Nanocomposite electrolytes with fumed silica in poly(methyl methacrylate): thermal,rheological and conductivity studies

Composite polymer electrolytes (CPEs), were prepared by adding hydrophilic fumed silica in different proportions upto 5 wt.% to gel polymeric electrolyte (GPE) comprising liquid electrolyte (1 M LiClO₄ in propylene carbonate) immobilized with 15 wt.% poly(methyl methacrylate) (PMMA). The effect of fumed silica content in the CPEs on the ionic conductivity and viscosity over a wide temperature range was investigated. The resultant CPEs showed room temperature conductivity (σ₂₅) as high as 3.8 mS cm⁻¹ along with viscosity value of 3700 P for 2 wt.% SiO₂ addition. Fumed silica addition both to the liquid electrolyte and to the GPE exhibits similar conductivity behaviour and this suggests a passive role of PMMA. The shear thinning behaviour, pointing towards easy processablity, high thermal stability and low volatility, makes these CPEs potential candidates as solid-like electrolytes for electrochemical devices.     

Poly(ethyl methacrylate) and poly(2-ethoxyethyl methacrylate) based polymer gel electrolytes

New poly(ethyl methacrylate) and poly(2-ethoxyethyl methacrylate) gel electrolytes containing immobilised lithium perchlorate solution in propylene carbonate were prepared by UV radical polymerisation. Materials exhibit high ionic conductivity up to 0.23 mS cm⁻¹ and long-term stability of chemical and mechanical properties. Both materials keep their suitable conductivity above −20 °C. The effect of material composition, temperature, cross-linking agent and salt concentration on the electrochemical and mechanical properties were studied using impedance spectroscopy and cyclic voltammetry. The accessible electrochemical window of both polymer electrolytes was estimated from −2.1 to 1.5 V versus Cd/Cd²⁺. Impedance measurements showed almost one-order increase of conductivity when ethylene dimethacrylate was used as a cross-linking agent in comparison with the polymer electrolyte without agent.     

Electrochemical characterization of blend polymer electrolytes based on poly(oligo[oxyethylene]oxyterephthaloyl) for rechargeable lithium metal polymer batteries

Solid polymer electrolytes composed of poly(ethylene oxide)(PEO), poly(oligo[oxyethylene]oxyterephthaloyl) and lithium perchlorate have been prepared and characterized. Addition of poly(oligo[oxyethylene]oxyterephthaloyl) to PEO/LiClO₄ reduced the degree of crystallinity and improved the ambient temperature ionic conductivity. The blend polymer electrolyte containing 40 wt.% of poly(oligo[oxyethylene]oxyterephthaloyl) showed an ionic conductivity of 2.0 × 10⁻⁵ S cm⁻¹ at room temperature and a sufficient electrochemical stability to allow application in the lithium batteries. By using the blend polymer electrolytes, the lithium metal polymer cells composed of lithium anode and LiCoO₂ cathode were assembled and their cycling performances were evaluated at 40 °C.     

Development of PVA based micro-porous polymer electrolyte by a novel preferential polymer dissolution process

A micro-porous polymer electrolyte based on PVA was obtained from PVA–PVC based polymer blend film by a novel preferential polymer dissolution technique. The ionic conductivity of micro-porous polymer electrolyte increases with increase in the removal of PVC content. Finally, the effect of variation of lithium salt concentration is studied for micro-porous polymer electrolyte of high ionic conductivity composition. The ionic conductivity of the micro-porous polymer electrolyte is measured in the temperature range of 301–351 K. It is observed that a 2 M LiClO₄ solution of micro-porous polymer electrolyte has high ionic conductivity of 1.5055 × 10⁻³ S cm⁻¹ at ambient temperature. Complexation and surface morphology of the micro-porous polymer electrolytes are studied by X-ray diffraction and SEM analysis. TG/DTA analysis informs that the micro-porous polymer electrolyte is thermally stable upto 277.9 °C. Chronoamperommetry and linear sweep voltammetry studies were made to find out lithium transference number and stability of micro-porous polymer electrolyte membrane, respectively. Cyclic voltammetry study was performed for carbon/micro-porous polymer electrolyte/LiMn₂O₄ cell to reveal the compatibility and electrochemical stability between electrode materials.     

Effect of ball milling on structural and electrochemical properties of (PEO)nLiX (LiX = LiCF3SO3 and LiBF4) polymer electrolytes

Polymer electrolytes consisting of poly(ethylene oxide) (PEO) and lithium salts, such as LiCF₃SO₃ and LiBF₄ are prepared by the ball-milling method. This is performed at various times (2, 4, 8, 12 h) with ball:sample ratio of 400:1. The electrochemical and thermal characteristics of the electrolytes are evaluated. The structure and morphology of PEO–LiX polymer electrolyte is changed to amorphous and smaller spherulite texture by ball milling. The ionic conductivity of the PEO–LiX polymer electrolytes increases by about one order of magnitude than that of electrolytes prepared without ball milling. Also, the ball milled electrolytes have remarkably higher ionic conductivity at low temperature. Maximum ionic conductivity is found for the PEO–LiX prepared by ball milling for 12 h, viz. 2.52×10⁻⁴ S cm⁻¹ for LiCF₃SO₃ and 4.99×10⁻⁴ S cm⁻¹ for LiBF₄ at 90 °C. The first discharge capacity of Li/S cells increases with increasing ball milling time. (PEO)₁₀LiCF₃SO₃ polymer electrolyte prepared by ball milling show the typical two plateau discharge curves in a Li/S battery. The upper voltage plateau for the polymer electrolyte containing LiBF₄ differs markedly from the typical shape.     

Effects of addition of TiO2 nanoparticles on mechanical properties and ionic conductivity of solvent-free polymer electrolytes based on porous P(VdF-HFP)/P(EO-EC) membranes

To enhance the performance (i.e., mechanical properties and ionic conductivity) of pore-filling polymer electrolytes, titanium dioxide (TiO₂) nanoparticles are added to both a porous membrane and its included viscous electrolyte, poly(ethylene oxide-co-ethylene carbonate) copolymer (P(EO-EC)). A porous membrane with 10 wt.% TiO₂ shows better performance (e.g., homogeneous distribution, high uptake, and good mechanical properties) than the others studied and is therefore chosen as the matrix to prepare polymer electrolytes. A maximum conductivity of 5.1 × 10⁻⁵ S cm⁻¹ at 25 °C is obtained for a polymer electrolyte containing 1.5 wt.% TiO₂ in a viscous electrolyte, compared with 3.2 × 10⁻⁵ S cm⁻¹ for a polymer electrolyte without TiO₂. The glass transition temperature, T_g is lowered by the addition of TiO₂ (up to 1.5 wt.% in a viscous electrolyte) due to interaction between P(EO-EC) and TiO₂, which weakens the interaction between oxide groups of the P(EO-EC) and lithium cations. The overall results indicate that the sample prepared with 10 wt.% TiO₂ for a porous membrane and 1.5 wt.% TiO₂ for a viscous electrolyte is a promising polymer electrolyte for rechargeable lithium batteries.     

Proton conducting behavior of a novel polymeric gel membrane based on poly(ethylene oxide)-grafted-poly(methacrylate)

A novel proton conducting polymeric gel membrane that consists of poly(ethylene oxide)-grafted-poly(methacrylate) (PEO-PMA) with poly(ethylene glycol) dimethyl ether (PEGDE) as a plasticizer doped with aqueous phosphoric acid (H₃PO₄) has been prepared and its physicochemical properties were studied in detail. The ionic conductivity was dependent much on the concentration of H₃PO₄, the immersion time, and content of the plasticizer. This type of proton conducting polymeric gels shares not only good mechanical properties but also thermal stability. Maximum conductivities up to 2.6×10⁻² S cm⁻¹ at room temperature (25 °C) and 2.8×10⁻² S cm⁻¹ at 70 °C were obtained for the composition of the polymer matrix to the plasticizer as 35/65 (in mass) after the H₃PO₄ doping from the aqueous solution with 2.93 mol l⁻¹. FT-IR spectra showed that these high proton conductivities are attributed to the presence of excesses free H₃PO₄ in the polymeric gel in addition to the hydrogen-bonded H₃PO₄ to the polymer matrix.     

Lithium ion conductivity of gel polymer electrolytes containing insoluble lithium tetrakis(pentafluorobenzenethiolato) borate

Lithium ion conducting gel polymer electrolytes composed of insoluble lithium tetrakis(pentafluorobenzenethiolato) borate (LiTPSB), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and ethylene carbonate–propylene carbonate mixed solvent (EC–PC) were prepared and their ionic conductivities and electrochemical stabilities were investigated. Ionic conductivity was largely dependent on the contents of EC–PC and LiTPSB. Gel polymer electrolyte containing optimized content of 50 (LiTPSB)–50 (PVDF-HFP/EC–PC (13:87 wt.%)) exhibited ionic conductivity of 4 × 10⁻⁴ S cm⁻¹ at 30 °C, lithium ion transference number of 0.33 and anodic oxidation potential of 4.2 V.     

Photocured PEO-based solid polymer electrolyte and its application to lithium–polymer batteries

A solid polymer electrolyte (SPE) based on polyethylene oxide (PEO) is prepared by photocuring of polyethylene glycol acrylates. The conductivity is greatly enhanced by adding low molecular weight poly(ethylene glycol) dimethylether (PEGDME). The maximum conducticity is 5.1×10⁻⁴ S cm⁻¹ at 30°C. These electrolytes display oxidation stability up to 4.5 V against a lithium reference electrode. Reversible electrochemical plating/stripping of lithium is observed on a stainless steel electrode. Li/SPE/LiMn₂O₄ as well as C(Li)/SPE/LiCoO₂ cells have been fabricated and tested to demonstrate the applicability of the resulting polymer electrolytes in lithium–polymer batteries.     

Structure and performance of porous polymer electrolytes based on P(VDF-HFP) for lithium ion batteries

In order to develop polymer electrolyte for lithium ion batteries, highly porous P(VDF-HFP) membranes were prepared by using phase inversion method, then they were immerged in 1 mol kg⁻¹ solution of LiClO₄-EC/PC(1:1) to form porous polymer electrolytes. Conductivity of the polymer electrolytes was found to be as high as 10⁻³ S cm⁻¹. Structures of the porous membranes were observed with SEM. Porous membranes with different structure, porosity and pore diameter were prepared by changing the processing conditions. There are two kinds of typical structure, one is honeycomb-like (type I), and the other is network-like (type II). Membrane structures were found to be important to the performance of the porous polymer electrolytes. Small pore diameter with narrow distribution is needed to prevent solution leakage and high porosity is needed to achieve high conductivity. The type II membranes can meet the requirements. The model lithium ion batteries made of the resulting porous polymer electrolytes have good cycleablity.     

P(DMS-co-EO)/P(EPI-co-EO) blend as a polymeric electrolyte

A new polymer electrolyte comprising the blend of poly(dimethylsiloxane-co-ethylene oxide) (P(DMS-co-EO)), and poly(epichlorohydrin-co-ethylene oxide) (P(EPI-co-EO)), with different concentrations of LiClO₄ is described. The polymer electrolyte was prepared by a solution-cast technique. The electrochemical properties were studied by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry techniques. The maximum ionic conductivity (σ=1.2×10⁻⁴ S cm⁻¹) was obtained for the P(DMS-co-EO)/P(EPI-co-EO) 15/85 and 20/80 blends with 6 wt.% LiClO₄. These same films had a wide electrochemical stability, higher than 5 V at room temperature. A stable passive layer at the interface between the polymer electrolyte and lithium metal was formed within the first few days and maintained during the follow storage period. UV-Vis absorption spectra of the blends showed a transparent polymer electrolyte in the visible region.     

Sulfonated poly(ether sulfone) for universal polymer electrolyte fuel cell operations

The performances of the proton exchange membrane fuel cell (PEMFC), direct formic acid fuel cell (DFAFC) and direct methanol fuel cell (DMFC) with sulfonated poly(ether sulfone) membrane are reported. Pt/C was coated on the membrane directly to fabricate a MEA for PEMFC operation. A single cell test was carried out using H₂/air as the fuel and oxidant. A current density of 730 mA cm⁻² at 0.60 V was obtained at 70 °C. Pt–Ru (anode) and Pt (cathode) were coated on the membrane for DMFC operations. It produced 83 mW cm⁻² maximum power density. The sulfonated poly(ether sulfone) membrane was also used for DFAFC operation under several different conditions. It showed good cell performances for several different kinds of polymer electrolyte fuel cell applications.     

A new comb-like copolymer and its blend with poly(ethylene oxide) for solid electrolytes and application in dye-sensitized solar cells

Poly(N-propyl-vinylimidazolium iodide-co-poly(ethylene glycol) methyl ether methacrylate) with a comb-like configuration was synthesized. The copolymer and its blend with poly(ethylene oxide) (PEO) were used to prepare the polymer electrolytes for solid dye-sensitized solar cells. The amorphous characteristics and the ion-crosslinking effects of the copolymer and its blend electrolyte were analyzed by WAXS, DSC and FT-IR. The copolymer and PEO in the blend electrolyte were shown to play the roles of decreasing the crystallinity and breaking the ion-crosslinking, respectively. The blend electrolytes thus presented the highest ionic conductivity among the prepared electrolytes. The as-prepared DSSCs yielded the energy conversion efficiency of 3.46% at 100 mW cm^?2. The impedance results indicated the improved photovoltaic performance of the blend electrolyte was originated from the increased ionic diffusion coefficient and the prevented downward movement of the conduction band edge of TiO₂.     

All solid-state lithium-polymer battery using poly(urethane acrylate)/nano-SiO2 composite electrolytes

New composite polymer electrolytes composed of polyurethane acrylate (PUA), nano-size SiO₂ as a ceramic filler, and LiN(CF₃SO₂)₂ as a lithium salt were examined in an all-solid-state lithium-polymer battery (Li/PUA-SiO₂/Li_0.33MnO₂). The addition of hydrophobic SiO₂ could increase the ionic conductivity of polymer electrolyte about one-fold. The dynamic modulus of polymer electrolyte increased 50 and 150% by adding 9.1% hydrophobic and hydrophilic SiO₂, respectively. The addition of nano-size SiO₂ powders enhanced greatly the interfacial stability between polymer electrolytes and lithium electrode. The capacity fading of the cell could be improved by the addition of nano-size SiO₂ powders. The cycling performance of the cell reached about 75 and 45% of initial capacity (192 mAh g⁻¹) after 100, and 500 cycles, respectively, with an efficiency of charge–discharge of about 100% at 60 °C.     

Synthesis,characterization and thermal properties of novel nanoencapsulated phase change materials for thermal energy storage

In this paper, nanocapsules containing n-octadecane with an average 50 nm thick shell of poly(ethyl methacrylate) (PEMA) and poly(methyl methacrylate) (PMMA), and a core/shell weight ratio of 80/20 were synthesized by the direct miniemulsion method, respectively. The average size of the capsules is 140 nm and 119 nm, respectively. The chemical structure of the sample was analyzed using Fourier Transformed Infrared Spectroscopy (FTIR). Crystallography of nanocapsules was investigated by X-ray diffractometer. The surface morphology was studied by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The thermal properties and thermal stability of the sample were obtained from Differential Scanning Calorimeter (DSC) and Thermal Gravimetric Analysis (TGA). The temperatures and latent heats of melting and crystallizing of PEMA nanocapsule were determined as 32.7 and 29.8 °C, 198.5 and ?197.1 kJ/kg, respectively. TGA analysis indicated that PEMA/octadecane nanocapsule had good thermal stability. The nanocapsules prepared in this work had a much higher encapsulation ratio (89.5%) and encapsulation efficiency (89.5%). Therefore, the findings of the work lead to the conclusion that the present work provides a novel method for fabricating nanoencapsulated phase change material, and it has a better potential for thermal energy storage.     

Electrochemical properties of the Li-ion polymer batteries with P(VdF-co-HFP)-based gel polymer electrolyte

Gel polymer electrolytes consisting of 25 wt.% P(VdF-co-HFP), 65 wt.% ethylene carbonate + propylene carbonate and 10 wt.% LiN(CF₃SO₂)₂ are prepared using by a solvent-casting technique. The electrodes are for use in lithium-ion polymer batteries. The electrochemical characteristics of the gel polymer electrolytes are evaluated by means of ac impedance and cyclic voltammetry. The charge–discharge performance of lithium polymer and lithium-ion polymer batteries is examined. A LiCoO₂ | gel polymer electrolyte (GPE) | mesocarbon microbeads (MCMB) cell delivers a discharge capacity of 146.8 and 144.5 mAh g⁻¹ on the first and the 20th cycle, respectively. The specific discharge capacity is greater than 140 mAh g⁻¹ for up to 20 cycle at all the current densities examined.     

The effect of nanosized TiO2 addition on poly(methylmethacrylate) based polymer electrolytes

The electrochemical, X-ray diffraction, thermal, rheological and spectroscopic studies have been carried out to examine the effect of nanosized TiO₂ addition in different concentration to polymethylmethacrylate (PMMA) based gel polymer electrolytes (GPE). This work demonstrates that with optimum concentration of TiO₂ loadings in GPE, the ionic conductivity enhances with negligible effect on other electrochemical properties. The obtained ionic conductivity value is >10⁻³ S cm⁻¹. An increase in viscosity by an order of magnitude is obtained which also restricts the flow property of GPE. The addition of TiO₂ retains the amorphicity of the GPE while the T_g increases. Enhanced mechanical stability of these composite polymer electrolytes (CPEs) with solid-like behavior is evident from their appearance. The activation energy has been calculated by fitting the conductivity profile in VTF equation, which decreases on the addition of fillers. FTIR characterization also confirms the interaction of filler with CO of PMMA. The capabilities and properties exhibited by these CPEs will be of immense interest for electrochemists to use them in solid-state devices.     

Ionic conductance of PDMAEMA/PEO polymeric electrolyte containing lithium salt mixed with plasticizer

Novel plasticized polymer electrolytes were synthesized with poly(N,N-dimethylamino-ethyl-methacrylate) (PDMAEMA), polyethylene oxide (PEO), LiTFSI as a salt, tetraethylene glycol dimethyl ether (tetraglyme), EC/PC and DEP as plasticizers. The ionic conductivity of various compositions of polymer electrolytes was investigated as a function of temperature, various concentrations of LiTFSI, plasticizers and various ratio of PDMAEMA/PEO. The ionic conductivity of PDMAEMA/PEO/LiTFSI (1.5 mol kg⁻¹) with DEP as a plasticizer (1.5 × 10⁻⁴ S cm⁻¹) exhibited lower than PDMAEMA/PEO/LiTFSI (1.2 mol kg⁻¹)/tetraglyme (5.24 × 10⁻⁴ S cm⁻¹) and PDMAEMA/PEO/LiTFSI (1.5 mol kg⁻¹)/EC + PC (2.1 × 10⁻⁴ S cm⁻¹). As increasing the PDMAEMA concentration up to 13.3%, the ionic conductivity was decreased rapidly. As increasing the PDMAEMA concentration the ionic conductivity was decreased due to high viscosity and some interactions reducing ion pairing. These plasticized polymer electrolytes were characterized by impedance spectroscopy and DSC.     

Interface properties between a lithium metal electrode and a poly(ethylene oxide) based composite polymer electrolyte

The interface resistance between a lithium metal electrode and a polymer electrolyte has been measured for composite polymer electrolytes using various ceramic fillers with poly(ethylene oxide) (PEO) and lithium salts (LiX). The interface resistance depended on the properties of added fillers and lithium salts. The PEO with LiClO₄ electrolyte contacted with lithium metal showed the high interfacial resistance of 1000 Ω cm² at 70°C for 25 days. In contrast, the interface resistance between lithium metal and PEO with Li(CF₃SO₂)₂N was as low as 67 Ω cm² after contacting at 80°C for 30 days. The interface stability and the lithium ion conductivity were improved by addition of a small amount of ferroelectric BaTiO₃ as the filler into the PEO–LiX electrolyte.     

The effect of type of the inorganic filler and dopant salt concentration on the PEO–LiClO4 based composite electrolyte–lithium electrode interfacial resistivity

In the present paper the effect of the type of inorganic filler on the composite polymeric electrolyte–lithium electrode interfacial behavior is analyzed. Studies are performed in the wide LiClO₄ concentration range using poly(ethylene oxide)dimethyl ether (PEODME) as an electrolyte matrix. It is demonstrated that both the formation and the growth of the resistive layers at the polymer electrolyte–lithium electrode interface are determined by the salt concentration range and depend also on the type of the filler used. It is demonstrated that for salt concentrations lower than 10⁻³ mol kg⁻¹ or higher than 1 mol kg⁻¹ addition of filler results in the suppression of the growth of the resistance of the interfacial layer. This effect has been related to an increase in lithium cation transference number observed in these salt concentration ranges in composite electrolytes compared to the pure PEODME–LiClO₄ analogues. The effect of the filler on conductivity, microstructure and thermal characteristic of electrolytes studied is also discussed.