Sodium Ion Conducting Gel Polymer Research Articles

Impact of Introducing EMIM-BF4 as Ionic Liquid Solvent on Electrochemical Properties of PVdF–HFP Based Sodium Ion Conducting Gel Polymer Electrolytes

Impact of Introducing EMIM-BF4 as Ionic Liquid Solvent on Electrochemical Properties of PVdF–HFP Based Sodium Ion Conducting Gel Polymer Electrolytes

A sodium ion conducting gel polymer electrolyte with counterbalance between 1-ethyl-3-methylimidazolium tetrafluoroborate and tetra ethylene glycol dimethyl ether for electrochemical applications.

For sodium batteries, the development of gel polymer electrolytes (GPEs) with remarkable electrochemical properties is in its early stage and persists to be a challenge. In this report we have synthesized a series of GPEs containing a poly(vinyllidene fluoride-co-hexafluoropropylene) (PVdF-HFP) and poly (methyl methacrylate) (PMMA) as blend polymer, sodium perchlorate (NaClO4) as ion-conducting salt and 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM-BF4) and tetra ethylene glycol dimethyl ether (TEGDME) as molecular solvents. The counter balance between EMIM-BF4 and TEGDME is maintained by the electrolyte, which is formed through the optimal weight ratio of 2 : 1. GPEs have an advantageous set of properties, including stability window of 5 V, Na+ transference number of 0.20, and a room-temperature ionic conductivity of 5.8 × 10-3 S cm-1. According to enthalpy and entropy calculations, optimized GPE yields the highest amount of disorder or amorphicity and contributes to greatest conductivity. XRD analysis supports this argument. Thermal investigations show that optimized GPE may preserve gel phase up to 125 °C. The prototype sodium cell fabricated with optimize GPE has a specific capacity of 281 mA h g-1 and open circuit voltage of 2.5 V. The optimized GPE exhibits potential for future electrochemical applications.

High‐performance sodium ion conducting gel polymer electrolyte based on a biodegradable polymer polycaprolactone

AbstractGel polymer electrolytes (GPEs) are gaining recent focus for high‐performance quasi‐solid‐state energy storage devices owing to their high ionic conductivity, good interfacial properties, flexibility with high safety in comparison to liquid electrolytes. Among various polymer hosts, developed so far, polycaprolactone (PCL) is attractive for its biodegradable and biocompatible nature. In this report, we demonstrate a novel GPE composition incorporating a liquid electrolyte 1 M sodium triflurosulfonate (NaTf) in ethylene carbonate (EC):propylene carbonate (PC) mixture, immobilized in PCL as the host polymer in the form of mechanically stable, free‐standing and flexible thick films. The GPE films are characterized using various physicochemical and electrochemical techniques. The GPE comprising an approximately 80 wt.% concentration of liquid electrolyte offers an optimum ionic conductivity of ~1.3 × 10−3 S cm−1, wide electrochemical stability window up to approximately 4.3 V and high sodium ion transport number (tNa+ ~ 0.67) at room temperature. Besides, the GPE film is thermally stable up to approximately 100°C. The sodium stripping/plating tests reveal highly stable cycling under ±46 mV for over 100 hours followed by ±30 mV at a current density of 0.05 mA cm−2 indicating reversible Na‐plating/stripping behavior. The high Na+‐conductivity and suitable Na‐storage properties make a favorable biodegradable electrolyte for practical sodium‐ion battery applications.

Diglyme-Incorporated Gelled Polymer: An Efficient Quasi-Solid-State Electrolyte for Sodium-Ion Batteries

Glyme-based electrolytes have been gaining increasing attention in sodium-ion batteries (NIBs) for their attractive electrochemistry involving good complexation ability with Na-ions, high electrochemical stability, good transport characteristics, low volatility, and high safety. Here, we report a flexible and freestanding sodium-ion conducting gel polymer electrolyte containing an equimolar ratio of Na-salt NaTFSI and diglyme (G2), referred to as a solvate ionic liquid (SIL), immobilized inside host polymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP). Fourier-transform infrared (FTIR) and Raman analyses are employed to investigate the conformational evolutions in PVdF-HFP on incorporating G2 and NaTFSI, whereas structural changes are observed using X-ray diffraction. The electrochemical investigations on the electrolyte revealing a wide electrochemical stability window (∼5.2 V) versus Na/Na+, high room-temperature ionic conductivity (∼1.12 × 10–3 S cm–1), and a large Na+ transference number (tNa+ ∼ 0.58) along with thermal stability up to ∼100 °C render the electrolyte suitable for Na-storage applications. The Na deposition/extraction tests over a long period indicate excellent cyclic stability of the cells, revealing low and stable polarization with values limited to ±19 mV at a current density of 0.01 mA cm–2. Further, the prepared solvate ionic liquid-incorporated gel polymer electrolyte (SIL-GPE) is tested in Na-ion battery cells comprising Na0.7CoO2 cathode using galvanostatic charge–discharge cycling, with a first discharge capacity of ∼91.76 mA h g–1 at a 0.05C rate. Studies indicate a class of gel polymer electrolytes based on solvate ionic liquids, suitable for Na-storage applications.

Structural and impedance analysis of PAN-based Na+ ion conducting gel polymer electrolytes for energy storage device application

The polymer electrolytes are used in energy storage devices. Sodium ion-conducting gel polymer electrolytes based on Polyacrylonitrile (PAN) complexed with an alkali salt (NaI) and Ethylene carbonate (EC) and Dimethylformamide (DMF) as plasticizing solvents were prepared from solution cast method. The developed membrane were dimensionally stable. Structural, Impedance and conductivity studies were carried on to the prepared samples. The electrical studies were performed using lab-made conductivity setup. The complex formation between NaI salt and PAN had been confirmed by XRD studies and revealed the amorphous behaviour of the prepared membranes. The conductivity and bulk resistance of gel polymer electrolytes were measured by impedance analysis by changing the composition concentration of PAN-NaI. The maximum conductivity (1x10-3 S/cm) was observed for PAN: NaI (70:30) at temperature 373 K. The conductivity dependence temperature of these mebranes obeys the principle of Arrhenius.

Ion Transport in Solvated Sodium-Ion Conducting Gel Polymer Electrolytes

Single ion conducting gel polymer electrolytes (GPEs) are characterized as having a certain amount of ionic liquid or solvent incorporated into a single ion-conducting polymer matrix and may afford the advantages of high conductivity and low electrolyte polarization under battery operation. Single ion conducting polymers often suffer from low conductivity due to their reliance on polymer segmental motion to achieve sufficient ion mobility. However, by incorporating specific solvents into a single ion conducting matrix, mobility of the polymer can be enhanced while still maintaining the advantages of single ion conduction. Although many of the solvents used to swell GPEs are mixtures of flammable organic solvents (such as dimethyl carbonate), there are many potential non-reactive, low vapor pressure solvents that could effectively solvate alkali-ion based GPEs and plasticize the polymer matrix to enhance ion conductivity. Adipate-based solvents are a group of non-volatile plasticizers with low viscosities and low vapor pressures at room temperature derived from adipic acid. The ester groups in these solvents may effectively solvate alkali ions such as Na+, leading to higher conductivity, while circumventing issues of flammability found in current alkali-ion conducting electrolytes. This study investigates the properties of sodium-ion conducting GPEs that have been swollen with varying adipate-based solvents and the subsequent dielectric response from the solvent addition. Dielectric relaxation spectroscopy was used to characterize the Na+ conductivity, static dielectric constant, ion-conducting content, and mobility of the membranes before and after the non-volatile solvent uptake. Understanding this relationship will pave the path toward safer, more efficient solid-state polymer electrolytes for battery applications.

Performance enhancement of Na+ ion conducting porous gel polymer electrolyte using NaAlO2 active filler

In this paper, we report the enhanced electrochemical characteristic performance of porous gel polymer electrolyte, due to dispersion of sodium aluminate (NaAlO2) active fillers in it. The salt solution consisting of, sodium perchlorate (NaClO4) dissolved in binary mixture of ethylene carbonate and propylene carbonate (EC:PC) was entrapped in poly(vinylidinefluoride-co-hexafluoropropylene) (PVdF-HFP) polymer matrix to obtain the micro-porous sodium ion conducting gel polymer electrolyte films by using the phase inversion technique. Small loading of the active NaAlO2 fillers in gel polymer electrolyte results in significantly improved ionic conductivity (σmax=0.68 mS cm−1 at room temperature), Na+ ion transference number (tNa+∼ 0.45) and electrochemical stability window (ESW ∼ 4.1 V). Dielectric studies have been performed to explore the ion dynamics in the electrolyte system. The Na-S prototype battery delivers maximum discharge capacities of ∼ 210, 139 and 51 mA h g−1 at drain currents of 0.10, 0.25 and 0.50 mA cm-2, respectively. The optimized electrolyte composition with high liquid retention, conductivity and transport properties can be utilized for upcoming sodium batteries operating at room temperature.

Designing Uniformly Layered FeTiO3 Assemblies Consisting of Fine Nanoparticles Enabling High-Performance Quasi-Solid-State Sodium-Ion Capacitors.

Sodium-ion capacitors (NICs) that have integrated the dual advantages of the high output of supercapacitors and the high energy density of batteries have stimulated growing attention for the next generation of practical electrochemical energy storage devices. The last years have seen the unprecedentedly rapid emergence of ilmenite materials, which present great promise in the realm of energy storage. However, NICs based on ilmenite materials have been scarcely researched so far. Instead, most of the current devices explored applied flammable liquid electrolytes, leading to a concern about unexpected leakage and potential safety problems. Herein, a quasi-solid-state NIC is constructed by employing the prepared uniformly layered FeTiO3 assemblies consisting of fine nanoparticles as anode and sodium ion conducting gel polymer as electrolyte. The resulting device delivers a high-energy-high-power density (79.8 Wh kg−1, 6,750 W kg−1), putting it among the state-of-the-art NICs. Furthermore, the assembled quasi-solid-state device also manifests long-term cycling stability over 2,000 cycles with a capacity retention ~80%. The uniformly layered FeTiO3 has great potential in developing low-cost and high-performance electrodes for the next generation of sodium and other metal ions-based energy storage devices.

Enhanced Cycle Performance of Polyimide Cathode Using a Quasi-Solid-State Electrolyte

Benefiting from flexible molecular structures, low limitation of cationic radius, and environmental friendliness, organic materials are regarded as promising candidates for rechargeable batteries. However, the high-solubility in organic electrolytes is the most challenging issue. Most efforts have been focused on modification of the electrode materials. Herein, we employ a sodium ion conducting gel polymer electrolyte with interconnected pores to improve the cycle performance of a polyimide (PI) cathode. Compared to a commercial glass fiber separator, the gel polymer electrolyte only lets through Na ions but prevents the dissolved PI, and thereby avoids further dissolution. After utilization of the membrane, organic sodium ion batteries based on a PI cathode shows a highly enhanced cyclability (80% after 1000 cycles). Such a strategy can be potentially extended to many organic materials used in rechargeable batteries to ensure stability and safety.

Quasi-Solid-State Sodium-Ion Full Battery with High-Power/Energy Densities.

Developing a high-performance, low-cost, and safer rechargeable battery is a primary challenge in next-generation electrochemical energy storage. In this work, a quasi-solid-state (QSS) sodium-ion full battery (SIFB) is designed and fabricated. Hard carbon cloth derived from cotton cloth and Na3V2(PO4)2O2F (NVPOF) are employed as the anode and the cathode, respectively, and a sodium ion-conducting gel-polymer membrane is used as both the QSS electrolyte and separator, accomplishing the high energy and power densities in the QSS sodium-ion batteries. The energy density can reach 460 W h kg-1 according to the mass of the cathode materials. Moreover, the fabricated QSS SIFB also exhibits an excellent rate performance (e.g., about 78.1 mA h g-1 specific capacity at 10 C) and a superior cycle performance (e.g., ∼90% capacity retention after 500 cycles at 10 C). These results show that the developed QSS SIFB is a hopeful candidate for large-scale energy storage.

Effect of organic solvent addition on electrochemical properties of ionic liquid based Na+ conducting gel electrolytes

A novel sodium ion conducting gel polymer electrolyte comprising room temperature ionic liquid, 1-ethyl 3-methyl imidazolium trifluoro-methane sulfonate (EMITf) incorporated with ethylene carbonate and propylene carbonate and its solution with sodium trifluoromethane sulfonate (NaTf) entrapped in poly(vinylidinefluoride-co-hexfluoropropylene) (PVdF-HFP) is prepared using solution cast technique. The gel electrolyte is obtained in the form of free-standing transparent film. The gel electrolyte offers electrical conductivity of ∼10−3Scm−1 at ∼30°C with good mechanical, thermal and electrochemical stability window. The electrical conductivity is measured as a function of temperature and found to be consistent with Vogel-Tamman-Fulcher (VTF) relationship in the temperature range from 30°C to 75°C.Sodium ion conduction in the gel electrolyte film is confirmed from cyclic voltammetry and transport number measurements. The value of the sodium ion transport number of the ionic liquid based gel electrolyte is ∼0.19. The sodium sulfur battery with the gel electrolytes delivers the first discharge capacity of 267mAhg−1 sulfur and then it decreases with repeated charge–discharge cycles.

Achieving High-Energy-High-Power Density in a Flexible Quasi-Solid-State Sodium Ion Capacitor.

Simultaneous integration of high-energy output with high-power delivery is a major challenge for electrochemical energy storage systems, limiting dual fine attributes on a device. We introduce a quasi-solid-state sodium ion capacitor (NIC) based on a battery type urchin-like Na2Ti3O7 anode and a capacitor type peanut shell derived carbon cathode, using a sodium ion conducting gel polymer as electrolyte, achieving high-energy-high-power characteristics in solid state. Energy densities can reach 111.2 Wh kg(-1) at power density of 800 W kg(-1), and 33.2 Wh kg(-1) at power density of 11200 W kg(-1), which are among the best reported state-of-the-art NICs. The designed device also exhibits long-term cycling stability over 3000 cycles with capacity retention ∼86%. Furthermore, we demonstrate the assembly of a highly flexible quasi-solid-state NIC and it shows no obvious capacity loss under different bending conditions.

Ionic conductivity and battery characteristic studies of a new PAN-based Na+ ion conducting gel polymer electrolyte system

Sodium ion conducting gel polymer electrolytes based on polyacrylonitrile (PAN) with ethylene carbonate and dimethyl formamide as plasticizing solvents are prepared by the solution cast technique. These electrolyte films are free standing, transparent and dimensionally stable. Na+ ions are derived from NaI. The structural properties of pure and complex formations have been examined by X-ray diffraction, Fourier transform infrared spectroscopic studies and differential scanning calorimetric studies. The variation of the conductivity with salt concentration ranging from 10 to 40 wt% is studied. The sample containing 30 wt% of NaI exhibits the highest conductivity of 2.35 × 10−4 S cm−1 at room temperature (303 K) and 1 × 10−3 S cm−1 at 373 K. The conductivity–temperature dependence of polymer electrolyte films obeys Arrhenius behavior with activation energy in the range of 0.25–0.46 eV. The transport numbers both electronic (te) and ionic (ti) are evaluated using Wagner’s polarization technique. It is revealed that the conducting species are predominantly due to ions. The ionic transport number of highest conducting film is found to be 0.991. Solid-state battery with configuration Na/(PAN + NaI)/(I2 + C + electrolyte) is developed using the highest conducting gel polymer electrolyte system and the discharge characteristics of the cell are evaluated over the load of 100 KΩ.

A sodium ion conducting gel polymer electrolyte

A sodium ion conducting gel polymer electrolyte based on poly(vinylidene difluoride-co-hexafluoropropylene) porous membrane is reported, which is prepared through a simple phase separation process. It exhibits high safety, good mechanical properties and good electrochemical stability. The gel polymer electrolyte provides the sodium ionic conductivity of 0.60mScm−1 at ambient temperature, while the commercial separator (Celgard 2730) offers only 0.16mScm−1. The temperature dependence of the ionic conductivity from 25 to 75°C is consistent with an Arrhenius-behavior. The ionic transference number of sodium ion (tNa+) in the gel polymer electrolyte is 0.30, higher than that (0.17) in the commercial separator. This provides a new direction to improve the safety of sodium ion batteries.

Studies on Sodium Ion Conducting Gel Polymer Electrolytes

Sodium ion conducting gel polymer electrolyte (GPE) films consisting of polyvinylidenefluoride-co-hexafluoropropylene (PVdF-HFP) as a polymer host were prepared using the solution casting technique. Sodium trifluoromethane-sulfonate (NaCF3SO3) was used as an ionic salt and the mixture of ethylene carbonate (EC) and propylene carbonate (PC) as the solvent plasticizer. The GPE films were found to be stable up to temperature of 145 °C as shown by TGA analysis. The AC impedance study show that the optimum conductivity of 2.50 x 10-3 S cm-1 at room temperature is achieved for the film containing 20 wt.% of NaCF3SO3 salt. The temperature dependence of conductivity obeys VTF relation in the temperature range of 303 K to 373 K.

Studies on poly(vinylidene fluoride-co-hexafluoropropylene) based gel electrolyte nanocomposite for sodium–sulfur batteries

Experimental investigations on a sodium ion conducting gel polymer electrolyte nanocomposite based on poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP), dispersed with silica nanoparticles are reported. The gel nanocomposites have been obtained in the form of dimensionally stable, transparent and free-standing thick films. Physical characterization by X-ray diffraction (XRD), Fourier transform Infra-red (FTIR) spectroscopy and Scanning electron microscopy (SEM) have been performed to study the structural changes and the ion–filler–polymer interactions due to the dispersion of SiO 2 nanoparticles in gel electrolytes. The highest ionic conductivity of the electrolyte has been observed to be 4.1 × 10 −3 S cm − 1 at room temperature with ~ 3 wt.% of SiO 2 particles. The temperature dependence of the ionic conductivity has been found to be consistent with Vogel-Tammen-Fulcher (VTF) relationship in the temperature range from 40 to 70 °C. The sodium ion conduction in the gel electrolyte film is confirmed from the cyclic voltammetry, impedance analysis and transport number measurements. The value of sodium ion transport number (t Na+) of the gel electrolyte is significantly enhanced to a maximum value of 0.52 on the 15 wt.% SiO 2 dispersion. The physical and electrochemical analyses indicate the suitability of the gel electrolyte films in the sodium batteries. A prototype sodium–sulfur battery, fabricated using optimized gel electrolyte, offers the first discharge capacity of ~165 mAh g − 1 of sulfur.

Ionic liquid based sodium ion conducting gel polymer electrolytes

A novel thermally and electrochemically stable sodium ion conducting gel polymer electrolyte has been reported, which comprises a solution of NaCF 3SO 3 (sodium triflate or NaTf) in a room temperature ionic liquid 1-ethyl 3-methyl imidazolium trifluoro-methane sulfonate (EMI-triflate or EMITf) immobilized in poly (vinylidine fluoride-co-hexafluoropropylene) (PVdF-HFP). Different structural, thermal, electrical and electrochemical studies demonstrate promising characteristics of the polymer films, suitable as electrolytes in rechargeable sodium batteries. The possible conformational/structural changes in the polymer PVdF-HFP due to the entrapment of EMITf or EMITf/NaTf solution have been investigated by Fourier transform infra-red (FTIR), scanning electron microscopic (SEM) and X-ray diffraction (XRD) techniques. The electrolyte with the composition of EMITf:PVdF-HFP (4:1 w/w) + 0.5 M NaTf possesses excellent dimensional stability in the form of free standing thick film, which offers the ionic conductivity of 5.74 × 10 − 3 S cm − 1 at room temperature (∼ 27 °C). The temperature dependence of electrical conductivity of polymer–ionic liquid blends and gel polymer electrolyte follows the Vogel–Tammen–Fulcher (VTF) behaviour. The sodium ion conduction in the gel polymer electrolyte film is confirmed from cyclic voltammetry and transport number measurement. The Na + ion transport number has been determined to be ∼ 0.23, which suggests the significant contribution of anionic transport along with the possible conduction of component ions of ionic liquid.