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.     

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.     

Four volts class solid lithium polymer batteries with a composite polymer electrolyte

Polyethylene oxide (PEO)-based polymer electrolytes with BaTiO₃ as a filler have been examined as electrolytes in 4 V class lithium polymer secondary batteries. A mixture of 90 wt.% LiN(CF₃SO₂)₂–10 wt.% LiPF₆ was found to be the best candidate as the salt in PEO, and showed high electrical conductivity, good corrosion resistance to the aluminum current collector and low interfacial resistance between the lithium metal anode and the polymer electrolyte. The cyclic performance of the cell, Li/[PEO₁₀–(LiN(CF₃SO₂)₂–10 wt.% LiPF₆)]–10 wt.% BaTiO₃/LiNi_0.8Co_0.2O₂/Al, showed good charge–discharge cycling performance. The observed capacity fading on charging up to 4.2 V at 80 °C in the cell was about 0.28% per cycle in the first 30 cycles, compared to that of 0.5% for the polymer electrolyte without LiPF₆ in the lithium salt.     

Improved performance of Li hybrid solid polymer electrolyte cells

The seminal research by Wright et al. on polyethylene oxide (PEO) solid polymer electrolyte (SPE) generated intense interest in all solid-state rechargeable lithium batteries. Following this a number of researchers have studied the physical, electrical and transport properties of thin film PEO electrolyte containing Li salt. These studies have clearly identified the limitations of the PEO electrolyte. Chief among the limitations are a low cation transport number (t₊), high crystallinity and segmental motion of the polymer chain, which carries the cation through the bulk electrolyte. While low t₊ leads to cell polarization and increase in cell resistance high T_g reduces conductivity at and around room temperatures. For example, the conductivity of PEO electrolyte containing lithium salt is <10⁻⁷ S cm⁻¹ at room temperature. Although modified PEO electrolytes with lower T_g exhibited higher conductivity (∼10⁻⁵ S cm⁻¹ at RT) the t₊ is still very low ∼0.25 for lithium ion. Numerous other attempts to improving t₊ have met with limited success. The latest approach involves integrating nano domains of inorganic moieties, such as silcate, alumosilicate, etc. within the polymer component. This approach yields an inorganic–organic component (OIC) based polymer electrolyte with higher conductivity and t₊ for Li⁺_. This paper describes the improved electrical and electrochemical properties of OIC-based polymer electrolyte and cells containing Li anode with either a TiS₂ cathode or Mag-10 carbon electrode. Several solid polymer electrolytes derived from silicate OIC and salt-in-polymer constituent based on Li triflate (LiTf) and PEO are studied. A typical composition of the SPE investigated in this work consists of 600 kDa PEO, lithium triflate (LiTf, LiSO₃CF₃) and 55% of silicate based on (3-glycidoxypropyl)trimethoxysilane and tetramethoxysilane at molar ratio 4:1 and 0.65 mol% of aluminum(tri-sec-butoxide) (GTMOS-Al1-900k-55%). Several pouch cells consisting of Li/OIC-based–SPE/cathode containing OIC-based–SPE–LiTf binder were fabricated and tested, these cells are called modified cells. The charge/discharge and impedance characteristics of the new cells (also called modified cells) are compared with that of the pouch cells containing the conventional PEO–LiTf electrolyte as the cathode binder, these cells are called non-modified cells. The new cells can be charged and discharged at 70 °C at higher currents. However, the old cells can be charged and discharged only at 80 °C or above and at lower currents. The cell impedance for the new cells is much lower than that for the old cells.     

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.     

Improving the interfacial resistance in lithium cells with additives

Improved interfacial resistance was observed in lithium cells by the use of new additives. The additives, nitrile sucrose and nitrile cellulose and their lithium salts, were evaluated in polyvinylidene difluoride (PVDF) thin-film gelled electrolytes containing a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC). The electrochemical properties of the films with and without the additives were measured as a function of temperature and compared. The interfacial resistance (R_in) of the films with the additives was significantly lower than that without the additives, especially at sub-ambient temperatures. For example, the R_in at −20°C for the films with additives was around 7000 Ω cm² and that for the films without the additives was >20,000 Ω cm². Results obtained from using the additives in lithium-ion (Li-ion) cells show significant improvements in the low frequency resistance of the cells.     

Intermediate temperature fuel cells based on doped ceria–LiCl–SrCl2 composite electrolyte

A new type of oxide-salt composite electrolyte, gadolinium-doped ceria (GDC)–LiCl–SrCl₂, was developed and demonstrated its promising use for intermediate temperature (400–700 °C) fuel cells (ITFCs). The dc electrical conductivity of this composite electrolyte (0.09–0.13 S cm⁻¹ at 500–650 °C) was 3–10 times higher than that of the pure GDC electrolyte, indicating remarkable proton or oxygen ion conduction existing in the LiCl–SrCl₂ chloride salts or at the interface between GDC and the chloride salts. Using this composite electrolyte, peak power densities of 260 and 510 mW cm⁻², with current densities of 650 and 1250 mA cm⁻² were achieved at 550 and 625 °C, respectively. This makes the new material a good candidate electrolyte for future low-cost ITFCs.     

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.     

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.     

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.     

Study of dc conductivity and battery application of polyethylene oxide/polyaniline and its composites

The polymer electrolyte based on polyethylene oxide (PEO) complexed with conducting polyaniline (PANI) and salts of AgNO₃ and NaNO₃ has been prepared in different weight percentage ratios. The complexation is confirmed by infra-red and X-ray diffraction studies. Conductivity (dc) measurements are carried out using a two-probe technique in the temperature range 30–80 °C. Electrochemical cell parameters for battery application at room temperature are also been determined. The electric conductivities are 1.5 × 10⁻⁵ S cm⁻¹ at 30 °C and 5.5 × l0⁻² S cm⁻¹ at 80 °C for a PEO:PANI (50:50) composite. The conductivity increases with increasing weight percentage of polyaniline in polyethylene oxide, which may be due to a strong hopping mechanism between the ether group of polyethylene oxide and conducting polyaniline. Samples are fabricated for battery application in configurations of Na:(PEO + PANI):(I₂ + C + sample) and their experimental data are measured using the Wagner polarization technique.     

Electrochemical properties of amorphous comb-shaped composite PEO polymer electrolyte

The electrochemical behaviour of a polyethylene oxide (PEO)-based composite polymer electrolyte are studied. The crystallinity of the PEO is suppressed by using a comb-shaped polymer to improve polymer chain mobility. An amorphous comb-shaped polymer, ‘TEC-24’, with a side-chain content of 24 mol%, is designed and fine silica powder is dispersed within it to enhance the mechanical properties above the melting point. The composite polymer electrolyte has an ionic conductivity of 1.6×10⁻⁴ and 1.6×10⁻³ S cm⁻¹ at 30 and 90 °C, respectively, with an electrochemical stability window close to 5.0 V, even at 80 °C (versus Li/Li⁺). The polymer electrolyte is evaluated using CuS as a cathode material and shows better cycle performance than that obtained with a liquid electrolyte.     

Solid-state Li/LiFePO4 polymer electrolyte batteries incorporating an ionic liquid cycled at 40 °C

The cycle behaviour and rate performance of solid-state Li/LiFePO₄ polymer electrolyte batteries incorporating the N-methyl-N-propylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR₁₃TFSI) room temperature ionic liquid (IL) into the P(EO)₂₀LiTFSI electrolyte and the cathode have been investigated at 40 °C. The ionic conductivity of the P(EO)₂₀LiTFSI + PYR₁₃TFSI polymer electrolyte was about 6 × 10⁻⁴ S cm⁻¹ at 40 °C for a PYR₁₃⁺/Li⁺ mole ratio of 1.73. Li/LiFePO₄ batteries retained about 86% of their initial discharge capacity (127 mAh g⁻¹) after 240 continuous cycles and showed excellent reversible cyclability with a capacity fade lower than 0.06% per cycle over about 500 cycles at various current densities. In addition, the Li/LiFePO₄ batteries exhibited some discharge capability at high currents up to 1.52 mA cm⁻² (2 C) at 40 °C which is very significant for a lithium metal-polymer electrolyte (solvent-free) battery systems. The addition of the IL to lithium metal-polymer electrolyte batteries has resulted in a very promising improvement in performance at moderate temperatures.     

PVDF–PEO blends based microporous polymer electrolyte: Effect of PEO on pore configurations and ionic conductivity

A novel microporous polymer electrolyte based on poly(vinylidene fluoride) and poly(ethylene oxide) (PVDF–PEO) blends was prepared by a simple phase inversion technique, in which the addition of PEO can obviously improve the pore configuration, such as pore size, porosity, and pore connectivity of PVDF-based microporous membranes, and hence, the room temperature ionic conductivity was greatly enhanced. The highest porosity of about 84% and ionic conductivity of about 2 mS cm⁻¹ can be obtained when the weight ratio of PEO to PVDF is 50%. This implies that PVDF–PEO blends based microporous polymer electrolyte can be used as candidate electrolyte and/or separator material for high-performance rechargeable lithium batteries.     

Gel-type polymer electrolytes with different types of ceramic fillers and lithium salts for lithium-ion polymer batteries

Gel-type polymer electrolytes are prepared using PVdF/PEGDA/PMMA, LiPF₆/LiCF₃SO₃ mixed lithium salts and ceramic fillers such as Al₂O₃, BaTiO₃ and TiO₂. The electrochemical properties of these electrolytes, such as electrochemical stability, ionic conductivity and compatibility with electrodes are investigated in addition to the physical properties. The charge–discharge performances of lithium-ion polymer batteries using these get-type polymer electrolytes are investigated. The gel-type polymer electrolytes containing a mixed lithium salt of LiPF₆/LiCF₃SO₃ (10/1, wt.%) exhibit more stable ionic conductivity and lower interfacial resistance than those containing only LiPF₆. In addition, an Al₂O₃ filler improves interfacial stability between the electrode and the polymer electrolyte. Stacking cells (MCMB 1028/LiCoO₂, 8 cm × 13 cm × 7 ea) composed of gel-type polymer electrolytes based on PVdF/PEGDA/PMMA, LiPF₆/LiCF₃SO₃ (10/1, wt.%) and Al₂O₃ filler maintain 95% of initial capacity after 100 cycles at a C/2 rate.     

Carbon anode for dry-polymer electrolyte lithium batteries

A spherical carbon material of meso-carbon microbead (MCMB) was examined as an anode in a polyethylene oxide (PEO) based polymer electrolyte lithium battery. The electrochemical performance of the carbon electrode with the polymer electrolyte depended on the electrode thickness and the particle size of MCMB. The 30 μm-thick electrode of MCMB with the particle size of 20–30 μm showed a reversible capacity comparable with that in a liquid electrolyte, but the 100 μm-thick electrode showed a half of the 30 μm-thick electrode. The smaller particle size of 5–8 μm exhibited a high irreversible capacity at the first charge–discharge cycle. The reaction heat between MCMB and the polymer electrolyte was 0.5 J mAh^?1, which was much lower compared to those between lithium metal and the polymer electrolyte, 1.2 J mAh^?1, and MCMB and conventional liquid electrolyte, 4.3 J mAh^?1.     

Resistance distribution in electrochemical capacitors with spiral-wound structure

The distribution of internal resistance in a Panasonic 10 F, 2.5 V electrochemical capacitor comprised of activated carbon electrode and organic electrolyte was analyzed. It was found that in the direction along the electrode surface, the resistance of the cell was mainly determined by the current collector and was 1.7 × 10⁻³ Ω cm⁻¹. In the direction perpendicular to the electrode surface, the resistance was dependent on the applied pressure and a minimum resistance of 13.66 Ω cm² was obtained at an applied pressure of about 1 kg cm⁻². The resistance distribution at the applied pressure of 1 kg cm⁻² was 0.86, 1.91 and 8.11 Ω cm² contributing to the electrode carbon material, contact between the current collector and electrode and separator/electrolyte, respectively. A transmission line model was used to describe the cell resistance with dependence parameters, electrode length and the location of the electrical leads.     

A new polymer electrolyte system (PEO)n:NaPO3

A new Na⁺ ion conducting polymer electrolyte, based on poly(ethylene oxide) (PEO) and sodium meta phosphate (NaPO₃) is investigated. (PEO)_n:NaPO₃ polymer metal salt complexes with different [ethylene oxide]/Na ratios (n = 3, 4, 6, 8 and 10) are prepared by the solution casting method. Dissolution of the salt into the polymer host is confirmed by X-ray diffraction, differential scanning calorimetry (DSC) and scanning electron microscopy. Further, interaction of the polymer chains with the metal salt is substantiated by Fourier transform infrared spectroscopy. The electrical conductivity of the samples is measured over the temperature range 322–351 K. The temperature dependent conductivity exhibits two different activation energies, below and above the softening point of the polymer. The composition (PEO)₆:NaPO₃ is found to exhibit the least crystallinity but the highest conductivity 2.8 × 10⁻⁸ S cm⁻¹ at 351 K. The electronic transport number, measured by the dc polarization technique, shows that the conducting species are ionic in nature. The effect of ethylene carbonate on the best conducting composition is investigated by DSC and impedance spectroscopy. The addition of 20 wt.% ethylene carbonate, increases the amorphous phase and enhances the conductivity by two orders of magnitude.     

Mixture of LiBF4 and lithium difluoro(oxalato)borate for application as a new electrolyte for lithium-ion batteries

An equimolar mixture of fluoroborate salts: LiBF₄ and lithium difluoro(oxalate)borate LiBF₂(C₂O₄) (MIX-LiFBs) was obtained from a simple one-step reaction of lithium oxalate and boron fluoride. Voltamperommetry shows that the salt obtained is stable in the potential range of 4.9 V. Impedance measurements of liquid electrolytes involving imidazolium ionic liquid and aliphatic carbonates have been carried out, which show the highest ionic conductivity of the order of 10^?3 S cm^?1 (and low activation energy of 0.14 eV) when using carbonates as the solvent. The mixture of fluoroborate salts MIX-LiFBs used as a component of solid polymer electrolytes provides much higher ionic conductivity values at high salt concentrations in “polymer-in-salt systems”. The conductivity of solid polymer electrolytes was considerably increased by adding a low-molecular-weight organic plasticizer.     

Alkaline composite PEO–PVA–glass-fibre-mat polymer electrolyte for Zn–air battery

An alkaline composite PEO–PVA–glass-fibre-mat polymer electrolyte with high ionic conductivity (10⁻² S cm⁻¹) at room temperature has been prepared and applied to solid-state primary Zn–air batteries. The electrolyte shows excellent mechanical strength. The electrochemical characteristics of the batteries were experimentally investigated by means of ac impedance spectroscopy and galvanostatic discharge. The results indicate that the PEO–PVA–glass-fibre-mat composite polymer electrolyte is a promising candidate for application in alkaline primary Zn–air batteries.