Ionic conductivity in the crystalline polymer electrolytes PEO6:LiXF6, X = P,As, Sb

Ionically conducting polymers (salts dissolved in a polymer matrix) are of great interest because they uniquely exhibit ionic conductivity in a soft but solid membrane. As such, they are critical to the development of devices such as all-solid-state lithium batteries. The established view of ionic conductivity in polymer electrolytes is that this occurs in amorphous materials above their glass transition temperature and that crystalline polymer electrolytes are insulators. In contrast, we show that three crystalline polymer electrolytes, poly(ethylene oxide)(6):LiXF(6), X = P, As, Sb, not only conduct but do so better than the analogous amorphous phases! It is also shown that the conductivities of all three 6:1 complexes are similar, consistent with the dimension of the bottlenecks to conduction derived from their crystal structures. An increase in ionic conductivity with reduction of molecular weight of the crystalline polymer electrolyte (from 2000 to 1000) is reported and shown to relate to the increase in crystallite size on reducing molecular weight.     

Ionic conductivity in crystalline–amorphous polymer electrolytes – P(EO)6:LiX phases

Recent reports have indicated higher ionic conductivities in crystalline polymer electrolytes consisting of isostructural P(EO)₆:LiX (X=PF₆, AsF₆, SbF₆) phases relative to the analogous amorphous materials. These reports challenge the conventional wisdom in polymer electrolyte research that amorphous electrolytes are much more conductive than crystalline ones. The higher conductivity in the crystalline materials was attributed to the structures in which Li⁺ cations are located within PEO cylinders uncoordinated by the anions. The conductivity and crystallinity of P(EO)_n–LiClO₄ (EO/Li=6 and 10) electrolytes have been examined here. In contrast to the recent reports, much lower conductivities are found for the isostructural P(EO)₆:LiClO₄ crystalline electrolyte relative to the same fully amorphous electrolyte.     

含硅氢键聚二硅氧烷/聚醚共混聚合物电解质 II. PSEMH对PEO结晶性能及离子电导率的影响

通过Raman,DSC和XRD等方法对PEO-PSEMH-LiClO4全固态共混聚合物电解质进行了研究,结果表明PSEMH能够显著地降低PEO-LiClO4电解质体系的PEO的结晶性和玻璃化转变温度,同时PSEMH分子的二硅醚链节中氧原子与Li+间具有配位作用,从而大幅提高x%PEO-y%PSEMH-LiClO4电解质在低温区的离子电导率。而当PSEMH交联硫化之后,虽然降低了PEO的结晶度和Tg,但是由于PSEMH的交联网络限制了聚合物链段的运动性,使得电解质的离子电导率在低温区高于100%PEO-LiClO4(约为12倍),而在高温区则低于100%PEO-LiClO4,充分证明了PSEMH对电解质的离子电导率的具有显著的贡献作用。     

Safety-enhanced Polymer Electrolytes with High Ambient-temperature Lithium-ion Conductivity Based on ABA Triblock Copolymers

Liquid electrolytes used in lithium-ion batteries suffer from leakage,flammability,and lithium dendrites,making polymer electrolyte a potential alternative.Herein,a series of ABA triblock copolymers(ABA-x)containing a mesogen-jacketed liquid crystalline polymer(MJLCP)with a polynorbornene backbone as segment A and a second polynorbornene-based polymer having poly(ethylene oxide)(PEO)side chains as segment B were synthesized through tandem ring-opening metathesis polymerizations.The block copolymers can self-assemble into ordered morphologies at 200℃.After doping of lithium salts and ionic liquid(IL),ABA-x self-assembles into cylindrical structures.The MJLCP segments with a high glass transition temperature and a stable liquid crystalline phase serve as physical crosslinking points,which significantly improve the mechanical performance of the polymer electrolytes.The ionic conductivity of ABA-x/lithium salt/IL is as high as 10-3 S·cm-1 at ambient temperature owing to the high IL uptake and the continuous phase of conducting PEO domains.The relationship between ionic conductivity and temperature fits the Vogel-Tamman-Fulcher(VTF)equation.In addition,the electrolyte films are flame retardant owing to the addition of IL.The polymer electrolytes with good safety and high ambient-temperature ionic conductivity developed in this work are potentially useful in solid lithium-ion batteries.     

Lithium environment in dilute poly(ethylene oxide)/lithium triflate polymer electrolyte from REDOR NMR spectroscopy

The role of the lithium ion environment is of fundamental interest regarding transport and conductivity in lithium polymer electrolytes. X-ray crystallography has been used to characterize the lithium environment in completely crystalline poly(ethylene oxide) (PEO) electrolytes, but this approach cannot be used with dilute PEO electrolytes. Here, using solid-state NMR data collected with the rotational-echo double-resonance 13C[7Li] (REDOR) pulse sequence, we have been able to characterize the crystalline microdomains of a PEO-lithium triflate sample with an oxygen/lithium ratio of 20:1. Our data clearly demonstrates that the lithium crystalline microdomains are nearly identical to those of a completely crystalline 3:1 sample, for which the crystal structure is known.     

高锂离子电导的有机-无机复合电解质的渗流结构设计

固态聚合物电解质被认为是解决传统液态锂金属电池安全隐患和循环性能的关键材料,但仍然存在离子电导率低,界面兼容性差等问题。近年来,基于无机填料与聚合物电解质的高锂离子电导的有机-无机复合电解质备受关注。根据渗流理论,有机-无机界面被认为是复合电解质离子电导率改善的主要原因。因此,设计与优化有机-无机渗流界面对提高复合电解质离子电导率具有重要意义。本文从渗流结构的设计出发,综述了不同维度结构的无机填料用于高锂离子电导的有机-无机复合电解质的研究进展,并对比分析了不同渗流结构的优缺点。基于上述评述,展望了有机-无机复合电解质的未来发展趋势和方向。     

红外光谱研究PEO基离子液体聚合物电解质

以聚氧化乙烯(PEO)为聚合物基体, 双三氟甲基磺酸亚酰胺锂(LiTFSI)为锂盐, 加入不同量的离子液体(BMIMPF₆)为增塑剂, 制备离子液体聚合物电解质. 运用发射FTIR光谱技术实时监测所制备聚合物电解质的结构随温度的变化. 结合FTIR透射光谱\, SEM和XRD的研究结果分析了离子液体对离子电导率的影响, 并初步提出离子导电增强机制.     

Conductivity behaviour of proton conducting polymer gel electrolytes with PVdF-HFP

Electrical conductivity of polymer gel electrolytes containing different hydroxy substituted benzoic acids and polyvinylidenefluoride-hexafluoropropylene (PVdF-HFP) has been studied. The conductivity of solution and gel electrolytes shows ortho effect and has been found to depend upon the acidity constant of the acid used and varies as σ (ortho-) > σ (meta-) > σ (para-). The addition of PVdF-HFP to solution electrolytes results in an increase in conductivity and the conductivity of gel electrolytes has been found to be higher than that of the corresponding liquid electrolytes for all the three acids studied i.e. σ (gel) >σ (liquid). The increase in conductivity with polymer addition has also been found to depend upon the acid concentration.     

共聚型氯醇橡胶锂离子聚合物电解质的制备和性能

以共聚型氯醇橡胶(ECO)为基体, 通过在基体中溶解不同浓度的LiCF₃SO₃制备了一系列聚合物电解质. 利用差示扫描量热技术(DSC)研究了该体系锂盐浓度对聚合物电解质玻璃化转变温度的影响, 用傅里叶变换红外光谱(FTIR)研究了体系内锂盐与聚合物基体的相互作用. 结果表明, 在相同锂盐浓度下, ECO基聚合物电解质的室温离子电导率比传统的聚环氧乙烷(PEO)基聚合物电解质提高了2个数量级, 并且体系电导率在升降温循环测试中没有弛豫现象产生. 这是由于ECO基体的非结晶性所致.     

Structure of poly(vinylidene fluoride) gel electrolytes

Polymer gel electrolytes have three constituents: polymer, salt and solvent. This paper gives structural information on polymer gel electrolytes made from poly(vinylidene fluoride), lithium triflate and tetraglyme. These electrolytes exhibit a room-temperature ionic conductivity in the region of 10⁻³ S cm⁻¹ while maintaining sufficient mechanical rigidity to form self-supporting films (having elastic moduli in the region of 100 kPa). Differential scanning calorimetry and dynamic mechanical analysis have been used to show that the majority of the network junctions of the gel are crystalline in nature. Wide angle X-ray diffraction has revealed that when no salt is included in the gel, these crystal junctions are almost an order of magnitude larger in their lateral dimensions than when salt is present. The salt is thought to nucleate crystallisation. The modulus is significantly reduced by inclusion of salt; however, DSC suggests that apparent crystallinity is only slightly reduced by the presence of salt. This discrepancy is attributed to either the uncertainty in the heat of fusion of PVDF, or to the formation of small crystalline particles that are not incorporated in the network junctions. Gels with polymer concentrations between 15 and 40% (by weight) maintain their mechanical rigidity up to temperatures around 100 °C. However, once melted, the gel structure only reforms at much lower temperatures. The variation of ionic conductivity of salted gels with temperature shows no such hysteresis, and it is concluded that the ionic conductivity is independent of the mechanical state of the gel.     

Distinct difference in ionic transport behavior in polymer electrolytes depending on the matrix polymers and incorporated salts

Two different electrolyte salts, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and a room temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMITFSI), were incorporated into network polymers to obtain ion-conductive polymer electrolytes. Network polymers of poly(ethylene oxide-co-propylene oxide) (P(EO/PO)) and poly(methyl methacrylate) (PMMA) were chosen as matrixes for LiTFSI and EMITFSI, respectively. Both of the polymer electrolytes were single-phase materials and were completely amorphous. Ionic conductivity of the polymer electrolytes was measured over a wide temperature range, with the lowest temperatures close to or below the glass transition temperatures (Tg). The Arrhenius plots of the conductivity for both of the systems exhibited positively curved profiles and could be well fit to the Vogel-Tamman-Fulcher (VTF) equation. The conductivity of the PMMA/EMITFSI electrolytes was higher at most by 3 orders of magnitude than that of the LiTFSI/P(EO/ PO) electrolytes at ambient temperature. When the ideal glass transition temperature, T0 (one of the VTF fitting parameters), was compared with the Tg, a difference in the ionic conduction was apparent in these systems. In the P(EO/PO)/LiTFSI electrolytes, the T0 and Tg increased in parallel with salt concentration and the T0 was lower than the Tg by ca. 50 degrees C. On the contrary, the difference between the T0 and the Tg increased with increasing content of PMMA in the PMMA/EMITFSI electrolytes, with the observed difference in the concentration range studied reaching up to ca. 100 degrees C. The conductivity at the Tg, sigma(Tg), for the LiTFSI/P(EO/PO) electrolytes was on the order of 10(-14-)10(-13) S cm(-1) and increased with increasing salt concentration, whereas that for the PMMA/EMITFSI polymer electrolytes reached 10(-7) S cm(-1) when the concentration of PMMA was high. The ion transport mechanism was discussed in terms of the concepts of coupling/decoupling and strong/fragile for the two different polymer electrolytes.     

On the way to high-conductivity single lithium-ion conductors

Solid electrolytes can potentially address three key limitations of the organic electrolytes used in today’s lithium-ion batteries, namely, their flammability, limited electrochemical stability and low cationic transference number. The pioneering works of Wright and Armand, suggesting the use of solid poly(ethylene oxide)-based polymer electrolytes (PE) for lithium batteries, paved the way to the development of solid-state batteries based on PEs. Yet, low cationic mobility–low Li⁺ transference number in polymer materials coupled with sufficiently high room-temperature conductivity remains inaccessible. The current strategies employed for the production of single-ion polymer conductors include designing new lithium salts, bonding of anions with the main polyether chain or incorporating them into the side chains of comb-branched polymers, plasticizing, adding inorganic fillers and anion receptors. Glass and crystalline superionic solids are classical single-ion-conducting electrolytes. However, because of grain boundaries and poor electrode/electrolyte interfacial contacts, achieving electrochemical performance in solid-state batteries comprising polycrystalline inorganic electrolytes, comparable to the existing batteries with liquid electrolytes, is particularly challenging. Quasi-elastic polymer-in-ceramic electrolytes provide good alternatives to the traditional lithium-ion-battery electrolytes and are believed to be the subject of extensive current research. This review provides an account of the advances over the past decade in the development of single-ion-conducting electrolytes and offers some directions and references that may be useful for further investigations.     

PEO基纳米复合聚合物电解质电化学性质的研究

以PEO8 LiClO4作母体,纳米SiO2为填料,制成PEO8 LiClO4 SiO2(x%)系列复合聚合物电解质,测定这该电解质的电导率、锂离子迁移数和电化学稳定窗口,并对其晶态结构作差热分析表征.结果表明,纳米SiO2的引入,显著提高了电解质的电导率,在22℃时达到4.3×10-5S·cm-1.此外,还探讨了填料对复合聚合物电解质电导率提高的影响机理.     

High ionic conductivity of all-solid polymer electrolytes based on polyorganophosphazenes

A series of all-solid polymer electrolytes were prepared by cross-linking new designed poly(organophosphazene) macromonomers. The ionic conductivities of these all-solid, dimensional steady polymer electrolytes were reported. The temperature dependence of ionic conductivity of the all-solid polymer electrolytes suggested that the ionic transport is correlated with the segmental motion of the polymer. The relationship between lithium salts content and ionic conductivity was discussed and investigated by Infrared spectrum. Furthermore, the polarity of the host materials was thought to be a key to the ionic conductivity of polymer electrolyte. The all-solid polymer electrolytes based on these poly(organophosphazenes) showed ionic conductivity of 10⁻⁴ S cm⁻¹ at room temperature.     

聚合物单阳离子导体的制备—羧酸型梳状单离子导体

本文报道一种制备聚合物单阳离子导体的新方法。马来酸酐－醋酸乙烯酯及马来酸酐－苯乙烯共聚物以聚乙二醇单甲醚醇解，使酸酐环打开而得到带有聚乙二醇侧链的羧酸型梳状聚合物，其锂盐在加入适当增塑剂成膜后，可作为聚合物单阳离子导体，其结构以非晶态为主，具有较低的玻璃化转变温度及较好的热稳定性，增塑后的室温电导率最高可达１０＾－６Ｓ／ｃｍ。此外还研究了聚合物结构、阳离子半径、增塑剂、温度及外加额率等因素对电导率     

Highly conductive oriented PEO-based polymer electrolytes

This contribution presents an overview of the study of the effect of stretching on semicrystalline and amorphous complexes of poly(ethylene oxide) (PEO) with different salts, such as lithium iodide, lithium trifluoromethane-sulfonate, lithium hexafluoroarsenate, lithium bis(oxalato)borate and lithium trifluoromethanesulfonimide. In spite of the conventional belief that ion transport in polymer electrolytes (PE) is mediated primarily by polymer segmental motion, we suggest that ion transport occurs preferentially along the PEO helical axis, at least in the crystalline phase. It was found that the more amorphous the PE, the less its lengthwise conductivity is influenced by stretching. It is suggested that the rate-determining step of ion conduction in semicrystalline LiX:P(EO)₂₀, polymer electrolytes below the melting point (T_m) is “interchain” hopping.     

原位聚合制备的离子液体/聚合物电解质的研究

采用原位聚合制备出新型的BMIPF6/PMMA聚合物电解质透明弹性膜. 研究结果表明, BMIPF6/PMMA聚合物电解质体系在305 ℃时仍具有较好的热稳定性, 其安全性能优于含有机溶剂的传统非水电解质体系. 随着离子液体含量的增加, 其玻璃化转变温度逐渐减小, 离子电导率升高; 且离子电导率与温度的关系服从VTF方程. 其中, 当BMIPF6的质量分数为50%时, 该聚合物电解质的室温离子电导率高达0.15 mS/cm.     

Molecular dynamics simulation of polymer electrolytes based on poly(ethylene oxide) and ionic liquids. II. Dynamical properties

Dynamical properties of polymer electrolytes based on poly(ethylene oxide) (PEO) and ionic liquids of 1-alkyl-3-methylimidazolium cations were calculated by molecular dynamics simulations with previously proposed models [L. T. Costa and M. C. Ribeiro, J. Chem. Phys. 124, 184902 (2006)]. The effect of changing the ionic liquid concentration, temperature, and the 1-alkyl-chain lengths, [1,3-dimethylimidazolium]PF(6) and [1-butyl-3-methylimidazolium]PF(6) ([dmim]PF(6) and [bmim]PF(6)), was investigated. Cation diffusion coefficient is higher than those of anion and oxygen atoms of PEO chains. Ionic mobility in PEO[bmim]PF(6) is higher than in PEO[dmim]PF(6), so that the ionic conductivity kappa of the former is approximately ten times larger than the latter. The ratio between kappa and its estimate from the Nernst-Einstein equation kappa/kappa(NE), which is inversely proportional to the strength of ion pairs, is higher in ionic liquid polymer electrolytes than in polymer electrolytes based on inorganic salts with Li(+) cations. Calculated time correlation functions corroborate previous evidence from the analysis of equilibrium structure that the ion pairs in ionic liquid polymer electrolytes are relatively weak. Structural relaxation at distinct spatial scales is revealed by the calculation of the intermediate scattering function at different wavevectors. These data are reproduced with stretched exponential functions, so that temperature and wavevector dependences of best fit parameters can be compared with corresponding results for polymer electrolytes containing simpler ions.     

Ionic liquids to the rescue? Overcoming the ionic conductivity limitations of polymer electrolytes

Polymer electrolytes – solid polymeric membranes with dissolved salts – are being intensively studied for use in all-solid-state lithium-metal-polymer (LMP) batteries to power consumer electronic devices. The low ionic conductivity at room temperature of existing polymer electrolytes, however, has seriously hindered the development of such batteries for many applications. The incorporation of salts molten at room temperature (room temperature ionic liquids or RTILs) into polymer electrolytes may be the necessary solution to overcoming the inherent ionic conductivity limitations of ‘dry’ polymer electrolytes.     

Superionic conductivity in lithium-rich anti-perovskites

Lithium ion batteries have shown great promise in electrical energy storage with enhanced energy density, power capacity, charge-discharge rates, and cycling lifetimes. However common fluid electrolytes consisting of lithium salts dissolved in solvents are toxic, corrosive, or flammable. Solid electrolytes with superionic conductivity can avoid those shortcomings and work with a metallic lithium anode, thereby allowing much higher energy densities. Here we present a novel class of solid electrolytes with three-dimensional conducting pathways based on lithium-rich anti-perovskites (LiRAP) with ionic conductivity of σ > 10(-3) S/cm at room temperature and activation energy of 0.2-0.3 eV. As temperature approaches the melting point, the ionic conductivity of the anti-perovskites increases to advanced superionic conductivity of σ > 10(-2) S/cm and beyond. The new crystalline materials can be readily manipulated via chemical, electronic, and structural means to boost ionic transport and serve as high-performance solid electrolytes for superionic Li(+) conduction in electrochemistry applications.