Prepared Electrolyte Films Research Articles

PVDF-HFP/LiTFSI based composite solid state electrolyte with different micromorphology of Li6.25Ga0.25La3Zr2O12 doping

Solid electrolytes are safer alternatives to liquid electrolytes. Adding Ga to lithium lanthanum zirconium oxide (LLZO) garnet-like solid-state electrolytes effectively improves their performance. The properties of solid-state electrolytes prepared using the two mainstream methods, namely, electrospinning and sol-gel, vary and directly affect the electrochemical performance of assembled batteries. In this study, we prepared Li6.25Ga0.25La3Zr2O12 (Ga-LLZO) nanoparticles and nanofibers using the sol-gel and electrospinning methods, respectively. The battery was also assembled with composite film consisting of the poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymer substrate within Ga-LLZO ceramic fillers. The electrolyte of the battery prepared by Ga-LLZO nanofibers has better conductivity. We fabricated a Li|10 wt% Ga-LLZO nanofiber/PVDF-HFP/60 wt% lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)|LiFePO4 button battery using the optimal concentration. The device demonstrated a stable cycle lasting up to 700 h, a Coulombic efficiency of 98%, a capacity retention rate of 96.5%, and an electrochemical window up to 5 V vs Li/Li+ at room temperature. Over time, a suitable contact interface generated a positive feedback loop. The ionic conductivity was 1.1 × 10−4 S·cm−1. The newly prepared electrolyte films aid the fabrication of future solid electrolytes.

Ameliorating the electrode/electrolyte interface compatibility in Li-ion solid-state batteries with plasticizer

Composite solid electrolytes (CSEs) based on poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)/LiTFSI/LLZO/different wt% of tetra-ethylene-glycol-dimethyl-ether (TEGDME) were prepared using the facile solution casting method or phase-inversion method. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy measurements were used to identify the structures and complexations of the prepared electrolyte films. The morphology and thermal stability of the electrolytes were investigated using field-emission scanning electron microscopy (FE-SEM) and thermogravimetric analysis (TGA). The ionic conductivity of all electrolyte films was analyzed using AC impedance analysis between 298 and 353 K. The data supports that the 30 wt% TEGDME CSE exhibited the highest ionic conductivity (6.2 × 10–5 S cm–1 at 25 ℃ and 3.6 × 10–4 S cm–1 at 60 ℃) and a wide electrochemical window (4.87 V vs. Li/Li+). A solid-state battery with LiFePO4/Li-metal was cycled using the 0.1 C rate at 60 °C for 100 cycles, resulting in a high initial discharge capacity of 157 mAh g–1 with a good coulombic efficiency of> 99%. This admirable electrochemical performance can be attributed to the high ionic conductivity of the electrolyte and its electrochemical stability. We emphasize the significant role of the TEGDME plasticizer in the performance of the CSE as well as the ionic conductivity and compatibility of the electrolyte with the electrode in the solid-state battery. All encouraging results confirm that the CSE has the potential to be a high-voltage electrolyte for Li-ion solid-state batteries.

Development of solid polymer electrolytes based on poly (ethylene oxide) complexed with 2-trifluoromethyl-4, 5-dicyanoimidazole lithium salt and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid for Li-ion batteries

Ion conducting solid polymer electrolyte films based on polymer poly (ethylene oxide) (PEO) complexed with 2-trifluoromethyl-4, 5-dicyanoimidazole lithium salt and ionic liquid (IL) 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide are synthesized using anhydrous acetonitrile as solvent. Prepared electrolyte films are characterized by X-ray diffraction (XRD), differential scanning calorimetry (DSC), complex impedance spectroscopy and cyclic voltammetry techniques. Incorporation of IL into the PEO20-LiTDI polymer electrolyte changes different physicochemical properties of these materials. By characterizations, particularly XRD, DSC and ionic conductivity studies, the synthesized SPEs showed decreased crystallinity, melting points and increased ionic conductivity by the introduction of ionic liquid. The 40 wt% of IL doped polymer electrolyte showed an ionic conductivity of the order of 1.78 × 10−4 S/cm at 60°C with better thermal stability. The optimum conducting composition showed very good electrochemical stability window at ambient temperature. These results suggested that the IL-doped polymer electrolyte would be a potential separator in Li-ion batteries.

The effects of solvents on the physical and electrochemical properties of potassium-ion conducting polymer gel electrolytes

The aim of present work is to investigate the effect of different solvent mixed within poly (vinylidiene fluoride-hexafluoropropylene) (PVDF-HFP) based Potassium ion conducting polymer gel electrolytes. The samples are prepared using solution casting method and the comparative behavior of adding carbonate and glyme in PVDF-HFP/KClO4 matrix is investigated. Subsequently, polymer gel electrolytes are characterized using X-ray diffractometer to analyze the structural features of the electrolyte films. The XRD results reveal that the prepared electrolyte films using both solvents demonstrate semi-crystalline nature. The surface morphology is studied using scanning electron microscopy and significant changes in surface morphology of the polymer gel electrolyte films is observed on introducing carbonate and glyme solvents. Thermal properties and effects of temperature on the prepared electrolytes is examined using differential scanning calorimetry and investigations reveal significant effect of temperature on the heat flow into the polymer gel electrolytes samples. The weight loss of the electrolyte samples with temperature is studied using Thermogravimetric analysis and it is observed that carbonate and glyme based electrolyte offer weight loss of about 7–8 %. The ionic conductivity of 2.53×10−7 Scm−1 and 3.67×10−4 Scm−1 while electrochemical stability window of ∼2.5 V is obtained for both polymer gel electrolytes with carbonate and glyme based solvents. The reversibility of K-ion has been established using cyclic voltammetry measurements.

Synthesis and dielectric properties of PAN-based Na+ ion polymer electrolytes

Polymer electrolytes have become more prominent due to various important applications in electro-chemical appliances and other rechargeable cells. Polymer polyacrylonitrile (PAN) based sodium iodide (NaI) doped composite conducting polymer electrolyte was synthesized by solution cast method. The prepared conducting polymer electrolyte films were mechanically stable and transparent. Complexation of the composition, interaction between cation of salt and nitrogen of PAN and vibrational modes of ions was confirmed by Fourier transform infrared spectroscopic (FTIR) studies. The electrical conductivity and dielectric properties information was obtained by LCR meter through impedance study for the prepared electrolyte films. Dielectric constant, dielectric loss and AC conductivity were observed for PAN: NaI (90:10; 80:20; 70:30; 60:40) composition. The dielectric behavior was analyzed using ε1 and ε11 values. The ε1 and ε11 values are high at lesser frequencies and less at higher frequencies.

Cellulose‐Based Plastic Crystal Electrolyte Membranes with Enhanced Interface for Solid‐State Lithium Batteries

Fabricating robust succinonitrile‐based plastic crystal electrolyte (PCE) membranes with abundant and sustainable polymer skeleton and reinforcing the stability of the PCE–lithium anode interface are essential for adopting PCE in all‐solid‐state lithium metal batteries (ASSLMBs). Herein, renewable and low‐cost cellulose is utilized as the mechanical support framework to prepare the self‐standing cellulose‐based PCE (C‐PCE) through the facile tape‐casting method. The cellulose matrix provides excellent robustness to the hybrid C‐PCE system. The fabricated C‐PCE shows an ionic conductivity of about 2.1 × 10−4 S cm−1 and a tensile strength of over 0.5 MPa at room temperature. Solid‐state lithium batteries assembled with the Li4Ti5O12 cathode, lithium metal anode, and the prepared electrolyte films exhibit an initial capacity surpassing 155 mAh g−1 at 0.2 C and room temperature. This work presents a new attempt to use low‐cost cellulose and common additives to prepare high‐performance PCE membranes for lithium‐battery applications.

Characteristics of Gel Electrolyte Composed of PEO-Based Polymer / Solvated Ionic Liquid for High Performance Li-S Batteries

IntroductionLithium-sulfur (Li-S) batteries as new secondly battery system type are attracted attention. The sulfur positive electrode of this system have theoretical capacity of 1672 mAhg-1, which shows approximately 10 times higher than conventional Li-ion battery positive electrode material (LiCoO2). The problem of this Li-S batteries is dissolution of sulfur component of positive electrode which reached a state of reaction intermediate (Li2S m : m=2~8) into electrolyte during charge / discharge processes. The dissolution and diffusion of Li2S m into electrolyte solution lead significant degradation of cycle characteristics and irreversible side reaction of Li-S batteries. Currently, as functional electrolyte solution that suppresses dissolution of Li2S m , “Solvate Ionic Liquid (SIL)” has been proposed [1]. SIL is equimolar mixed electrolyte of glyme solvent and Li salt, and has strongly interaction between glyme / Li+ to form complex cation. SIL was suppressed dissolution of Li2S m because of weak Lewis acidity / basesity. By application of SIL electrolyte, Li-S battery exhibited stable charge / discharge reaction more than 800 cycles [2]. However, equimolar composition of SIL was destroyed at electrolyte / electrode interface during charge and discharge, and free glyme which have not coordinated Li+ is temporary formed. Thus, it is dynamically possible that Li2S m dissolution into generated free glyme [3]. To solve this problem, we attempted increasing carrier cation (suppression of free glyme generation), solidification of SIL electrolyte by introduction of polymer matrix (diffusion suppression of dissolved chemical species).ExperimentalIn this study, all procedures of sample preparation were conducted in argon-filled glovebox. At first, as highly concentrated SILs, [Li a (G4)1]TFSA a (a = 1 and 1.25) (G4 : CH3-O-(C2H4O)4-CH3, LiTFSA: LiN(SO2CF3)2 = 1 : a) were prepared [4]. Gel electrolyte were prepared by mixing of SILs (a = 1, 1.25), polyether-based P(EO/PO) macromonomer and photo initiator. Composition ratio of gel electrolyte were SILs : polymer = 7 : 3, 8 : 2, 9 : 1 (wt%), respectively. After stirring, samples casted to glass substrate and polymerized by UV irradiation to obtain thin-films, which was transparent and self-standing gel electrolyte films. Prepared electrolyte films ware evaluated by differential scanning calorimetry (DSC) and AC impedance measurements.Result and discussionFig.1(a) show DSC thermograms of prepared liquid and solid electrolytes. All electrolytes exhibited glass transition temperatures (T gs). Gel electrolyte showed lower T g than that neat polymer electrolyte (without SIL). From the results, it was considered that mobility of PEO chain was increased by SIL electrolyte solutions. With increasing SIL amount into the gel electrolyte, T g appeared low temperature side, and therefore, the gel electrolyte with high SIL composition should indicate high ionic conductivity.Fig.1(b) shows temperature dependence of the ionic conductivity (σ) of gel electrolytes, respectively. Owing to increase of viscosity with high Li salt concentration, σ value of high Li salt composition SIL electrolyte (a=1.25) was lower than equimolar SIL (a=1). At 303 K, σ of [Li1(G4)1]TFSA1 : polymer = 8 : 2 electrolyte was 1.5×10−3 Scm−1, which was almost same σ value with SIL electrolyte solution.Fig.1(c) shows charge/discharge curves of Li-S cell using gel electrolyte of [Li1(G4)1]TFSA1 : polymer = 8 : 2. The Li-S battery using the equimolar SIL of gel electrolyte was confirmed first discharge capacity of 1100 mAhg-1. However, this system showed unstable voltage profiles during charge process, and this charge capacity exhibited larger than that discharging capacity. From the unstable and large voltage in this charging process, Li2S m was dissolved into gel electrolyte and side reactions occurred, was considered. This result correlates with the report that the co-migration of glyme molecule and Li cation is destroyed in when PEO matrix introduction by NMR spectroscopy method measurement [5].

Structural and electrochemical studies of bromide derived ionic liquid-based gel polymer electrolyte for energy storage application

In the present studies, poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), ionic liquid {1-Ethyl-3-methylimidazolium bromide} (EMIM)(Br), and magnesium perchlorate Mg(ClO4)2 as salt were used to synthesize free standing electrolyte films by using solution cast technique. The prepared electrolyte films were investigated by using various structural and electrochemical techniques like scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) as well as ionic and temperature dependence studies. It has been observed that addition of ionic liquid significantly increases the properties like ionic conductivity, thermal stability, transparency etc. The maximum room temperature ionic conductivity for the optimized system was found to be of the order of 2.05 × 10−2 S cm−1 which is suitable for device fabrication point of view. The optimized electrolyte films are suitable for supercapacitor application.

PEO + NaSCN and ionic liquid based polymer electrolyte for supercapacitor

In this study, initially ion conducting solid polymer electrolyte films (SPEs) based on polyethylene oxide (PEO) and sodium thiocyanate (NaSCN) have been prepared using the standard solution cast technique. For further enhancement in the ionic conductivity value of optimized film, an ionic liquid (IL; 1-ethyl-3-methyl-imidazolium tricyanomethanide) ([EMIM][TCM]) has been incorporated in different weight ratios into the optimized polymer-salt complex matrix. The prepared SPEs are free-standing, flexible and exhibit good thermal and mechanical stabilities. Polarized optical microscopy (POM) shows a change in the surface morphology of IL doped polymer electrolyte films. The composition nature of polymer electrolyte films was confirmed using fourier transform infrared spectroscopy (FT-IR) via studying ion-ion and ion-polymer interactions. The FTIR studies confirm that complexation occurs between polymer-salt and polymer-salt-ionic liquid interactions. Polymer electrolyte films have been also characterized using X-Ray Diffraction (XRD). The structural analysis confirms that the intensity of crystalline peaks existing in solid polymer electrolyte films decreases after doping IL which enhances its amorphous nature. The thermal stability of different prepared electrolyte films has been investigated using thermogravinometric analysis (TGA). Ionic liquid doped polymer electrolyte films show more stable behavior than polymer host PEO and polymer-salt complex at high temperatures. IL doped polymer electrolyte film shows reduction in the degradation process with a residue mass of 29% at 400 °C. Polymer electrolyte films were also characterized using impedance spectroscopy (IS) to check their electrical properties. The maximum ionic conductivity is found to be 8.44 × 10−5 S cm−1 for 4 wt% IL doped solid polymer electrolyte film and the calculated value of ionic transference number (tion) for optimized electrolyte film is 0.98. Using this maximum ion-conducting polymer electrolyte film, we have developed a electrical double layer capacitor (EDLC). The calculated value of the specific capacitance of prepared EDLC is 1.07 Fg−1.

Chitosan-PEG-NaI based bio-polymer electrolytes: structural, thermal and ion dynamics studies

BPE films based on [Chitosan (CS)-PEG]-NaI were prepared using solution cast technique. The prepared electrolyte films were subjected to thermal, structure and conductivity studies using TGA, XRD, ATR-FTIR and AC impedance spectroscopic techniques. The thermal gravimetric analysis (TGA) reveals that the CS and [CS-PEG]-NaI based films decomposes in multi step. Onset decomposition temperature (Td,onset) also decreases with increasing NaI content in CS-PEG based films. The [CS-PEG]-NaI based films are thermally stable upto ∼220.2 °C. XRD result shows that CS has semi-crystalline in nature having its characteristic peak appeared at 2θ ∼ 23.1°. The % degree of crystallinity (Xc) decreases with increasing NaI content in CS-PEG based films. ATR-FTIR study confirms the interaction between bio-polymer, CS with PEG and NaI. The sample containing 40 wt%NaI shows dc conductivity value ∼7.25 × 10−4 Scm−1at 30 °C. The values of frequency exponent s for BPE films were found to be 0.68 to 0.22. Scaling of ac conductivity with respect to NaI concentration has been performed. Mobility (μ) and total number density of charge carriers (N) were estimated from loss tangent spectra.

Vibrational, electrical, dielectric and optical properties of PVA-LiPF6 solid polymer electrolytes

Abstract Solid polymer electrolytes based on polyvinyl alcohol (PVA) doped with LiPF6 have been prepared using solution casting technique. Electrical properties of prepared electrolyte films were analyzed using AC impedance spectroscopy. The ionic conductivity was found to increase with increasing salt concentration. The maximum conductivity of 8.94 × 10−3 S·cm−1 was obtained at ambient temperature for the film containing 20 mol% of LiPF6. The conductivity enhancement was correlated to the enhancement of available charge carriers. The formation of a complex between the polymer and salt was confirmed by Fourier transform infrared spectroscopy (FT-IR). The optical nature of the polymer electrolyte films was analyzed through UV-Vis spectroscopy.

Microstructural, Relaxation and Transport Properties of Electron Irradiated Ion Conducting Polymer Electrolyte for Solid State Battery Applications

Poly (vinyl alcohol) (PVA) doped with KBr composite electrolytes was prepared by solvent casting method, prepared electrolyte films are irradiated with electron beam. The induced modification on the structure of the electrolyte has been confirmed by XRD studies. The XRD results reveal that the crystal structure of the electrolyte has disrupted, thus the amorphous nature increases upon electron irradiation and creates free radicals due to chain scission. Impedance analysis showed that the ionic conductivity increases upon electron irradiation and the maximum conductivity of 6.2388×10−2 S/cm is attained for 300 kGy dose of electron irradiation at 373K. The ion transportation is determined by using Wagner’s polarization technique, and the TIC study confirms the presence of single ionic species within the electrolyte for both pristine and 300 kGy dose electron irradiated electrolyte. This study shows the ion transportation inside the polymer fabrics can be improved by electron beam irradiation method.

Study of time-ageing effect on the ionic conduction and structural dynamics in solid polymer electrolytes by dielectric relaxation spectroscopy

This research work demonstrates the effect of time-ageing on the dielectric and electrical properties, and also the structural dynamics of solid polymer electrolyte (SPE) and nanocomposite solid polymer electrolyte (NSPE) films over a period of one-year. The SPE and NSPE films based on polymer blend matrix of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) (50/50 wt%) with lithium triflate (LiCF3SO3) as dopant ionic salt (22 wt%) and montmorillonite (MMT) clay (3 wt%) as inorganic nanofiller have been prepared by solution-cast method followed by melt-pressing technique. These films are characterized by employing scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), dielectric relaxation spectroscopy (DRS) and electrochemical analysis (ECA) techniques. The influence of MMT filler on the polymer-ion interactions was confirmed from comparative analysis of the structural and electrochemical properties of the SPE and NSPE films. The XRD and DRS measurements on these films were repeated at various time intervals over one-year duration in order to explore the time-ageing effect on the structural properties, dielectric parameters, and ionic conduction mechanisms in the electrolyte samples. The XRD study reveals the irregular variation of PEO crystalline phase in these films and also the intercalated/exfoliated MMT phases in the NSPE film with time-ageing. The ionic conductivity of the SPE and NSPE films increases by about one order of magnitude over the time-ageing period of 2 to 3 months of these films, whereas it drops by more than one order of magnitude at the one-year ageing in comparison to that of the freshly prepared films measured on day first. It is found that the ionic conductivity of these materials has a correlation with the relaxation time of polymers cooperative chain segmental motion which validates the fact that the ions transport in the solid ion-dipolar complexes occurs through hopping mechanism coupled with polymers structural dynamics not only for the freshly prepared electrolyte films but also for the films with time-ageing. Further, these electrolyte films have good electrochemical stability, better reversibility and cyclability, and the ion transference number close to unity.

Lithium ion conduction and ion-polymer interaction in poly(vinyl pyrrolidone) based electrolytes blended with different plasticizers

Poly(ethylene oxide), poly(vinyl pyrrolidone) (PEO/PVP), lithium perchlorate salt (LiClO4) and different plasticizer based, gel polymer electrolytes were prepared by the solvent casting technique. XRD results show that the crystallinity decreases with the addition of different plasticizers. Consequently, there is an enhancement in the amorphousity of the samples responsible for the process of ion transport. FTIR spectroscopy is used to characterize the structure of the polymer and confirms the complexation of plasticizer with host polymer matrix. The ionic conductivity has been calculated using the bulk impedance obtained through impedance spectroscopy. Among the various plasticizers, the ethylene carbonate (EC) based complex exhibits a maximum ionic conductivity value of the order of 2.7279 × 10−4 S cm−1. Thermal stability of the prepared electrolyte films shows that they can be used in batteries at elevated temperatures. PEO (72%)/PVP (8%)/LiClO4 (8%)/EC (12%) has the maximum ionic conductivity value which is supported by the lowest optical band gap and lowest intensity in photoluminescence spectroscopy near 400–450 nm. Two and three dimensional topographic images of the sample having a maximum ionic conductivity show the presence of micropores.

Preparation of electrolyte foils La 0.85Sr 0.15Ga 0.85Mg 0.15O 2.85 (LSGM) by means of tape casting

The oxide LaGaO 3 with the perovskite structure is the most promising solid electrolyte used for solid oxide fuel cells (SOFCs). The powders La 0.85Sr 0.15Ga 0.85Mg 0.15O 2.85 (LSGM) were prepared by means of solid state reaction. The pH values of water solution of the powders increase firstly, reach the maximum value, then decrease gradually with the prolongation of time. The LSGM powders prepared are very stable in the water so that they can be used to prepare slurries by using water as the solvent in order to prepare electrolyte films. The preparation of slurries is of great importance in the manufacturing process of LSGM foils by means of methods of tape casting, screen printing, slurry coating as well as spray coating. In the process of preparation of LSGM slurries, the PBMA-b-PMAS block copolymer (PEO/PMAA), polyvinyl alcohol (PVA), polyethylenglykol 200 (PEG), Agitan 280 and water were used as dispersant, binder, plasticizer, defoamer and solvent, respectively. The foils were made by tape casting. The results show that the foils are free of macro-defect, and can be bent. The densified LSGM foils were made after sintering at 1500 °C for 10–24 h.