Dielectric relaxation and ionic transport in poly(ethylene carbonate)‐based electrolytes

To study the ion‐conductive and dielectric properties of polymer electrolytes based on poly(ethylene carbonate) (PEC) with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), the complex permittivity and conductivity were measured using broadband dielectric spectroscopy. The temperature dependence of the relaxation frequency and ionic conductivity for PEC‐LiTFSI electrolytes (1 – 200 mol%) indicates that the segmental motion of PEC chains decreases with the addition of just 1 mol% of Li salt and increases with increasing concentration above 10 mol%. According to the Walden rule for PEC‐based electrolytes, the value of deviation from the reference line increased, and the fragility and decoupling exponents decreased with increasing salt concentration. These results indicate that there are large numbers of ion pairs and aggregated ions, which imply low ionicity and reduced fragility in highly concentrated PEC‐based electrolytes. Copyright © 2016 John Wiley & Sons, Ltd.     

Conductive networked polymer gel electrolytes composed of poly(meth)acrylate,lithium salt,and ionic liquid

Self‐standing films of (meth)acrylate‐based polymer gel electrolytes with high ionic liquid content (80 wt %) were prepared by in situ thermally or photo induced radical copolymerization of mono‐functional and di‐functional (meth)acrylates in an ionic liquid in the presence/absence of a lithium salt. Their ionic conductivity, thermal property, mechanical property, and flammability were examined. 1‐Ethyl‐3‐methylimidazolium bis(trifluoromethanesulfonyl)imide (EMImTFSI) or 1‐ethyl‐3‐methylimidazolium bis(fluorosulfonyl)imide (EMImFSI) was used as the ionic liquid, and lithium bis(trifluoromethanesulfonyl)imide LiTFSI was used as the lithium salt. The obtained films were semitransparent and flexible with good to moderate thermal stability and mechanical strength with high ionic conductivity. The EMImFSI‐containing gel electrolytes showed higher ionic conductivity than the corresponding EMImTFSI‐containing gel electrolytes. The ionic conductivity in the acrylate‐based gel electrolytes was slightly increased by addition of lithium salt, while that in the corresponding methacrylate‐based electrolytes was decreased significantly. The flame test showed the ionic liquid containing networked polymer gel electrolytes to have low if any flammability and was therefore confirmed to be highly safe. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Composite poly(ethylene carbonate) electrolytes with electrospun silica nanofibers

We prepared a ternary composite polymer electrolyte from poly(ethylene carbonate) (PEC), lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) and non‐calcined silica nanofibers (SNFs) having 3 average diameters (300, 700, and 1000 nm). The SNF composite electrolytes were obtained as homogeneous, self‐standing membranes. The ionic conductivity of PEC/LiTFSI 100 mol% was increased by the addition of SNFs, and the thinner SNFs with average diameter 300 nm were most effective in improving the conductivity. The conductivity was of the order of 10⁻⁴ S/cm at 60°C. The lithium transference number of the SNF₃₀₀ composite was greater than 0.7. Stress‐strain curves of the composites indicated significant increases in Young's modulus and maximum stress for the PEC electrolytes. The 5% weight‐loss temperature of the composites also improved with the addition of SNF.     

Effect of thermal history on the ionic conductivity of block copolymer electrolytes

We have studied the effect of thermal history on ionic conductivity of block copolymer electrolytes. Previous work on block copolymer electrolytes composed of polystyrene‐b‐poly(ethylene oxide) (SEO) and lithium bis(trifluoromethanesulfone) imide (LiTFSI) salt was restricted to lamellar morphologies. This study addresses both cylindrical and lamellar morphologies. The conductivity of low molecular weight samples decreases after they are annealed. In contrast, the conductivity of high molecular weight samples is generally unaffected by annealing. These results are explained in the context of connectivity and composition of the conducting phase. © 2013 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2013 , 51, 927–934     

Preparation and properties of ionic‐liquid‐containing poly(ethylene glycol)‐based networked polymer films having lithium salt structures

Ionic‐liquid‐containing polymer films were prepared by swelling poly(ethylene glycol)‐based networked polymers having lithium salt structures with an ionic liquid, 1‐ethyl‐3‐methylimidazolium bis(fluorosulfonyl)imide (EMImFSI), or with an EMImFSI solution of lithium bis(trifluoromethanesulfonyl) imide (LiTFSI). Their fundamental physical properties were investigated. The networked polymer films having lithium salt structures were prepared by curing a mixture of poly(ethylene glycol) diglycidyl ether and lithium 3‐glycidyloxypropanesulfonate or lithium 3‐(glycidyloxypropanesulfonyl)(trifluoromethanesulfonyl)imide with poly(ethylene glycol) bis(3‐aminopropyl) terminated. The obtained ionic‐liquid‐containing films were flexible and self‐standing. They showed high ionic conductivity at room temperature, 1.16–2.09 S/m for samples without LiTFSI and 0.29–0.43 S/m for those with 10 wt % LiTFSI. Their thermal decomposition temperature was above 220 °C, and melting temperature of the ionic liquid incorporated in the film was around ?16 °C. They exhibited high safety due to good nonflammability of the ionic liquid. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Interactions and Transport in Highly Concentrated LiTFSI-based Electrolytes

To elucidate what properties control and practically limit ion transport in highly concentrated electrolytes (HCEs), the viscosity, ionic conductivity, ionicity, and transport numbers were studied for nine model electrolytes and connected to the rate capability in Li-ion battery (LIB) cells. The electrolytes employed the LiTFSI salt in three molar ratio concentrations; 1 : 2, 1 : 4, and 1 : 16 (LiTFSI:X) vs. solvents (X) with different permittivities; tert-butyl methyl ether (MTBE), tetrahydrofuran (THF) and propylene carbonate (PC). While the low polarity MTBE creates liquid electrolytes, ion-pairing limits the ionic conductivity despite extremely low viscosities. For the less concentrated 1 : 16 LiTFSI:MTBE and 1 : 16 LiTFSI:THF electrolytes the ionic diffusivities decrease with increased temperature, a sign of aggregation, but still their ionic conductivities and LIB performance increase. In general, the low ionic conductivity and high viscosity both limit the use of HCEs in LIBs, and no compensating mechanism seems to be present.     

Simulation of local ion transport in lamellar block copolymer electrolytes based on electron micrographs

A method is presented to relate local morphology and ionic conductivity in a solid, lamellar block copolymer electrolyte for lithium batteries, by simulating conductivity through transmission electron micrographs. The electrolyte consists of polystyrene‐block‐poly(ethylene oxide) mixed with lithium bis(trifluoromethanesulfonyl) imide salt (SEO/LiTFSI), where the polystyrene phase is structural phase and the poly(ethylene oxide)/LiTFSI phase is ionically conductive. The electric potential distribution is simulated in binarized micrographs by solving the Laplace equation with constant potential boundary conditions. A morphology factor, f, is reported for each image by calculating the effective conductivity relative to a homogenous conductor. Images from two samples are examined, one annealed with large lamellar grains and one unannealed with small grains. The average value of f is 0.45 ± 0.04 for the annealed sample, and 0.37 ± 0.03 for the unannealed sample, both close to the value predicted by effective medium theory, 1/2. Simulated conductivities are compared to published experimental conductivities. The value of f_Unannealed/f_Annealed is 0.82 for simulations and 6.2 for experiments. Simulation results correspond well to predictions by effective medium theory but do not explain the experimental measurements. Observation of nanoscale morphology over length scales greater than the size of the micrographs (～1 μm) may be required to explain the experimental results. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 266–274     

Improved properties of polymer electrolyte by ionic liquid PP1.3TFSI for secondary lithium ion battery

A new kind of polymer electrolyte is prepared from N-methyl-N-propylpiperidinium bis (trifluoromethanesulfonyl) imide (PP1.3TFSI), polyethylene oxide (PEO), and lithium bis (trifluoromethanesulfonyl) imide (LiTFSI). IR and X-ray diffraction results demonstrate that the addition of ionic liquid decreases the crystallization of PEO. Thermal and electrochemical properties have been tested for the solid polymer electrolytes, the addition of the room temperature molten salt PP1.3TFSI to the conventional P(EO)₂₀LiTFSI polymer electrolyte leads to the improvement of the thermal stability and the ionic conductivity (x = 1.27, 2.06 × 10⁻⁴ S cm⁻¹ at room temperature), and the reasonable lithium transference number is also obtained. The Li/LiFePO₄ cell using this polymer electrolyte shows promising reversible capacity, 120 mAh g⁻¹ at room temperature and 164 mAh g⁻¹ at 55 °C.     

Synthesis of networked polymers by copolymerization of monoepoxy‐substituted lithium sulfonylimide and diepoxy‐substituted poly(ethylene glycol), and their properties

Networked polymers that had poly(ethylene glycol) (PEG) chains and lithium sulfonylimide salt structures were prepared by curing a mixture of poly(ethylene glycol) diglycidyl ether and lithium 3‐glycidyloxypropanesulfonyl‐trifluoromethanesulfonylimide with poly(ethylene glycol) bis(3‐aminopropyl) terminated. The obtained flexible self‐standing networked polymer films showed high thermal and mechanical stability with relatively high ionic conductivity. The room temperature ionic conductivity under a dry condition was in the range of 10^?5 ～ 10^?4 S m^?1, which is one order of magnitude higher than the corresponding networked polymers having lithium sulfonate salt structures (10^?6 ～ 10^?5 S m^?1). The film sample became swollen by immersing in propylene carbonate (PC) or PC solution of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The sample swollen in PC showed higher ionic conductivity (7.2 × 10^?3 S m^?1 at room temperature), and the sample swollen in 1.0 M LiTFSI/PC showed much higher ionic conductivity (8.2 × 10^?1 S m^?1 at room temperature). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of networked polymers with lithium counter cations from a difunctional epoxide containing poly(ethylene glycol) and an epoxide monomer carrying a lithium sulfonate salt moiety

Poly(ethylene glycol)‐based networked polymers that had lithium sulfonate salt structures on the network were prepared by heating a mixture of poly(ethylene glycol) diglycidyl ether (PEGGE), poly(ethylene glycol) bis(3‐aminopropyl) terminated (PEGBA), and an ionic epoxy monomer, lithium 3‐glycidyloxypropanesulfonate (LiGPS). Flexible self‐standing networked polymer films showed high thermal stability, low crystallinity, low glass transition temperature, and good mechanical strength. The materials were ion conductive at room temperature even under a dry condition, although the ionic conductivity was rather low (10^?6 to 10^?5 S/m). The ionic conductivity increased with the increase in temperature to above 1 × 10^?4 S/m at 90 °C. The film samples became swollen by immersing in propylene carbonate (PC) or PC solution of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The samples swollen in PC showed higher ionic conductivity (ca.1 × 10^?3 S/m at room temperature), and the samples swollen in LiTFSI/PC showed much higher ionic conductivity (nearly 1 S/m at room temperature). © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3113–3118, 2010     

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.     

Cold Sintering of Li6.4La3Zr1.4Ta0.6O12/PEO Composite Solid Electrolytes

Ceramic/polymer composite solid electrolytes integrate the high ionic conductivity of in ceramics and the flexibility of organic polymers. In practice, ceramic/polymer composite solid electrolytes are generally made into thin films rather than sintered into bulk due to processing temperature limitations. In this work, Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZTO)/polyethylene-oxide (PEO) electrolyte containing bis(trifluoromethanesulfonyl)imide (LiTFSI) as the lithium salt was successfully fabricated into bulk pellets via the cold sintering process (CSP). Using CSP, above 80% dense composite electrolyte pellets were obtained, and a high Li-ion conductivity of 2.4 × 10⁻⁴ S cm^–1 was achieved at room temperature. This work focuses on the conductivity contributions and microstructural development within the CSP process of composite solid electrolytes. Cold sintering provides an approach for bridging the gap in processing temperatures of ceramics and polymers, thereby enabling high-performance composites for electrochemical systems.     

Polymer electrolyte membranes by in situ polymerization of poly(ethylene carbonate‐co‐ethylene oxide) macromonomers in blends with poly(vinylidene fluoride‐co‐hexafluoropropylene)

Salt‐containing membranes based on polymethacrylates having poly(ethylene carbonate‐co‐ethylene oxide) side chains, as well as their blends with poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP), have been studied. Self‐supportive ion conductive membranes were prepared by casting films of methacrylate functional poly(ethylene carbonate‐co‐ethylene oxide) macromonomers containing lithium bis(trifluorosulfonyl)imide (LiTFSI) salt, followed by irradiation with UV‐light to polymerize the methacrylate units in situ. Homogenous electrolyte membranes based on the polymerized macromonomers showed a conductivity of 6.3 × 10^?6 S cm^?1 at 20 °C. The preparation of polymer blends, by the addition of PVDF‐HFP to the electrolytes, was found to greatly improve the mechanical properties. However, the addition led to an increase of the glass transition temperature (T_g) of the ion conductive phase by ～5 °C. The conductivity of the blend membranes was thus lower in relation to the corresponding homogeneous polymer electrolytes, and 2.5 × 10^?6 S cm^?1 was recorded for a membrane containing 10 wt % PVDF‐HFP at 20 °C. Increasing the salt concentration in the blend membranes was found to increase the T_g of the ion conductive component and decrease the propensity for the crystallization of the PVDF‐HFP component. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 79–90, 2007     

Electrochemical Properties of PP13TFSI-LiTFSI-P(VdF-HFP) Ionic Liquid Gel Polymer Electrolytes (cited: 1)

N-Methyl-N-propylpiperidiniumbis(trifluoromethanesulfonyl)imide (PP13TFSI), bis(triflu-oromethanesulfonyl)imide lithium salt (LiTFSI), and poly(vinylidene difluoride-co-hexafluoropropylene) (P(VdF-HFP)) were mixed and made into ionic liquid gel polymerelectrolytes (ILGPEs) by solution casting. The morphology of ILGPEs was observed by scanning electron microscopy. It was found that the ILGPE had a loosened structure with liquid phase uniformly distributed. The ionic conductivity, lithium ion transference num-ber and electrochemical window were measured by electrochemical impedance spectroscopy, chronoamperometric and linear sweep voltammetry. The ionic conductivity and lithium ion transference number of this ILGPE reached 0.79 mS/cm and 0.71 at room temperature, and the electrochemical window was 0 to 5.1 V vs. Li⁺/Li. Battery tests indicated that the ILGPE is stable when being operated in Li/LiFePO₄ batteries. The discharge capacity maintained at about 135, 117, and 100 mAh/g at 30, 75, and 150 mA/g rates, respectively. The capacity retentions were almost 100% after 100 cycles without little capacity fading.     

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.     

离子液体凝胶聚合物电解质的三元组分相互作用研究

采用Raman光谱、傅里叶转换红外光谱和X-射线衍射光谱研究N-甲基-N-丙基哌啶双三氟甲磺酸亚胺离子液体（PP13TFSI）和双三氟甲磺酸亚胺锂盐（LiTFSI）对PVDF-HFP聚合物聚合方式的影响,结果表明,PP13TFSI、LiTFSI和PVDF-HFP是共混存在的,同时加入PP13TFSI和LiTFSI会使聚合物的聚合方式由晶体结构转变为无定形结构. 通过对电解质及其各组分的线性扫描伏安曲线和热重曲线分析可知,溶剂N-甲基吡咯烷酮（NMP）容易残留在凝胶聚合物电解质（ILGPE）中,这会降低ILGPE的电化学稳定性和热稳定性. 作者对固态LiFePO₄|ILGPE|Li电池的倍率性能进行了研究,实验结果表明其具有较好的倍率性能,当电池倍率由C/10增大至2C,然后再回到C/10时,其容量可以恢复到原来的90.9%左右. 该研究结果对理解PP13TFSI和LiTFSI在ILGPE中的作用机理具有重要的意义.     

Synthesis and properties of all solid polymer electrolytes based on poly(vinyl acetate‐co‐acetyl ethylene oxide acrylate)

Poly(acetyl ethylene oxide acrylate‐co‐vinyl acetate) (P(AEOA‐VAc)) was synthesized and used as a host for lithium perchlorate to prepare an all solid polymer electrolyte. Introduction of carbonyl groups into the copolymer increased ionic conductivity. All solid polymer electrolytes based on P(AEOA‐VAc) at 14.3 wt% VAc with 12wt% LiClO₄ showed conductivity as high as 1.2 × 10^?4 S cm^?1 at room temperature. The temperature dependence of the ionic conductivity followed the VTF behavior, indicating that the ion transport was related to segmental movement of the polymer. FTIR was used to investigate the effect of the carbonyl group on ionic conductivity. The interaction between the lithium salt and carbonyl groups accelerated the dissociation of the lithium salt and thus resulted in a maximum ionic conductivity at a salt concentration higher than pure PAEO‐salts system. Copyright © 2010 John Wiley & Sons, Ltd.     

New fluorine-containing plasticized low lattice energy lithium salt for plastic batteries

The synthesis of a new plasticized low lattice energy lithium salt (PLI), structurally related to lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), is described. Incorporation of the plasticizing moiety in a single salt molecule greatly simplifies the solid polymer electrolyte (SPE) processing formulation without compromising performance. Thermally and electrochemically stable polymer electrolyte films of PLI exhibit good ionic conductivity, though somewhat lower than that for LiTFSI. The pentafluorophenyl analog of LiTFSI, prepared by two approaches, exhibits behavior similar to that of LiTFSI.     

Ion–Dipole Interactions in Concentrated Organic Electrolytes

An algorithm is proposed for calculating the energy of ion–dipole interactions in concentrated organic electrolytes. The ion–dipole interactions increase with increasing salt concentration and must be taken into account when the activation energy for the conductivity is calculated. In this case, the contribution of ion–dipole interactions to the activation energy for this transport process is of the same order of magnitude as the contribution of ion–ion interactions. The ion–dipole interaction energy was calculated for a cell of eight ions, alternatingly anions and cations, placed on the vertices of an expanded cubic lattice whose parameter is related to the mean interionic distance (pseudolattice theory). The solvent dipoles were introduced randomly into the cell by assuming a randomness compacity of 0.58. The energy of the dipole assembly in the cell was minimized by using a Newton–Raphson numerical method. The dielectric field gradient around ions was taken into account by a distance parameter and a dielectric constant of ε=3 at the surfaces of the ions. A fair agreement between experimental and calculated activation energy has been found for systems composed of γ‐butyrolactone (BL) as solvent and lithium perchlorate (LiClO₄), lithium tetrafluoroborate (LiBF₄), lithium hexafluorophosphate (LiPF₆), lithium hexafluoroarsenate (LiAsF₆), and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) as salts.     

Plastic crystalline lithium salt with solid-state ionic conductivity and high lithium transport number

Plastic crystallinity of lithium salt, [LiB(OCH(2)CH(2)OCH(3))(4)] (1), and its solid-state ionic conductivity are disclosed. The addition of small amounts of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) to borate 1 led to the drastic increase of the ionic conductivity and lithium transport number of the electrolyte.