and the degree of alloying of Pt_z-Sn/C catalysts used as the anode material.     

Nano-textured topography introduced at room temperature for light-trapping enhancement

In this paper, a unique two-step method is developed to fabricate a nano-textured SnO₂ coating. Nano-textured topography is successfully introduced at room temperature by evaporating Sn in a relatively high pressure. Nano-textured SnO₂ coating is obtained by annealing in air, with lateral size of nearly 1 μm and root-mean-roughness of over 140 nm. Two structures: substrate and superstrate, are investigated to reveal the light-trapping efficiency. With only 300 nm thick Si absorber layer, the average reflectivity under AM 1.5 illumination spectrum can be limited at 14% and 7%, respectively. This technology is suitable for mass production.     

Microwave plasma chemical vapor deposition of nano-structured Sn/C composite thin-film anodes for Li-ion batteries

A novel synthesis method of thin-film composite Sn/C anodes for lithium batteries is reported. Thin layers of graphitic carbon decorated with uniformly distributed Sn nanoparticles were synthesized from a solid organic precursor Sn(IV) tert-butoxide by a one-step microwave plasma chemical vapor deposition (MPCVD). The thin-film Sn/C electrodes were electrochemically tested in lithium half cells and produced a reversible capacity of 423 and 297 mAh g⁻¹ at C/25 and 5C discharge rates, respectively. A long-term cycling of the Sn/C nanocomposite anodes showed 40% capacity loss after 500 cycles at 1C rate.     

Effect of Mo-doping in SnO2 thin film photoanodes for water oxidation

New semiconducting metal oxides of various compositions are of great interest for efficient solar water oxidation. In this report, Mo-doped SnO₂ (Mo:SnO₂) thin films deposited by reactive magnetron co-sputtering in the Ar and O₂ gas environment are studied. The Sn to Mo ratio in the films can be controlled by changing the O₂ partial pressure and the deposition power of the Sn and Mo targets. Increasing the Mo concentration in the film leads to the increase in the oxygen vacancy density, which limits the maximum achievable photocurrent density. The thin films exhibit a direct band gap of 2.7 eV, the maximum achievable photocurrent density of 0.6 mA cm⁻² at 0 V_RHE and the onset potential of 0.14 V_RHE. The incident photon to current transfer (IPCE) efficiency of 22% is shown at a 450 nm wavelength. The initial performance of the Mo:SnO₂ thin films is evaluated for solar water oxidation.     

CuFe2O4/SnO2 nanocomposites as anodes for Li-ion batteries

Ultrafine powders of nanocrystalline CuFe₂O₄ and CuFe₂O₄/10 wt.% SnO₂ nanocomposites are prepared by a urea–nitrate combustion method. Phase pure and highly crystalline CuFe₂O₄ (tetragonal structure) and CuFe₂O₄/SnO₂ (cubic structure) are obtained after sintering at 1100 °C. The average particle size is 10–20 and 20–30 nm, respectively. Both the nanoferrite anodes have an excellent specific capacity of greater than 800 mAh g⁻¹ versus Li metal. It is concluded that SnO₂ doping improves the coulombic efficiency of copper ferrite anodes from 65 to 99.5% via an enhanced structural stability.     

Bio-enzymatic synthesis of nitrogen-doped porous carbon/SnO2/carbon microspheres as high-performance composite materials for lithium-ion and sodium-ion batteries

In this study, a nitrogen-doped 3D porous starch-derived carbon/SnO₂/carbon (PSC/SnO₂/C) composite is synthesized with porous starch as a carbon source by biological enzymatic hydrolysis. Compared with the traditional complex acid-base reagent method, the biological enzymatic method is more environmentally friendly and economical, and it can also naturally introduce nitrogen sources and dope the carbon layer. Many mesoporous nanostructures provide enough buffer space and promote the ions' and electrons’ transmission rate. The formation of the Sn–O–C bond between SnO₂ and carbon ensures the stability of the structure. As a result, the PSC/SnO₂/C composite exhibits a high initial discharge capacity (1802 mAhg⁻¹ at 0.2 A g⁻¹ for LIBs and 549 mAh g⁻¹ at 0.1 A g⁻¹ for SIBs) and good cycle stability (701 mAh g⁻¹ at 0.2 A g⁻¹ after 100 cycles for LIBs and 271 mAh g⁻¹ at 0.1 A g⁻¹ after 100 cycles for SIBs). This synthesis method can prepare other energy storage systems such as fuel cells, supercapacitors, and metal ion batteries.     

Free-standing SnO2/MWCNT nanocomposite anodes produced by different rate spin coatings for Li-ion batteries

Free standing SnO₂/multiwalled carbon nanotube (MWCNT) nanocomposite anode materials were prepared for Li-ion batteries by sol–gel technique. Firstly, SnO₂ precursor sols were synthesized after removing chloride ions. Then the sols coated on MWCNT buckypapers, which used as substrates to form nanocomposite electrodes by spin coating method. Sintered nanocomposite structures were then characterized by field emission gun-scanning electron microscopy (FEG-SEM), energy dispersive X-ray spectrometer (EDS), and X-ray diffraction (XRD) analyses. Electrochemical tests were performed for the produced electrodes, assembled as CR2016 cells. The effect of spin rate on the anode capacity was investigated. Coating on the MWCNT buckypapers was thought to use as mechanical support to prevent electrode failure and prevented the formation of cracks of the sol–gel thin film on the MWCNT surfaces. The results showed beneficial effects to prevent mechanical disintegration and subsequent anode pulverization of SnO₂ anodes because of huge volume increase during lithium intercalation. The results indicated that the nanocrystalline SnO₂/MWCNT composites are suitable for applying as an anode electrode for Li-ion batteries to increase electrochemical energy storage performance.     

Properties of Pt-based electrocatalysts containing selectively deposited Sn as the anode for polymer electrolyte membrane fuel cells

Sn-promoted Pt-based catalysts were prepared by the chemical vapor deposition (CVD) of Sn on commercial Pt/C and PtRu/C catalysts using Sn(CH₃)₄ as an Sn precursor. The prepared catalysts showed higher CO tolerance than those prepared by adding Sn using an impregnation (IMP) method. This result was obtained because Sn added by CVD was selectively deposited on the Pt and Ru surfaces, instead of on a carbon support, such that the interfacial contact between Pt and Sn was greater in the Sn-CVD catalyst than in the others, as confirmed by in-situ infrared and X-ray photoelectron spectroscopic observations of the catalysts.     

Synthesis and characterization of macroporous tin oxide composite as an anode material for Li-ion batteries

A macroporous SnO₂/C composite anode material was synthesized using an organic template-assisted method. Polystyrene spheres were synthesized and used as template and lead to macroporous morphology with pores of 300-500 nm in diameter and a surface area of 54.7 m² g⁻¹. X-ray diffraction showed that the SnO₂ nanoparticles are crystallized in a rutile P42/mnm lattice with the presence of Sn metal traces. The synthesized macroporous SnO₂/C composite provided promising performance in lithium half cells showing a discharge capacity of 607 mAh g⁻¹ after 55 cycles. It was found that the macroporous SnO₂/C composite is stable and resistant to pulverization upon cycling.     

Doped tin oxide aerogels as oxygen evolution reaction catalyst supports

Designing low cost, highly-active and stable oxygen evolution reaction (OER) catalysts for Proton Exchange Membrane Water Electrolysers (PEMWE) anodes is an important topic for industry and academia. A possible strategy to alleviate the cost of the anodic catalyst consists in synthesizing iridium oxide (IrO_x) nanoparticles and dispersing them on an electron-conducting and highly-porous support such as SnO₂ doped with hypervalent cations e.g. Sb(V) or Ta(V). Herein, we show the benefits of Sb- and Ta- doped SnO₂ aerogels synthesized by a sol-gel route. The effect of the dopant nature on the aerogel's properties (as morphology, structure, conductivity, etc.) was investigated using a set of physical and chemical techniques. The electrocatalytic performance of the synthesized nanocatalysts towards the OER was also assessed in rotating disk electrode (RDE). Supported IrO_x catalysts showed both higher specific and mass activity and stability than unsupported IrO_x nanoparticles.     

Composition effect of oxygen reduction reaction on PtSn nanorods: An experimental and computational study

In the development of emerging energy, proton exchange membrane fuel cells (PEMFCs) have been widely researched. Nevertheless, because of the high price and scarcity of Pt and its sluggish kinetics for oxygen reduction reaction (ORR), the preparation of highly effective cathode catalysts becomes one of the main challenges for PEMFCs in the practical application. In this study, carbon supported PtSn nanorods (NRs) with metal loading of 50 wt % and different Pt/Sn ratios of 80/20, 65/35 and 50/50 have been prepared by formic acid reduction method. The ORR performance of the catalysts can be promoted synergistically by one-dimensional (1-D) NRs and is varied with the Pt/Sn ratios. The experimental and computational efforts reveal that the Sn addition can lower the unoccupied d-band of neighboring Pt and the oxygen-containing species (OCS) on Sn can suppress their oxidation through the repulsion effect. Consequently, PtSn electrodes show the improved ORR activity; Pt₅₀Sn₅₀ with the highest Sn content results in the highest mass activity. On the other hand, the negatively charged OCS on Sn attracts the positively charged Pt and destructs the structures of PtSn NRs. Accordingly, Pt₈₀Sn₂₀ with the lowest Sn contain has the highest concentration of 1-D PtSn NRs and shows the best stability in the accelerated durability test (ADT). Our results clarify the mechanism of ORR on PtSn electrodes and suggest the importance of the precise control of atomic ratios on PtSn catalysts for the practical purpose. The findings open new perspectives about the origins of the activity and stability of the PtSn catalysts, especially for 1-D catalysts.     

Electroless-plated tin compounds on carbonaceous mixture as anode for lithium-ion battery

A composite anode materials was prepared that contained tin compounds of Sn₆O₄(OH)₄, SnO₂ and Sn₃PO₄ on the surface of carbonaceous mixture mesophase graphite particles (MGP) and nature graphite (NG). The nanosize tin compounds were electrolessly plated from aqueous solutions onto the carbonaceous mixture. The morphology and structure of tin compounds were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). It was found that the tin compounds particle size was a crucial factor to improve Sn compounds/Carbon composite anodes for cyclability and reversible capacity. The homogeneous dispersion and smaller particle size of tin compounds was attributed to the additive of NG. As the carbonaceous substrate was C-C mixture carbon, the particle size of Sn compounds was about 20-30 nm. However, the particle size was 100-200 nm, as the carbon substrate was singular MGP. Electrochemical performance test of the Sn compounds/C-C composite electrode shows the maximum specific charge capacity of 583 mAh g⁻¹ at the 5th cycle. The charge capacity retention of Sn compounds/C-C electrode was 85% after 20 cycles. The reversible capacity of Sn compounds/C-C electrode increased 292 and 97 mAh g⁻¹ more than pristine (NG + MGP) electrode and Sn compounds/C electrode at the 5th cycle, respectively.     

Electrocatalysts for ethanol and ethylene glycol oxidation reactions. Part I: Effects of the polyol synthesis conditions on the characteristics and catalytic activity of Pt–Sn/C anodes

In this work, Pt–Sn/C electrocatalysts with nominal Pt:Sn ratio of 1:1 (at.%) were synthesized by a polyol/alcohol process. The effect of different ethylene glycol:ethanol:water (EG:EtOH:H₂O) volume ratios on the physicochemical characteristics (i.e., Pt:Sn ratio and SnOx formation) of the Pt–Sn/C alloys was evaluated. In some cases, no water was used for the synthesis. Afterwards, the electrocatalytic activity of the alloys for the Ethanol and the Ethylene Glycol Oxidation Reaction (EOR and EGOR, respectively) was studied. XRD characterization showed that the degree of alloying calculated by using Vegard's law ranges from about 15% (synthesis in the presence of water) to roughly 49% (synthesis in the absence of water). The average particle size was calculated with the Scherrer equation to be within 1.8–4.7 nm, smaller sizes obtained in the absence of water. The chemical analysis by EDS indicated the formation of oxides regardless of the presence or not of water during the synthesis. The oxides were attributed to the presence of SnO_x phases in the materials. The electrochemical characterization showed that the synthesis conditions have an important effect on the electrocatalytic activity of the Pt–Sn/C materials for the EOR and the EGOR. As a result, the alloys synthesized in the absence of H₂O delivered a higher performance for both reactions.     

Sn self-doped α-Fe2O3 nanobranch arrays supported on a transparent,conductive SnO2 trunk to improve photoelectrochemical water oxidation

We produced hierarchically branched Fe₂O₃ nanorods on a Sb:SnO₂ transparent conducting oxide (TCO) nanobelt structure as photoanodes for photoelectrochemical water splitting. Single-crystalline SnO₂ nanobelts (NBs) surrounded by Fe₂O₃ nanorods (NRs) were synthesized by thermal evaporation, then underwent chemical bath deposition and annealing. When Fe₂O₃ was crystallized by annealing, Sn was diffused from SnO₂ NBs and incorporated to Fe₂O₃ NRs, which was confirmed through Energy dispersive spectroscopy. Unlike previous high temperature sintering (∼800 °C), Sn doped hematite NRs were obtained at a low temperature (∼650 °C). This occurred since SnO₂ NBs directly connected to Fe₂O₃ NRs are an abundant source of Sn dopant. The 3D hematite NRs on SnO₂ NBs annealed at 650 °C produce a photocurrent density of 0.88 mA/cm² at 1.23 V vs. RHE, which is 3 times higher than that of hematite NRs on a fluorine doped tin oxide (FTO) glass substrate annealed at the same temperature. The enhanced photocurrent is attributed to the improved electrical conductivity of Fe₂O₃ NRs by Sn doping, the efficient electron transport pathway by TCO nanowire and the increased surface area by hierarchically branched structure.     

The effect of SnO2 on enhancing electrocatalytic property of palladium toward formic acid oxidation

Although palladium (Pd) based materials are considered the best catalyst for formic acid oxidation reaction (FAOR), they are still confronted with a lot of barriers, such as the growth/sintering of Pd nanoparticles (NPs) and the accumulation of adsorbed poisoning intermediates. Herein, tin dioxide (SnO₂) decorated carbon black was utilized as the catalyst carrier to synthesize Pd/SnO₂/C for FAOR. The introduction of SnO₂ significantly reduced the particle size of Pd NPs and forming the Pd–O–Sn structure. Compared with Pd/C, Pd/SnO₂/C owned higher concentration of O_ads and less adsorption amount of poisoning intermediates. The oxygen atoms adsorbed on Pd surface were rapidly transferred to SnO₂ due to the spillover effect. The FAOR reaction kinetic results showed that the introduction of SnO₂ accelerated the diffusion rate of formic acid on the electrode surface. Pd/SnO₂/C exhibited high specific activity (5.97 mA cm⁻²), excellent durability, and high anti-CO poisoning ability toward FAOR due to the introduction of SnO₂.