Lead-based systems as suitable anode materials for Li-ion batteries

Three lead-based materials formed by PbO₂, PbO and Pb as main phases were prepared by following different synthetic procedures and tested as anodic materials in Li-ion batteries by using potentiostatic and galvanostatic methods. While the reduction of Pb(IV) to Pb(II) takes place in a single step, that of Pb(II) to Pb is a complex process involving several steps. Both reduction reactions are irreversible. Lead, whether electrochemically or chemically formed, undergoes an electrochemical reaction with lithium that over the 1.0-0.0 V potential range yields Li_xPb alloys (0≤x≤4.4). The anodic and cathodic potentiostatic curves exhibit various signals that account for: (i) the formation of different intermediates with variable lithium contents; (ii) the reversibility of the alloying/de-alloying processes; (iii) the increase in complexity of such processes as the oxidation state of lead in them decreases. This results in capacity fading with cycling, particularly in the samples having Pb as the main component. One way of avoiding the capacity loss on cycling involves depositing the active material on lead sheets from spraying suspensions. These coatings exhibit a good capacity retention, which can be ascribed to the formation of a Li_xPb layer at the active material/substrate interface that facilitates electron and ion transfer across the electrode.     

Effect of aluminum annealing on the galvanoluminescence properties of anodic oxide films formed in organic electrolytes

The galvanoluminescence (GL) properties of anodic oxide films formed in organic electrolytes were investigated at different aluminum annealing temperatures. The results of the spectral measurements showed two different types of GL sources: carboxylate ions incorporated in oxide films during the anodization and the molecules AlH, AlO, Al₂, AlH₂, also formed during anodization process and already recognized in the case of inorganic electrolytes. The latter was related to gamma alumina crystalline regions formed by annealing of the aluminum samples at temperatures above 500 °C.     

Mechanism of anodic oxidation of molybdenum in nearly-neutral electrolytes studied by electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy

Anodic oxidation of molybdenum in weakly acidic, nearly neutral and weakly alkaline electrolytes was studied by voltammetric and electrochemical impedance spectroscopic measurements in a wide potential and pH range. Current vs. potential curves were found to exhibit two pseudo-Tafel regions suggesting two parallel pathways of the dissolution process. Electrochemical impedance spectra indicated the presence of at least two reaction intermediates. X-ray photoelectron spectroscopic (XPS) results pointed to the formation of an oxide containing Mo(IV), Mo(V) and Mo(VI), the exact ratio between different valence states depending on potential and pH of the solution. A physico-chemical model of the processes is proposed and a set of kinetic equations for the steady-state current vs. potential curve and the impedance response are derived. The model is found to reproduce quantitatively the current vs. potential curves and impedance spectra at a range of potentials and pH and to agree qualitatively with the XPS results. Subject to further improvement, the model could serve as a starting point for the optimization of the electrochemical fabrication of functional molybdenum oxide coatings.     

Oxidation chemistry of indole-2-carboxylic acid: Mechanism and products formed in neutral aqueous solution

The oxidation chemistry of indole-2-carboxylic acid has been investigated in phosphate containing supporting electrolytes in the pH range 1.4-9.8 at a pyrolytic graphite electrode by voltammetric studies, spectral studies, controlled potential electrolysis and related techniques. The kinetics of decay of the UV-absorbing intermediate generated during electrooxidation was followed spectrophotometrically and the decay occurred in a pseudo-first-order reaction. The products of the electrode reaction were characterized as 2,4-, 2,6- and 2,7-dioxindoles, COC- and CC-linked dimers by using GC-MS, IR and ¹H NMR. A detailed interpretation of the redox mechanism of indole-2-carboxylic acid in neutral aqueous medium has been presented to account for the formation of various products.     

Mineralization of herbicide 3,6-dichloro-2-methoxybenzoic acid in aqueous medium by anodic oxidation, electro-Fenton and photoelectro-Fenton

The mineralization of acidic aqueous solutions with 230 and 115 ppm of herbicide 3,6-dichloro-2-methoxybenzoic acid (dicamba) in 0.05 M Na₂SO₄ of pH 3.0 has been studied by electro-Fenton and photoelectro-Fenton using a Pt anode and an O₂-diffusion cathode, where oxidizing hydroxyl radicals are produced from Fenton's reaction between added Fe²⁺ and H₂O₂ generated by the cathode. While electro-Fenton only yields 60-70% mineralization, photoelectro-Fenton allows a fast and complete depollution of herbicide solutions, even at low currents, by the action of UV irradiation. In both treatments, the initial chlorine is rapidly released to the medium as chloride ion. Comparative electrolyses by anodic oxidation in the absence and presence of electrogenerated H₂O₂ give very poor degradation. The dicamba decay follows a pseudo-first-order reaction, as determined by reverse-phase chromatography. Formic, maleic and oxalic acids have been detected in the electrolyzed solutions by ion-exclusion chromatography. In electro-Fenton, all formic acid is transformed into CO₂, and maleic acid is completely converted into oxalic acid, remaining stable Fe³⁺-oxalato complexes in the solution. The fast mineralization of such complexes by UV light explains the highest oxidative ability of photoelectro-Fenton.     

Structure,stability, and ionic conductivity of perovskite Li2x-ySr1-x-yLayTiO3 solid electrolytes

Solid electrolytes with high lithium-ion conductivity and superior stability are key components in the development of all-solid-state lithium-ion batteries. In this study, novel quaternary solid electrolytes Li_2x-ySr_1-x-yLa_yTiO₃ (x = 3y/4, y = 1/7, 2/7, 3/7, 1/2, 15/28, and 4/7) were synthesized by conventional solid-state reaction approach. X-ray diffraction analysis revealed that with the increase in La³⁺ content, Li_2x−ySr_1−x−yLa_yTiO₃ structure changes from cubic to tetragonal perovskite-type structure. Electrochemical impedance spectroscopy revealed that with the increase in y-value, enhanced conductivity was initial observed, followed by a decrease. Li_15/56Sr_1/16La_15/28TiO₃ electrolyte exhibited optimal total Li-ion conductivity of 4.84 × 10⁻⁴ S cm⁻¹, electronic conductivity of 6.84 × 10⁻¹⁰ S cm⁻¹, and activation energy of 0.29 eV. On the other hand, cyclic voltammetry revealed unstable Li_1/8Sr_1/8La_1/2TiO₃, Li_15/56Sr_1/16La_15/28TiO₃, and Li_2/7La_4/7TiO₃ specimens at voltages of less than ~2 V, indicative of their incompatibility with lithium metal or Li₄Ti₅O₁₂ in all-solid-state batteries. Charge-discharge tests confirmed the utility of electrolytes as solid separators with good performance in semi-solid-state batteries. Overall, these results are beneficial for future research on solid electrolytes and their applications in all-solid-state lithium-ion batteries.     

New graphite-antimony composites as anodic materials for lithium-ion batteries.: Preparation, characterisation and electrochemical performance

Antimony-based graphite composite has been studied as a potential material for negative electrodes for lithium-ion batteries. This material has been synthesised by antimony pentachloride intercalated graphite compound reduction using an original method consisting in the use of activated sodium hydride as reducing agent in tetrahydrofuran. The composites have been characterised by X-ray diffraction and transmission electron microscopy. Graphite deintercalated and antimony nanoparticles embedded in organic matrix have been observed. The electrochemical properties of this new material as lithium-ion anode have been investigated. The obtained results highlight not only the leading role of the particle size of the active material but also the influence of a stabilising organic matrix. In our case, volume changes generally occurring during insertion/extraction of lithium into/from metallic host material, which lead to rapid disintegration and deterioration of Li-alloy electrode seem to be avoided. Indeed the presence of the matrix and the conductivity of graphite work in unison to prevent antimony nanoparticles against agglomeration and lead to a good cycling stability of such composite systems.     

Estimation of the wear and corrosion synergism of borided Inconel 718 alloy immersed in a neutral aqueous solution

This work investigates the tribocorrosion properties of the nickel boride layer on an Inconel 718 superalloy immersed in a neutral solution of sodium sulfate and sodium chloride. The solution simulates the corrosive environment created by the combustion reaction of sodium, sulfur, and oxygen when Ni-based superalloys are used in turbine blades. A powder-pack boriding process was conducted at 950 °C for 6 h, obtaining a nickel boride layer thickness of around 50 μm on the surface of the superalloy; microstructural analysis revealed that the boride layer was composed of Ni₄B₃–Ni₂B–Ni₃B. Further, depth-sensing Vickers microindentation tests were performed to assess the ratios of H/E and H³/E² on the nickel boride layer.Additionally, tribocorrosion tests were conducted with a reciprocating tribometer and a typical three-electrode electrochemical cell. The counterpart was a 4.8 mm diameter alumina ball that applied 20 N for a sliding distance of 100 m. According to the ASTM G119-09 procedure, the total material loss rate due to tribocorrosion (T), which includes mass loss rate due to wear (W_c) and corrosion (C_w), was estimated.The results revealed a wear-dominant regime for the Reference material (Inconel 718 superalloy), attributed to passive film removal and high contact pressure at the tribopair, which increases the volume loss rate. On the other hand, the nickel boride layer on the Inconel 718 superalloy displayed a wear-corrosion regime due to boride layer debris that increased the corroded area. Under these experimental conditions, the presence of the nickel boride layer on the Inconel 718 superalloy improved tribocorrosion resistance by approximately three times.     

锂离子电池正极材料合成及改性

电动汽车续航里程的提升主要依赖于锂离子电池的能量密度,其中发展高容量的正极材料成为关键。富锂锰基层状氧化物（LLOs）和高镍三元层状氧化物（NCM,Ni≥80%）等高容量正极材料成为了研究热点,其前体的开发对正极材料电化学性能的发挥有重要的影响。本文从工业化的角度对共沉淀法制备LLOs和NCM正极材料前体的反应过程和影响因素进行了介绍,分析了球形团聚体、单晶和浓度梯度等正极材料的结构和性能,并详细阐述了正极材料中晶面取向调控、掺杂及表界面处理等改性策略的原理及优缺点。文章指出,综合来看单晶材料表现出较好的循环稳定性和热稳定性,但倍率性能有待进一步提升。浓度梯度正极材料不仅保持了高容量特性,还兼顾良好的结构稳定性和热稳定性,有望突破高容量正极材料进一步发展的技术瓶颈。最后,基于本文作者课题组在高容量正极材料方面的研究,对正极材料的未来发展趋势给出了一些建议。     

Electrochemical oxidation of organic pollutants in water at metal oxide electrodes: A simple theoretical model including direct and indirect oxidation processes at the anodic surface

The electrochemical oxidation of organics in water at metal oxide electrodes was investigated with the aim to discuss the correlations between the instantaneous current efficiency ICE and operative conditions by considering both the hypothesis of a direct oxidation process and of an indirect process mediated by adsorbed hydroxyl radicals or chemisorbed “oxygen”, in order to explicit the main differences expected between these cases. Thus, a simple theoretical model was discussed, as an extension of previous studies of Comnnellis and co-workers which were focused on indirect oxidation paths [C. Comninellis, Electrochim. Acta 39 (1994) 1857; O. Simond, V. Schaller, Ch. Comninellis, Electrochim. Acta, 42 (1997) 2009], concerning both the cases of mass transfer control and oxidation reaction control and mixed kinetic regimes. A very good agreement, between theoretical predictions and experimental data pertaining to the electrochemical oxidation of oxalic and formic acid at IrO₂–Ta₂O₅, was observed.     

磷酸铁锂正极材料的制备及性能强化研究进展

橄榄石型磷酸铁锂是目前应用十分广泛的锂离子电池正极材料之一,具有成本低、安全性高、环境友好、循环寿命长和工作电压稳定的特点。近年来,随着CTP技术、刀片电池技术等取得的突破性进展,磷酸铁锂的商业化程度得到了大幅提高。但磷酸铁锂存在电子导电性较差和离子扩散系数低的缺陷,严重限制了锂离子电池的电化学容量,因此开展磷酸铁锂制备工艺和性能强化研究对磷酸铁锂的性能提升具有重要意义。对比了磷酸铁锂电池与其他正极材料锂离子电池的性能差异和发展现状,系统总结了磷酸铁锂正极材料制备与强化的改性方法及相关研究进展与挑战,并提出了未来的发展方向与研究思路。     

废锂离子电池负极活性材料的分析测试

目前关于废锂离子电池资源化的研究主要集中在正极贵金属和负极铜材料的分离回收和精制方面,但对负极活性材料的资源化研究很少。本文采用XRD、SEM、GC-MS、ICP-AES等检测手段对废锂离子电池负极活性材料中石墨的结构、有机物的种类以及Li、Gu等金属的含量进行测试分析。结果显示,其主要组分石墨的本体结构基本无变化,仍保持完整的层状结构,但是其中含有一定量的有机物质,如有机电解质及增塑剂等。经过提纯,可以将其作为石墨原料进行资源化再利用;此外,稀有金属Li含量较高,为31.03 mg/g,分离回收的价值较高。     

Hydrothermal synthesis of carbon/vanadium dioxide core-shell microspheres with good cycling performance in both organic and aqueous electrolytes

Carbon/vanadium dioxide (C/VO₂(B)) core-shell microspheres were prepared by a one-step hydrothermal process and characterized by X-ray diffraction and scanning electron microscopy. The electric cycling performance of C/VO₂(B) in organic and LiCl aqueous electrolytes was evaluated by the galvanostatic method and by cyclic voltammetry, respectively. The results showed that the product had very stable cycling performance in both types of electrolytes compared to pure VO₂(B).     

Encapsulation of SnO2 by carbon nanotubes and WS2 to form high-performance lithium-ion batteries materials

Optimizing the structure of materials has proven to be an efficient solution for improving the electrochemical performance of lithium-ion batteries. In this work, SnO₂-WS₂-CNTS (SWC) ternary composites were prepared by hydrothermal and ball milling methods to first obtain SnO₂-WS₂ mixture, which was then embedded on CNTS to form a special multi-level structure. Due to the special 2D structure of transition metal sulfide WS₂ and CNTS, the de-intercalation speed of lithium ions is greatly increased and the inherent particle aggregation phenomenon of SnO₂ is weakened. The three materials show their advantages while compensating for each other's disadvantages, forming an interesting synergistic effect which results in extremely stable anode materials. At 0.2Ag^-1, the capacity of SWC reaches 930.71 mAhg^-1 after 100 cycles, and reaches 1043 mAhg^-1 after 1000 cycles at 1.0Ag^-1. It is worth noting that after multiple cycles, SWC still exhibits an extremely stable state in the SEM image. The above results confirm that the special structure of SWC leads to excellent electrochemical performance, and its simple preparation method makes it a potential leading battery anode material in the future.     

Impedance spectroscopy studies of the dissolution of ferrous- and zinc-based materials in aqueous timber preservatives

The relative degradation rates of metallic materials in aqueous, copper-based timber preservatives have been investigated using electrochemical impedance spectroscopy. The metals examined were AS/NZS 1595:1998, grade CA1 mild steel, AISI 316 stainless steel (UNS S31600) and AS 1397, grade Z275 hot-dipped galvanised coil-coated sheet. The electrolytes consisted of commercially sourced copper–chrome–arsenate, copper azole and alkaline copper quaternary electrolytes diluted to a concentration of 0.1 mol dm⁻³ copper. The electrochemical impedance response of each system has been modelled and the resulting relative rates of corrosion have been shown to broadly correspond to general trends taken from previous weight loss and direct current studies incorporating similar electrolytes. The hot-dipped galvanised steel corroded in an active manner at rates that were two to four orders of magnitude greater than that of the ferrous-based materials; the latter appeared to passivate in all instances.     

Measurement of the melting temperature of ZrB2 as determined by laser heating and spectrometric analysis

The melting temperatures of two different ZrB₂ ceramics were studied using laser induced melting. ZrB₂ having a low Hf content, produced by reaction hot pressing, had a melting temperature of 3546 K and a commercial grade ZrB₂ had a melting temperature of 3553 K. Uncertainty of the temperature measurements was 1% of the absolute temperature, or ~35 K for both materials based upon 2-sigma and a 95% confidence interval. While these values were consistent with the previously reported ZrB₂ melting temperature of 3518 K, this study was able to measure T_m with less uncertainty than previous studies (±45 K). Furthermore, this study assessed the effect of Hf content on melting temperature, finding that melting temperature did not change significantly for hafnium contents of 1.75 to 0.01 at%. This study also measured a normal spectral emissivity of 0.34 for ZrB₂ at 3000 K. The emissivity decreased to 0.28 at the melting temperature, then, stabilized at 0.30 in a liquid phase.     

Solubility of neutral and charged polymers in ionic liquids studied by laser light scattering

The solubility and chain conformation of different types of homopolymers in low viscosity ionic liquids (ILs), 1-allyl-3-methylimidazolium chloride ([AMIM][Cl]) at 50 °C and 1-butyl-3-methylimidazolium formate ([BMIM][COOH]) at 25 °C, were studied by laser light scattering (LLS). For neutral polymers, such as polyvinyl alcohol and polysulfonamide, aggregation occurred in all the cases except for polyvinyl alcohol in [BMIM][COOH]. For negative polyelectrolytes, such as DNA and polystyrene sulfonate, single chain conformation was observed. However, the hydrodynamic radius of both polymers was much smaller than that in good solvents, suggesting that the chains were condensed. Cellulose was soluble in [AMIM][Cl], and non-diffusive mode was observed by dynamic light scattering. Zeta potential analysis indicated that cellulose exhibited the feature of polyelectrolyte. The solubility of homopolymers could be qualitatively explained by treating polymer/IL as a ternary system: polymer, cation, and anion. It was the mutual interactions determined the solubility and conformation of polymers in ILs.     

Xanthene dyes/amine as photoinitiators of radical polymerization: A comparative and photochemical study in aqueous medium

The efficiency of several xanthene dyes as photoinitiators of the free radical polymerization in aqueous medium was evaluated. These results show that dyes with triplet quantum yield higher than 0.1 present similar efficiencies, independently of their different chemical structure. A detailed study of the photophysics of the dyes under the polymerization conditions was carried out using laser time-resolved spectroscopies. These studies show that the active radicals are those which formed in the interaction of excited triplet state of the dye with the amine through an electron transfer process. In spite of this, the photoinitiation efficiency is not correlated with the triplet quantum yield. Also, the photophysics studies show that the quantum yield of the different pathways of the decomposition of the charge transfer intermediate is an important parameter to predict the efficiency of these photoinitiator systems. The experimentally measured active radical formation is well correlated with that calculated from the polymerization rate. The presence of heavy atoms in the xanthene ring increases the triplet quantum yield, but decreases the active radical yield, and then the polymerization rate.     

Facile preparation of Cu2O microcrystals with morphologies of octahedron, half circular and rectangular plates by anodic dissolution of bulk Cu in alkaline aqueous solutions

In this work, a facile electrochemical route i.e., anodic dissolution of bulk Cu at 2.0 V or more (vs. SCE) in a NaOH solution containing NH₂OH·HCl, was introduced for the synthesis of clean Cu₂O microcrystals (Cu₂O MCs) with morphologies of octahedron, half circular plate, etc. The bulk Cu electrode can be facilely dispersed into Cu(OH)₄²⁻ in alkaline solutions with the help of intense O₂ releasing. In the presence of reductive NH₂OH·HCl, Cu(II) was quickly reduced to Cu(I). Due to the concentration gradient of Cu(I) and OH⁻ resulting from the electrochemical reaction and the selective adsorption of OH⁻ on different crystal facets, half circular plate Cu₂O MCs were for the first time, synthesized. By changing the NaOH concentration or applied potential, octahedron and rectangular plate Cu₂O MCs could also be obtained. Scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffraction (XRD) techniques, etc. were used to characterize the oxides. The Cu₂O MCs were phase-pure cubic Cu₂O. This electrochemical route is simple, basically green and can be used to synthesize Cu₂O MCs with different morphologies.     

Surface-related capacitance of microporous carbons in aqueous and organic electrolytes

This paper examines the surface-related capacitance C/S of carbons with average micropore widths between 0.73 and 1.80 nm, using 1–2 M H₂SO₄, 6 M KOH and 1 M (C₂H₅)₄NBF₄ in acetonitrile as electrolytes. Following corrections for pseudocapacitance effects for the aqueous electrolytes and the use of an average surface area suggested by independent techniques, different from the BET area, it appears that C/S is practically independent of the micropore width. The analysis of the data with the help of recent models suggests that the dielectric constants ?_r of the different electrolytes may decrease with the pore size. It is surprising that the coexistence of two sets of values for the surface area of microporous carbons and its consequence on C/S have not received more attention in the past.