Lithium-ion conducting electrolyte salts for lithium batteries

This paper presents an overview of the various types of lithium salts used to conduct Li(+) ions in electrolyte solutions for lithium rechargeable batteries. More emphasis is paid towards lithium salts and their ionic conductivity in conventional solutions, solid-electrolyte interface (SEI) formation towards carbonaceous anodes and the effect of anions on the aluminium current collector. The physicochemical and functional parameters relevant to electrochemical properties, that is, electrochemical stabilities, are also presented. The new types of lithium salts, such as the bis(oxalato)borate (LiBOB), oxalyldifluoroborate (LiODFB) and fluoroalkylphosphate (LiFAP), are described in detail with their appropriate synthesis procedures, possible decomposition mechanism for SEI formation and prospect of using them in future generation lithium-ion batteries. Finally, the state-of-the-art of the system is given and some interesting strategies for the future developments are illustrated.     

单离子导体聚合硼酸锂盐的研究进展

目前商业化锂离子电池常用的锂盐LiPF6,对水极其敏感,热稳定性差,尤其是在高温条件下的应用存在着一定的安全隐患.种类多且环境友好的新型有机硼酸锂盐越来越受到人们的重视.本文综述了近年来几种锂盐的合成方法,电化学性能,各自存在的优点和不足以及本课题组在聚合硼酸锂盐方向取得的系列研究进展,并对锂盐和聚合物电解质的发展方向进行了展望.     

不同碳源对LiFePO4/C锂离子电池正极材料性能的影响

以自制的正磷酸铁为铁和磷源,氢氧化锂为锂源,分别以酚醛树脂、葡萄糖、柠檬酸为碳源,采用碳热还原法合成LiFePO4/C锂离子电池正极材料.采用X射线衍射(XRD)、扫描电镜(SEM)、四探针电导测定及恒流充放电测试分别对合成样品的物相、粒径、表面形貌、电导率及电性能进行了分析.结果表明以酚醛树脂为碳源制备的Li FeP...     

Recent Advances in Porous Carbon Materials for Electrochemical Energy Storage

Climate change and the energy crisis have promoted the rapid development of electrochemical energy‐storage devices. Owing to many intriguing physicochemical properties, such as excellent chemical stability, high electronic conductivity, and a large specific surface area, porous carbon materials have always been considering as a promising candidate for electrochemical energy storage. To date, a wide variety of porous carbon materials based upon molecular design, pore control, and compositional tailoring have been proposed for energy‐storage applications. This focus review summarizes recent advances in the synthesis of various porous carbon materials from the view of energy storage, particularly in the past three years. Their applications in representative electrochemical energy‐storage devices, such as lithium‐ion batteries, supercapacitors, and lithium‐ion hybrid capacitors, are discussed in this review, with a look forward to offer some inspiration and guidelines for the exploitation of advanced carbon‐based energy‐storage materials.     

增塑聚合物电解质电化学性能

以GBL/EC复配体系为增塑剂, PVDF HFP和PMMA为聚合物基体制备胶态聚合物电解质. 研究聚合物电解质的离子传输特性和电化学稳定性. 实验表明,室温离子电导率达到 1. 2mS·cm-1, 电化学稳定窗口在 4. 5V以上. 以GBL/EC增塑聚合物电解质与表面经修饰的锂金属电极组成锂金属聚合物电池,其电极稳定性较好,充放电循环寿命得到很大的提高.     

Thermochemical and Electrochemical Stability of Electrolyte Systems based on Sulfolane

UV spectroscopy and cyclic voltammetry were used to examine the thermochemical and electrochemical stabilities of liquid sulfolane-based electrolyte systems for lithium and lithium-ion batteries. It was found that solutions of lithium salts in sulfolane are stable in prolonged keeping at 100°C. The thermochemical stability of lithium salt solutions in sulfolane changes in the order LiBF₄ > LiClO₄ ≈ LiN(CF₃SO₂)₂ > LiCF₃SO₃. It was shown that the electrochemical stability of lithium salt solutions in sulfolane is in the range from 5.5 to 5.9 V (relative to Li/Li⁺) and prolonged action of high temperatures (100°C) does not yield electrochemically active thermal destruction products.     

Low-melting, low-viscous, hydrophobic ionic liquids: aliphatic quaternary ammonium salts with perfluoroalkyltrifluoroborates

A novel class of low-melting, hydrophobic ionic liquids based on relatively small aliphatic quaternary ammonium cations ([R(1)R(2)R(3)NR](+), wherein R(1), R(2), R(3) = CH(3) or C(2)H(5), R = n-C(3)H(7), n-C(4)H(9), CH(2)CH(2)OCH(3)) and perfluoroalkyltrifluoroborate anions ([R(F)BF(3)](-), R(F) = CF(3), C(2)F(5), n-C(3)F(7), n-C(4)F(9)) have been prepared and characterized. The important physicochemical and electrochemical properties of these salts, including melting point, glass transition, viscosity, density, ionic conductivity, thermal and electrochemical stability, have been determined and comparatively studied with those based on the corresponding [BF(4)](-) and [(CF(3)SO(2))(2)N](-) salts. The influence of the structure variation in the quaternary ammonium cation and perfluoroalkyltrifluoroborate ([R(F)BF(3)](-)) anion on the above physicochemical properties is discussed. Most of these salts are liquids at 25 degrees C and exhibit low viscosities (58-210 cP at 25 degrees C) and moderate conductivities (1.1-3.8 mS cm(-1)). The electrochemical windows of these salts are much larger than those of the corresponding 1,3-dialkyimidazolium salts. Additionally, a number of [R(F)BF(3)](-) salts exhibit plastic crystal behavior.     

Physicochemical properties of imidazolium-derived ionic liquids with different C-2 substitutions

Five room temperature ionic liquids based on C-2 substituted imidazolium cations and bis(trifluoromethanesulfonyl)imide (TFSI) anions were synthesized and their physicochemical properties: thermal property, density, viscosity, ionic conductivity, self-diffusion coefficients, and electrochemical stability, were systematically investigated. The temperature dependence of both viscosity and ionic conductivities of these ionic liquids can be described by the Vogel-Fulcher-Tamman (VFT) equation. Compared with the reference, 1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, the introduction of functional groups at the C-2 position generally increased the viscosity and lowered the ionic conductivity. The introduction of an ether group (-CH(2)OCH(2)CH(2)CH(2)CH(3)) at the C-2 position not only enhanced the reduction stability of the ionic liquids but also exhibited the lowest solid electrolyte interfacial resistance (R(SEI)). In contrast, the introduction of a cyano group (-CN) at the C-2 position not only decreased the reduction stability but also adversely increased the SEI resistance. The effect of the C-2 substitution on the reduction stability was explained by the change in the energy level of the lowest unoccupied molecular orbital. The self-diffusion coefficients (D) of each ion were measured by pulsed field gradient nuclear magnetic resonance (PFG-NMR). The lithium transference number (t(Li)) of 0.5 M LiTFSI/IL solutions calculated from the self-diffusion coefficients was in the range of 0.04 to 0.09.     

New ionic liquids with tris(perfluoroalkyl)trifluorophosphate (FAP) anions

The synthesis of new ionic liquids with tris(perfluoroalkyl)trifluorophosphate (FAP) anions is described. The physico-chemical properties (conductivity, viscosity, electrochemical and thermal stability) of this new generation of ionic liquids (molten salts) are discussed. FAP-ionic liquids show an excellent hydrolytic stability, low viscosity and high electrochemical and thermal stability that makes them attractive for use in electrochemical devices and as a new media for application in modern technologies and chemical synthesis.     

Electrical conductivity of lithium chloride solutions in the system isopropyl alcohol-water

Electrical conductivity of lithium chloride solutions in the system isopropyl alcohol-water in the temperature range 290–323 K was studied. The dependences of the specific and molar electrical conductivity of the solutions on the concentration of water and lithium chloride were determined.     

Electrochemical properties of composition solid electrolytes LiClO<Subscript>4</Subscript>-MgO

Composition solid electrolytes (1 ? x)LiClO₄-xMgO are synthesized and their physicochemical properties are studied. According to the data of differential scanning calorimetry, for sufficiently high oxide concentrations, all lithium perchlorate is present in the composite in the amorphous state. Impedance spectroscopic studies demonstrate that the conductivity of composites passes through a maximum at x = 0.8?0.9, reaching ～10^?2 S/cm at 200°C. Based on voltammetric characteristics, it is shown that the voltage of electrochemical decomposition of composites in vacuum does not exceed 3.5–4.0 V, decreasing to 1.8–2.0 V in humid atmosphere. The conductivity of studied composites in vacuum may apparently be attributed to lithium ions, and these solid electrolytes can be used in solid-state electrochemical lithium cells.     

Composite gel membranes: a new class of improved polymer electrolytes for lithium batteries

Novel composite, gel-type polymer electrolytes have been prepared by dispersing selected ceramic powders into a matrix formed by a lithium salt solution contained in a poly(acrylonitrile) (PAN) network. The electrochemical characterization demonstrates that these new types of composite gel electrolytes have high ionic conductivity, wide electrochemical stability and, particularly, high chemical integrity (no liquid leakage) even at temperatures above ambient. These unique properties make the composite gel membranes particularly suitable as electrolyte separators in lithium ion polymer batteries.     

Studies on the melts of alkali metal acetates

The density, viscosity, and electrical conductivity of alkali metal acetates were measured over the temperature interval between melting and decomposition. The apparent activation energies of the equivalent conductivities and viscosities were calculated. It has been concluded from the results that alkali metal acetates, similarly to alkali metal benzenesulphonates studied earlier, exhibit properties quite unlike those of alkali metal halides. In the dependence of equivalent conductivity on the nature of the cation, the anomalous behaviour of lithium salts appears to be due to association prevailing in the melt phase.     

The Effect of Strong Electrolytes on Aqueous Solutions of Sodium Salts of Native and Sulfonated Humic Acids

Solutions of sodium salts of native and sulfonated humic acids are studied as to their stability with respect to strong electrolytes. The parameters proposed for determining the physicochemical properties of humate solutions include not only their stability with respect to salts of alkaline-earth metals (coagulation thresholds) but also the sensitivity of these compounds to the action of HCl (humic acid formation thresholds) and KCl (salting-out thresholds).     

Synthesis and electrochemistry of polymer based electrolytes for lithium batteries

An overview is presented on the development of improved polymer based electrolytes during the past years. The emphasis lies on new approaches regarding chemical concepts that achieve a higher total conductivity and lithium transference number as well as an increased electrochemical, mechanical and thermal stability. With respect to the polymer chemistry, the focus is laid on siloxane and phosphazene derived systems. Topics are the chemical modification of the polymeric, cyclic and low molecular derivates of these systems, the formation of stable membranes from these by suitable cross-linking strategies and an extensive electrochemical characterization in corresponding lithium cells. Recent trends towards composite and hybrid materials are illustrated with examples and newly developed hybrid electrolytes. A particular chance for improvements comes from the design and use of stable small molecular additives in combination with optimized and electrochemically stable polymer networks. Special compounds are introduced which may act themselves as novel solvents with increased electrochemical stabilities. The relevance of chosen lithium salts for polymer electrolytes is discussed, too, and a new family of pyrazolide anions is introduced. In all cases, the electrochemical performance has been characterized by standard experimental techniques.     

Electrochemical recognition of charged species using quaternary ammonium binaphthyl salts.

The effects of ionic analytes on the electrochemical properties of quaternary ammonium binaphthyl salts are described in this work. The stability of the binaphthyl radicals and hence the reversibility of the electrochemical response are discussed in terms of molecular structure. The ability of azacrown derivatised binaphthyl salts to act as amperometric receptors is ascribed to the strain imparted in the cyclic ammonium ring when Li+ ions complex with them. It is also shown that the redox properties of quaternary ammonium binaphthyl salts are pH dependent in aqueous solutions, but that reversible redox properties can be observed in extremely basic solutions. The effect of anions binding to the quaternary ammonium cation can be seen in the redox properties of the binaphthyl moiety and the use of a chiral binding site for enantiomeric recognition is also demonstrated.     

梳形聚醚全固态聚合物电解质的电导率研究

应用阳离子开环聚合反应合成含二缩三乙二醇单甲醚侧链的梳形聚醚POE,并与高氯酸锂复配制成聚合物电解质.交流阻抗测试表明,当POE电解质内的氧锂比(O/L i)为20时,其电导率最高,室温下为10-4.43S/cm,80℃时则达到10-3.44S/cm.用DSC和XPS分别表征了链段运动能力和锂盐在POE中的溶解状态对电导率的影响.     

PEO-LiClO4-ZSM5复合聚合物电解质 I. 电化学研究

首次以“择形”分子筛ZSM5为填料, 通过溶液浇铸法制得PEO-LiClO₄-ZSM5全固态复合聚合物电解质(CPE)膜. 交流阻抗实验表明ZSM5的引入可以显著地提高CPE的离子电导率. 利用交流阻抗-稳态电流相结合的方法对CPE的锂离子迁移数进行了测定, 结果表明掺入ZSM5后锂离子迁移数明显升高. ZSM5的含量为10%时, CPE同时具有最高离子电导率1.4×10^－5 S•cm^－1(25 ℃)和最大锂离子迁移数0.353. PEO-LiClO₄-ZSM5/Li电极界面稳定性实验表明PEO-LiClO₄-ZSM5复合聚合物电解质在全固态锂离子电池领域具有良好的应用前景.     

The electrodeposition of magnesium using solutions of organomagnesium halides,amidomagnesium halides and magnesium organoborates

The electrochemical behaviour of three groups of electrolyte systems having the ability of electrochemical magnesium deposition, were investigated against the background of galvanotechnical or battery application. Solutions of organomagnesium halides, amidomagnesium halides and magnesium organoborates dissolved in tetrahydrofuran were characterized in terms of conductivity, reversibility of the magnesium deposition process and stability of the electrolytes versus irreversible oxidation. Furthermore the open circuit potential of a magnesium electrode in contact with these electrolytes was measured versus a Ag/Ag⁺ reference electrode. A high reoxidation efficiency was found for magnesium electrodeposited from solutions of organomagnesium halides and amidomagnesium halides. The solutions of magnesium organoborates were superior in terms of electrical conductivity and oxidation stability, the process of magnesium electrodeposition and reoxidation, however turned out to be poor.     

Novel Cyclic Sulfonium‐Based Ionic Liquids: Synthesis,Characterization, and Physicochemical Properties

A new series of ionic liquids composed of three cyclic sulfonium cations and four anions has been synthesized and characterized. Their physicochemical properties, including their spectroscopic characteristics, ion cluster behavior, surface properties, phase transitions, thermal stability, density, viscosity, refractive index, tribological properties, ion conductivity, and electrochemical window have been comprehensively studied. Eight of these salts are liquids at room temperature, at which some salts based on [NO₃]^? and [NTf₂]^? ions exhibit organic plastic crystal behaviors, and all the saccharin‐based salts display relatively high refractive indices (1.442–1.594). In addition, some ionic liquids with the [NTf₂]^? ion exhibit peculiar spectroscopic characteristics in FTIR and UV/Vis regions, whilst those salts based on the [DCA]^? ion show lower viscosities (34.2–62.6 mPa s at 20 °C) and much higher conductivities (7.6–17.6 mS cm^?1 at 20 °C) than most traditional 1,3‐dialkylimidazolium salts.