Self-discharge behavior of LaNi5-based hydrogen storage electrodes in different electrolytes

Nickel–metal hydride (Ni–MH) batteries using hydrogen storage alloys as negative electrode materials have been developed and commercialized because of their high energy density, high rate capability and long cycle life, without causing environmental pollution (Song et al. J Alloys Comp 298:254, 2000; Jang et al. J Alloys Comp 268:290, 1998). However, the self-discharge rate is relatively higher than that of the Ni–Cd batteries, which would certainly be disadvantageous in practical applications. The capacity loss of a battery during storage is often related to self-discharge in the cells. Self-discharge takes place from a highly charged state of a cell to a lower state of charge (SOC) and is typically caused by the highly oxidizing or reducing characteristic of one or both of the electrodes in the cell. This self-discharge behavior may be affected by various factors such as gases, impurities, temperature, type of alloy electrode, electrolytes, or charge/discharge methods. The loss of capacity can be permanent or recoverable, depending on the nature of the mechanism (chemical or electrochemical) and aging condition. In this paper, the effects of electrolyte composition and temperature on self-discharge behavior of LaNi₅-based hydrogen storage alloy electrodes for Ni–MH batteries have been investigated. It was found that both reversible and irreversible capacity loss of MH electrode tested at 333 K were higher than that at 298 K. When tested at 298 K and 333 K, reversible capacity loss was mainly affected by the electrolyte, while the irreversible capacity loss was not affected. The dissolution of Al from the electrode can be reduced more effectively in an electrolyte with Al addition, compared with that in normal electrolyte. This resulted in a lower reversible capacity loss for the electrode exposed in the Al³⁺-rich electrolyte. SEM analysis has shown that some needle shape and hexagonal corrosion products were formed on the surface of the alloy electrodes, especially after storage at high temperature.     

The interaction of alkaline solutions of potassium borohydride with LaNi4.5M0.5 (M = Ni,Mn, Cr,Co, Fe,Cu, Al) intermetallic compounds

The behavior of LaNi_4.5M_0.5 (M = Ni, Mn, Cc Co, Fe, Cu, Al) interinctallic compounds (IMC) in alkaline solutions of KBH₄ (0.1; 1.0; 4.0 mol L^–1 KOH) Was investigated in the temperature range 298–318 K. The catalytic hydrolysis of KBH₄ is zero order with respect to KBH₄ and not order with respect to IMC. Activation energies of the catalytic hydrolysis of KBH₄ in the presence of' IMC are in the range of 60–65 U mol^–1. The rate of hydrolysis of KBH₄ increases with the concentration of the KOH solution. The hydrogenation of LaNi_4.5M_0.5 in alkaline solutions of KBH₄ yields -hybride phases for M = Min, Cr, Co, Cu, Al and -hybride phases for M = Ni, Fe.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1632–1635, July, 1996.     

Electrochemical performances of inorganic membrane coated electrodes for li-ion batteries

In the present study, we prepared new Li-ion batteries with inorganic membrane-coated electrodes fabricated by the direct coating of a 400-nm-sized Al₂O₃ particles onto the anodes and studied their charge–discharge characteristics for the first time. Being made of 94 wt.% Al₂O₃ powder and 6 wt.% polymeric binder, the membranes on the anodes showed excellent wettability with the liquid electrolytes, due to their high porosity and capillarity. The Li-ion batteries prepared by the assembly of the inorganic membrane-coated electrodes showed excellent charge–discharge behavior compared to conventional Li-ion batteries with a polymeric separator. However, their high-rate performance was affected by the binder contents in the inorganic membranes. The thermal properties of the Li-ion battery with the inorganic membrane-coated electrodes were compared with those of a conventional one with a polymeric separator.     

Preparation and performance characterization of polymer Li-ion batteries using gel poly(diacrylate) electrolyte prepared by in situ thermal polymerization

A gel polymer electrolyte (GPE) was prepared by in-situ thermal polymerization of 1,3-butanediol diacrylate (BDDA) in a EC/EMC/DMC electrolyte solution at 100 °C. The GPE with 15 wt.% polymer content appears as apparently dry polymer with sufficient mechanical strength and shows a high ionic conductivity of 3.2×10^–3 S cm^–1 at 20 °C. The MCMB–LiCoO₂ type polymer Li-ion batteries (PLIB) prepared using this in-situ internal polymerization method exhibit a very high initial charge–discharge efficiency of 92.1%, and can deliver 94.4% of its nominal capacity at 1.0 C rate and 70.7% of its room temperature capacity at –20 °C. Also, the PLIB cells show very good cycling ability with >85% capacity retention after 300 cycles. The excellent charge–discharge properties of the PLIB cells are attributed to the integrated structure in which the polymer matrix spreads over entire region of the cell acting as a strong binder and electrolyte carrier to produce a stabilized electrode–electrolyte interface. In addition, the fabricating process of the polymer cell is quite simple and convenient for practical applications.     

Synthesis and supercapacitance of flower-like Co(OH)<Subscript>2</Subscript> hierarchical superstructures self-assembled by mesoporous nanobelts

A facile hydrothermal strategy was first proposed to synthesize flower-like Co(OH)₂ hierarchical microspheres. Further physical characterizations revealed that the flower-like Co(OH)₂ microspherical superstructures were self-assembled by one-dimension nanobelts with rich mesopores. Electrochemical performance of the flower-like Co(OH)₂ hierarchical superstructures were investigated by cyclic voltammgoram, galvanostatic charge–discharge and electrochemical impedance spectroscopy in 3 M KOH aqueous electrolyte. Electrochemical data indicated that the flower-like Co(OH)₂ superstructures delivered a specific capacitance of 434 F g⁻¹ at 10 mA cm⁻² (about 1.33 A g⁻¹), and even kept it as high as 365 F g⁻¹ at about 5.33 A g⁻¹. Furthermore, the SC degradation of about 8% after 1,500 continuous charge–discharge cycles at 5.33 A g⁻¹ demonstrates their good electrochemical stability at large current densities.     

Lithium-ion conduction in elastomeric binder in Li-ion batteries

This paper describes two kinds of elastomeric binders which are styrene–butadiene (ST–BD) copolymer and 2-ethylhexyl acrylate–acrylonitrile (2EHA–AN) copolymer for electrode materials of rechargeable Li-ion batteries. These elastomeric binders were swollen by electrolyte solution (EC/DEC=1/2, 1 M LiPF₆), and 2EHA–AN copolymer retained larger amount of electrolyte solution than ST–BD copolymer. The Li-ionic conduction behavior was investigated for both copolymer films swollen by electrolyte solution. The Li-ion conductivity of ST–BD copolymer was 9.45 × 10⁻⁸ S·cm⁻¹ and that of 2EHA–AN copolymer was 1.25 × 10⁻⁵ S·cm⁻¹ at room temperature, and the corresponding amounts of activation energy were 0.31 and 0.26 eV, respectively. Because the observed activation energy in elastomeric binder was different from that in the bulk of electrolyte solution (0.09 eV), Li-ion conduction of the bulk of elastomeric binder swollen by electrolyte was affected by the polymer structure of binders. Electrochemical performance of cathode material, LiCoO₂, was investigated with three kinds of binders: ST–BD copolymer, 2EHA–AN copolymer, and poly(vinylidene fluoride). The initial charge–discharge capacity of the LiCoO₂ electrode with 2EHA–AN copolymer showed highest capacity, suggesting that Li⁺-ion conduction inside of the elastomeric binder contributes to the enhancement of charging and discharging capacity. This result indicates that elastomeric binder with sufficient Li-ionic conductivity can be an attractive candidate for improving cathode of lithium-ion battery.     

Fe部分替代Cu对低钴AB_5型贮氢合金相结构和电化学性能的影响

为了获得既具有较高电化学容量又具有良好循环稳定性的低钴AB5型贮氢合金,研究了Fe部分替代Cu对低钴AB5型贮氢合金相结构和电化学性能的影响.采用真空感应熔炼方法,制备了一系列含Cu和Fe的低钴AB5型贮氢合金LaNi3.55Mn0.35Co0.20Al0.20Cu0.85-xFex(x=0.10,0.20,0.25,0.40,0.60).粉末X射线衍射(XRD)分析表明,合金含有单一CaCu5型六方结构的LaNi5相,Fe部分替代Cu并没有改变合金的本体相结构,但随着Fe含量的增大,晶格参数a,c和晶胞体积V增大.电化学性能测试表明,随着x增加,合金的放电容量和高倍率放电能力降低,但是循环稳定性得到了显著提高.当x从0.10增加到0.60时,合金的200周循环稳定性(S200)从77.6%提高到89.9%.Fe替代Cu有利于提高合金的循环稳定性,这主要是随着Fe替代量增大,晶胞体积增大,晶格体积膨胀率明显减小,合金的抗粉化能力增强.     

The structural and thermal stability,electrochemical hydrogenation and corrosion behavior of LaT5−xMx(T = Co,Ni and M = Al,Ge, Li) phases

The structural and thermal stability, electrochemical hydrogenation and corrosion behavior of LaT_5−x(M/Li)_x (T = Co, Ni and M = Al, Ge) alloys have been investigated using x-ray diffraction, SEM with WDS/EDX, DSC and electrochemical techniques. The prepared ternary and quaternary samples are solid solutions on the base of binary LaCo₅ and LaNi₅ compounds with hexagonal CaCu₅ structure type. By partial substitution of transition metals (Ni and Co) by Al, Ge and Li in the LaT_5−x(M/Li)_x alloys the discharge capacity increased by 25%. Doping of LaCo₅ and LaNi₅ binary phases by Al, Ge and Li improves corrosion resistance, thermal stability and absorption capacity during the electrochemical hydrogenation. These alloys passivate effectively in strong alkaline solution.     

Influence of the PVdF binder on the stability of LiCoO2 electrodes

We report herein on the effect of the PVdF binder on the stability of composite LiCoO₂ electrodes at elevated temperatures in 1 M LiPF₆ EC/EMC solutions at open circuit conditions. The structure and morphology of composite LiCoO₂ electrodes with different combinations of electrode components (LiCoO₂ active material, PVdF binder, carbon black and current collector) were evaluated by Raman spectroscopy, X-ray diffraction and SEM. The content of Co ions in the electrolyte solutions was determined by ICP. A new effect was discovered, namely, a detrimental impact of the contact between PVdF and LiCoO₂ on the stability of the active mass. The formation of surface Co₃O₄ and dissolution of Co ions at elevated temperatures is accelerated at the contact points between the active mass and the binder. The effect of water content in the electrolyte solutions on the stability of LiCoO₂ was also studied. The presence of water (and/or HF) is a necessary condition for the accelerated dissolution of Co ions from the active mass. LiCoO₂ oxidizes the solvents at elevated temperatures thus forming CO₂.     

橄榄石结构磷酸盐脱/嵌锂过程的控制步骤研究

本文详细研究了橄榄石结构磷酸盐脱嵌锂过程的控制步骤,发现就多元橄榄石结构Li(FeMnCo)PO4磷酸盐而言,碳含量比较低时在充放电曲线之间存在非对称现象.充电时与Fe2+/Fe3+电对对应的容量小于理论容量,与Co2+/Co3+电对对应的容量大于理论容量;放电时与Co2+/Co3+电对对应的容量远小于相应的充电容量,但是与Fe2+/Fe3+电对对应的放电容量远大于与该电对对应的充电容量.电极呈现出以Co2+/Co3+电对充电,以Fe2+/Fe3+电对放电的行为.作者认为在充电和放电过程中活性材料颗粒内部存在内界面,充电时内界面内部组成是Fe2+、Co2+、Mn2+和低浓度的Fe3+,而内界面外部组成是Co3+、Mn2+、Fe3+和低浓度的Co2+.非对称现象的主要原因是内界面移动速度缓慢,碳含量低时慢的内界面移动速度是电化学脱嵌锂过程的主要控制步骤.     

Molding versus dispersion: effect of the preparation procedure on the capacitive and cycle life of carbon nanotubes aerogel composites

Binderless carbon nanotubes aerogel (CNAG) composites represent a new class of high-performing electrodes for energy storage applications such as electrochemical double layer capacitors. The composites developed here differ significantly from these previously prepared with dispersion processes. The CNAG material was prepared by a molding procedure that is the synthesis by a chemical vapor deposition method to grow carbon nanotubes directly onto a microfibrous carbon paper substrate. Then the carbon aerogel is synthesized on the carbon nanotubes. The key feature of the method is eliminating the need of controlling the carbon nanotube concentration, which permits optimized dispersion processes to reinforce the aerogel's networks. The CNAG electrode delivered very high specific capacitances of 524 F g⁻¹ in KOH electrolyte and 280 F g⁻¹ in H₂SO₄ electrolyte. Furthermore, this better integration of carbon nanotubes in the matrix of carbon aerogel improved its resistance to the attack by the electrolyte and conferred an excellent cycle life over 5,000 cycles of charge–discharge in both electrolytes.     

Preparation and performances of carbon aerogel microspheres for the application of supercapacitor

Carbon aerogel (CA) microspheres were successfully synthesized by an inverse emulsion polymerization routine. Morphology and physical properties of the CA microspheres were characterized by scanning electron microscopy, N₂ sorption isotherm, and transmission electron microscopy. The results showed that the CA microspheres were all fine spheres with diameters about 4 μm, and the CA microsphere was a typical mesoporous material with ordered mesoporous nano-network structure. The maximum capacitance of the electrode obtained from cyclic voltammetry was 187.08 F/g and the capacitance of the supercapacitor resulted from galvanostatic charge–discharge tests was up to 45.98 F/g. The supercapacitor using CA microsphere as electrode material presented a long cycle life, high charge–discharge efficiency, and low R _s of 0.70 Ω in 6 M KOH electrolyte.     

Effects of Sintering Temperature and Press Pressure on the Microstructure and Electrochemical Behaviour of the Ag2O/GO Nanocomposite

The purpose of this study was to evaluate the effects of press pressure and sintering temperature on the microstructure and electrochemical performance of silver oxide-graphene oxide composite as a novel electrode produced by the powder metallurgy (PM) route. Scanning electron microscopy method used to investigate the microstructure of electrodes and energy dispersive X-ray spectroscopy analysis method was used for point analysis. Potentiodynamic polarization and electrochemical impedance spectroscopy methods were used to research the effects of sintering temperature and press pressure on the electrochemical behaviour in the 1.4 wt % KOH solution and electrical discharge test was used for evaluate the ultimate electrical capacity of silver oxide-zinc batteries with electrolyte of the 1.4 wt % KOH solution.

     

High loading LiFePO<Subscript>4</Subscript> on activated carbon fiber cloth as a high capacity cathode for Li-ion battery

The LiFePO₄/carbon fiber (LFP/CF) cathodes were prepared by using activated carbon fiber cloth as current collector in place of conventional Al foil. The electrochemical properties of LFP/CF electrodes were analyzed by the cyclic voltammetry and galvanostatic charge/discharge tests. The results indicate that the activated carbon fiber cloth with high specific surface area and high porosity makes the LFP/CF electrode that possesses higher mass loading of 18–21 mg cm^–2 and stronger redox reaction ability compared with Al foil-based electrode. The LFP/CF electrode shows excellent rate performance and cycle stability. At 0.1C, the discharge capacity is up to 190.1 mAh g^–1 that exceeds the theoretical capacity due to the combination effect of battery and capacitor. Furthermore, the LFP/CF electrode shows an initial capacity of 150.4 mAh g^–1 at 1C with a capacity retention of 74.7% after 425 cycles, which is higher than 62.4% for LFP/Al foil electrode, and an initial discharge capacity of 130 mAh g^–1 at 5C with a capacity retention of 61.5% after 370 cycles. But this composite electrode is not suitable for charging/discharging at higher rate as 10C due to too much mass loading.     

Electrochemical properties of tetravalent Ti-doped spinel LiMn2O4

Ti-doped spinel LiMn₂O₄ is synthesized by solid-state reaction. The X-ray photoelectron spectroscopy and X-ray diffraction analysis indicate that the structure of the doped sample is Li( Mn^{3 +} Mn_{1 - x} ^{4 +} Ti_x^{4 +} )O₄ {\hbox{Li}}\left( {{\hbox{M}}{{\hbox{n}}^{3 + }}{\hbox{Mn}}_{1 - x\,}^{4 + }{\hbox{Ti}}_x^{4 + }} \right){\hbox{O}}{}_4 . The first principle-based calculation shows that the lattice energy increases as Ti doping content increases, which indicates that Ti doping reinforces the stability of the spinel structure. The galvanostatic charge–discharge results show that the doped sample LiMn_1.97Ti_0.03O₄ exhibits maximum discharge capacity of 135.7 mAh g⁻¹ (C/2 rate). Moreover, after 70 cycles, the capacity retention of LiMn_1.97Ti_0.03O₄ is 95.0% while the undoped sample LiMn₂O₄ shows only 84.6% retention under the same condition. Additionally, as charge–discharge rate increases to 12C, the doped sample delivers the capacity of 107 mAh g⁻¹, which is much higher than that of the undoped sample of only 82 mAh g⁻¹. The significantly enhanced capacity retention and rate capability are attributed to the more stable spinel structure, higher ion diffusion coefficient, and lower charge transfer resistance of the Ti-doped spinel.     

Influence of alkaline cation on the electrochemical behavior of stabilized alpha-Ni(OH)2

Cyclic voltammograms of nanostructured nickel hydroxide modified platinum disk electrodes were interpreted as combinations of the contribution of alpha and beta-phase materials in different proportions. The electrolyte cation influenced more significantly the cathodic wave profile, where KOH seems to decrease the discharge rate more than NaOH and LiOH. Unexpectedly, the heat treatment does not seem to be required to get stabilized alpha-Ni(OH)₂. Reproducible charge–discharge responses and up to 2.45 times higher specific charge capacity (490 mA h g^?1) were registered for nanostructured α-Ni^II(OH)₂ after 100 charge–discharge cycles, suggesting that they are stable enough for application in electrochemical devices such as batteries and sensors.     

Effect of TiMn1.5 alloying on the structure,hydrogen storage properties and electrochemical properties of LaNi3.8Co1.1Mn0.1 hydrogen storage alloys

A series of experiments were performed to investigate the effect of TiMn_1.5 alloying on the structure, hydrogen storage properties and electrochemical properties of LaNi_3.8Co_1.1Mn_0.1 hydrogen storage alloys at 303 K. For simple, A, B, and C are used to represent alloys (x = 0 wt %, x = 4 wt % and x = 8 wt %) respectively. The results of XRD and SEM show that LaNi_3.8Co_1.1Mn_0.1?xTiMn_1.5 hydrogen storage alloys have LaNi₅ phase and (NiCo)₃Ti phase. Based on the results of PCT curves, the hydrogen storage capacities of LaNi_3.8Co_1.1Mn_0.1?xTiMn_1.5 hydrogen storage alloys are about 1.28 wt % (A), 1.16 wt % (B) and 1.01 wt % (C) at 303 K. And the released pressure platform and the pressure hysteresis decrease with the increase of TiMn_1.5 content. Meanwhile the activation curves show that LaNi_3.8Co_1.1Mn_0.1?xTiMn_1.5 hydrogen storage alloy electrodes can be activated in three times and the maximum discharge capacity is 343.74 mA h/g at 303 K. In addition, with the increase of TiMn_1.5 content, the cyclic stability of the hydrogen storage alloy electrodes decreases obviously and the capacity retention decreases from 76.70% to 70.00% when TiMn_1.5 content increases from A to C. It also can be seen that LaNi_3.8Co_1.1Mn_0.1?xTiMn_1.5 hydrogen storage alloy electrode C and B have the best self-discharge ability and the best high-rate discharge ability from self-discharge curves and high-rate discharge curves.     

High-Energy Aqueous/Organic Hybrid Batteries Enabled by Cu2+ Redox Charge Carriers

Lithium||sulfur (Li||S) batteries are considered as one of the promising next-generation batteries due to the high theoretical capacity and low cost of S cathodes, as well as the low redox potential of Li metal anodes (−3.04 V vs. standard hydrogen electrode). However, the S reduction reaction from S to Li₂S leads to limited discharge voltage and capacity, largely hindering the energy density of Li||S batteries. Herein, high-energy Li||S hybrid batteries were designed via an electrolyte decoupling strategy. In cathodes, S electrodes undergo the solid-solid conversion reaction from S to Cu₂S with four-electron transfer in a Cu²⁺-based aqueous electrolyte. Such an energy storage mechanism contributes to enhanced electrochemical performance of S electrodes, including high discharge potential and capacity, superior rate performance and stable cycling behavior. As a result, the assembled Li||S hybrid batteries exhibit a high discharge voltage of 3.4 V and satisfactory capacity of 2.3 Ah g⁻¹, contributing to incredible energy density. This work provides an opportunity for the construction of high-energy Li||S batteries.     

Influence of addition of cobalt oxide on microstructure and electrochemical capacitive performance of nickel oxide

Ni–Co oxide nanocomposite was prepared by thermal decomposition of the precursor obtained via a new method—coordination homogeneous coprecipitation method. The synthesized sample was characterized physically by X-ray diffraction, scanning electron microcopy, energy dispersive spectrum, transmission electron microscope, and Brunauer–Emmett–Teller surface area measurement, respectively. Electrochemical characterization of Ni–Co oxide electrode was examined by cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance measurements in 6-mol L⁻¹ KOH aqueous solution electrolyte. The results indicated that the addition of cobalt oxide not only changed the morphology of NiO but also enhance its electrochemical capacitance value. A specific capacitance value of 306 F g⁻¹ of Ni–Co oxide nanocomposite with n _Co = 0.5 (n _Co is the mole fraction of Co with respect to the sum of Co and Ni) was measured at the current density of 0.2 A g⁻¹, nearly 1.5 times greater than that of pure NiO electrode. Lower resistance and better rate capability can also be observed.     

Glycine-assisted hydrothermal synthesis of nanostructured Co x Ni1−x –Al layered triple hydroxides as electrode materials for high-performance supercapacitors

Nanostructured Co _x Ni_1−x –Al layered triple hydroxides (Co _x Ni_1−x –Al LTHs) have been successfully synthesized by a facile hydrothermal method using glycine as chelating agent. The samples were characterized by X-ray diffraction, thermogravimetry, Fourier transform infrared spectroscopy and scanning electron microscopy. The morphologies of Co _x Ni_1−x –Al LTHs varied with the Co content and its effect on the electrochemical behavior was studied by cyclic voltammetry and galvanostatic charge–discharge techniques. Electrochemical data demonstrated that the Co _x Ni_1−x –Al LTHs with Co/Ni molar ratio of 3:2 owned the best performance and delivered a maximum specific capacitance of 1,375 F g⁻¹ at a current density of 0.5 A g⁻¹ and a good high-rate capability. The capacitance retained 93.3% of the initial value after 1,000 continuous charge–discharge cycles at a current density of 2 A g⁻¹.