Electrochemical studies of ferrocene in a lithium ion conducting organic carbonate electrolyte

We carried out a detailed study of the kinetics of oxidation of ferrocene (Fc) to ferrocenium ion (Fc⁺) in the non-aqueous lithium ion conducting electrolyte composed of a solution of 1 M LiPF₆ in 1:1 EC:EMC solvent mixture. This study using cyclic (CV) and rotating disk electrode (RDE) voltammetry showed that the Fc⁰/Fc⁺ redox couple is reversible in this highly concentrated electrolyte. The ferrocene and ferrocenium ion diffusion coefficients (D) were calculated from these results. In addition, the electron transfer rate constant (k⁰) and the exchange current density for the oxidation of ferrocene were determined. A comparison of the kinetic data obtained from the two electrochemical techniques appears to show that the data from the RDE experiments are more reliable because they are collected under strict mass transport control. A Tafel slope of c.a. 79 mV/decade and a transfer coefficient α of 0.3 obtained from analysis of the RDE data for ferrocene oxidation suggest that the structure of the activated complex is closer to that of the oxidized specie due to strong interactions with the carbonate solvents. The experiments reported here are relevant to the study of redox reagents for the chemical overcharge protection of Li-ion batteries.     

Electrochemical features of combustion-synthesized lithium cobaltate as cathode material for lithium ion battery

Lithium cobaltate (LiCoO₂) was produced by carbon combustion synthesis of oxide (CCSO) using carbon nanoparticles as a fuel. In this method, the exothermic oxidation of carbon nanoparticles with an average size of 5 nm (specific surface 80 m²/g) gives rise to a self-propagating thermal wave with maximum temperatures of up to 900°C. The thermal front rapidly propagates through the mixture of solid reactants converting it to lithium cobaltate. XRD data suggest that the as-synthesized products were single phase. Carbon is not incorporated in the product and is evolved from the reaction zone as gaseous CO₂. Thermogravimetric analysis was used to identify the features of interaction in the LiNO₃-Co₃O₄-C system. The key features affecting the process-carbon pre-concentration in the reacting mixture and oxygen infiltration to the reaction zone-led to the formation of layered structure of LiCoO₂ and affected the particle sizes. The synthesized crystalline nanoparticles were nearly spherical, and their average particle diameters ranged between 60 and 200 nm.     

Electrochemical performance of nano-Pt-supported carbon anode for lithium ion batteries

A nano-Pt-supported carbon anode was prepared by supporting Pt nanoparticles onto carbon powder. Ultrafine Pt nanoparticles could be well distributed on the surface of carbon particles. Transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), cyclic voltammetry (CV), FTIR, and impedance spectroscopy were used to study on the electrode structure and electrochemical performance. Nano-Pt-supported carbon anode enhanced the Li discharge reaction and suppressed the solvent decomposition reaction, which are favorable for lithium batteries.     

Electrochemical formation of lithium iron(copper)silicide alloys

The behaviour of copper silicide and of some iron silicides with different silicon contents to lithium deposited electro chemically from organic solvents is investigated. The silicide phases show marked differences. Whereas with copper silicide a time-dependent alloy formation with lithium is observed, the iron silicides exhibit a behaviour ranging from no alloy formation to very rapid alloy formation (depending on the silicon content). The alloyed lithium may be recovered during oxidation with high yields. If some lithium is deposited at the supporting grid of iron silicide electrodes with high silicon content, a rapid surface diffusion with alloy formation is observed.     

Electrochemical properties of heat-treated polymer-derived SiCN anode for lithium ion batteries

Silicon-carbon-nitrogen material (SiCN) is pyrolyzed from polysilylethylenediamine (PSEDA) derivation, followed by a heat-treating process at 1000 °C in Ar atmosphere. This heat-treated SiCN material has an excellent electrochemical performance as an anode for lithium ion batteries. Charge-discharge cycle measurements show that the heat-treated SiCN material exhibits a high first cycle discharge capacity of 829.0 mAh g⁻¹ and stays between 400 and 370 mAh g⁻¹ after 30 cycles. The discharge capacity remains above 300 mAh g⁻¹ at the high current density of 80 and 160 mA g⁻¹. These values are higher than untreated SiCN and commercial graphite anodes, which indicates that the heat-treating process improves the charge-discharge capacity, cycle stability and high-rate ability of SiCN anode. It is seemed that changes of SiCN structure, the formation of loose nano-holes on material surface and the formation of graphitic carbon phase in heat-treating process contribute to the improvement of electrochemical properties for SiCN anode.     

Electrochemical stability of silicon/carbon composite anode for lithium ion batteries

Silicon/carbon composite anode materials were prepared by pyrolyzing the phenol-formaldehyde resin (PFR) mixed with silicon and graphite powders. Scanning electron microscopic (SEM) observation showed that the morphology stability of the composite electrodes can be retained during cycling. A structure evolution mechanism is proposed to illuminate the enhancement of cycleability of the composite electrode. The composite used as anode material for lithium ion batteries possesses a reversible capacity of over 700 mAh/g.     

Electrochemical lithium ion storage properties of single-walled carbon nanotubes containing organic molecules

The Li ion storage properties of single-walled carbon nanotube peapods containing one of three organic molecules (9,10-dichloroanthracene, β-carotene, coronene) were measured. It was found by electrochemical charge-discharge measurements that the reversible storage capacity of the SWCNTs significantly increased as a result of the inclusion, although unfortunately the samples are still not appropriate for the practical use as an anode material in Li ion battery because of the high irreversible capacity (>900 mAh/g). In the most effective case, the tube containing the organic molecule can store about 2.5 times more Li ions compared to an empty tube.     

超级电容器及锂电池中锂离子相互作用模型的构建

超级电容器及锂电池中锂离子高度富集,构建准确的锂离子相互作用模型对于预测超级电容器及锂电池性能、设计电极材料具有重要的指导作用。通过量子密度泛函理论计算了超级电容器及锂电池中锂离子间的相互作用,重点考察了锂离子间短程范德华相互作用的特点及溶剂化效应对范德华作用的影响,发现短程区域内范德华作用能在很大程度上屏蔽库仑排斥作用,溶剂化效应对范德华作用有很大贡献。通过数值拟合建立了能适用于不同溶剂环境下的锂离子相互作用分子模型（隐式溶剂模型）。另外还考察了锂离子间三体相互作用,发现三体相互作用为吸引作用,且仅对局部大量富集的锂离子有较大影响。     

Electrochemical evaluation of the a carbon-paste electrode modified with spinel manganese(IV) oxide under flow conditions for amperometric determination of lithium

The participation of cations in redox reactions of manganese oxides provides an opportunity for development of chemical sensors for non-electroactive ions. This paper describes the amperometric determination of lithium ions using carbon-paste electrode modified with spinel manganese(IV) oxide under flow conditions. Systematic investigations were made to optimize the experimental parameters for lithium sensor by flow injection analysis. The detection was based on the measurement of anodic current generated by oxidation of Mn(III) to Mn(IV) at the surface of the electrode and consequently the lithium ions extraction into the spinel structure. An operating potential of 0.50 V (vs. Ag/AgCl/3 KCl mol/L) was exploited for amperometric monitoring. The amperometric signal was linearly dependent on the lithium ions concentration over the range 4.0 × 10⁻⁵ to 1.0 × 10⁻³ mol L⁻¹. The equilibrium constant of insertion/extraction of the lithium ion in the spinel structure, apparent Gibbs energy of insertion, and surface coverage of the electrode with manganese oxide, were calculated by peak charge (Q) in different concentration under flow conditions. Considering selectivity, the peak charge of the sensor was found to be linearly dependent on the ionic radius of the alkaline and earth-alkaline cations.     

吡嗪酰胺在聚茜素红膜修饰电极上的电化学行为研究

采用电聚合方法成功制备了聚茜素红膜修饰电极,并研究了吡嗪酰胺在该修饰电极上的电化学行为,进而建立了对吡嗪酰胺含量进行定量分析的方法。在0.02 mol/L的HAc-Na Ac(p H 4.5)缓冲溶液中,吡嗪酰胺的浓度在5.0×10-6~1.0×10-4mol/L范围内与峰电流呈良好的线性关系,线性回归方程为:Ip(μA)=1.187c+0.028 6,r=0.994,检出限可达1.2×10-6mol/L。利用该法对吡嗪酰胺片进行定量分析,10次分析结果的相对标准偏差4.0%,满足微量分析要求。     

Qualitative Electrochemical Impedance Spectroscopy study of ion transport into sub-nanometer carbon pores in Electrochemical Double Layer Capacitor electrodes

Ion adsorption onto high surface area microporous Carbide Derived Carbons (CDCs) with pore sizes in the sub-nanometer range was studied by means of the Electrochemical Impedance Spectroscopy (EIS) technique in two electrolytes, Tetraethylammonium Tetrafluoroborate (NEt₄BF₄) in Acetonitrile (AN) and in Propylene Carbonate (PC). Polarization at two bias voltages (0.5 V/Ref and −1 V/Ref) for EIS measurements enabled comparing the capacitive behaviors resulting from anions and cations adsorption, respectively, it was confirmed that the effective size of NEt₄⁺ is bigger than the one of BF₄⁻. Higher transport limitation was then observed for cations and was exalted in PC-based electrolyte. Although slow ion transport kinetics, it was found that the low frequency vertical line observed on the Nyquist plots was preserved meaning that carbon electrodes were fully charged. This study confirmed the importance of choosing an electrode carbon pore size adapted to the effective ion size. Finally, the best performances would be got in 1.5 M NEt₄BF₄ AN-based electrolyte with a 0.76 nm pore size negative electrode and a 0.68 nm pore size positive electrode.     

Electrochemical behavior of biphenyl as polymerizable additive for overcharge protection of lithium ion batteries

Electrochemical properties and working mechanism of biphenyl as a polymerizable electrolyte additive for overcharge protection of lithium ion batteries are studied by microelectrode voltammetry, charge-discharge measurements and SEM characterization of the overcharged cell’s components. The experimental results reveal that biphenyl can electrochemically polymerize at the overcharge potential of 4.5-4.75 V (versus Li/Li⁺) to form a layer of conductive film on the cathode surface and the polymer deposits may develop to penetrate the separator to reach the anode surface, resulting an internal short-circuit to prevent from the cell voltage runaway. On the other hand, the electro-oxidative polymerization of biphenyl produces excessive gas and heat, which help to enhance the sensitivities of electric disconnecting devices. In addition, it is also found that the use of biphenyl as an electrolyte additive does not significantly influence the normal performances of the lithium ion batteries.     

动力锂离子电池仿真模型研究进展

锂离子电池作为新能源电动汽车优异的动力来源受到广泛关注,获得高性能的锂离子电池对电动汽车的发展至关重要。数值仿真技术突破了传统实验的限制而极大地促进了锂离子电池的研究工作。高效、实用的仿真模型可以将多种化学反应及物理场相互耦合,预测多种因素对于电池各种性能的影响,使仿真结果尽可能地接近真实情况。本文主要介绍了仿真研究的优势和重要意义,分别从电池热模型、电学特性模型、老化模型等出发,比较了众多仿真模型针对锂离子电池性能的仿真结果,总结不同模型的优势以及存在的薄弱环节,并提出仿真研究以后的发展趋势为：①从机理出发,研究多物理场相互作用关系,实现多场耦合;②从模型和算法入手,扩大模型的研究范围,兼顾简化模型和提高精确度;③从电池本身入手,注重电池材料的性能改善以及成组方式和结构优化。     

Electrochemical performances of lithium ion battery using alkoxides of group 13 as electrolyte solvent

Tris(methoxy polyethylenglycol) borate ester (B-PEG) and aluminum tris(polyethylenglycoxide) (Al-PEG) were used as electrolyte solvent for lithium ion battery, and the electrochemical property of these electrolytes were investigated. These electrolytes, especially B-PEG, showed poor electrochemical stability, leading to insufficient discharge capacity and rapid degradation with cycling. These observations would be ascribed to the decomposition of electrolyte, causing formation of unstable passive layer on the surface of electrode in lithium ion battery at high voltage. However, significant improvement was observed by the addition of aluminum phosphate (AlPO₄) powder into electrolyte solvent. AC impedance technique revealed that the increase of interfacial resistance of electrode/electrolyte during cycling was suppressed by adding AlPO₄, and this suppression could enhance the cell capabilities. We infer that dissolved AlPO₄ components formed electrochemically stable layer on the surface of electrode.     

Electrochemical characteristics of Co-Si alloy and multilayer films as anodes for lithium ion microbatteries

The cycling behaviors of Co-Si alloy and multilayered films, which were prepared by co-deposition from separate pure metal sources and by alternating deposition of different metals, respectively, are investigated. The alloy films with near stoichiometric compound composition of CoSi_2.06 and CoSi_2.2 exhibit an excellent cycling stability, but alloying with large excess Si results in capacity fading during cycling. The cycling stability of multilayers with average composition of CoSi_2.9 is improved significantly by post-annealing treatment at 350 °C. Nano-structured multilayer films are suggested as promising anode materials for thin-film batteries.     

Electrochemical effect of graphite fluoride modification on Li-rich cathode material in lithium ion battery

Recently, Li-rich layered structure has been used in the cathode of lithium ion batteries because of its high specific capacity. However, this structure still has some problems including large irreversible capacity loss, significant deterioration of cycling performance and poor rate property. Therefore, in our study, graphite fluoride is used to modify the surface of Li_1.14Ni_0.133Co_0.133Mn_0.544O₂ through a facile solvent evaporating method. Due to conversion reaction of the graphite fluoride, the huge discharge capacity compensation during the first discharging can improve the coulombic efficiency significantly. As reaction products, the layer of LiF@carbon reduces the interfacial reactions and increases the reversible capacity. After modification by graphite fluoride, the discharge capacities are improved by 22% from 266 to 325?mAh?g^?1 at 0.1?C, and 13% at 2?C. After 100 cycles, the discharge capability at 1?C is increased by 13% from 180 to 203?mAh?g^?1.