Design of alkaline metal ion conducting polymer electrolytes

Polysiloxanes with covalently attached oligo ethylene oxide and di-t-butylphenol ( I ), naphthol ( II ), and hexafluoropropanol ( III ) were synthesized. The crosslinked polymers with a hexamethylene spacer were also prepared. The ion conductivities of the Li, Na, and K salts were measured as a function of temperature. The highest conductivities for K and Na of I at 30°C were 5.5 × 10^?5 and 5.0 × 10^?5 S/cm, respectively, when the ratio of the ion to ethylene oxide unit was 0.014. On the other hand, Li conductivity was 8.0 × 10^?6 S/cm when the ratio between Li and ethylene oxide unit was 0.019. The maximum conductivities of Li ions of II and III were in the order of 10^?6 and 10^?7 S/cm at 30°C, respectively. When the polymers were crosslinked by a hexamethylene residue, the ion conductivities decreased while the degree of crosslinking increased. The temperature dependence of the cation conductivities of these systems could be described by the Williams-Landel-Ferry (WLF) and the Vogel-Tammann-Fulcher (VTF) equation. The results demonstrate that ion movement in these polymers is correlated with the polymer segmental motion. The order of ionic conductivity was K⁺ > Na⁺ ? Li⁺. This suggests that steric hindrance and π-electron delocalization of the anions attached to polymer backbone have a large effect on ion-pair separation and their ionic conductivities. Thermogravimetric analysis of the polymers indicated that the degradation temperature for I and II were about 100°C higher than for poly(siloxane-g-ethylene oxide). This is due to the antioxidant properties of sterically hindered phenols and naphthols. © 1993 John Wiley & Sons, Inc.     

Preparation and ionic conductivities of the plasticized polymer electrolytes based on poly(methyl methacrylate-co-alkali metal methacrylate)

Ionic conductivities of the polymer electrolytes prepared from the ionomer (poly(methyl methacrylate-co-alkali metal methacrylate)), lithium perchlorate, and ethylene carbonate as a plasticizer, were studied as a function of the ion content and the alkali-metal cation of the ionomer. It was possible to obtain tough films with room-temperature ionic conductivities of ∼ 10^-3 S/cm. The maximum ion conductivities of the polymer electrolytes were obtained at the ion content of 5 mol % for both Li and Na ionomer. The effects of the ion content of the ionomer on the ionic conductivities of the polymer electrolytes were mainly interpreted in terms of the characteristics of the ion aggregate formed in the polymer electrolytes. The thermal dependence of the ionic conductivity was shown to be a non-VTF pattern in some of the polymer electrolytes investigated, which is expected to be due to the presence of the ion aggregate. © John Wiley & Sons, Inc.     

Copolymerization of methacrylic acid alkali metal salts and polyether-containing monomers in solid polymer electrolytes

Copolymerization of methacrylic acid alkali metal salts (MAAM; M = Li, Na, K, Rb or Cs) and oligo(oxyethylene) methacrylate (MEO) was carried out in bulk or in poly(oligo(oxyethylene) methacrylate) (PMEO) at 60°C. The copolymers of MAAM and MEO which were obtained by bulk polymerization showed a cation conductivity of around 1 × 10^?7 S/cm at room temperature. On the other hand, the copolymers obtained by radical polymerization in PMEO, showed a higher cation conductivity (10^?6–10^?5 S/cm). Furthermore, higher cation conductivity was observed for the copolymer systems containing alkali metal cations with a larger ion radius. This tendency was explained by the strength of the bond between alkali metal cation and ether oxygens. The degree of dissociation had little effect on this difference in the conductivity. The effective dissociation of methacrylic salts was enhanced in the copolymer compared to the homopolymer because of the suppression of the adjacent dissociative carboxylic acid groups. Arrhenius plots for ionic conductivity show the migration of ions along with the segmental motion of the polymer matrix.     

A study of the mechanism of response of liquid ion exchanger calcium selective electrodes: Part II. Conductimetric investigation of the ionic dissociation in liquid ion exchangers

Measurements of conductivities of didecyl phosphate salts in DOPP have been undertaken using a dielectric constant determination cell. For concentrations greater than 10^?4M these salts are highly associated. Dissociated constants have been determined for Li and Na DDP in DOPP in the range concentration where ion pairs are formed (C<10^?4 M). The values are identical for the two salts studied. The presence of water and inorganic salts enhances the conductivity of ion exchanger solutions. Aggregation under micellar form or even as a pseudo-liquid crystal is discussed.     

Design of Single Ionic Conduction in Polymeric Solid Electrolytes

Oligo(oxyethylene) methacrylate, MEO, has been synthesized as a basic material to design a polymeric solid electrolyte. The homopolymer P(MEO) has a glass transition temperature of -78°C. P(MEO) solubilizes inorganic salts without solvent, and the dissociated ions migrate fast to give very high ionic conductivity, above 10^?5 S/cm for ac. Although the ac conductivity is high, the current decreases gradually under dc conditions. This is improved by the design of an ionic conductor using only cations. Poly[oligo(oxyethylene) methacrylate-co-alkali metal methacrylate], P(MEO-MAM), is prepared as an organic solid electrolytes which allows cationic single-ion conduction. The ionic conductivity of the films depends on the electrolyte content, the dissociation energy of the comonomeric electrolytes, and the degree of segmental motion surrounding the ions in the polymer matrix. The ionic conductivity of Li or K is around 10^?6 S/cm in these polymeric systems at 80°C. The plot of logarithmic conducticity vs reciprocal absolute temperature is a curved line. The Williams-Landel-Ferry parameters, calculated from the temperature dependence of the conductivity, coincided with theoretical values within a certain range. The single-ion conduction in these films is concluded to be affected considerably by the segmental motion of the matrix polymer. This is also confirmed by the Vogel-Tammann-Fulcher plot.     

Conductivity studies of polymer electrolytes based on aliphatic polyesters

A series of aliphatic polyesters of sebacoyl chloride and poly(ethylene glycol) containing a different number of ethylene oxide groups was synthesized and characterized. These polyesters were complexed with lithium perchlorate to obtain a new class of polymer electrolyte. The relationships between the structure and properties of these polymer electrolytes were investigated. The main factor that affects the ionic conductivity in these systems was found to be the solvating capacity of the polyester for the lithium salt. These polymer electrolytes showed ionic conductivities up to 10^?5 ? 10^?4 S/cm at 25°C. The mechanical strength was improved by cross-linking, and the cross-linked polyester complexed with a LiCIO₄ salt showed an ionic conductivity of 2 × 10^?5 S/cm at room temperature. ⁷Li NMR spin-spin relaxation and dielectric relaxation studies were also carried out to investigate the local environments and dynamics of ions in the polymer electrolytes. © 1995 John Wiley & Sons, Inc.     

Single Lithium‐Ion Conducting Polymer Electrolytes Based on a Super‐Delocalized Polyanion

A novel single lithium‐ion (Li‐ion) conducting polymer electrolyte is presented that is composed of the lithium salt of a polyanion, poly[(4‐styrenesulfonyl)(trifluoromethyl(S‐trifluoromethylsulfonylimino)sulfonyl)imide] (PSsTFSI^?), and high‐molecular‐weight poly(ethylene oxide) (PEO). The neat LiPSsTFSI ionomer displays a low glass‐transition temperature (44.3 °C; that is, strongly plasticizing effect). The complex of LiPSsTFSI/PEO exhibits a high Li‐ion transference number (t_Li⁺=0.91) and is thermally stable up to 300 °C. Meanwhile, it exhibits a Li‐ion conductivity as high as 1.35×10^?4 S cm^?1 at 90 °C, which is comparable to that for the classic ambipolar LiTFSI/PEO SPEs at the same temperature. These outstanding properties of the LiPSsTFSI/PEO blended polymer electrolyte would make it promising as solid polymer electrolytes for Li batteries.     

Effects of gamma and electron beam irradiation on polymer electrolytes

Polymer electrolytes based on poly(ethylene oxide) and lithium salts have been widely studied in recent years. In order to enhance the room temperature ionic conductivity of PEO-LiX complexes, various techniques, such as addition of plasticizers and crown ether, and also irradiation by γ and electron beams have been investigated. The enhancement of the conductivity by irradiation has been accounted for the decreasing of the crystallinity of PEO-LiX. We reviewed these results and have investigated the degradation processes of PEO using Tb³⁺ fluorescence probes. We have also studied on the effects of irradiation of polymers such as poly(acrylic acid) (PAA), poly(methacrylic acid) (PMA) and PEO using Tb⁺³ fluorescence probe. Various monomers containing SO₃H and COOH have been grafted on poly(ethylene oxide) using irradiation technique. The structures and ionic conductivities of Li and Na salts of irradiated products were investigated in detail.     

Quantum and Classical Molecular Dynamics of Ionic Liquid Electrolytes for Na/Li‐based Batteries: Molecular Origins of the Conductivity Behavior

Compositional effects on the charge‐transport properties of electrolytes for batteries based on room‐temperature ionic liquids (RTILs) are well‐known. However, further understanding is required about the molecular origins of these effects, in particular regarding the replacement of Li by Na. In this work, we investigate the use of RTILs in batteries, by means of both classical molecular dynamics (MD), which provides information about structure and molecular transport, and ab initio molecular dynamics (AIMD), which provides information about structure. The focus has been placed on the effect of adding either Na⁺ or Li⁺ to 1‐methyl‐1‐butyl‐pyrrolidinium [C₄PYR]⁺ bis(trifluoromethanesulfonyl)imide [Tf₂N]^?. Radial distribution functions show excellent agreement between MD and AIMD, which ensures the validity of the force fields used in the MD. This is corroborated by the MD results for the density, the diffusion coefficients, and the total conductivity of the electrolytes, which reproduce remarkably well the experimental observations for all studied Na/Li concentrations. By extracting partial conductivities, it is demonstrated that the main contribution to the conductivity is that of [C₄PYR]⁺ and [Tf₂N]^?. However, addition of Na⁺/Li⁺, although not significant on its own, produces a dramatic decrease in the partial conductivities of the RTIL ions. The origin of this indirect effect can be traced to the modification of the microscopic structure of the liquid as observed from the radial distribution functions, owing to the formation of [Na(Tf₂N)_n]^(n?1)? and [Li(Tf₂N)_n]^(n?1)? clusters at high concentrations. This formation hinders the motion of the large ions, hence reducing the total conductivity. We demonstrate that this clustering effect is common to both Li and Na, showing that both ions behave in a similar manner at a microscopic level in spite of their distinct ionic radii. This is an interesting finding for extending Li‐ion and Li‐air technologies to their potentially cheaper Na‐based counterparts.     

Oxocarbon Salts for Fast Rechargeable Batteries

Oxocarbon salts (M₂(CO)_n) prepared through one‐pot proton exchange reactions with different metal ions (M=Li, Na, K) and frameworks (n=4, 5, 6) have been rationally designed and used as electrodes in rechargeable Li, Na, and K‐ion batteries. The results show that M₂(CO)₅/M₂(CO)₆ salts can insert two or four metal ions reversibly, while M₂(CO)₄ shows less electrochemical activity. Especially, we discover that the K₂C₆O₆ electrode enables ultrafast potassium‐ion insertion/extraction with 212 mA h g^?1 at 0.2 C and 164 mA h g^?1 at 10 C. This behavior can be ascribed to the natural semiconductor property of K₂C₆O₆ with a narrow band gap close to 0.9 eV, the high ionic conductivity of the K‐ion electrolyte, and the facilitated K‐ion diffusion process. Moreover, a first example of a K‐ion battery with a rocking‐chair reaction mechanism of K₂C₆O₆ as cathode and K₄C₆O₆ as anode is introduced, displaying an operation voltage of 1.1 V and an energy density of 35 Wh kg^?1. This work provides an interesting strategy for constructing rapid K‐ion batteries with renewable and abundant potassium materials.     

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.     

Synthesis and characterization of polymer electrolytes based on cross‐linked phenoxy‐containing polyphosphazenes

A new method to prepare the polymer electrolytes for lithium‐ion batteries is proposed. The polymer electrolytes were prepared by reacting poly(phosphazene)s (MEEPP) having 2‐(2‐methoxyethoxy)ethoxy and 2‐(phenoxy)ethoxy units with 2,4,6‐tris[bis(methoxymethyl)amino]‐1,3,5‐triazine (CYMEL) as a cross‐linking agent. This method is simple and reliable for controlling the cross‐linking extent, thereby providing a straightforward way to produce a flexible polymer electrolyte membrane. The 6 mol % cross‐linked polymer electrolyte (ethylene oxide unit (EO)/Li = 24:1) exhibited a maximum ionic conductivity of 5.36 × 10^?5 S cm^?1 at 100 °C. The ⁷Li linewidths of solid‐state static NMR showed that the ionic conductivity was strongly related to polymer segment motion. Moreover, the electrochemical stability of the MEEPP polymer electrolytes increased with an increasing extent of cross‐linking, the highest oxidation voltage of which reached as high as 7.0 V. Moreover, phenoxy‐containing polyphosphazenes are very useful model polymers to study the relationship between the polymer flexibility; that is, the cross‐linking extent and the mobility of metal ions. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 352–358     

Effect of solvents on properties of polymer gel-electrolyte based on polyester diacrylate

New polymer gel electrolytes based on polyester diacrylates and LiClO₄ salt solutions in organic solvents are developed for lithium ion and lithium polymer batteries with a high ionic conductivity up to 2.7 × 10^?3 Ohm^?1cm^?1 at the room temperature. To choose the optimum liquid electrolyte composition, the dependence is studied of physico-chemical parameters of new gel electrolytes on the composition of the mixture of aprotic organic solvents: ethylene carbonate, propylene carbonate, and λ-butyrolacton. The bulk conductivity of gel electrolytes and exchange currents at the gel electrolyte/Li interface are studied using the electrochemical impedance method in symmetrical cells with two Li electrodes. The glass transition temperature and gel homogeneity are determined using the method of differential scanning calorimetry. It is found that the optimum mixture is that of propylene carbonate and λ-butyrolacton, in which a homogeneous polymer gel is formed in a wide temperature range of ?150 to +50°C.     

Ionic conductivities of the complexes of LiClO4 and alternating copolymers of oligomeric poly(ethylene oxide) having biphenyl units in the backbone

A series of copolymers of predominantly poly(ethylene oxide) (PEO) with biphenyl (BP) units in the backbone were synthesized. The solid polymer electrolytes (SPEs) were prepared from these copolymers (BP-PEG) employing lithium perchlolate (LiClO₄) as a lithium salt and their ionic conductivities were investigated to exploit the structure–ionic conductivity relationships as a function of chain length ratio between the flexible PEO chains and rigid BP units. The ionic conductivity increases with increasing PEO length in BP-PEG. The salt concentrations in BP-PEG/LiClO₄ complexes were also changed and the results show that maximum conductivity is obtained at [EO]/[Li⁺]≈8. The reasons for these findings are discussed in terms of the number of charge carriers and the mobility of the polymer chain.     

Alkali metal ion conductors based on sulfonated poly(p-phenylene terephthalamide)

To obtain thermally stable and mechanically strong sodium and lithium conducting polymers, we prepared Na⁺ and Li⁺ poly(phenylene terephthalamide sulfonate salts) (MW ～ 5500). We also synthesized oligo(ethylene oxide) (3, 5, or 7 units of ethylene oxide) substituted ethylene carbonate and poly[oxymethylene-oligo(oxyethylene)]. These are high boiling point liquids with high dielectric constants as well as metal chelating properties. Polyelectrolyte systems were prepared by mixing Na⁺ or Li⁺ poly(phenylene terephthalamide sulfonate) salts with various amounts of modified ethylene carbonate and/or poly[oxymethylene-oligo(oxyethylene)]. Films (0.1–0.5 mm thick) obtained from the blends were found to have considerable mechanical strength; forming free standing films. The ionic conductivities of the Na⁺ and Li⁺ polyelectrolyte systems were 10^?6?10^?5 S/cm at 25°C. Thermal properties of these blend systems were investigated in detail. © 1994 John Wiley & Sons, Inc.     

Cation-complexation-induced aggregation and specific ion conduction of lipophilic crowned azobenzenes

Lipophilic azobenzene derivatives incorporating a monoazacrown or oligooxyethylene moiety were employed as a component of ion-conducting composite films containing a polyester elastomer and an alkali metal (Li⁺, Na⁺, K^–) perchlorate. Composite films of monoaza-15-crown-5-containing azobenzene1 exhibited ionic conductivities following the order of Na > Li > K, reflecting the cation-binding selectivity of the 15-crown-5 ring. The ion-conducting behavior of composite films of1 is quite different from that of composite films containing a 1 : 1 mixture of an azobenzene derivative without any crown moiety andN-phenyl-monoaza-15-crown-5 (ionic conductivity order of Li > Na > K >). It was suggested that cation and anion migration is predominant in the LiClO₄ and NaClO₄ systems, respectively. The specific ion conduction can be attributed to ordered aggregation of1 induced by cation complex formation of its crown moiety. Azobenzene derivatives incorporating a monoaza-12-crown-4, monaza-18-crown-6, or oligooxyethylene moiety cannot afford such aggregate formation and specific ion-conduction as is seen in the1 system.     

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.     

Synthesis,characterization and ionic conductivity of poly[(oligoethylene oxide) ethoxysilane] and poly[(oligoethylene oxide) ethoxysilane]/(EuCl3)0.67

Poly[(oligoethylene oxide) ethoxysilane)] ( I ) and poly[(oligoethylene oxide) ethoxysilane)]/(EuCl₃)_0.67 ( II ) were synthesized by reacting tetraethoxysilane with oligo(ethylene glycol) of molecular weight 400 and oligo(ethylene glycol)400/(EuCl₃)_0.317, respectively. The products so obtained are very transparent and rubbery. By Fourier transform infrared and Raman spectroscopy studies and by using analytical results it was concluded that these products are crosslinked macromolecular materials where the Si atom is bonded to one OEt group and to three poly(ethylene oxide) 400 chains. Scanning electronic microscopy studies showed that the presence of EuCl₃ in polymer host significantly affects the morphology of the material. Laser luminescence investigations on (II) showed that Eu³⁺ ion in the polymer host is accommodated in two different types of sites having a distorted C_2v symmetry. Moreover, the ionic conductivity of these systems was investigated and the data were satisfactorily fitted by the empirical Vogel Tamman Fulcher equation. At 70°C the conductivities of ( I ) and ( II ) were 9 × 10⁻⁶ and 14.3 × 10⁻⁶ Ω⁻¹ cm⁻¹ respectively.     

Ionic conductivity of multiarm star polymer/LiClO4 electrolytes

A series of polymer electrolytes based on multiarm polymers and lithium salt complexes were characterized by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), and impedance measurement. The relationships of conductivity with salt concentration, temperature, and arm numbers are discussed. It is suggested that the star polymer has a higher solvency and ion transfer ability on lithium salts than on linear polymers. The conductivity maximum appeared at a higher salt concentration ([EO]/[Li] = 4). Impedance measurement suggested that the optimum conductivity was 2 × 10^?4 s · cm^?1. The conductivity increased with temperature and the dependence of ionic conductivity on temperature fits the Arrhenius equation. Among the studied systems, the star polymer with a five arm number performs better than other structures. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4195–4198, 2004     

The Effect of Oligo(Ethylene Oxide) Side Chains: A Strategy to Improve Contrast and Switching Speed in Electrochromic Polymers

Solution-processable electrochromic polymers (ECPs) with high performance are urgently needed for extensive applications. Nevertheless, they suffer from slow switching speed because of low ionic conductivities. Herein, we present an effective strategy to improve the contrast and switching speed in ECPs via facile side-chain engineering. A novel electrochromic thieno[3,2-b]thiophene-based polymer (PmOTTBTD) is designed and successfully synthesized by introducing oligo(ethylene oxide) side chains with high ionic conductivity. Compared to the counterpart POTTBTD without modification by oligo(ethylene oxide) chains, PmOTTBTD demonstrates nearly double contrast (42 % vs. 24 %) with a fast oxidation switching process that just takes half of the time when detected under 400 nm, as well as much higher coloration efficiencies (e. g. 239.04 cm² C⁻¹ vs. 226.26 cm² C⁻¹ @ 400 nm and 314.04 cm² C⁻¹ vs. 174.00 cm² C⁻¹ @ 650∼700 nm). Besides, PmOTTBTD exhibits excellent stability with negligible decay after 3000 cycles. Our work suggests a facile strategy that could be adopted to realize high-performance ECPs via molecular design tuning.