Performance of acrylate-poly(ethylene oxide) polymer electrolytes in lithium batteries

Results for the performance of lithium/Mn0₂ batteries containing solid polymer electrolytes based on poly(ethylene oxide) blends with some acrylic derivatives are presented. The ionic conductivities of the electrolytes are promising for battery application. It was found, however, that interfacial phenomena impair the battery efficiency. Impedance spectroscopy shows resistive limitations at the anode interface of the batteries, caused either by formation of an electrically distinguishable resistive layer or by chemical interaction between the polymer and lithium, influencing, most probably, the kinetics of the lithium oxidation reaction.     

Poly(vinylidenefluoride)-hexafluoropropylene–methyl N-methylpyrrolidinium-N-acetate trifluoromethanesulfonylimide–lithium trifluoromethanesulfonylimide gel electrolytes

New polymer-ionic liquid-lithium salt gel electrolytes (PILGEs) were prepared using poly(vinylidenefluoride)-hexafluoropropylene copolymer (PVdF(HFP)), methyl N-methylpyrrolidinium-N-acetate trifluoromethanesulfonimide ([MMEPyr][TFSI]), and lithium trifluoromethanesulfonylimide (LiTFSI) in order to investigate the effects of ionic liquids containing an ester group on the electrochemical properties of polymer gel electrolytes. Free standing ionic gels consisting of PVdF(HFP), [MMEPyr][TFSI], and LiTFSI were prepared in a range of weight ratio of polymer/[MMEPyr][TFSI]/LiTFSI = 1/2/0.1 ～ 1. Ionic conductivities for the prepared PILGEs were measured with changing temperature and weight ratio of LiTFSI and the obtained values were found to be reasonable (10^?4 S cm^?1) over the operating temperatures.     

Explosivity of lithium perchlorate in gel polymer electrolytes

In this article, we report the synthesis and characterization of novel methacrylate‐based polymer electrolyte membranes for lithium batteries. The safety requirement is a top priority for rechargeable Li‐ion batteries, and especially these are used in hybrid electric vehicles and power tools. After several serious fire accidents, the safety must be submitted to the intensive investigation and this danger must be minimalized. This article describes the differences between lithium perchlorate and tetrafluoroborate as conductive component in methacrylate‐based gel electrolytes. The gel polymer electrolytes were prepared by UV irradiation process, which is well known for being easy, low cost, and fast. POLYM. COMPOS., 34:1969–1973, 2013. © 2013 Society of Plastics Engineers     

离子液体电解质在锂二次电池中的应用

锂二次电池作为动力电池,被寄予厚望。但锂二次电池面临的安全隐患也是不容忽视的,是当前亟需解决的问题,而这与电解质的性质有着紧密的联系。离子液体由于具有较宽电化学窗口、良好的导电性、高热稳定性、几乎无挥发及不燃烧等优良的特性,正在作为一种新型绿色替代溶剂被电化学领域所关注。离子液体的不燃烧特性,对于替代传统有机电解质具有十分重要的意义。本文阐述了新型溶剂“离子液体”作为电解质在锂二次电池中的应用,其中重点阐述了在碳、硅、钛酸锂(Li₄Ti₅O₁₂)、磷酸亚铁锂(LiFePO₄)、钴酸锂LiCoO₂、镍锰酸锂(LiNi_xMn_yO_z),镍钴锰锂(LiNi_xCo_yMn_zO_w)及在锂硫(Li-S)电池中的应用。     

Glyme-based nonaqueous electrolytes for rechargeable lithium cells

Poly(ethylene glycol)dimethyl ethers [(CH₃O(CH₂CH₂O)_nCH₃, n = 1, 2, 3, and 4)] are generally known as “glymes”. This study examines the conductivity, lithium ion solvation state and charge-discharge cycling efficiency of lithium metal anodes in glyme-based electrolytes for rechargeable lithium cells. 1 M (M: mol l⁻¹) LiPF₆ was used as the solute. The properties of the glymes were investigated by using a ternary mixed solvent consisting of n-glyme, ethylene carbonate (EC) and methylethylcarbonate (MEC). This was because the solubility of LiPF₆ is far less than 1 M in an n-glyme single solvent. The glyme solutions exhibited higher conductivity and higher lithium cycling efficiency than EC/MEC. The conductivity tended to increase with decreases in ethylene oxide chain number (n) and solution viscosity. The decrease in the solution viscosity resulted from the change in the lithium ion solvation structure that occurred when a glyme was added to EC/MEC. The selective solvation of the glyme with respect to lithium ions was clearly demonstrated by -NMR measurements. The lithium cycling efficiency value depended on the charge-discharge current (I_ps). When n increased there was an increase in lithium cycling efficiency at a low I_ps and a decrease in the reduction potential of the glymes. When the conductivities including those at low temperature (below 0 °C), and charge-discharge cycling at a high current are taken into account, di- or tri-glyme is superior to the other glymes tested here.     

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.     

Ionic conduction in polyether-based lithium arylfluorosulfonimide ionic melt electrolytes

We report synthesis, characterization and ion transport in polyether-based ionic melt electrolytes consisting of Li salts of low-basicity anions covalently attached to polyether oligomers. Purity of the materials was investigated by HPLC analysis and electrospray ionization mass spectrometry. The highest ionic conductivity of 7.1 × 10⁻⁶ S/cm at 30 °C was obtained for the sample consisting of a lithium salt of an arylfluorosulfonimide anion attached to a polyether oligomer with an ethyleneoxide (EO) to lithium ratio of 12. The conductivity order of various ionic melts having different polyether chain lengths suggests that at higher EO:Li ratios the conductivity of the electrolytes at room temperature is determined in part by the amount of crystallization of the polyether portion of the ionic melt.     

High lithium conductivities in weakly-ionophilic low-dimensional block copolymer electrolytes

The structure of amphiphilic low-dimensional copolymer electrolytes I of similar overall composition but prepared by different synthetic procedures X and Y are described. I are copolymers of poly[2,5,8,11,14-pentaoxapentadecamethylene(5-alkyloxy-1,3-phenylene)] (CmO5) and poly[2,-oxatrimethylene(5-alkyloxy-1,3-phenylene)] (CmO1) where the alkyl side chains having m carbons are hexadecyl or mixed dodecyl/octadecyl (50/50). ¹H NMR shows that the copolymers have 50% (m = 16) or only 18 and 13% of CmO5 units and DSC indicates that the copolymers have ‘block’ sequencing of CmO1 and CmO5 segments. Molecular dynamics modelling indicates that in CmO5 Li⁺ and BF₄⁻ ions are separated by Li⁺ encapsulation in tetraethoxy segments but in ionophobic CmO1 units the salt is mostly present as neutral aggregates decoupled from the polymer. Conductivities of these microphase-separated mixtures with salt-bridge amphiphilic polyethers II and III of each system are similar. They have low temperature dependence over the range 20 °C to 110 °C at ∼10⁻³ S cm⁻¹. ⁷Li NMR linewidth measurements confirm high lithium mobilities at −20 °C. A conduction mechanism is proposed whereby Li⁺ hopping takes place along rows of decoupled aggregates (dimers/quadrupoles) within an essentially block copolymer structure. Subambient measurements to −10 °C gave a conductivity of 4 × 10⁻⁵ S cm⁻¹.     

锂离子电池电解质六氟磷酸锂市场分析

通过对未来5 a锂离子电池在动力电池、储能电池、数码电池市场的发展情况分析,预测锂离子电池生产的平均增长率将达到26%以上,到2025年对应锂离子电池电解液的需求量和六氟磷酸锂需求量将分别达到93.0万t和10.3万t。分析目前六氟磷酸锂产能情况和后期各生产企业扩产计划,预测六氟磷酸锂产能在2022年以前满足市场需求;若2025年以前各生产企业扩产到位,供需将会达到平衡,并且六氟磷酸锂价格趋于平稳,在原材料价格波动不大的情况下预计其价格在8.5万元/t左右。     

Charge-discharge characteristics of the lithium electrode in mixed ether electrolytes

Mixed ether solutions of 1,2-dialkoxyethanes with 1,3-dioxolane or tetrahydrofuran containing some lithium salts have been examined as electrolytes for ambient temperature, rechargeable lithium (Li) batteries. The electrolytic conductivity and the charge-discharge behaviour of the Li electrode were investigated in the alkoxyethane-based electrolytes. The solutions containing LiPF₆ showed high conductance. The polarization behavoiur and the charge-discharge efficiency of the Li electrode were markedly affected by the size of an alkoxy group of ether. The cycling efficiency also depended on the electrolytic salt and the blended co-solvent. The highest efficiency was observed in the mixed system of 1,2-dimethoxyethane-tetrahydrofuran containing LiPF₆.     

聚合物及离子液体电解质在锂二次电池中的应用

系统地介绍了锂离子二次电池电解质,特别是聚合物电解质及离子液体电解质的应用研究现状。开发具有高能量密度、稳定的充放电性能、循环寿命长、可塑性、高安全性与低成本的锂离子电池是当前的研究热点。离子液体具有较高的离子电导率、宽电化窗口,且无蒸汽压,而聚合物具有良好的机械加工性能。二者的结合将为锂离子电池电解质的研究提供了新的开发思路。     

Characteristics of the lithium electrode in organic and polymeric electrolytes

The characteristics of the lithium electrode were examined in an organic and a polymeric electrolyte of interest for the development of rechargeable batteries. Results obtained by frequency response analysis and by polarization curves, were used to identify charge-transfer resistance, double layer capacity and properties of passivation films.     

Review on composite polymer electrolytes for lithium batteries

This paper reviews the state of the art of composite polymer electrolytes (CPE) in view of their electrochemical and physical properties for the applications in lithium batteries. This review mainly encompasses on composite polymer electrolyte hosts namely poly(ethylene oxide) (PEO), poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride) (PVdF) studied so far. Also the ionic conductivity, transference number, compatibility and the cycling behavior of poly(vinylidene fluoride-hexafluoro propylene) (PVdF-HFP)-[AlO(OH)]_n-LiPF₆/LiClO₄ composite electrolytes have been studied and the results are discussed.     

Ternary and quaternary mixed electrolytes for lithium cells

This paper reports the influence of composition of mixed solvent electrolyte composition on the discharge capacity and charge–discharge cycle life of lithium metal/amorphous V2O5–P2O5 (95:5 in molar ratio) cells. The solvents used were ethylene carbonate (EC), propylene carbonate (PC), 2-methyltetrahydrofuran (2MeTHF) and THF. LiAsF6 was used as the solute. The electrolyte solutions examined here contain ternary and quaternary mixed systems. The purpose of this work is to obtain an electrolyte solution which realizes a higher rate capability and/or a longer cycle life than the previously studied EC:PC:2MeTHF (15:70:15) ternary mixed system. Of the electrolyte systems examined here, the EC:PC:2MeTHF (30:40:30 in volume) ternary mixed solvent system showed the best cell performance. In addition, a heating test was carried out on an AA- size lithium cell with EC:PC:2MeTHF (30:40:30) as a fundamental abuse test to ensure cell safety.     

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.     

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.     

New boron compounds as additives for lithium polymer electrolytes

A new class of difluoroalkoxyborane compounds ([R_nOBF₂]₂) containing oligooxyethylene groups of various molecular weight in the form of a methyl monoether (R_n = CH₃(OCH₂CH₂)_n, n = 1, 2, 3 and 7) has been obtained in the reaction of BF₃ etherate with appropriate glycols. ¹H, ¹¹B and ¹⁹F NMR spectral analysis of the derivatives obtained was carried out and the properties as Lewis acids of these derivatives have been compared with that of corresponding trialkoxyboranes and boron trifluoride in reaction with pyridine. The strength of the interaction of [R₂OBF₂]₂ with the differing in “hardness” anions of various lithium salts has been analyzed on the basis of NMR spectra. The [R_nOBF₂]₂ obtained were used as additives for polymer electrolytes containing PEO as polymer matrix and various lithium salts at an equimolar ratio of the boron compound to salt. The highest ionic conductivities, in the order 10⁻⁵ to 10⁻⁴ S cm⁻¹ at 20-70 °C, were achieved for systems containing LiI and LiN(CF₃SO₂)₂. The lithium transference number (t₊) values, determined by the electrochemical method by steady-state technique for LiF and LiCF₃SO₃ are in the 0.6-0.8 range.     

Single-ion conducting polymer-silicate nanocomposite electrolytes for lithium battery applications

Solid-state polymer-silicate nanocomposite electrolytes based on an amorphous polymer poly[(oxyethylene)₈ methacrylate], POEM, and lithium montmorillonite clay were fabricated and characterized to investigate the feasibility of their use as ‘salt-free’ electrolytes in lithium polymer batteries. X-ray scattering and transmission electron microscopy studies indicate the formation of an intercalated morphology in the nanocomposites due to favorable interactions between the polymer matrix and the clay. The morphology of the nanocomposite is intricately linked to the amount of silicate in the system. At low clay contents, dynamic rheological testing verifies that silicate incorporation enhances the mechanical properties of POEM, while impedance spectroscopy shows an improvement in electrical properties. With clay content ≥15 wt.%, mechanical properties are further improved but the formation of an apparent superlattice structure correlates with a loss in the electrical properties of the nanocomposite. The use of suitably modified clays in nanocomposites with high clay contents eliminates this superstructure formation, yielding materials with enhanced performance.