锂离子电池用（聚）离子液体电解质

锂离子电池已广泛应用于便携式电子设备和电动汽车等领域,然而商用锂离子电池中含有大量易燃的碳酸酯类有机溶剂,容易造成安全隐患。离子液体具有蒸汽压低、化学结构设计多样性、热稳定性及电化学稳定性优异等优点,可以用来代替易燃有机溶剂,在电化学储能领域具有广阔的应用前景。聚离子液体是一类聚合物重复单元上含有阴、阳离子的新型聚合物电解质材料,兼具离子液体和聚合物固态电解质不漏液、易于加工的优势。根据离子液体和聚离子液体化学结构的设计合成及其在锂离子电池中的应用形式,综述了近年来离子液体电解质的研究进展,并提出了离子液体电解质未来的应用挑战和发展方向。     

Anodic behavior of Al current collector in 1-alkyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl] amide ionic liquid electrolytes

The anodic behaviors of aluminum current collector for lithium ion batteries were investigated in a series of 1-alkyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl] amide room temperature ionic liquids (RTILs) and EC + DMC electrolytes. It was found that the aluminum corrosion, which occurred in EC + DMC electrolytes containing LiTFSI, was not observed in the RTIL electrolytes. Further research showed that a passive film with amide compounds as main components formed firmly on aluminum surface during the anodic polarization in the RTIL electrolytes, which inhabited the aluminum corrosion. In addition, the additives generally used in the batteries, such as ethylene carbonate, ethylene sulfite and vinyl carbonate, as well as temperature did not obviously affect the aluminum passive film, the oxidation of the RTILs increased at the elevated temperature, which only resulted in the corrosion potential of aluminum in the RTIL electrolytes shifted to more negative potential, a passive film still firmly formed on the aluminum surface to surpassed the further oxidation of the aluminum current collector. Those results lead to a potential for the practical use of LiTFSI salt in the room temperature ionic liquid electrolytes for lithium ion batteries.     

Electrochemical stability of bis(trifluoromethanesulfonyl)imide-based ionic liquids at elevated temperature as a solvent for a titanium oxide bronze electrode

Four different electrolytes are prepared by dissolving a Li salt in three different room-temperature ionic liquids (RTILs) and also in a conventional organic solvent. The cathodic (electrochemical reduction) stability of these electrolytes is compared at both ambient and elevated temperature by potential cycling on a TiO₂-B electrode. At room temperature, the stability of pyrrolidinium- and piperidinium-based RTILs is comparable with that of the carbonate-based organic solvent, which is in contrast to the severely decomposed imidazolium-based RTIL. At elevated temperature (120 °C), the imidazolium-based RTIL undergoes even more significant cathodic decomposition that results in the deposition of a resistive surface film and leads to eventual cell degradation. By contrast, the cathodic decomposition and concomitant film deposition are not serious with pyrrolidinium- and piperidinium-based RTILs even at this high-temperature, so that the TiO₂-B/Li cell operates with reasonably good cycle performance. The latter two RTILs appear to be promising solvents for lithium-ion batteries that are durable against occasional exposure to high-temperature.     

Effect of zwitterion on the lithium solid electrolyte interphase in ionic liquid electrolytes

An understanding of the solid electrolyte interphase (SEI) that forms on the lithium-metal surface is essential to the further development of rechargeable lithium-metal batteries. Currently, the formation of dendrites during cycling, which can lead to catastrophic failure of the cell, has mostly halted research on these power sources. The discovery of ionic liquids as electrolytes has rekindled the possibility of safe, rechargeable, lithium-metal batteries. The current limitation of ionic liquid electrolytes, however, is that when compared with conventional non-aqueous electrolytes the device rate capability is limited. Recently, we have shown that the addition of a zwitterion such as N-methyl-N-(butyl sulfonate) pyrrolidinium resulted in enhancement of the achievable current densities by 100%. It was also found that the resistance of the SEI layer in the presence of a zwitterion is 50% lower. In this study, a detailed chemical and electrochemical analysis of the SEI that forms in both the presence and absence of a zwitterion has been conducted. Clear differences in the chemical nature and also the thickness of the SEI are observed and these may account for the enhancement of operating current densities.     

Research progress of high safety flame retardant electrolytes for lithium-ion batteries

商品锂离子电池在机械冲击、热冲击和过充短路等滥用条件下易发生起火燃烧甚至爆炸。为了解决这一安全性问题,需要开发高安全性阻燃电解液取代传统易燃烧的碳酸酯电解液。本文综述了高安全性阻燃电解液的研究进展,首先介绍了燃烧机理、阻燃机理和阻燃测试方法,再阐述锂离子电池对阻燃电解液的性质要求,并对阻燃电解液进行分类探讨,包括阻燃添加剂、阻燃溶剂（共溶剂）、高浓度阻燃电解液、离子液体和阻燃型凝胶聚合物电解质。重点对这些高安全性阻燃电解液的配方、阻燃效果、适用的电池体系进行详细阐述。最后对高安全性阻燃电解液未来的研究方向进行展望。     

Recent progress in electrode materials for aqueous lithium-ion batteries

水系锂离子电池是以水溶液为电解质的二次电池,它克服了传统有机体系电池电解液昂贵,有毒,易燃,离子电导率低,制作成本高等缺点,成为继风能,太阳能后最具发展潜力的绿色能源之一.本文归纳了近年来国内外水系锂离子电池正负极材料的研究进展,介绍了各种电极材料存在的主要问题(如电极材料在电解液中的溶解,电解液中质子活性大导致电极材料发生副反应等)以及改性方法,并提出对电极材料进行修饰是水系锂离子电池未来的发展趋势.     

Research progress on lithium based Water-in-salt electrolytes

与传统的商用有机锂离子电池相比,水系锂离子电池具有高安全性、成本低、环境友好等优点,但由于水的热力学窗口较窄（1.23 V）,从而大大限制了其输出电压和能量密度。Water-in-salt电解液的提出将水溶液的电化学窗口拓宽到3.0 V以上,为实现新型高电压水系锂离子电池提供了有利前提保证。本综述意在介绍Water-in-salt电解液及其相关衍生体系以及其在锂离子电池、锂硫电池以及混合离子电池中的相关应用拓展。与此同时,对该新体系中所引出的新的基础科学问题,包括水系固态电解质界面（SEI）膜的生长机理及锂离子的传输机制做了简单归纳和总结。     

Lithium insertion in graphite from ternary ionic liquid-lithium salt electrolytes: I. Electrochemical characterization of the electrolytes

In this paper we report the results of chemical-physical investigation performed on ternary room temperature ionic liquid-lithium salt mixtures as electrolytes for lithium-ion battery systems. The ternary electrolytes were made by mixing N-methyl-N-propyl pyrrolidinium bis(fluorosulfonyl) imide (PYR₁₃FSI) and N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (PYR₁₄TFSI) ionic liquids with lithium hexafluorophosphate (LiPF₆) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The mixtures were developed based on preliminary results on the cyclability of graphite electrodes in the IL-LiX binary electrolytes. The results clearly show the beneficial synergic effect of the two ionic liquids on the electrochemical properties of the mixtures.     

Differential pulse effects of solid electrolyte interface formation for improving performance on high-power lithium ion battery

Solid electrolyte interface (SEI) formation is a key that utilizes to protect the structure of graphite anode and enhances the redox stability of lithium-ion batteries before entering the market. The effect of SEI formation applies a differential pulse (DP) and constant current (CC) charging on charge-discharge performance and cycling behavior into brand new commercial lithium ion batteries is investigated. The morphologies and electrochemical properties on the anode surface are also inspected by employing SEM and EDS. The electrochemical impedance spectra of the anode electrode in both charging protocols shows that the interfacial resistance on graphite anodes whose SEI layer formed by DP charging is smaller than that of CC charging. Moreover, the cycle life result shows that the DP charging SEI formation is more helpful in increasing the long-term stability and maintaining the capacity of batteries even under high power rate charge-discharge cycling. The DP charging method can provide a SEI layer with ameliorated properties to improve the performance of lithium ion batteries.     

Graft copolymer-based lithium-ion battery for high-temperature operation

The use of conventional lithium-ion batteries in high temperature applications (>50 °C) is currently inhibited by the high reactivity and volatility of liquid electrolytes. Solvent-free, solid-state polymer electrolytes allow for safe and stable operation of lithium-ion batteries, even at elevated temperatures. Recent advances in polymer synthesis have led to the development of novel materials that exhibit solid-like mechanical behavior while providing the ionic conductivities approaching that of liquid electrolytes. Here we report the successful charge and discharge cycling of a graft copolymer electrolyte (GCE)-based lithium-ion battery at temperatures up to 120 °C. The GCE consists of poly(oxyethylene) methacrylate-g-poly(dimethyl siloxane) (POEM-g-PDMS) doped with lithium triflate. Using electrochemical impedance spectroscopy (EIS), we analyze the temperature stability and cycling behavior of GCE-based lithium-ion batteries comprised of a LiFePO₄ cathode, a metallic lithium anode, and an electrolyte consisting of a 20-μm-thick layer of lithium triflate-doped POEM-g-PDMS. Our results demonstrate the great potential of GCE-based Li-ion batteries for high-temperature applications.     

单离子导体聚合物电解质研究进展

聚合物电解质能够避免传统液态电解液漏液的隐患,抑制锂枝晶的生长,提高电池的安全性能。单离子导体是一类锂离子迁移数接近1的聚合物电解质,能有效避免阴离子移动产生浓差极化,降低内部阻抗,从而提高锂电池的容量以及循环性能,成为近年来聚合物电解质的研究热点。本文综述了单离子导体聚合物电解质的研究进展,尤其关注离子电导率和锂离子迁移数较高的体系,并探讨了单离子导体聚合物电解质所面临的挑战以及发展前景。     

2-Cyanofuran—A novel vinylene electrolyte additive for PC-based electrolytes in lithium-ion batteries

In this contribution, we focus on propylene carbonate (PC)-based electrolytes for lithium-ion batteries. In order to avoid solvent co-intercalation into graphite the presence of a solid electrolyte interphase (SEI) is required. This film is formed due to a film-forming species, i.e. a film-forming electrolyte additive. In this contribution, we focus on a vinylene compound, 2-cyanofuran (2CF) which proves to perform well in propylene carbonate electrolytes. 2CF is investigated by in situ Fourier transform infrared (FTIR) spectroscopy in a specially developed IR cell. We conclude that the cathodic reduction of the vinylene groups (=via reduction of the double bond) in the electrolyte additive is the initiating, and thus an important step of the SEI formation process. The possibility of an electropolymerization reaction of the vinylene monomers in the used electrolytes is critically discussed on the basis of the obtained IR data.     

Flame-retardant properties of in situ sol-gel synthesized inorganic borosilicate/silicate polymer scaffold matrix comprising ionic liquid

This paper focuses on the superiority of organic-inorganic hybrid ion-gel electrolytes for lithium-ion batteries (LiBs) over commercial electrolytes, such as 1 M LiPF₆ in 1:1 ethylene carbonate (EC): dimethyl carbonate (DMC) {1 M LiPF₆-EC: DMC}, in terms of their flame susceptibility. These ion-gel electrolytes possess ionic liquid monomers, which are confined within the borosilicate or silicate matrices that are ideal for non-flammability. Naked flame tests confirm that the organic-inorganic hybrid electrolytes are less susceptible to flames, and these electrolytes do not suffer from a major loss in terms of weight. In addition, the hybrids are self-extinguishable. Therefore, these hybrids are only oxidized when subjected to a flame unlike other commercial electrolytes used in lithium-ion batteries. Supplementary analyses using differential scanning calorimetric studies reveal that the hybrids are glassy until the temperature reaches more than 100°C. The current results are consistent with previously published data on the organic-inorganic hybrids.     

Thermal stability and flammability of electrolytes for lithium-ion batteries

Safety is the key-feature of large-size lithium-ion batteries and thermal stability of the electrolytes is crucial. We investigated the thermal and flammability properties of mixed electrolytes based on the conventional ethylene carbonate-dimethyl carbonate (1:1 wt/wt)-1 M LiPF₆ and the hydrophobic ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (Pyr₁₄TFSI). The results of thermogravimetric analyses and flammability tests of mixed electrolytes of different compositions are reported and discussed. An important finding is that though the mixtures with high contents of ionic liquid are more difficult to ignite, they burn for a longer time, once they are ignited.     

Characterization of low-flammability electrolytes for lithium-ion batteries

In an effort to develop low-flammability electrolytes for a new generation of Li-ion batteries, we have evaluated physical and electrochemical properties of electrolytes with two novel phosphazene additives. We have studied performance quantities including conductivity, viscosity, flash point, and electrochemical window of electrolytes as well as formation of solid electrolyte interphase (SEI) films. In the course of study, the necessity for a simple method of SEI characterization was realized. Therefore, a new method and new criteria were developed and validated on 10 variations of electrolyte/electrode substrates. Based on the summation of determined physical and electrochemical properties of phosphazene-based electrolytes, one structure of phosphazene compound was found better than the other. This capability helps to direct our further synthetic work in phosphazene chemistry.     

Analysis of SEI formed with cyano-containing imidazolium-based ionic liquid electrolyte in lithium secondary batteries

Two kinds of cyano-containing imidazolium-based ionic liquid, 1-cyanopropyl-3-methylimidazolium-bis(trifluoromethanesulfonyl)imide (CpMI-TFSI) and 1-cyanomethyl-3-methylimidazolium-bis(trifluoromethanesulfonyl)imide (CmMI-TFSI), each of which contained 20 wt% dissolved LiTFSI, were used as electrolytes for lithium secondary batteries. Compared with 1-ethyl-3-methylimidazolium-bis(trifluoromethane-sulfonyl)imide (EMI-TFSI) electrolyte, a reversible lithium deposition/dissolution on a stainless-steel working electrode was observed during CV measurements in these cyano-containing electrolytes, which indicated that a passivation layer (solid electrolyte interphase, SEI) was formed during potential scanning. The morphology of the working electrode with each electrolyte system was studied by SEM. Different dentrite forms were found on the electrodes with each electrolyte. The SEI that formed in CpMI-TFSI electrolyte showed the best passivating effect, while the deposited film formed in EMI-TFSI electrolyte showed no passivating effect. The chemical characteristics of the deposited films on the working electrodes were compared by XPS measurements. A component with a cyano group was found in SEIs in CpMI-TFSI and CmMI-TFSI electrolytes. The introduction of a cyano functional group suppressed the decomposition of electrolyte and improved the cathodic stability of the imidazolium-based ionic liquid. The reduction reaction route of imidazolium-based ionic liquid was considered to be different depending on whether or not the molecular structure contained a cyano functional group.     

Research progress of solid electrolytes

商业化的锂离子电池大多采用有机液体作为电解质体系,有机液体电解质在电池的工作过程中,会发生泄漏、挥发、燃烧甚至爆炸,存在严重的安全隐患,研究高效、环保、安全的电解质是解决这一问题的主要途径。固体电解质取代传统的液体电解质,不仅可以在传输导锂的同时抑制锂枝晶的生长,而且具有高的机械强度,简化电池的制备工艺,降低电池的制造成本。由于具有以上的优点,固体电解质的研发不断引起人们的广泛关注。本文综述了硫化物固体电解质的研究进展,包括二元和三元硫化物固体电解质,同时讨论了掺杂改性或复合改性对其性能影响,并展望了硫化物固体电解质未来的发展方向。     

Research progress on electrolyte additives for high voltage lithium-ion batteries

普通锂离子电池在高电压下的氧化分解限制了高压锂离子电池的发展,为了解决这一问题,可以设计、合成新型的耐高压电解液;寻找合适的电解液添加剂,然而从经济效益考虑,发展合适的电解液添加剂来稳定电极/电解液界面更加受到研究者们的青睐。本文综述了最近几年在高压锂离子电池电解液添加剂方面的研究进展,并按照添加剂的种类将其分为6部分进行探讨：含硼类添加剂、有机磷类添加剂、碳酸酯类添加剂、含硫添加剂、离子液体添加剂及其它类型添加剂。分别对这些添加剂的作用机理、作用效果进行了阐述,展望了添加剂在高压锂离子电池中的发展前景及未来研究方向。     

Application of ionic liquids as an electrolyte additive on the electrochemical behavior of lead acid battery

Ionic liquids (ILs) belong to new branch of salts with unique properties which their applications have been increasing in electrochemical systems especially lithium-ion batteries. In the present work, for the first time, the effects of four ionic liquids as an electrolyte additive in battery's electrolyte were studied on the hydrogen and oxygen evolution overpotential and anodic layer formation on lead–antimony–tin grid alloy of lead acid battery. Cyclic and linear sweep voltammetric methods were used for this study in aqueous sulfuric acid solution. The morphology of grid surface after cyclic redox reaction was studied using scanning electron microscopy. The results show that most of added ionic liquids increase hydrogen overpotential and whereas they have no significant effect on oxygen overpotential. Furthermore ionic liquids increase antimony dissolution that might be related to interaction between Sb³⁺ and ionic liquids. Crystalline structure of PbSO₄ layer changed with presence of ionic liquids and larger PbSO₄ crystals were formed with some of them. These additives decrease the porosity of PbSO₄ perm selective membrane layer at the surface of electrode. Also cyclic voltammogram on carbon–PbO paste electrode shows that with the presence of ionic liquids, oxidation and reduction peak current intensively increased.