Blend Electrolytes Research Articles

Electrical properties enhancement of Liquid and Polymer Gel based electrolytes used for DSSC applications

Electrolytes have been considered a major component of DSSC and play a vital role in determining the ionic conductivity and efficiency of the cell. Emphasis was laid on the confirming the conductivity upon fabrication of an electrolyte using in situ gelation process from a newfangled combination of Triiodide (KI/I2/Glacial acetic acid/distilled water) and gel-based polymer electrolyte (Gelator: PMMA/THF/PC/EC) in the ratio 8:2. The electrolyte portion so framed generated a photo conversion efficiency of 11.32% and a fill factor of 0.439. The conductivity of the sample characterized by Scanning Electron Microscopy showed that the uniform tracks confirmed extreme ionic conductivity of the blend electrolyte which showed dependance on the layered movement of PMMA- co- THF- KI2/PC/EC based electrolyte system. Energy Dispersive x-ray Analysis (EDX) reports engrained the percentage weight proportions of conductive elements (C & O with a wt% of 65.48 and 30.18 in one spectrum and K & I with a wt% of 44.7 & 35.25 in another spectrum respectively). FTIR test analysis was performed to identify the functional groups of the PGE which identified the ionic conductivity of the sample, shown by the intensity of peak absorbance in the range 400–4000 cm−1. Further it was observed, the conductivity of the different concentrations of the liquid and gelator solution demonstrated an increase in exhibiting ionic conductivity and the same was depicted by the morphological studies that featured dark pores of the sample which were spread consistently indicating the amorphous nature of the material (at room temperature).

The Study of Electrical and Electrochemical Properties of Magnesium Ion Conducting CS: PVA Based Polymer Blend Electrolytes: Role of Lattice Energy of Magnesium Salts on EDLC Performance.

Plasticized magnesium ion conducting polymer blend electrolytes based on chitosan (CS): polyvinyl alcohol (PVA) was synthesized with a casting technique. The source of ions is magnesium triflate Mg(CF3SO3)2, and glycerol was used as a plasticizer. The electrical and electrochemical characteristics were examined. The outcome from X-ray diffraction (XRD) examination illustrates that the electrolyte with highest conductivity exhibits the minimum degree of crystallinity. The study of the dielectric relaxation has shown that the peak appearance obeys the non-Debye type of relaxation process. An enhancement in conductivity of ions of the electrolyte system was achieved by insertion of glycerol. The total conductivity is essentially ascribed to ions instead of electrons. The maximum DC ionic conductivity was measured to be 1.016 × 10−5 S cm−1 when 42 wt.% of plasticizer was added. Potential stability of the highest conducting electrolyte was found to be 2.4 V. The cyclic voltammetry (CV) response shows the behavior of the capacitor is non-Faradaic where no redox peaks appear. The shape of the CV response and EDLC specific capacitance are influenced by the scan rate. The specific capacitance values were 7.41 F/g and 32.69 F/g at 100 mV/s and 10 mV/s, respectively. Finally, the electrolyte with maximum conductivity value is obtained and used as electrodes separator in the electrochemical double-layer capacitor (EDLC) applications. The role of lattice energy of magnesium salts in energy storage performance is discussed in detail.

Impact of single vs. blended functional electrolyte additives on interphase formation and overall lithium ion battery performance

Two functional high-voltage additives, namely 2-(2,2,3,3,3-pentafluoropropoxy)-1,3,2-dioxaphospholane (PFPOEPi) and 1-methyl-3,5-bis(trifluoromethyl)-1H-pyrazole (MBTFMP) were combined as functional additive mixture in organic carbonate–based electrolyte formulation for high-voltage lithium battery application. Their impact on the overall performance in NMC111 cathode-based cells was compared with the single-additive–containing electrolyte counterpart. The obtained results point to similar cycling performance of the additive mixture containing electrolyte formulation compared with the MBTFMP-containing cells, whereas the single PFPOEPi-containing cells displayed the best cycling performance in NMC111||graphite cells. With regard to the cathode electrolyte interphase (CEI), characterized and analyzed by means of scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), both the MBTFMP and the PFPOEPi functional additives decompose on the NMC111 surface in single-additive–containing electrolyte formulations. However, the thickness of the CEI formed in the additive mixture–containing electrolyte formulation is determined by the MBTFMP additive, whereas the PFPOEPi additive impacts a change in the composition of the CEI. Furthermore, the MBTFMP additive decomposes prior to the PFPOEPi and, therefore, dominates the cycling performance of NMC111||graphite cells containing functional additive mixture–based electrolyte. This systematic approach allows us to understand the synergistic impact of each functional additive in an electrolyte formulation containing an additive mixture and helps to identify the right additive combination for advanced electrolyte formulation as well as to elucidate whether the single-additive or the additive mixture approach is more effective for the development of advanced functional electrolytes for lithium-based cell chemistries.Graphical abstract

Plasticized H+ ion-conducting PVA:CS-based polymer blend electrolytes for energy storage EDLC application

In this work, plasticized proton-conducting polymer blend electrolytes based on poly (vinyl alcohol): chitosan were synthesized, characterized, and utilized in an electric double-layer capacitor (EDLC). A structural study was performed using X-ray diffraction. The scarification and decrease of intensity of the crystalline peak were detected upon the addition of glycerol plasticizer (GP). The morphological appearance of the plasticized blend electrolyte films was examined through scanning electron microscopy, in which the role of GP on ion dissociation was indicated to be important. Electrochemical impedance spectroscopy was performed to estimate the conductivity of the films. Before the EDLC application, other electrochemical techniques, such as transference number measurement (TNM), linear sweep voltammetry (LSV), and cyclic voltammetry (CV), were carried out. To evaluate the performance of the EDLC, the charge–discharge profile was then examined. The EDLC has been cycled 250 times at a current density of 0.75 mA cm−2. The specific capacitance (Cspe) of the EDLC, which is known as an essential parameter, was found to be constant after the first cycle. The reduction in Cspe value was correlated with the increase of equivalent series resistance. Finally, the manners of energy (E) and power (P) densities as a function of the number of cycles were studied.

Characterization of proton conducting poly[ethylene oxide]: Poly[vinyl pyrrolidone] based polymer blend electrolytes for electrochemical devices

HighlightsHighly amorphous PEO/PVP/xwt% NH4NO3polymer electrolytes are prepared by simple solution casting technique The XRD analysis confirms the amorphous nature of PEO/PVP films and the FTIR and SEM confirm the blending of polymers. Transference number analysis confirms that the prepared polymer electrolytes are mostly ionic conductors. The prepared polymer electrolyte shows potential window between −1.7 to 1.7V. The specific capacitance of the polymer electrolyte decreases with higher scan rate. The proton electrochemical cell was fabricated and the maximum OCV is 0.82V.

The Study of Plasticized Amorphous Biopolymer Blend Electrolytes Based on Polyvinyl Alcohol (PVA): Chitosan with High Ion Conductivity for Energy Storage Electrical Double-Layer Capacitors (EDLC) Device Application.

In this study, plasticized films of polyvinyl alcohol (PVA): chitosan (CS) based electrolyte impregnated with ammonium thiocyanate (NH4SCN) were successfully prepared using a solution-casting technique. The structural features of the electrolyte films were investigated through the X-ray diffraction (XRD) pattern. The enrichment of the amorphous phase with increasing glycerol concentration was confirmed by observing broad humps. The electrical impedance spectroscopy (EIS) portrays the improvement of ionic conductivity from 10−5 S/cm to 10−3 S/cm upon the addition of plasticizer. The electrolytes incorporated with 28 wt.% and 42 wt.% of glycerol were observed to be mainly ionic conductor as the ionic transference number measurement (TNM) was found to be 0.97 and 0.989, respectively. The linear sweep voltammetry (LSV) investigation indicates that the maximum conducting sample is stable up to 2 V. An electrolyte with the highest conductivity was used to make an energy storage electrical double-layer capacitor (EDLC) device. The cyclic voltammetry (CV) plot depicts no distinguishable peaks in the polarization curve, which means no redox reaction has occurred at the electrode/electrolyte interface. The fabricated EDLC displays the initial specific capacitance, equivalent series resistance, energy density, and power density of 35.5 F/g, 65 Ω, 4.9 Wh/kg, and 399 W/kg, respectively.

Drawbacks of Low Lattice Energy Ammonium Salts for Ion-Conducting Polymer Electrolyte Preparation: Structural, Morphological and Electrical Characteristics of CS:PEO:NH4BF4-Based Polymer Blend Electrolytes.

In the present work it was shown that low lattice energy ammonium salts are not favorable for polymer electrolyte preparation for electrochemical device applications. Polymer blend electrolytes based on chitosan:poly(ethylene oxide) (CS:PEO) incorporated with various amounts of low lattice energy NH4BF4ammonium salt have been prepared using the solution cast technique. Both structural and morphological studies were carried out to understand the phenomenon of ion association. Sharp peaks appeared in X-ray diffraction (XRD) spectra of the samples with high salt concentration. The degree of crystallinity increased from 8.52 to 65.84 as the salt concentration increased up to 40 wt.%. These are correlated to the leakage of the associated anions and cations of the salt to the surface of the polymer. The structural behaviors were further confirmed by morphological study. The morphological results revealed the large-sized protruded salts at high salt concentration. Based on lattice energy of salts, the phenomena of salt leakage were interpreted. Ammonium salts with lattice energy lower than 600 kJ/mol are not preferred for polymer electrolyte preparation due to the significant tendency of ion association among cations and anions. Electrical impedance spectroscopy was used to estimate the conductivity of the samples. It was found that the bulk resistance increased from 1.1 × 104 ohm to 0.7 × 105 ohm when the salt concentration raised from 20 wt.% to 40 wt.%, respectively; due to the association of cations and anions. The low value of direct current (DC) conductivity (7.93 × 10−7 S/cm) addressed the non-suitability of the electrolytes for electrochemical device applications. The calculated values of the capacitance over the interfaces of electrodes-electrolytes (C2) were found to drop from 1.32 × 10−6 F to 3.13 × 10−7 F with increasing salt concentration. The large values of dielectric constant at low frequencies are correlated to the electrode polarization phenomena while their decrements with rising frequency are attributed to the lag of ion polarization in respect of the fast orientation of the applied alternating current (AC) field. The imaginary part of the electric modulus shows obvious peaks known as conduction relaxation peaks.

Investigating the Effects of Lithium Phosphorous Oxynitride Coating on Blended Solid Polymer Electrolytes.

Solid-state electrolytes are very promising to enhance the safety of lithium-ion batteries. Two classes of solid electrolytes, polymer and ceramic, can be combined to yield a hybrid electrolyte that can synergistically combine the properties of both materials. Chemical stability, thermal stability, and high mechanical modulus of ceramic electrolytes against dendrite penetration can be combined with the flexibility and ease of processing of polymer electrolytes. By coating a polymer electrolyte with a ceramic electrolyte, the stability of the solid electrolyte is expected to improve against lithium metal, and the ionic conductivity could remain close to the value of the original polymer electrolyte, as long as an appropriate thickness of the ceramic electrolyte is applied. Here, we report a bilayered lithium-ion conducting hybrid solid electrolyte consisting of a blended polymer electrolyte (BPE) coated with a thin layer of the inorganic solid electrolyte lithium phosphorous oxynitride (LiPON). The hybrid system was thoroughly studied. First, we investigated the influence of the polymer chain length and lithium salt ratio on the ionic conductivity of the BPE based on poly(ethylene oxide) (PEO) and poly(propylene carbonate) (PPC) with the salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The optimized BPE consisted of 100 k molecular weight PEO, 50 k molecular weight PPC, and 25(w/w)% LiTFSI, (denoted as PEO100PPC50LiTFSI25), which exhibited an ionic conductivity of 2.11 × 10-5 S/cm, and the ionic conductivity showed no thermal memory effects as the PEO crystallites were well disrupted by PPC and LiTFSI. Second, the effects of LiPON coating on the BPE were evaluated as a function of thickness down to 20 nm. The resulting bilayer structure showed an increase in the voltage window from 5.2 to 5.5 V (vs Li/Li+) and thermal activation energies that approached the activation energy of the BPE when thinner LiPON layers were used, resulting in similar ionic conductivities for 30 nm LiPON coatings on PEO100PPC50LiTFSI25. Coating BPEs with a thin layer of LiPON is shown to be an effective strategy to improve the long-term stability against lithium.

Enhancement of energy storage capacity in lithium polymer batteries incorporated with zirconium oxide nano powders

In this work, three poly-methyl methacrylate (PMMA) hosted solid polymer electrolyte systems were prepared by a solution cast technique. A fixed amount of PMMA and nano Zirconium dioxide (ZrO2) were implemented as ceramic filler and lithium hexafluorophosphate (LiPF6) as dopant salt. The study was carried out using Electrochemical Impedance Spectroscopy (EIS) and Scanning Electron Microscope (SEM). The integrating 20 wt% of Propylene carbonate (PC) into PMMA enhanced the ionic conductivity with another addition of 5 wt% of LiPF6, the ionic conductivity is increased to from 1.94 × 10–11 Scm−1 to 2.97 × 10–09 Scm−1. This has inferred the enhancement of charge carrier density in the polymer electrolyte. A further addition of ceramic fillers with 10 wt% of ZrO2, boosted the ionic conductivity to 9.45 × 10–11 Scm−1 and 4.44 × 10–9 Scm−1, respectively. The SEM images showed the formation of three-dimensional networks with dispersion of ceramic fillers. It can be concluded that appropriate amount of lithium salt (5 wt% of LiPF6) and ceramic filler (10 wt% of ZrO2) enhances the ionic conductivity of the PMMA-based solid polymer electrolyte. The electrical conductivity of PMMA-LiPF6 polymer blend with different concentrations of ZrO2 as a nano filler has been studied. The polymer blend electrolyte was prepared in the form of thin films using solution casting technique. The blend was characterized by Scanning Electron Microscopy (SEM).

Effect of K+ ion doping on structural and physical properties of PVA/MAA:EA polymer blend electrolytes

ABSTRACT A solid polymer blend electrolyte was prepared by using Polyvinyl alcohol (PVA) and Methacrylic Acid Ethyl acrylate (MAA: EA) polymers with different weight percentages (Wt%) of Potassium Chloride (KCl) by using solution casting technique, with water as a solvent. The structural, thermal, optical, and electrical properties of the prepared samples were studied. The X-ray diffraction pattern shows the decreasing trend in the degree of crystallinity due to the incorporation of KCl into the polymeric matrix. From the FTIR analysis, some peak intensities were decreasing and shifted in the case of KCl complexed films, which results in the complexation between the polymer blend and dopant ions. The TGA analysis reveals that the thermal stability of the KCl complexed films increases as dopant concentration increases. The SEM images reveal the structural reorganisation of polymer chains in the KCl complexed polymer blend electrolytes. UV-VIS spectra show that the optical constants such as absorption edge and band gap (both direct and indirect) values are decreased with an increase in KCl concentration. From conductivity data, it was noticed that the conductivity increased with the increase in the K+ ion concentration. The maximum ionic conductivity of 1.85 × 10−7 S/cm was obtained for the sample having 15 wt% of KCl salt.

Effect of SiO2 Nano-particles on Plasticized Polymer Blend Electrolytes: Vibrational, Thermal, and Ionic Conductivity Study

ABSTRACT In this paper, the effect of SiO2 nano-particles on PVA-PVP-PEG-NaI based polymer blend electrolyte (PBE) films was studied and optimized. X-ray diffraction (XRD) and attenuated total reflection (ATR)-FTIR, thermo-gravimetric analysis (TGA), and ac impedance spectroscopic techniques have been used to study the structural, thermal, and dc conductivity, respectively. XRD results reveal that the characteristic peaks of PVA-PVP-PEG-SiO2 based nano-composite PBEs appeared at 2θ~22° with broad halo. ATR-FTIR result shows the complexation/interaction of silica nano-particles with the functional groups of PBEs. TGA analysis shows the thermal stability and decomposition temperature peak (T d, peak) of the NCPBEs decrease with SiO2 content. The prepared NCPBE film having 0.6 wt% SiO2 shows maximum dc conductivity ~5.13x10−6 S/cm at 30°C. The ionic transference number measurement was performed by a dc polarization method, and the results reveal that the conducting species are predominately ions only. Linear sweepvoltametric and cyclic voltammetric measurements have been done for electrochemical stability window study.

From Cellulose, Shrimp and Crab Shells to Energy Storage EDLC Cells: The Study of Structural and Electrochemical Properties of Proton Conducting Chitosan-Based Biopolymer Blend Electrolytes.

In this study, solid polymer blend electrolytes (SPBEs) based on chitosan (CS) and methylcellulose (MC) incorporated with different concentrations of ammonium fluoride (NH4F) salt were synthesized using a solution cast technique. Both Fourier transformation infrared spectroscopy (FTIR) and X-ray diffraction (XRD) results confirmed a strong interaction and dispersion of the amorphous region within the CS:MC system in the presence of NH4F. To gain better insights into the electrical properties of the samples, the results of electrochemical impedance spectroscopy (EIS) were analyzed by electrical equivalent circuit (EEC) modeling. The highest conductivity of 2.96 × 10−3 S cm−1 was recorded for the sample incorporated with 40 wt.% of NH4F. Through transference number measurement (TNM) analysis, the fraction of ions was specified. The electrochemical stability of the electrolyte sample was found to be up to 2.3 V via the linear sweep voltammetry (LSV) study. The value of specific capacitance was determined to be around 58.3 F/g. The stability test showed that the electrical double layer capacitor (EDLC) system can be recharged and discharged for up to 100 cycles with an average specific capacitance of 64.1 F/g. The synthesized EDLC cell was found to exhibit high efficiency (90%). In the 1st cycle, the values of internal resistance, energy density and power density of the EDLC cell were determined to be 65 Ω, 9.3 Wh/kg and 1282 W/kg, respectively.

Influence of nano SrTiO3 and ultrasonic irradiation on the properties of polymer blend electrolytes

ABSTRACT Lithium (Li+) ion conducting nanocomposite polymer blend electrolytes (NCPBEs) based on poly(ethylene oxide) (PEO), poly(vinylidene fluoride hexafluoropropylene) (P(VdF-HFP)) as polymer hosts, lithium perchlorate (LiClO4) as an electrolyte and strontium titanate (SrTiO3) as a nanofiller have been prepared by both the conventional stirring and ultrasonic irradiation methods. Complex formation and hence the structural changes of the prepared samples have been confirmed by X-ray diffraction analysis. Conductivity studies have been carried out by means of AC impedance spectroscopy. In order to highlight the role of ultrasonic irradiation, conductivity values have been compared with the values obtained through conventional mechanical stirring method. It has been found that the system with 15 minutes of ultrasonic irradiation resulted in better homogenous dispersion of SrTiO3 in PEO/P(VDF-HFP)/LiClO4 matrix. Maximum ionic conductivity of 2.519 × 10−4 Scm−1 has been obtained for 6 wt% of SrTiO3 system which is a magnitude higher than the ionic conductivity value, 2.031 × 10−5 Scm−1 obtained for the original NCPBE prepared using conventional mechanical stirring at room temperature. Further, ionic conductivity value increases with the increase of temperature and it exhibit the Arrhenius relation. Higher degree of free ionic motion in the samples has been proven by the increase in intensity of photoluminescence spectra peaks. The dielectric properties of the prepared samples have also been studied using the complex dielectric permittivity spectra and complex electric modulus spectra. The morphology and hence the surface roughness of the samples have been depicted through AFM study.

Structural, Impedance and Electrochemical Characteristics of Electrical Double Layer Capacitor Devices Based on Chitosan: Dextran Biopolymer Blend Electrolytes.

This report presents the preparation and characterizations of solid biopolymer blend electrolyte films of chitosan as cationic polysaccharide and anionic dextran (CS: Dextran) doped with ammonium iodide (NH4I) to be utilized as electrolyte and electrode separator in electrical double-layer capacitor (EDLC) devices. FTIR and XRD techniques were used to study the structural behavior of the films. From the FTIR band analysis, shifting and broadening of the bands were observed with increasing salt concentration. The XRD analysis indicates amorphousness of the blended electrolyte samples whereby the peaks underwent broadening. The analysis of the impedance spectra emphasized that incorporation of 40 wt.% of NH4I salt into polymer electrolyte exhibited a relatively high conductivity (5.16 × 10−3 S/cm). The transference number measurement (TNM) confirmed that ion (tion = 0.928) is the main charge carriers in the conduction process. The linear sweep voltammetry (LSV) revealed the extent of durability of the relatively high conducting film which was 1.8 V. The mechanism of charge storage within the fabricated EDLC has been explained to be fully capacitive behavior with no redox peaks appearance in the cyclic voltammogram (CV). From this findings, four important parameters of the EDLC; specific capacitance, equivalent series resistance, energy density and power density were calculated as 67.5 F/g, 160 ohm, 7.59 Wh/kg and 520.8 W/kg, respectively.

Electrochemical characteristics of solid state double-layer capacitor constructed from proton conducting chitosan-based polymer blend electrolytes

This research is about the preparation of polymer blend electrolytes based on chitosan using solution cast technique. Field emission scanning electron microscopy and Fourier transform infrared spectroscopy (FTIR) routes were utilized for studying morphological and structural properties, respectively. Electrical impedance spectroscopy (EIS) was engaged for determining the direct current electrical conductivity of the films. The ion association at the highest salt concentration was actually present as confirmed by EIS and FTIR achievements. The sample surface displays the protrude salts at the highest salt concentration. Proton conducting polymer electrolyte with NH4Br as H+ (proton) provider has been used in electric double-layer capacitor (EDLC) applications. The highest conducting sample was used to fabricate EDLC. The transference number measurement indicated that the sample is mostly includes ion charge carriers which are vital for application in electrochemical devices. The linear sweep voltammetry study revealed that the decomposition of the sample takes place above 1.54 V. The fabricated EDLC device was performed capacitive behavior, as it can be seen from the cyclic voltammetry (CV) plot. Since no redox peaks have appeared, it can be concluded that the EDLC did not undergo either oxidation or reduction. The acquired value of specific capacitance (132.5 Fg−1) is considered to be of great interest from the application viewpoints.

Effect of glycerol on EDLC characteristics of chitosan:methylcellulose polymer blend electrolytes

Chitosan (CS):methylcellulose (MC):NH4I based solid polymer electrolyte (SPE) has been plasticized using glycerol due to its hydroxyl-rich structure. All SPEs are prepared using solution cast technique at room temperature. Prior to device application, structural, electrical and electrochemical characteristics were examined for the prepared samples using various techniques. X-ray diffraction (XRD) investigation was used to explain the structural changes. Electrical impedance spectroscopy (EIS) was used to evaluate the DC conductivity. The potential stability of the highest conducting film (6.65×10−4Scm−1) was found to be 2.2V as well as shows the characteristic of an ionic conductor where tion>te. The layers of the electrical double-layer capacitor (EDLC) consist of two identical activated carbon electrodes sandwiching the highest conducting SPE. The existence of charge double-layer in the fabricated EDLC has been verified using cyclic voltammetry test. From galvanostatic charge–discharge measurements, several crucial EDLC parameters have been obtained, e.g. specific capacitance, internal resistance, energy density and power density. The addition of glycerol improved the performance of the EDLC.

Structural, electrical and electrochemical studies of sodium ion conducting blend polymer electrolytes

In the present study sodium ion conducting polymer blend electrolytes has been prepared using poly (vinylidene fluoride – hexafluoro – propylene) (PVdF-HFP), poly (methyl methacrylate) (PMMA), and sodium thiocyanate (NaSCN) salt by solution-cast technique. The highest ionic conductivity of the optimized blend polymer electrolyte system [PVdF(HFP)-PMMA (4:1)] (20 wt%)-[NaSCN (1 M)] (80 wt%) has been found to be 4.54 × 10−2 S cm−1 at room temperature. The temperature dependence conductivity plot shows the Arrhenius behaviour and its activation energy calculated from the plot were found to be 0.13 eV. The structural and morphological studies of polymer blend electrolyte were investigated by XRD, SEM and FTIR spectroscopy. Complex formation between polymer and salt has been confirmed by these studies. The thermal properties of optimized electrolyte system were examined by differential scanning calorimetry (DSC) techniques. The ionic transport number was calculated using d.c polarization techniques and was found to be 0.92, which shows that electrolyte system is predominantly ionic in nature. The electrochemical potential window of optimized polymer blend electrolyte was tested and observed to be ∼2.8 V.

Study of impedance and solid-state double-layer capacitor behavior of proton (H+)-conducting polymer blend electrolyte-based CS:PS polymers

A series of proton-conducting polymer blend electrolytes (PBEs) were prepared using solution casting techniques. Chitosan (CS) and starch of potato (PS) were blended and doped with various amounts of ammonium fluoride (NH4F). The highest DC conductivity was found to be 1.38 × 10−3 S/cm for the sample incorporated with 40 wt.% NH4F salt using electrical impedance spectroscopy (EIS). A good complex formation between the polymer blends and the doped salt was confirmed from the morphology of the sample’s surface using field emission scanning electron microscope (FESEM). The crystalline peak broadening and intensity reduction of CS:PS polymer blend with the increasing salt concentration was observed in the X-ray diffraction (XRD) analysis. The type of charge carrier in the PBEs was examined via transference number measurements (TNM), and the dominancy of ion was approved. The extent of electrochemical stability of electrolyte was determined to be up to 1.78 V using linear sweep voltammetry (LSV). The specific capacitance of 6.85 F/g was obtained from cyclic voltammetry (CV) measurement. The rechargeability of the electric double-layer capacitor (EDLC) exhibited stability up to 100 cycles with average specific capacitance of 4.1 F/g. Three criteria were determined, which are internal resistance, energy density, and power density (550 Ω, 0.57 Wh/kg, and 155 W/kg, respectively) of the EDLC at the first cycle.

Investigating the Effects of Lithium Phosphorous Oxynitride Lamination on PEO/PPC Blended Hybrid Electrolytes

Solid-state electrolytes play an important role in the development of new generations of technology including lithium metal batteries. Lithium conducting solid materials offer a solution to the safety issues that are present in lithium-ion batteries (LIBs). Conventional LIBs typically use highly flammable organic solvents as a transport medium for lithium ions, potential risks that arise due to these solvents include fire, volatilization, and explosions. Solid polymer electrolytes (SPEs) are great as electrolyte material because fabrication of the electrolyte films is cheap, and processing is simple. However, SPEs can have stability issues when in contact with lithium metal for extended periods which is a problem for cells required to offer long lifetimes. Poly (ethylene oxide) (PEO) has been extensively studied since the conception of SPEs, due to its ability to solvate ions due to its polar ether groups. However, PEO, being a semi-crystalline polymer, exhibits thermal history effects due to recrystallization behavior. Amorphous SPEs are highly desirable because there are no recrystallization kinetics at play, and the properties are consistent regardless of the thermal history. Poly(propylene carbonate) (PPC), an amorphous, biodegradable polymer, can offer high ionic conductivities. Blending PEO and PPC offers a solution to resolve the thermal history effects of PEO by interfering with the crystalline structures in blended electrolyte systems with the salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Inorganic solid electrolytes (ISEs) can offer better chemical stability and excellent mechanical properties compared to SPEs; however, brittleness may decrease the structural stability over time. Thin films ISE’s also tend to cost much more than SPEs due to the fabrication methods required such as electron beam evaporation, and chemical vapor deposition. Lithium phosphorous oxynitride (LiPON), produced through RF magnetron sputtering, was developed in the 1990s at Oakridge National Laboratories and offers great electrochemical stability against lithium and relatively high ionic conductivities on the order of 10-6 S/cm at room temperature. A new bilayer lithium-ion conducting hybrid solid electrolyte (HSE) consisting of a blended polymer electrolyte (BPE) coated with a thin layer of the ISE LiPON, has been prepared. PEO and PPC are blended in a 1:1 mass ratio, then the salt LiTFSI is incorporated. BPE films are then produced through a facile solution casting method using acetonitrile as the solvent. Structure-property relationships are then systematically evaluated to understand the effects of molecular weight and mass loading of LiTFSI on the BPE systems. Influences of molecular weight and salt loading on crystallinity is observed though X-ray diffraction and optical microscopy of the BPE films. Ionic conductivity is evaluated through impedance spectroscopy between two stainless steel blocking electrodes, thermal history measurements were taken by heating and cooling the SPE while recording EIS at specified temperatures. The best BPE based on ionic conductivity, consists of 100k molecular weight PEO, 50k molecular weight PPC, and 25(w/w)% LiTFSI, (denoted as PEO100PPC50LiTFSI25) and exhibits an ionic conductivity of ~2x10-5S/cm. Temperature dependent EIS shows that the lowest molecular weight polymers offer lower activation energies as a result of the higher degree of free volume and molecular motion of the polymer chain. The optimized BPE system is then coated with various thicknesses of LiPON. The effects of LiPON coating are evaluated and show promise for the development of lithium stable solid electrolytes. Linear sweep voltammetry (LSV) is used to assess the anodic voltage stability against lithium metal. Incorporating very thin layers of LiPON down to 20nm on the BPE shows an increase in the voltage window of the electrolyte system from 5.2 to 5.5V (vs Li/Li+). However, the incorporation of LiPON decreases the ionic conductivity of the BPE. Thinner layers of LiPON show the ionic conductivity approaches that of the BPE, with thicker LiPON layers offering lower ionic conductivies. To assess the stability against lithium metal over time, impedance spectroscopy is used. Cells consisting of the solid electrolyte against lithium metal are prepared, and impedance measurements are taken over a 20-day period to assess the changes in charge transfer resistance. From these measurements, it has been shown that only a 30nm thin layer of LiPON is required to improve the stability of the resulting HSE. Therefore, coating BPEs with a thin layer of LiPON is shown to be an effective strategy to improve the long-term stability of solid-state lithium ion conductors.

Polymer Blends of Poly(ethylene oxide) and Phosphonium Ionenes As Solid Polymer Electrolyte Membranes for Lithium Ion Batteries

Solid polymer electrolytes offer potential improvements to lithium ion batteries that include extending their operating temperature range and improving the safe use of the batteries by inhibiting lithium dendrite formation. Because solid polymer electrolytes replace traditional liquid electrolytes as the lithium ion transport medium and also act as the electrode separator, these materials must offer good ionic conductivity along with providing good interfacial contact with the electrode material. This work presents the synthesis and characterization of polymer blends comprised poly(ethylene oxide) and phosphonium ionenes. Ionenes are a class of polycation that includes positive charges within the polymer backbone. Because the positive charge is a part of the polymer chain, the spacing and distribution of these charges have a significant impact on the properties of ionenes. This research focuses on determining the role of charge spacing and distribution of charges along the backbone of phosphonium ionenes on their ability to transport lithium ions. To accomplish this, phosphonium ionenes are blended with low molecular weight poly(ethylene oxide) (e.g. less than 3,000 g/mol) at mass ratios of 20:1, 10:1, and 5:1. The resulting blended solid polymer electrolyte membranes are evaluated for their thermal, mechanical and electrochemical properties along with their charge/discharge performance in coin cell batteries. The dependence of phosphonium ionene structure as well as the composition of SPE blends will be presented.