Influence of initial surface condition of lithium metal anodes on surface modification with HF

Surface modification of as-received lithium foils was carried out using acid-base reactions of the native surface films on lithium metal with HF. Two types of as-received lithium foils covered with different native films were used as samples for this surface modification. One was a lithium foil having a very thin native surface film and the other one had a thicker native surface film. The surface condition of the lithium metal was analysed by X-ray photoelectron spectroscopy before and after the surface modification using HF, and the coulombic efficiency was measured electrochemically. The thickness of the surface film on the modified lithium foils was related to the Li₂O layer thickness in the native film on the as-received lithium foils. The modified lithium foil which had the thinner native surface film provided more uniform deposition of lithium and a higher coulombic efficiency during charge and discharge cycles when propylene carbonate electrolyte with 1.0 m LiPF₆ was used as the electrolyte. These results show that the initial condition of the native surface film plays an important role in surface modification with HF.     

Dimethyl sulfoxide-based electrolytes for rechargeable lithium batteries

Mixed solutions of dimethyl sulfoxide (DMSO) and low viscosity solvents have been examined as a solvent of the electrolyte for rechargeable lithium (Li) batteries. The electrolytic conductivities of LiClO₄. LiBF₄ and LiPF₆ were measured as a function of the solvent composition. Maximum conductivities were observed in the DMSO concentration ranges of 60–80 mol% for LiClO₄ and LiBF₄, and 20–60 mol% for LiPF₆. The highest conductivity of all examined systems was 1.6 × 10⁻² S cm⁻¹ in the solution containing 1,2-dimethoxyethane (DME) and LiPF₆ as the co-solvent and the electrolyte, respectively. Polarization behavior and charge-discharge characteristics of the lithium electrode were investigated in the DMSO-based solutions. The cycling efficiency was markedly dependent not only on the co-solvent but also the Li salt. The highest efficiency on the nickel substrate was observed in LiPF₆ (1 mol dm⁻³)/DMSO-DME (1:1 by volume). High rechargeability of Li was also expected in the solution containing LiClO₄ or LiBF₄ when aluminum was used as the substrate.     

A study of electrochemical kinetics of lithium ion in organic electrolytes

Limiting current densities equivalent to the transport-controlling step of lithium ions in organic electrolytes were measured by using a rotating disk electrode (RDE). The diffusion coefficients of lithium ion in the electrolyte of PC/LiClO₄, EC : DEC/LiPF₆ and EC : DMC/LiPF₆ were determined by the limiting current density data according to the Levich equation. The diffusion coefficients increased in the order of PC/LiClO₄<EC : DEC/LiPF₆<EC : DMC/ LiPF₆ with respect to molar concentration of lithium salt. The maximum value of diffusivity was 1.39x10-5cm²/s for 1M LiPF₆ in EC : DMC=1 : 1. Exchange current densities and transfer coefficients of each electrolyte were determined according to the Butler-Volmer equation.     

Analysis of the interaction using FTIR within the components of OREC composite GPE based on the synthesized copolymer matrix of P(MMA-MAh)

Poly(methyl methacrylate-maleic anhydride) (P(MMA-MAh)) has been synthesized from methyl methacrylate (MMA) and maleic anhydride (MAh) monomers. The molar ratio of monomers was found to be 1MAh:8MMA. The molecular weight of copolymer was determined in the order 10⁴ (g/mol).Rectorite modified with dodecyl benzyl dimethyl ammonium chloride (OREC) was used as a filler additive to modify gel polymer electrolytes (GPEs) which consisted of P(MMA-MAh) used as polymer matrix, propylene carbonate (PC) as a plasticizer and LiClO₄ as lithium ion producer. Characterization of interaction of CO in PC and copolymer with Li⁺ and OH group on OREC surface has been thoroughly examined using FTIR. The quantitative analysis of FTIR shows that the absorptivity coefficient a of copolymer/LiClO₄, PC/LiClO₄, PC/OREC and copolymer/OREC is 0.756, 0.113, 0.430 and 0.602, respectively, which means that the Li⁺ or OH bonded CO is more sensitive than free CO in FTIR spectra. The limit value of bonded CO equivalent fraction of copolymer/LiClO₄, PC/LiClO₄, PC/OREC and copolymer/OREC is 55, 94, 57 and 26%, respectively, which implies that all the interaction within the components is reversible and the intensity of interaction is ordered as PC/LiClO₄, PC/OREC, copolymer/OREC and copolymer/LiClO₄.     

Methyl phenyl bis-methoxydiethoxysilane as bi-functional additive to propylene carbonate-based electrolyte for lithium ion batteries

Methyl phenyl bis-methoxydiethoxysilane (MPBMDS) was prepared and its effects were investigated as an additive in 1.0 mol dm⁻³ LiPF₆-propylene carbonate (PC)/dimethyl carbonate (DMC) (1:1, v/v) electrolyte for lithium ion batteries. The electrochemical properties of the electrolyte with MPBMDS were characterized by discharge/charge tests, cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The addition of MPBMDS can effectively prevent the decomposition and the co-intercalation of PC. In addition, burning tests showed that the addition of 4–13 wt.% MPBMDS to the bare PC-based electrolyte effectively reduces the flammability. This eco-friendly compound provides a new promising direction for the development of bi- or multi-functional additives for lithium ion batteries.     

Influence of manganese(II), cobalt(II), and nickel(II) additives in electrolyte on performance of graphite anode for lithium-ion batteries

Manganese dissolution into an electrolyte from the spinel LiMn₂O₄ in the lithium-ion cell has been recently investigated. In order to study the influence of the dissolved manganese species on the lithium intercalation/deintercalation into a natural graphite electrode, the electrochemical behavior of graphite was investigated in 1 mol dm⁻³ LiClO₄ electrolyte solution containing a small amount of Mn(II) by the addition of manganese(II) perchlorate. During the charging process, Mn(II) ions were firstly electroreduced on the electrode around 1.0 V versus Li/Li⁺ followed by irreversible decomposition of the electrolyte and lithium intercalation into the graphite. By microscopic observation of the graphite surface, manganese deposition was confirmed after the charge/discharge test. Due to the manganese deposition, the reversible capacity of the graphite electrode was drastically decreased. Furthermore, the cyclability of the anode was degraded with the amount of the manganese additive increasing. We compared these results with those of the cobalt(II) and nickel(II) additives by dissolving the corresponding perchlorates. Furthermore, we discussed the influence in practical cells based on the consideration of electrochemistry of the deposited metals.     

Effects of quinoneimine dyes on lithium cycling efficiency for LiClO4-propylene carbonate

Additive effects of quinoneimine dyes (QIDs) on Li cycling efficiency (E _ff) were examined in 1 M LiClO₄-propylene carbonate (PC). TheE _ff values were measured galvanostatically on a Pt working electrode. TheE _ff values for solutions with QID addition were higher than those for PC alone and theE _k values depended on cycling current density and on the amounts of QID added. For example, 1 M LiClO₄-PC with added methylene blue (MB) (10^–3 M addition) showedE _ff values exceeding 90% at 0.5mA cm^–2, 0.6 C cm^–2, while theE _ff values for PC alone were approximately 65%. From observation with a scanning electron microscope the morphology for the deposited Li in solution with MB added was found to be smoother than that in PC alone. TheE _ff values for solutions with QID added tended to increase with an increase in the reduction potential for QID vs Li-Li₊. The enhancement of the Li cycling efficiency by QID addition seems to be caused by Li₊ ion-conductive film formation on the deposited Li surface, resulting from the reaction between QID and the deposited Li, that suppresses the reaction between PC and the deposited Li. This film formation was strongly suggested by the measurement of the resistance on the Li surface.     

Electrochemical stability of thin film LiMn2O4 cathode in organic electrolyte solutions with different compositions at 55 °C

A survey of the electrochemical stability of electrostatic spray deposited thin film of LiMn₂O₄ was performed in LiClO₄-EC-PC, LiBF₄-EC-PC, and LiPF₆-EC-PC solutions at 55 °C. The solution resistance, the surface film resistance, and the charge-transfer resistance were all found to depend on the electrolyte composition. Among the LiX-salts studied, the lowest charge transfer-resistance, and surface layer resistance were obtained in LiBF₄-EC-PC solution. There is no major influence of the electrolyte solution compositions upon lithium ion transport in the LiMn₂O₄ bulk at 55 °C. The diffusion coefficient of lithium in the solid phase varied within 10⁻¹⁰-10⁻⁸ cm² s⁻¹ in the three solutions. In general, it seems that in LiBF₄ solutions, the surface chemistry is the most stable in the three solutions examined, and hence the electrode impedance in LiBF₄ solutions was the lowest. In LiPF₆ solutions, HF seems to play an important role, and thus, the electrode impedance is relatively high due to the precipitation of surface LiF.     

Surface film formation on a graphite negative electrode in lithium-ion batteries: AFM study on the effects of co-solvents in ethylene carbonate-based solutions

In situ AFM observation of the basal plane of highly oriented pyrolytic graphite (HOPG) was performed before and after cyclic voltammetry in 1 mol dm⁻³ LiClO₄ dissolved in ethylene carbonate (EC), EC+diethyl carbonate (DEC), and EC+dimethyl carbonate (DMC) to clarify the effects of co-solvents in EC-based solutions on surface film formation on graphite negative electrodes in lithium-ion cells. In each solution, surface film formation involved the following two different processes: (i) intercalation of solvated lithium ions and their decomposition beneath the surface; and (ii) direct decomposition of solvent molecules on the basal plane to form a precipitate layer. The most remarkable difference among these solvent systems was that solvent co-intercalation took place more extensively in EC+DEC than in EC+DMC or EC. Raman analysis of ion-solvent interactions revealed that a lithium ion is solvated by three EC molecules and one DEC molecule in EC+DEC, whereas it is solvated exclusively by EC in EC+DMC and in EC, which suggested that the presence of linear alkyl carbonates in the solvation shell of lithium ion enhance the degree of solvent co-intercalation that occurs in the initial stage of the surface film formation.     

Morphology and electrochemical and mechanical properties of polyethylene‐oxide‐based nanofibrous electrolytes applicable in lithium ion batteries

We report the synthesis of all‐solid‐state polymeric electrolytes based on electrospun nanofibers. These nanofibers are composed of polyethylene oxide (PEO) as the matrix, lithium perchlorate (LiClO₄) as the lithium salt and propylene carbonate (PC) as the plasticizer. The effects of the PEO, LiClO₄ and PC ratios on the morphological, mechanical and electrochemical characteristics were investigated using the response surface method (RSM) and analysis of variance test. The prepared nanofibrous electrolytes were characterized using SEM, Fourier transform infrared, XRD and DSC analyses. Conductivity measurements and tensile tests were conducted on the prepared electrolytes. The results show that the average diameter of the nanofibers decreased on reduction of the PEO concentration and addition of PC and LiClO₄. Fourier transport infrared analysis confirmed the complexation between PEO and the additives. The highest conductivity was 0.05 mS cm^?1 at room temperature for the nanofibrous electrolyte with the lowest PEO concentration and the highest ratio of LiClO₄. The optimum nanofibrous electrolyte showed stable cycling over 30 cycles. The conductivity of a polymer film electrolyte was 29 times lower than that of the prepared nanofibrous electrolyte with similar chemical composition. Furthermore, significant fading in mechanical properties was observed on addition of the PC plasticizer. The results obtained imply that further optimization might lead to practical uses of nanofibrous electrolytes in lithium ion batteries. © 2019 Society of Chemical Industry     

Extraction separation of Ir(III) and Rh(III) with Cyanex 923 from chloride media: a possible recovery from spent autocatalysts

Liquid–liquid extraction of Ir(III) and Rh(III) with Cyanex 923 from aqueous hydrochloric acid media has been studied. Quantitative extraction of Ir(III) was observed in the range of 5.0–8.0 mol dm^?3 HCl with 0.1 mol dm^?3 Cyanex 923, while Rh(III) was extracted quantitatively in the range of 1.0–2.0 mol dm^?3 HCl with 0.05 mol dm^?3 Cyanex 923 in toluene along with 0.2 mol dm^?3 SnCl₂. The Ir(III) was back extracted with 4.0 mol dm^?3 HNO₃ quantitatively from the organic phase while Rh(III) was stripped with 3.0 mol dm^?3 HNO₃. The extraction of Rh(III) with Cyanex 923 was not quantitative without use of SnCl₂. However in the extraction of Ir(III) a negative trend was observed in the presence of SnCl₂. Varying the temperature of extraction showed that the extraction reactions of both the metal ions are exothermic in nature, and the stoichiometric ratio of Ir(III)/Rh(III) to Cyanex 923 in organic phase was found to be 1:3. The methods developed were applied to the recovery of these metal ions from a synthetic solution of similar composition to that from leaching of spent autocatalysts in 6.0 mol dm^?3 HCl. © 2002 Society of Chemical Industry     

Anodic stability of propylene carbonate electrolytes at potentials above 4V against lithium: An on-line MS andin situ FTIR study

On-line mass spectroscopy (DEMS) andin situ FTIR spectroscopy provide a valuable extension to classical cyclic voltammetry since they enable the identification of reaction products as a function of applied potential. We have compared the CO₂ evolution during the electrooxidation of 0.5 M LiAsF₆, 0.5 M LiBF₄ and 0.5 M LiClO₄/propylene carbonate on platinum combining these techniques. The highest CO₂ formation rate was measured for 0.5 M LiClO₄/PC and the lowest for 0.5 M LiAsF₆, both with an on-set potential at 4.0 V against Li/Li⁺. On-line MS results in 0.5 M LiBF₄/PC show strong evidence for the formation (above 4.7 V) of carbonyl fluoride and other fluorinated species parallel to the CO₂ evolution. This indicates an anodic decomposition of BF ₄ ^– anions interacting with oxidized PC species. The role of the OH^–ions on the film formation on platinum at 2.0 V against Li/Li⁺ was also investigated within situ FTIR for the three electrolytes.This paper is dedicated to Professor Dr Fritz Beck on the occasion of his 60th birthday.     

Electroplating of Fe-Ni alloys: a sulphate-amine bath

Thin films of Fe-Ni alloys have been electroplated from acidic sulphate bath (0.06 mol dm^–3 NiSO₄, O.O15 mol dm^–3 FeSO₄, 0.005 mol dm^–3 ascorbic acid, 20 g dm^–3 boric acid and 1 g dm^–3 saccharin) containing aliphatic amines. The percentage Ni in the alloy varied with bath composition (Fe/Ni), current density, stirring of the medium, nature and concentration of the amine. Increase of temperature and pH of the medium increased the percentage Ni in the deposit. The composition of the alloy remained constant with thickness of the film. The cathodic current efficiency depends on the plating variables. The plating potential in acidic sulphate bath was shifted in the less noble direction by the presence of amines. Smooth and bright films are obtained with small grain size when the Ni in the film is 75% or above. Electroplating conditions are optimized to get thin, magnetic 2080 Fe-Ni films.Presented at the International Symposium on Recent Aspects of Electroanalytical Chemistry and Electrochemical Technology at Chanigarh, India.     

Preliminary investigations on the anodic oxidation of Ti–13Nb–13Zr alloy in a solution containing calcium and phosphorus

Investigations on the surface modification of Ti–13Nb–13Zr alloy by anodic oxidation are reported here. The oxidation process was carried out in a solution containing 4 mol dm⁻³ H₃PO₄ and 100 g dm⁻³ Ca(H₂PO₂)₂. The anodising was realised at voltages of 80 V and 150 V. Moreover, a portion of the samples that had been oxidised at 150 V were held at a temperature of 500 °C. It was found that the morphology of the sample surface did not change during the oxidation of the alloy at 80 V. An application of 150 V led to the incorporation of calcium and phosphorus into the formed oxide layer and to significant modification of the surface morphology. The electrochemical characteristics of the modified alloy was also determined in Ringer's solution. It was shown that the electropolishing and anodising result in a considerable increase in the corrosion resistance of the Ti–13Nb–13Zr alloy.     

On the difference in cycling behaviors of lithium-ion battery cell between the ethylene carbonate- and propylene carbonate-based electrolytes

Density functional theory (DFT) calculations and classical molecular dynamics (MD) simulations have been performed to gain insight into the difference in cycling behaviors between the ethylene carbonate (EC)-based and the propylene carbonate (PC)-based electrolytes in lithium-ion battery cells. DFT calculations of the lithium solvation, Li⁺(S)_i (S = EC or PC; i = 1–4) with and without the presence of the counter anion showed that the desolvation energy to remove one solvent molecule from the first solvation shell of the lithium ion was significantly reduced by as much as 70 kcal mol⁻¹ (293.08 kJ mol⁻¹) in the presence of the counter anion, suggesting the lithium ion is more likely to be desolvated at high salt concentrations. The thermodynamic stability of the ternary graphite intercalation compounds, Li⁺(S)_iC₇₂, in which Li⁺(S)_i was inserted into a graphite cell, was also examined by DFT calculations. The results suggested that Li⁺(EC)_iC₇₂ was more stable than Li⁺(PC)_iC₇₂ for a given i. Furthermore, some of Li⁺(PC)_iC₇₂ were found to be energetically unfavorable, while all of Li⁺(EC)_i=1–4C₇₂ were stable, relative to their corresponding Li⁺(S)_i in the bulk electrolyte. In addition, the interlayer distances of Li⁺(PC)_iC₇₂ were more than 0.1 nm longer than those of Li⁺(EC)_iC₇₂. MD simulations were also carried out to examine the solvation structures at a high salt concentration of LiPF₆: 2.45 mol kg⁻¹. The results showed that the solvation structure was significantly interrupted by the counter anions, having a smaller solvation number than that at a lower salt concentration (0.83 mol kg⁻¹). We propose that at high salt concentrations, the lithium desolvation may be facilitated due to the increased contact ion pairs so as to form a stable ternary GIC with less solvent molecules without destruction of graphite particles, followed by solid–electrolyte-interface film formation reactions. The results from both DFT calculations and MD simulations are consistent with the recent experimental observations.     

Interfacial properties between ionic-liquid-based electrolytes and lithium-ion-battery separator

For lithium salts, ionic liquids (ILs) are promising alternatives to conventional solvents in lithium-ion batteries (LIBs) due to a more favorable high-voltage operating window, and due to improved safety through reduction of flammability. Toward better understanding of wetting properties of IL-based electrolytes on a LIB separator, wetting properties affect electrochemical performance, experimental studies were made to determine the influence of solvent, lithium-salt type and salt concentration. Surface tensions and advancing contact angles were measured for two pure ILs ([C₄C₁im][BF₄] and [C₄C₁im][OTf]) and for four IL/alkylcarbonate solvent blends (1:1 mass ratio, [C₄C₁im][BF₄]/PC, [C₄C₁im][BF₄]/DMC, [C₄C₁im][OTf]/PC, and [C₄C₁im][OTf]/ DMC) with several concentrations of a lithium salt (LiClO₄, LiPF₆, and LiTFSI). A significant improvement of wettability of pure ILs was observed by adding DMC, while adding PC with surface tension higher than that of pure ILs is detrimental to wetting behavior. Contact angles decrease by adding LiTFSI but show almost no change upon addition of LiPF₆ or LiClO₄. Surface tensions follow the same trend as that for contact angles. Incorporation of TFSI⁻ anion gives favorable separator wettability. Estimates were made for interfacial properties of the separator (dispersive and polar components of the surface free energy for solid-vapor, for liquid–vapor, and for solid–liquid interfacial free energy).     

Aluminum-doping effects on three-dimensional Li3V2(PO4)3@C/CNTs microspheres for electrochemical energy storage

A series of three-dimensional Al³⁺-doped Li₃V₂(PO₄)₃@C/CNTs microspheres have been fabricated for the first time using a facile spray drying route followed through a solid-state reaction process. The crystalline structure, morphology, microstructure and lithium storage performance for the fabricated composites have been researched using Raman spectrum, XRD, XPS, SEM, TEM, EDS and various electrochemical tests. Benefiting from the Al³⁺ doping and formed three-dimensional networks by the carbon film and CNTs, the Li ⁺ diffusion coefficient and electrical conductivity of Li₃V₂(PO₄)₃ are significantly enhanced. All the Al³⁺-doped composites possess superior lithium storage properties including high capacity and good cyclic-life. Thus, Al³⁺ doping is a prospective strategy to promote the rate properties of Li₃V₂(PO₄)₃ for lithium energy storage.     

Effects of the addition of LiCl,LiClO4, and LiCF3SO3 salts on the chemical structure,density, electrical,and mechanical properties of rigid polyurethane foam composite

The effect of the incorporation of several lithium salts on the electrical and mechanical properties of polyurethane rigid (PUR) foams was investigated. Different amounts of lithium chloride (LiCl), lithium perchlorate (LiClO₄), and lithium trifluoromethanesulfonate (LiCF₃SO₃) were added to the polyuretanic precursor. The salts affected the cellular microstructures and consequently the mechanical properties of the composite. Composite foams containing an amount of LiCl greater than 2 wt% showed low‐surface resistivity (～10⁶ Ω), whereas the LiClO₄ and LiCF₃SO₃ composites showed, in all range of filler percentage analyzed, high‐surface resistivity values (～10¹¹ Ω). This behavior was related to the different interactions between PUR and lithium salts, as confirmed by FTIR/Attenuated Total Reflectance analysis. Only the LiCl was able to create a motion of the ions Li⁺ and Cl^? along the polyurethanic chains, because LiCl was completely dissociated. On the contrary, LiClO₄ and LiCF₃SO₃ that affected the macromolecular structure of the polymeric network did not permit the formation of polyurethanic channels, where the ions could move, thus creating a charge motion. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Ethylene carbonate—propylene carbonate mixed electrolytes for lithium batteries

Electrolytic characteristics of propylene carbonate (PC)ethylene carbonate (EC) mixed electrolytes were studied, compared with those in PC electrolytes. Conductivity and Li charge—discharge efficiency values increased with EC contents increasing. For example, 1 M LiClO₄ECPC (EC mixing molar ratio; [EC]/[PC] = 4) showed the conductivity of 8.5 ohm^?1 cm^?1, which value was 40% higher than that in PC. Also, 1 M LiClO₄ECPC([EC]/[PC] = 5) showed the Li charge—discharge efficiency of 90.5% at 0.5 mA cm^?2, 0.6 C cm^?2, which value was ca. 25% higher than that in PC. ECPC mixed electrolytes were considered to be practically available for ambient lithium batteries in regard to the high Li⁺ ion conductivity and also high Li charge—discharge efficiency.     

Anodic dissolution of rapidly quenched amorphous Ni81P19 alloys of different initial melt temperatures

The anodic behaviour of rapidly quenched Ni₈₁P₁₉ samples prepared at different melt temperatures was investigated in 1.0 mol dm^–3 aqueous HCl solution. The electrochemical properties of the alloys kept in melt at different temperatures are significantly influenced by the initial melt temperature. X-ray diffractometry suggests that this behaviour is associated with the presence of different quantities of crystalline secondary phase(s). On the basis of potentiodynamic polarization curves and potential-time functions recorded at constant current the alloys were characterized by a charge per surface unit amount proportional to the secondary phase content. A new model was proposed to characterize the anodic dissolution of alloys containing crystalline clusters.