The conductivity and characterization of the plasticized polymer electrolyte based on the P(AN-co-GMA-IDA) copolymer with chelating group (II): The effect of free ion in the plasticized polymer electrolyte

A new gel-type polymer electrolyte (GPE) was made by the copolymerizing acrylonitrile (AN) and (2-methylacrylic acid 3-(bis-carboxymethylamino)-2-hydroxy-propyl ester) (GMA-IDA). The copolymer mixed with a plasticizer—propylene carbonate (PC) and lithium salt to form GPE. The lithium salts are LiCF₃SO₃, LiBr and LiClO₄. FT-IR spectra show that the lithium ion in the LiClO₄ system has the strongest interaction with the group based on the plasticized polymer. FT-IR spectra also indicate that CF₃SO₃⁻ prefers producing anion-cation association. Moreover, the ¹³C solid state NMR spectra for the carbons attached to the PC of GPE exhibited different level of chemical shift (158.5 ppm) when the different lithium salts were added to the electrolyte. The results of differential scanning calorimeter (DSC) also indicate that the LiClO₄ system has more free lithium ions; therefore, it has the maximum conductivity. In this study, the highest conductivity 2.98 × 10⁻³ S cm⁻¹ exists in AG2/PC = 20/80 wt.% system which contain 3 mmole (g-polymer)⁻¹ LiClO₄. Additionally, the polymer electrolytes, which contain GMA-IDA have better interfacial resistance stability with lithium electrode.     

The effects of anion structure of lithium salts on the properties of in-situ polymerized thermoplastic polyurethane electrolytes

Thermoplastic polyurethane (TPU) electrolytes with lithium salts were prepared by an in-situ polymerization method. Three different lithium salts were used to study the effects of the anion structure on the properties of polyurethane electrolytes: LiCl, LiClO₄, LiN(SO₂CF₃)₂ (LiTFSI). The effects of the anion structure on monomer (PTMG) prior to polymerization and on the properties of TPU electrolytes post polymerization were investigated. The anion structure of lithium salt has a significant influence on the ionic conductivity, thermal stability and tensile property of TPU electrolytes. The TPU electrolytes with LiTFSI demonstrated a high ionic conductivity up to 10⁻⁵ S/cm at 300 K. The ionic conductivity of polyurethane electrolytes with lithium salts is in the order: LiCl < LiClO₄ < LiTFSI. It was found that the lithium salts with larger anions were easily dissociated in TPU and had stronger interaction with TPU, which provided more charge carriers and gave higher ionic conductivity.     

The effect of different lithium salts on conductivity of comb-like polymer electrolyte with chelating functional group

The behaviors of lithium ions in a comb-like polymer electrolyte with chelating functional group complexed with LiCF₃SO₃, LiBr and LiClO₄ were characterized by differential scanning calorimeter (DSC), thermogravimetric analysis (TGA), Fourier transform infrared (FT-IR) spectroscopy, AC impedance, and ¹³C solid-state NMR measurement. The comb-like copolymer was synthesized from poly(ethylene glycol) methyl ether methacrylate (PEGMEM) and (2-methylacrylic acid 3-(bis-carboxymethylamino)-2-hydroxy-propyl ester) (GMA-IDA). FT-IR spectra reveal the interactions of Li⁺ ions with both the ether oxygen of the PEGMEM and the nitrogen atom of the GMA-IDA segments. FT-IR spectra also indicate an increasing anion-cation association consistent with increasing LiCF₃SO₃ concentrations. Moreover, the ¹³C solid-state NMR spectra for the carbons attached to the ether oxygen atoms exhibited significant line broadening and a slight upfield chemical shift when the dopant was added to the polymer. These findings indicate coordination between the Li cation and the ether oxygens in the PEG segment. T_g and T_d of copolymers doped with salts clearly increase, as shown by DSC and TGA measurements. These results indicate the interactions of Li⁺ with both PEGMEM and GMA-IDA segments form transient cross-links inside the copolymers. The Vogel-Tamman-Fulcher (VTF)-like behavior of conductivity implies the coupling of the charge carriers with the segmental motion of the polymer chain in this study. The maximum conductivity of copolymers relates to the composition of the copolymers and the concentration of doping lithium ions. In summary, the GMA-IDA unit in the copolymer promotes the dissociation of the lithium salt, the mechanical strength and the conductivity of the polyelectrolyte.     

Solid polymer electrolytes of blends of polyurethane and polyether modified polysiloxane and their ionic conductivity

Polymer electrolytes based on thermoplastic polyurethane (TPU) and polyether modified polysiloxane (PEMPS) blend with lithium salts were developed via an in-situ polymerization of TPU with the presence of PEMPS and salts. Morphological study of TPU/PEMPS electrolytes showed that TPU and PEMPS were immiscible and TPU/PEMPS electrolytes had a multiphase morphology. The lithium salt enhanced the interfacial compatibilization between TPU and PEMPS via the interaction of lithium ions with different phases. Three lithium salts with different interaction strengths with TPU and PEMPS were used to prepare TPU/PEMPS electrolytes with different levels of phase compatibilization: LiCl, LiClO₄, and LiN(SO₂CF₃)₂ (LiTFSI). The effect of PEMPS on ionic conductivity, dimensional stability and thermal stability of TPU/PEMPS electrolytes and their relationship with the blend morphology were investigated. TPU/PEMPS electrolytes showed good dimensional stability and thermal stability. The addition of PEMPS to TPU increased the ionic conductivity of TPU/PEMPS electrolytes. The room temperature ionic conductivity of TPU/PEMPS electrolytes with LiTFSI can reach up to 2.49 × 10⁻⁵ S/cm.     

Potentiometric measurements of ionic transport parameters in poly(ethylene oxide)-LiX electrolytes

An electrochemical technique based on concentration cell e.m.f. measurements is used to determine the lithium transference number and diffusion coefficient in poly(ethylene oxide)-lithium salt complexes. Measurements were carried out at 90°C on PEO–LiI, PEO–LiClO₄ and PEO–LiCF₃SO₃ electrolytes. According to the phase diagram of the PEO-lithium salt system these complexes are fully amorphous at 90°C. Accurate determination oft _Li ⁺ by the e.m.f. concentration cell method generally requires knowledge of the mean salt activity coefficients. However, this becomes unnecessary when the two electrolyte concentrations differ only slightly. As a first step the mean salt activity coefficient was estimated using a galvanic cell of the lithium/PEO-LiX/MX _n /M type withM ⁿ⁺=Ag⁺ or Pb²⁺, and X^–=I^– or CF₃SO₃ ^–. The resulting lithium transference numbers are 0.34 for the PEO–LiI complex and 0.7 for PEO–LiCF₃SO₃. Discrepancies between thet _Li ⁺ values can be explained by the formation of triplets in the PEO–LiCF₃SO₃ electrolyte. By recording concentration cell potential versus time and comparing with theoretical curves, the salt lithium diffusion coefficient was obtained.D _LiI was found to be around 4×10^–8 cm² s^–1 in PEO–LiI and 8×10^–8 cm² s^–1 in PEO–LiCF₃SO₃ at 90°C. These results suggest a liquid-like behaviour for the microscopic transport mechanism.     

Modifying the thermal and mechanical properties of poly(lactic acid) by adding lithium trifluoromethanesulfonate

The effect of the addition of lithium trifluoromethanesulfonate (LiCF₃SO₃) on the linear viscoelastic properties, crystallization behavior, and mechanical properties of poly(lactic acid) (PLA) was studied. The glass transition temperature (T_g) was enhanced by adding LiCF₃SO₃, without any loss of transparency of the PLA. This was attributed to the ion-dipole interaction between the lithium cation and oxygen atom in the PLA carbonyl group. The interaction weakened at higher temperature. Consequently, the rheological terminal region was clearly detected, which suggested that the system possessed good melt-processability. The Young’s modulus and yield stress at room temperature were also enhanced by the addition of LiCF₃SO₃, although the toughness was reduced due to the brittle failure. Finally, the presence of LiCF₃SO₃ retarded the crystallization of PLA, because the segmental motion of the PLA chains was reduced.     

Morphological and conductivity studies of di-ureasil xerogels containing lithium triflate

Sol-gel derived poly(oxyethylene)/siloxane hybrids doped with lithium triflate, LiCF₃SO₃, have been investigated. The host hybrid matrix of these materials, named di-ureasil and represented by U(600), is composed by a siliceous framework to which polyether chains containing 8.5 oxyethylene repeat units are covalently bonded through urea linkages. Xerogel samples U(600)_nLiCF₃SO₃ with n (where n is the molar ratio of oxyethylene moieties per Li⁺ ion) between ∞ and 0.1 have been examined. X-ray diffraction and differential scanning calorimetry have provided conclusive evidence that the xerogels analyzed are entirely amorphous. The salt-rich material with n=1 exhibits the highest conductivity over the whole range of temperature analyzed (e.g. 4.3×10⁻⁶ and 2.0×10⁻⁴ Ω⁻¹ cm⁻¹, respectively, at 25 and 94 °C).     

The influence of lithium salt on the interfacial reactions controlling the thermal stability of graphite anodes

The thermal stability of graphite anodes used in Li-ion batteries has been investigated, with the influence of electrolyte salt under special scrutiny, LiPF₆, LiBF₄, LiCF₃SO₃ and LiN(SO₂CF₃)₂ in an ethylene carbonate (EC)/dimethyl carbonate (DMC) solvent mixture. Differential scanning calorimetry (DSC) showed exothermic reactions in the temperature range 60-200 °C for all electrolyte systems. The reactions were coupled to decomposition of the solid electrolyte interphase (SEI) and reactions involving intercalated lithium. The onset temperature of the exothermic reactions increased with type of salt in the order: LiBF₄<LiPF₆<LiCF₃SO₃<LiN(SO₂CF₃)₂. X-ray photoelectron spectroscopy (XPS) was used to identify surface species formed prior to and after the exothermic reactions, to clarify different thermal behaviour for different salts. The decomposed SEI's in LiCF₃SO₃ and LiN(SO₂CF₃)₂ electrolytes were found to be mainly solvent-based, including lithium alkyl carbonate decomposition to stable Li₂CO₃ and the formation of poly(ethylene oxide) (PEO)-type polymers. In the LiBF₄ and LiPF₆ systems, decomposition was governed by salt reactions, which decomposed the salts and resulted in the main product LiF.     

Preparation and characterization of a solid polymer electrolyte PEO‐ENR50 (80/20)‐LiCF3SO3

The preparation and characterization of a polymer electrolyte films containing 80 wt % of poly (ethylene oxide) (PEO) and 20 wt % epoxidized natural rubber (ENR50) complexed with LiCF₃SO₃ has been reported. The ac impedance data showed good conducting properties of the solid polymer electrolyte (SPE) films. The greatest room temperature ionic conductivity of 7.5 × 10^?5 S cm^?1 was obtained at 25 wt % of LiCF₃SO₃ salt. This result has been supported by differential scanning calorimeter and X‐ray diffraction analysis. Analysis differential scanning calorimetry showed the relative percentage of crystallinity and T_m of PEO decreased with the increasing wt % of LiCF₃SO₃. Analysis with X‐ray diffraction suggested that the semicrystalline nature of PEO turned to amorphous due to the presence of LiCF₃SO₃. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Morphological,infrared, and ionic conductivity studies of poly(ethylene oxide)–49% poly(methyl methacrylate) grafted natural rubber–lithium perchlorate salt based solid polymer electrolytes

The potential of poly(ethylene oxide) (PEO) and 49% poly(methyl methacrylate) grafted natural rubber (MG49) as a polymer host in solid polymer electrolytes (SPE) was explored for electrochemical applications. PEO–MG49 SPEs with various weight percentages of lithium perchlorate salt (LiClO₄) was prepared with the solution casting technique. Characterization by scanning electron microscopy, Fourier transform infrared spectroscopy, and impedance spectroscopy was done to investigate the effect of LiClO₄ on the morphological properties, chemical interaction, and ionic conductivity behavior of PEO–MG49. Scanning electron microscopy analysis showed that the surface morphology of the sample underwent a change from rough to smooth with the addition of lithium salts. Infrared analysis showed that the interaction occurred in the polymer host between the oxygen atom from the ether group (C? O? C) and the Li⁺ cation from doping salts. The ionic conductivity value increased with the addition of salts because of the increase in charge carrier up to the optimum value. The highest ionic conductivity obtained was 8.0 × 10^?6 S/cm at 15 wt % LiClO₄. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Lithium transference number measurements and complex abilities in anion trapping triphenyloborane-poly(ethylene oxide) dimethyl ether-lithium trifluoromethanesulfonate composite electrolyte

In this paper we report the combined, positive effect of triphenyloborane (BPh₃) additive on conductivity and lithium cation transference numbers in poly(ethylene oxide) dimethyl ether (PEODME)-lithium trifluoromethanesulfonate (LiCF₃SO₃, LiTf) electrolytes. The transport mechanism is discussed on the basis of impedance measurements, restricted diffusion t⁺ measurements, ionic association semi-empirical quantitative estimation and spectroscopic studies. A substantial increase in the lithium transference number values in triphenylborane enriched composite electrolytes was observed in comparison with the pure PEODME-LiCF₃SO₃ electrolyte. This effect is assisted by ionic conductivity enhancement.     

Lithium ionic conductivity in poly(ether urethanes) derived from poly(ethylene glycol) and lysine ethyl ester

Poly(ether urethanes) obtained by the copolymerization of poly(ethylene glycol) (PEG) and lysine ethyl ester (LysOEt) are elastomeric materials that can be processed readily to form flexible, soft films. In view of these desirable physicomechanical properties, the potential use of these new materials as solid polymer electrolytes was explored. Solid polymer electrolytes were prepared with copolymers containing PEG blocks of different lengths and with different concentrations of lithium triflate (LiCF₃SO₃). Correlations between the length of the PEG block, the concentration of lithium triflate in the formulation, and the observed Li⁺ ion conductivity were investigated. Solid electrolyte formulations were characterized by differential scanning calorimetry for glass transition temperatures (T_g), melting points (T_m), and crystallinity. Ionic conductivity measurements were carried out on thin films of the polymer electrolytes that had been cast on a microelectrode assembly using conventional ac-impedance spectroscopy. These polymer electrolytes showed inherently high ionic conductivity at room temperature. The optimum concentration of lithium triflate was about 25–30% (w/w), resulting at room temperature in an ionic conductivity of about 10⁻⁵ S cm⁻¹. For poly(PEG₂₀₀₀-LysOEt) containing 30% of LiCF₃SO₃, the activation energy was ∼ 1.1 eV. Our results indicate that block copolymers of PEG and lysine ethyl ester are promising candidates for the development of polymeric, solvent-free electrolytes. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1449–1456, 1997     

Calcium phosphate incorporated poly(ethylene oxide)‐based nanocomposite electrolytes for lithium batteries. I. Ionic conductivity and positron annihilation lifetime spectroscopy studies

Nanocomposite polymer electrolytes (NCPEs) composed of poly(ethylene oxide), calcium phosphate [Ca₃(PO₄)₂], and lithium perchlorate (LiClO₄)/lithium bis(trifluoromethane sulfonyl)imide [LiN(CF₃SO₂)₂ or LiTFSI] in various proportions were prepared by a hot‐press method. The membranes were characterized by scanning electron microscopy, differential scanning calorimetry, thermogravimetry–differential thermal analysis, ionic conductivity testing, and transference number studies. The free volume of the membranes was probed by positron annihilation lifetime spectroscopy at 30°C, and the results supported the ionic conductivity data. The NCPEs with LiClO₄ exhibited higher ionic conductivities than the NCPE with LiTFSI as a salt. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effects of Inorganic Salts and Polymers on the Foam Performance of 1-Tetradecyl-3-methylimidazolium Bromide Aqueous Solution

The foaming performance of 1-tetradecyl-3-methylimidazolium bromide (C₁₄mimBr) aqueous solution, in the presence of polymers (PEG or PVA) or inorganic salts (NaBr, MgCl₂, NaNO₃, Na₂SO₄ or Na₃PO₄), was investigated at 25.0?°C by using the self-made apparatus and the conductivity method. The experimental results show that the foaming ability and foam stability of the ternary aqueous systems of C₁₄mimBr coexisting with PEG or PVA are stronger than those of the C₁₄mimBr solutions in the absence of a polymer, and both the efficiency of foaming ability and foam stability of the surfactant solutions are evidently enhanced with an increase in polymer concentration. However, the addition of inorganic salts can decrease the foaming ability and foam stability of C₁₄mimBr solution. Especially, the inorganic salts, with high valence state of the anion (SO₄ ^2? and PO₄ ^3?), are good antifoam agents which can remove and inhibit foam quickly. For the aqueous solution of the surfactant, the effect of temperature on foaming properties was also examined. The results show that both the foaming ability and stability of the foams of the surfactant solutions decrease with an increase in the temperature within the range from 25.0 to 45.0?°C.     

The crystalline to amorphous transition in PEO-based composite electrolytes: role of lithium salts

The effect of lithium salts (LiBF₄, LiPF₆, and LiClO₄) on the crystalline to amorphous transition in the poly(ethylene oxide) (PEO):LiX (8:1)-Al₂O₃ (20 wt.%, 24 nm) system was investigated and analyzed. Differential scanning calorimetry (DSC) and impedance measurements were conducted to characterize the transition. It was determined that among the three salts, lithium perchlorate (LiClO₄) was the most effective in producing and stabilizing the amorphous structure. Long-term stabilization of the specimens, predominantly in an amorphous state around ambient temperature, leads to a significant conductivity enhancement.     

The effect of additives on lithium cycling in methyl acetate

Methyl acetate (MA) was examined as a solvent for use in non-aqueous secondary lithium batteries. The efficiency of cycling lithium on nickel in MA/1 M LiClO₄ containing less than 10 ppm H₂O was less than 10%. Addition of nitromethane (NM), SO₂ or small amounts of H₂O improved the efficiency markedly. Compared to propylene carbonate (PC), MA plus SO₂ or NM afforded more repeated cycles before failure of the working electrode. Unlike PC, the open circuit lithium disappearance rate in MA is decreased in the presence of additives, eg from about 300 μA/cm^2-70 μA/cm² with >0.2 M nitromethane, and to essentially 0 μA/cm², under the proper conditions, with 3 M SO₂. The differences in behavior between PC and MA are attributed to the greater solubility of the MA-lithium reaction products, allowing greater opportunity for buildup of additive-induced conductive films on the metallic deposit.     

Preparation and characterization of thermoplastic antistatic polyurethane synthesized by in situ polymerization

Antistatic polyurethane (APU) is prepared by in situ polymerization of polyester glycol (PEL), 4,4′‐diphenylmethane diisocyanate (MDI), 1,4‐butanediol (BDO), and antistatic agent (AA) formed by dissolving sodium salts in polyethylene glycol (PEG). Comprehensive properties of the APU are investigated by the FT‐IR, mechanical characterization, surface resistivity measurement, relative humidity (RH) study, and TGA, respectively. It is found that the surface resistivity of the APU can be effectively reduced to 10^9.15 Ω, showing a good antistatic property. Moreover, the APU maintains a low surface resistivity (～10^9.43 Ω) at the RH of 0.1%, revealing a non‐RH‐sensitive capacity of the APU. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39921.     

Improvement in voltage,thermal, mechanical stability and ion transport properties in polymer‐clay nanocomposites

We report novel results on optimization of intercalated polymer‐clay nanocomposite endowed with desirable properties like, (i) very high ionic conductivity (～ 10^?3 S cm^?1) at room temperature, (ii) substantial improvement in voltage stability (～ 5.6 V), mechanical stability (25 MPa), and thermal stability (250°C) (iii) t_ion ～ 99% and cation transport number (t_Li+) ～ 67%: Intercalation of polymer salt (PAN)₈LiCF₃SO₃ complex into dodecylamine modified montmorillonite clay (DMMT) nanometric channels has been confirmed by X‐ray diffraction and Transmission electron microscopy analysis. Complex impedance spectroscopy suggests bulk electrical conduction in the high frequency region and electrode polarization effect at the low frequencies. The experimental value of conductivity, voltage, and mechanical stability is observed to be invariably higher in polymer nanocomposite film when compared with clay free polymer‐salt complex film. The same is true for cation transport. The optimized polymer film serves dual purpose of electrolyte and separator in energy storage devices. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Hydrogen bonding effect on the poly(ethylene oxide), phenolic resin,and lithium perchlorate–based solid‐state electrolyte

The interaction behavior of solid‐state polymer electrolytes composed of poly(ethylene oxide) (PEO)/novolac‐type phenolic resin and lithium perchlorate (LiClO₄) was investigated in detail by DSC, FTIR, ac impedance, DEA, solid‐state NMR, and TGA. The hydrogen bonding between the hydroxyl group of phenolic and ether oxygen of the PEO results in higher basicity of the PEO. The higher basicity of the ether group can dissolve the lithium salts more easily and results in a greater fraction of “free” anions and thus higher ionic conductivity. DEA results demonstrated that addition of the phenolic increases the dielectric constant because of the partially negative charge on the ether group induced by the hydrogen bonding interaction between ether oxygen and the hydroxyl group. The study showed that the blend of PEO(100)/LiClO₄(25)/phenolic(15) possesses the highest ionic conductivity (1.5 × 10^?5 S cm^?1) with dimensional stability. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1207–1216, 2004     

Impact of “Super Acid” like filler on the properties of a PEGDME/LiClO4 system

Composite polymer electrolyte based on a new class of filler added to a PEGDME/LiClO₄ model system has been investigated. “Ceramic super acids” used consist of grafted SO₄²⁻ groups on Al₂O₃ particles surface obtained by calcinations route. Conductivity, DSC and FT-IR measurements performed on such composite electrolytes, when compared to the model PEGDME/LiClO₄ electrolyte, showed only slight improvement of their inner characteristics. In contrary, Li/Li symmetric cells study, by means of impedance spectroscopy, has presented a spectacular decrease of the interfacial resistance compare to the model electrolyte. This result opens a new pathway of investigation to master the lithium metal/polymer electrolyte interface.