Investigation of the anodic behavior of Al current collector in room temperature ionic liquid electrolytes

We have investigated the anodic behaviors of aluminum as a cathodic current collector for lithium ion batteries in several kinds of room temperature ionic liquids (RTILs) and EC + DMC solutions containing LiN(CF₃SO₂)₂ by cyclic voltammetry (CV), chronoamperometry (CA), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy and X-ray photoelectron spectroscopy (XPS). Cyclic voltammetry and chronoamperometry data showed that the current density for aluminum foil with the RTIL electrolytes was less than that of aluminum foil in the EC + DMC solutions. Besides, much corrosion pits appeared on the aluminum foil surface after the electrochemical measurement in the EC + DMC solutions, while they were not observed on the aluminum foil with the RTIL electrolytes, suggesting that aluminum current collector was stable in the RTIL electrolytes. Further research by EDX and XPS analysis revealed that a good passivating film composed mainly of the products from the oxidation between aluminum and the anions of the RTIL electrolytes on the aluminum foil surface after the anodic polarization which suppressed the aluminum corrosion.     

Comparative study on surface behaviors of copper current collector in electrolyte for lithium-ion batteries

The chemical and electrochemical stability of Cu current collectors in electrolyte for lithium-ion batteries is investigated. During long-term storage, the surface section of Cu foil is oxidized to copper compounds along with the reduction reaction of electrolyte. A continuous surface film can be formed on the Cu current collector after the foil is immersed in electrolyte for lithium ion batteries at room temperature for 30 days. This surface film is composed of inorganic compounds located in the inner layer and organic/inorganic mixed components stayed outside. It comes from the spontaneous reaction at the interface between Cu foil and electrolyte for the existence of trace water in electrolyte. Different from SEI film spontaneous formation during storage, surface film generated on Cu foil during electrochemical process shows different characteristic and mechanism. By using metal lithium as counter electrode, SEI film on Cu foil in Cu foil/metal Li battery is formed from surface chemical species floating from lithium counter electrode and electrochemical oxidation/reduction process. In contrast, thinner SEI film can be generated merely from electrochemical electrolyte decomposition and precipitation. All the evidences reveal that the structure of SEI film from different conditions is similar, which shows inorganic fluorides located in the inner layer and organic/inorganic mixed lied in the outer layer.     

Preparation and electrochemical properties of nonwoven reinforced solid polymer electrolytes

Summary Reinforced PEO-based polymer electrolytes were prepared by UV curing method. In this study, nonwoven sheets which were polyethylene terephthalate and polypropylene were used for that purpose. To enhance the ionic conductivity of reinforced PEO-based polymer electrolytes, oligomeric poly(ethylene glycol) dimethyl ether was added as a plasticizer, which is a sort of nonvolatile chemicals. The reinforced PEO-based polymer electrolytes showed the ionic conductivity of around 1.2 × 10⁻⁴ S/cm at 30°C, which was a little bit lower than the value of not reinforced one, that is pristine UV cured SPE. Even though the reinforced PEO-based polymer electrolytes didn't have any organic solvent such as ethylene carbonate, lithium ionic type polymer cell containing the polymer electrolyte showed reasonable specific discharge capacity of 116 mAh/g at room temperature. Received: 25 February 2000/Accepted: 14 April 2000     

Electrochemical performance of nanoporous Si as anode for lithium ion batteries in alkyl carbonate and ionic liquid-based electrolytes

Nanoporous Si was obtained by means of metal-assisted chemical etching. Li ion insertion–extraction was tested by voltammetric and galvanostatic electrochemical cycling in conventional 1 M LiPF₆ ethylene carbonate/dimethyl carbonate EC/DMC and in 1 M LiTFSI 1-butyl-1-methyl-pyrrolidinium bis (trifluoromethyl) sulfonylimide [BMP] [TFSI] electrolytes. The nanoporous Si demonstrated high reversibility when cycled in 1 M LiPF₆ EC/DMC electrolyte and showed superior activity compared to the non-structured sample. In contrast to the organic carbonate electrolyte, the material cycling in ionic liquid media showed reduced capacity and reversibility of the Li ion exchange. The latter results were discussed in terms of the high viscosity of the ionic liquid and ineffective cathodic passivation of the Si substrate in the ionic liquid-based electrolyte. Scanning electron microscopy imaging showed minor morphological changes due to the large volume change during Li insertion. No signs of crack formation and propagation were detected during the time span of the measurement.     

Gel electrolytes based on lithium modified silica nano-particles

In this work lithium modified silica (Li-SiO₂) nano-particles were synthesized and used as a single ion lithium conductor source in gel electrolytes. It was found that Li-SiO₂ exhibited good compatibility with DMSO, DMA/EC (a mixture of N,N-dimethyl acetamide and ethylene carbonate) and the ionic liquid, N-methyl-N-propyl pyrrolidinium bis(trifluoromethylsulfonyl) amide ([C₃mpyr][NTf₂]). Several gel electrolytes based on Li-SiO₂ were obtained. These gel electrolytes were investigated by DSC, solid state NMR, conductivity measurements and cyclic voltammetry. Conductivities as high as 10⁻³ S/cm at room temperature were observed in these nano-particle gel electrolytes. The results of electrochemical tests showed that some of these materials were promising for using as lithium conductive electrolytes in electrochemical devices, with high lithium cycling efficiency evident.     

Electrochemical intercalation of lithium into a natural graphite anode in quaternary ammonium-based ionic liquid electrolytes

Electrochemical intercalation of lithium into a natural graphite anode was investigated in electrolytes based on a room temperature ionic liquid consisting of trimethyl-n-hexylammonium (TMHA) cation and bis(trifluoromethanesulfone) imide (TFSI) anion. Graphite electrode was less prone to forming effective passivation film in 1 M LiTFSI/TMHA-TFSI ionic electrolyte. Reversible intercalation/de-intercalation of TMHA cations into/from the graphene interlayer was confirmed by using cyclic voltammetry, galvanostatic measurements, and ex situ X-ray diffraction technique. Addition of 20 vol% chloroethylenene carbonate (Cl-EC), ethylene carbonate (EC), vinyl carbonate (VC), or ethylene sulfite (ES) into the ionic electrolyte resulted in the formation of solid electrolyte interface (SEI) film prior to TMHA intercalation and allowed the formation of Li-C₆ graphite interlayer compound. In the ionic electrolyte containing 20 vol% Cl-EC, the natural graphite anode exhibited excellent electrochemical behavior with 352.9 mAh/g discharge capacity and 87.1% coulombic efficiency at the first cycle. A stable reversible capacity of around 360 mAh/g was obtained in the initial 20 cycles without any noticeable capacity loss. Mechanisms concerning the significant electrochemical improvement of the graphite anode were discussed. Ac impedance and SEM studies demonstrated the formation of a thin, homogenous, compact and more conductive SEI layer on the graphite electrode surface.     

Rechargeable lithium/sulfur battery with suitable mixed liquid electrolytes

The suitability of some single/binary liquid electrolytes and polymer electrolytes with a 1 M solution of LiCF₃SO₃ was evaluated for discharge capacity and cycle performance of Li/S cells at room temperature. The liquid electrolyte content in the cell was found to have a profound influence on the first discharge capacity and cycle property. The optimum, stable cycle performance at about 450 mAh g⁻¹ was obtained with a medium content (12 μl) of electrolyte. Comparison of cycle performance of cells with tetra(ethylene glycol)dimethyl ether (TEGDME), TEGDME/1,3-dioxolane (DIOX) (1:1, v/v) and 1,2-dimethoxyethane (DME)/di(ethylene glycol)dimethyl ether (DEGDME) (1:1, v/v) showed better results with the mixed electrolytes based on TEGDME. The addition of 5 vol.% of toluene in TEGDME had a remarkable effect of increasing the initial discharge capacity from 386 to 736 mAh g⁻¹ (by >90%) and stabilizing the cycle properties, attributed to the reduced lithium metal interfacial resistance obtained for the system. Polymer electrolyte based on microporous poly(vinylidene fluoride) (PVdF) membrane and TEGDME/DIOX was evaluated for ionic conductivity at room temperature, lithium metal interfacial resistance and cycle performance in room-temperature Li/S cells. A comparison of the liquid electrolyte and polymer electrolyte showed a better performance of the former.     

Fabrication and characterization of PEO/PPC polymer electrolyte for lithium‐ion battery

A new poly(propylene carbonate)/poly(ethylene oxide) (PEO/PPC) polymer electrolytes (PEs) have been developed by solution‐casting technique using biodegradable PPC and PEO. The morphology, structure, and thermal properties of the PEO/PPC polymer electrolytes were investigated by scanning electron microscopy, X‐ray diffraction, and differential scanning calorimetry methods. The ionic conductivity and the electrochemical stability window of the PEO/PPC polymer electrolytes were also measured. The results showed that the T_g and the crystallinity of PEO decrease, and consequently, the ionic conductivity increases because of the addition of amorphous PPC. The PEO/50%PPC/10%LiClO₄ polymer electrolyte possesses good properties such as 6.83 × 10^?5 S cm^?1 of ionic conductivity at room temperature and 4.5 V of the electrochemical stability window. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Ionic conductivity of lithium conducting SiO2 gels at room temperature

Fresh silica gels have been used as hosts for liquid organic lithium electrolytes. The residual liquid inside the fresh gels was exchanged by the solutions of selected lithium salts (lithium hexafluorophosphate, lithium tetrafluoroborate) in organic solvents: propylene carbonate (PC), dimethyl sulfoxide (DMSO), dimethyl formamide (DMF), 1,2-diethoxyethane (DEE) and dimethyl carbonate (DMC). The immersion of the gels in solutions based on DEE, DMF and DMC leads to the fast deterioration of the gels. The gels immersed in the solutions based on PC and DMSO exhibit stable conductivities in the range of 10–3Scm–1 at room temperature. That conductivity is close to the conductivity of the corresponding lithium salt solutions.     

硝基苯在离子液体BPyBF4/H2O中的电化学行为

在离子液体1-丁基吡啶四氟硼酸盐(BPyBF₄)的水溶液中,采用循环伏安法(CV)、计时电流法(CA)、恒电位电解及原位红外光谱法(in-situ FTIRS)等研究了硝基苯在铂电极上的电化学还原行为。研究结果表明:硝基苯在离子液体BPyBF₄/H₂O体系中的还原过程是受扩散控制的,其还原产物主要是偶氮苯,经估算得到硝基苯在该体系中的扩散系数为3.1×10^-7 cm²·s^-1,提高温度和加入一定浓度的水均有利于硝基苯在该体系中的电化学还原。     

Ionically conductive polymer gel electrolytes consisting of crosslinked methacrylonitrile and organic electrolyte

To develop a highly ion‐conductive polymer electrolyte, we copolymerized methacrylonitrile (MAN) with ethylene glycol dimethacrylate (EGDMA) in propylene carbonate that contained tetraethylammonium tetrafluoroborate (TEATFB), changing the TEATFB concentration and the MAN/EGDMA molar ratio. We characterized the obtained polymer gel electrolytes with complex impedance analysis and cyclic voltammetry, intending to apply them to electric double‐layer capacitors. The ionic conductivities of the polymer gel electrolytes were dependent on the TEATFB concentration, the temperature, and particularly the crosslinking degree. The polymer gel electrolytes in this system exhibited high room‐temperature conductivities (>10^?3 S/cm). Furthermore, these polymer electrolytes showed good electrochemical stability windows ranging from ?4.0 to +4.0 V versus Ag. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2655–2659, 2002     

Study of the formation of a solid electrolyte interphase (SEI) in ionically crosslinked polyampholytic gel electrolytes

An ionic complex of anionic and cationic monomers was obtained by protonation of (N,N-diethylamino)ethylmethacrylate with acrylic acid. A novel ionically crosslinked polyampholytic gel electrolyte was prepared through the free radical copolymerization of the ionic complex and acrylamide in a solvent mixture of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate (1:1:1, v/v) containing 1 mol/L of LiPF₆. The impedance analysis indicated that the ionic conductivity of the polyampholytic gel electrolyte was rather close to that of solution electrolytes in the absence of a polymer at the same temperature. The temperature dependence of the conductivity was found to be well in accord with the Arrhenius behavior. The formation processes of the solid electrolyte interphase (SEI) formed in both gel and solution electrolytes during the cycles of charge-discharge were investigated by cyclic voltammetry and electrochemical impedance spectroscopy. The cyclic voltammetry curves show a strong peak at a potential of 0.68 V and an increase of the interfacial resistance from 17.2 Ω to 35.8 Ω after the first cycle of charge-discharge. The results indicate that the formation process of SEI formed in both gel and solution electrolytes was similar which could effectively prevent the organic electrolyte from further decomposition and inserting into the graphite electrode. The morphologies of SEI formed in both gel and solution electrolytes were analyzed by field emission scanning electron microscopy. The results indicate that the SEI formed in the gel electrolyte showed a rough surface consisting of smaller solid depositions. Moreover, the SEI formed in the gel electrolyte became more compact and thicker as the cycling increased.     

Electrochemical performances of electric double layer capacitor with UV-cured gel polymer electrolyte based on poly[(ethylene glycol)diacrylate]-poly(vinylidene fluoride) blend

Poly[(ethylene glycol)diacrylate]-poly(vinylidene fluoride), a gel polymer blend with ethylene carbonate:dimethyl carbonate:ethylmethyl carbonate (EC:DMC:EMC, 1:1:1 volume ratio) and containing 1.0 M of lithium hexafluoro phosphate (LiPF₆) as liquid components, is employed as a gel polymer electrolyte for an electric double layer capacitor (EDLC). Its electrochemical characteristics is compared with that of liquid organic electrolyte mixture of ethylene carbonate, dimethyl carbonate and ethylmethyl carbonate in a 1:1:1 volume ratio containing 1.0 M LiPF₆ salt. The specific surface area of the activated carbon powder as an active material is 1908 m²/g. Liquid poly[(ethylene glycol)diacrylate] (PEGDA) oligomer with a high retention capability of liquid electrolytes is cured by UV irradiation and poly(vinylidene fluoride)-hexafluoropropylene (PVdF-HFP) copolymer with a porous structure endows polymer matrix with high mechanical strength.The specific capacitance of EDLC using the gel polymer electrolyte (GPE-EDLC) shows 120 F/g, which is better than the liquid organic electrolyte. Good cycling efficiency is observed for a GPE-EDLC with high retention capability of liquid components. The high specific capacitance and good cycling efficiency are most likely due to the polarization resistance of EDLC with the gel polymer electrolyte, which is lower than the liquid organic electrolyte. This may result from the distinguished adhesion between the activated carbon electrode and the gel polymer electrolyte, as well as high retention capability of liquid components.Power densities of GPE-EDLC and LOE-EDLC shows 1.88 kW/kg and 1.21 kW/kg, respectively. However, the energy densities are low in both electrolytes.The GPE-EDLC exhibits rectangular cyclic voltammogram similar to an ideal EDLC within operating voltage range of 0 V-2.5 V. It should be noted that a region of electric double layer means a wide voltage and a rapid formation. Redox currents of both EDLCs are not observed in the sweep region and the cyclic voltammograms are unchanged on repeated runs. The observed leakage current shows 49 μA after 720 s at a constant voltage of 2.5 V, due to the high ionic conductivity of 1.5 × 10⁻³ S cm⁻¹ during storage time. Swelling and well-developed pore structures of the GPE blend films allow ions and solvents to move easily.     

Electrospun poly(lithium 2‐acrylamido‐2‐methylpropanesulfonic acid) fiber‐based polymer electrolytes for lithium‐ion batteries

Novel single‐ion conducting polymer electrolytes based on electrospun poly(lithium 2‐acrylamido‐2‐methylpropanesulfonic acid) (PAMPSLi) membranes were prepared for lithium‐ion batteries. The preparation started with the synthesis of polymeric lithium salt PAMPSLi by free‐radical polymerization of 2‐acrylamido‐2‐methylpropanesulfonic acid, followed by ion‐exchange of H⁺ with Li⁺. Then, the electrospun PAMPSLi membranes were prepared by electrospinning technology, and the resultant PAMPSLi fiber‐based polymer electrolytes were fabricated by immersing the electrospun membranes into a plasticizer composed of ethylene carbonate and dimethyl carbonate. PAMPSLi exhibited high thermal stability and its decomposition did not occur until 304°C. The specific surface area of the electrospun PAMPSLi membranes was raised from 9.9 m²/g to 19.5 m²/g by varying the solvent composition of polymer solutions. The ionic conductivity of the resultant PAMPSLi fiber‐based polymer electrolytes at 20°C increased from 0.815 × 10^?5 S/cm to 2.12 × 10^?5 S/cm with the increase of the specific surface area. The polymer electrolytes exhibited good dimensional stability and electrochemical stability up to 4.4 V vs. Li⁺/Li. These results show that the PAMPSLi fiber‐based polymer electrolytes are promising materials for lithium‐ion batteries. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis and electrochemical properties of lithium methacrylate-based self-doped gel polymer electrolytes

In this study, a strategy for synthesizing lithium methacrylate (LiMA)-based self-doped gel polymer electrolytes was described and the electrochemical properties were investigated by impedance spectroscopy and linear sweep voltammetry. LiMA was found to dissolve in ethylene carbonate (EC)/diethyl carbonate (DEC) (3/7, v/v) solvent after complexing with boron trifluoride (BF₃). This was achieved by lowering the ionic interactions between the methacrylic anion and lithium cation. As a result, gel polymer electrolytes consisting of BF₃-LiMA complexes and poly(ethylene glycol) diacrylate were successfully synthesized by radical polymerization in an EC/DEC liquid electrolyte. The FT-IR and AC impedance measurements revealed that the incorporation of BF₃ into the gel polymer electrolytes increases the solubility of LiMA and the ionic conductivity by enhancing the ion disassociations. Despite the self-doped nature of the LiMA salt, an ionic conductivity value of 3.0 × 10⁻⁵ S cm⁻¹ was achieved at 25 °C in the gel polymer electrolyte with 49 wt% of polymer content. Furthermore, linear sweep voltammetry measurements showed that the electrochemical stability of the gel polymer electrolyte was around 5.0 V at 25 °C.     

Novel amphiphilic polymer gel electrolytes based on (PEG‐b‐GMA)‐co‐MMA

Amphiphilic conetwork–structured copolymers containing different lengths of ethylene oxide (EO) chains as ionophilic units and methyl methacrylate (MMA) chains as ionophobic units were prepared by free radical copolymerization and characterized by FTIR and thermal analysis. Polymer gel electrolytes based on the copolymers complexed with liquid lithium electrolytes (dimethyl carbonate (DMC) : diethyl carbonate (DEC) : ethylene carbonate (EC) = 1 : 1 : 1 (W/W/W), LiPF₆ 1.0M) were characterized by differential scanning calorimetry and impedance spectroscopy. A maximum ion conductivity of 4.27 × 10^?4 S/cm at 25^oC was found for the polymer electrolyte based on (PEG2000‐b‐GMA)‐co‐MMA with long EO groups. Moreover, the effect of temperature on conductivity of the amphiphilic polymer electrolytes obeys the Arrhenius equation. The good room temperature conductivity of the polymer electrolytes is proposed to relate to the enhancement in the amorphous domain of the copolymers due to their amphiphilic conetwork structure. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The electrochemistry of lithium in ionic liquid/organic diluent mixtures

The electrochemistry of lithium is investigated in a number of electrolytes that consist of a lithium salt dissolved in a combined ionic liquid-organic diluent medium. We find that ethylene carbonate and vinylene carbonate improve electrochemical behaviour, while toluene and tetrahydrofuran are less promising.We also present insights into the electrode passivation caused by these diluents in an ionic liquid electrolyte during lithium cycling. We observe that during lithium cycling those electrolytes with carbonate based diluents are the most able to utilise their previously reported improved lithium ion diffusivities. Conversely, tetrahydrofuran, the most promising diluent of those studied in terms of its known ability to increase lithium ion diffusivity is found not to be as advantageous as a diluent. It appears that the poor electrochemical interfacial properties of the tetrahydrofuran electrolyte prevented the realisation of the benefits of the high solution lithium ion diffusivity.     

丁二酸酐在锂离子电池电解液中的应用

在锂离子电池电解液1 mol/L六氟磷酸锂/碳酸乙烯酯+碳酸二甲酯+碳酸甲乙酯（体积比为1∶1∶1）溶液中添加丁二酸酐作为提高电池充放电效率的添加剂。 采用恒流充放电测试、循环伏安曲线、线性伏安曲线和电化学阻抗谱等手段,研究了添加剂丁二酸酐对电解液电化学稳定窗口的影响,以及丁二酸酐与锰酸锂材料的相容性。结果表明：在电解液中添加2%（质量分数）的丁二酸酐,提高了LiMn2O4/Li电池常温和高温容量保持率。丁二酸酐可以优先于基础电解液发生少量氧化分解,从而降低了LiMn2O4/Li电池的极化。同时,丁二酸酐也可降低电池循环过程的阻抗。     

碳酸二甲酯实验室开发的合成方法

综述了碳酸二甲酯(DMC)实验室开发的合成方法：甲醇气相氧化羰基化直接合成法、甲酵和二氧化碳直接合成法、尿素和甲醇合成法和甲醇电羰基化合成法。对甲醇和二氧化碳合成法的催化剂的研究进行了详细的总结，指出甲醇和二氧化碳直接合成法是具有理论和现实意义，对其开发新的催化体系，使其工业化，是目前研究的热点。并结合目前离子液体研究现状指出将离子液体引入到DMC的合成路线中，是今后研究发展的趋势。     

Measurement of transference numbers for lithium ion electrolytes via four different methods, a comparative study

We report here on comparative measurements of cationic transference numbers of some lithium battery related electrolytes including lithium tetrafluoroborate in propylene carbonate, lithium hexafluorophosphate in blends of ethylene carbonate/diethyl carbonate and ethylene carbonate/propylene carbonate/dimethyl carbonate, as well as lithium difluoromono (oxalate) borate in an ethylene carbonate/diethyl carbonate blend via four different methods. Whereas three electrochemical methods yield transference numbers decreasing with concentration in accordance with electrostatic theories, valid for low to intermediate concentrations of the electrolyte, nuclear magnetic resonance spectroscopy measurements show increasing transference numbers with increasing concentration. The discrepancy is attributed to effects of ion–ion and ion–solvent interaction.