A polymer electrolyte containing ionic liquid for possible applications in photoelectrochemical solar cells

Various iodide ion conducting polymer electrolytes have been studied as candidate materials for fabricating photoelectrochemical (PEC) solar cells and energy storage devices. In this study, enhanced ionic conductivity values were obtained for the ionic liquid tetrahexylammonium iodide containing polyethylene oxide (PEO)-based plasticized electrolytes. The analysis of thermal properties revealed the existence of two phases in the electrolyte, and the conductivity measurements showed a marked conductivity enhancement during the melting of the plasticizer-rich phase of the electrolyte. Annealed electrolyte samples showed better conductivity than nonannealed samples, revealing the existence of hysteresis. The optimum conductivity was shown for the electrolytes with PEO:salt = 100:15 mass ratio, and this sample exhibited the minimum glass transition temperature of 72.2 °C. For this optimum PEO to salt ratio, the conductivity of nonannealed electrolyte was 4.4 × 10⁻⁴ S cm⁻¹ and that of the annealed sample was 4.6 × 10⁻⁴ S cm⁻¹ at 30 °C. An all solid PEC solar cell was fabricated using this annealed electrolyte. The short circuit current density (I _SC), the open circuit voltage (V _OC), and the power conversion efficiency of the cell are 0.63 mA cm⁻², 0.76 V, and 0.47% under the irradiation of 600 W m⁻² light.     

Improved properties of polymer electrolyte by ionic liquid PP1.3TFSI for secondary lithium ion battery

A new kind of polymer electrolyte is prepared from N-methyl-N-propylpiperidinium bis (trifluoromethanesulfonyl) imide (PP1.3TFSI), polyethylene oxide (PEO), and lithium bis (trifluoromethanesulfonyl) imide (LiTFSI). IR and X-ray diffraction results demonstrate that the addition of ionic liquid decreases the crystallization of PEO. Thermal and electrochemical properties have been tested for the solid polymer electrolytes, the addition of the room temperature molten salt PP1.3TFSI to the conventional P(EO)₂₀LiTFSI polymer electrolyte leads to the improvement of the thermal stability and the ionic conductivity (x = 1.27, 2.06 × 10⁻⁴ S cm⁻¹ at room temperature), and the reasonable lithium transference number is also obtained. The Li/LiFePO₄ cell using this polymer electrolyte shows promising reversible capacity, 120 mAh g⁻¹ at room temperature and 164 mAh g⁻¹ at 55 °C.     

Synthesis and electrochemical characterization of aPEO-based polymer electrolytes

In this paper, the preparation and purification of an amorphous polymer network, poly[oxymethylene-oligo(oxyethylene)], designated as aPEO, are described. The flexible CH₂CH₂O segments in this host polymer combine appropriate mechanical properties, over a critical temperature range from −20 to 60 °C, with labile salt-host interactions. The intensity of these interactions is sufficient to permit solubilisation of the guest salt in the host polymer while permitting adequate mobility of ionic guest species. We also report the preparation and characterisation of a novel polymer electrolyte based on this host polymer with lithium tetrafluoroborate, LiBF₄, as guest salt. Electrolyte samples are thermally stable up to approximately 250 °C and completely amorphous above room temperature. The electrolyte composition determines the glass transition temperature of electrolytes and was found to vary between −50.8 and −62.4 °C. The electrolyte composition that supports the maximum room temperature conductivity of this electrolyte system is n = 5 (2.10 × 10⁻⁵ S cm⁻¹ at 25 °C). The electrochemical stability domain of the sample with n = 5 spans about 5 V measured against a Li/Li⁺ reference. This new electrolyte system represents a promising alternative to LiCF₃SO₃ and LiClO₄-doped PEO analogues.     

Synthesis and properties of Co–Pt alloy silica core-shell particles

This paper describes a method for fabrication of silica-coated Co–Pt alloy nanoparticles in a liquid phase process. The Co–Pt nanoparticles were prepared from CoCl₂ (4.2 × 10⁻⁵ M), H₂PtCl₆ (1.8 × 10⁻⁵ M), citric acid (4 × 10⁻⁴ M) and NaBH₄ (1.2 × 10⁻² M) with a Co:Pt mole ratio of 7:3. The silica coating was performed in water/ethanol solution with a silane coupling agent, 3-aminopropyltrimethoxysilane (8 × 10⁻⁵ M), and a silica source, tetraethoxyorthosilicate (7.2 × 10⁻⁴ M) in the presence of the Co–Pt nanoparticles. Observations with a transmittance electron microscope and a scanning transmission electron microscope revealed that the Co-rich and Pt-rich nanoparticles were coated with silica. According to X-ray diffraction measurements, core particles were crystallized to metallic Co crystallites and fcc Co–Pt alloy crystallites with annealing in air at 300–500 °C. Magnetic properties of the silica-coated particles were strongly dependent on annealing temperature. Maximum values of 11.4 emu/g-sample for saturation magnetization and 365 Oe for coercive field were obtained for the particles annealed at 300 and 500 °C, respectively. Annealing at a temperature as high as 700 °C destroyed the coating structures because of crystallization of silica shell, resulting in reduction in saturation magnetization and coercive field.     

Low-temperature behavior of Li3V2(PO4)3/C as cathode material for lithium ion batteries

The electrochemical performance of Li₃V₂(PO₄)₃/C was investigated at various low temperatures in the electrolyte 1.0 mol dm⁻³ LiPF₆/ethyl carbonate (EC)+diethyl carbonate (DEC)+dimethyl carbonate (DMC) (volume ratio 1:1:1). The stable specific discharge capacity is 125.4, 122.6, 119.3, 116.6, 111.4, and 105.7 mAh g⁻¹ at 26, 10, 0, −10, −20, and −30 °C, respectively, in the voltage range of 2.3–4.5 V at 0.2 C rate. When the temperature decreases from −30 to −40 °C, there is a rapid decline in the capacity from 105.7 to 69.5 mAh g⁻¹, implying that there is a nonlinear relationship between the performance and temperature. With temperature decreasing, R _ct (corresponding to charge transfer resistance) increases rapidly, D (the lithium ion diffusion coefficients) decreases sharply, and the performance of electrolyte degenerates obviously, illustrating that the low-temperature electrochemical performance of Li₃V₂(PO₄)₃/C is mainly limited by R _ct, D _Li, and electrolyte.     

DSC study of the deposition reactions of zinc pack coatings up to 550°C

Zn pack coating formation takes place in three steps as differential scanning calorimetry shows. The initial step (at 193.9°C) is endothermic and involves the transformation of α-NH₄Cl to β-NH₄Cl and the NH₄Cl decomposition to NH₃ and HCl. During the second step (at 248.6°C), which is exothermic, Zn²⁺ salts are formed and most probably ZnCl₂. Finally at 264.1°C (endothermic reaction) it seems that ZnCl2 is decomposed to form Zn that is deposited on the ferrous substrate. The as-cast Zn diffuses in the iron substrate forming the gamma and delta phase of the Fe–Zn phase diagram. Al₂O₃ is not involved in the above-mentioned mechanism and acts only as filler.     

PEO-LITFSI-SiO2-SN System Promotes the Application of Polymer Electrolytes in All-Solid-State Lithium-ion Batteries

All-solid-state polymer lithium-ion batteries are ideal choice for the next generation of rechargeable lithium-ion batteries due to their high energy, safety and flexibility. Among all polymer electrolytes, PEO-based polymer electrolytes have attracted extensive attention because they can dissolve various lithium salts. However, the ionic conductivity of pure PEO-based polymer electrolytes is limited due to high crystallinity and poor segment motion. An inorganic filler SiO₂ nanospheres and a plasticizer Succinonitrile (SN) are introduced into the PEO matrix to improve the crystallization of PEO, promote the formation of amorphous region, and thus improve the movement of PEO chain segment. Herein, a PEO₁₈−LiTFSI−5 %SiO₂−5 %SN composite solid polymer electrolyte (CSPE) was prepared by solution-casting. The high ionic conductivity of the electrolyte was demonstrated at 60 °C up to 3.3×10⁻⁴ S cm⁻¹. Meanwhile, the electrochemical performance of LiFePO₄/CSPE/Li all-solid-state battery was tested, with discharge capacity of 157.5 mAh g⁻¹ at 0.5 C, and capacity retention rate of 99 % after 100 cycles at 60 °C. This system provides a feasible strategy for the development of efficient all-solid-state lithium-ion batteries.     

Electrochemical studies on Zn deposition and dissolution in sulphate electrolyte

The electrochemical deposition and dissolution of Zn on Pt electrode in sulphate electrolyte was investigated by electrochemical methods in an attempt to contribute to the better understanding of the more complex Zn–Cr alloy electrodeposition process. A decrease of the Zn electrolyte pH (from 5.4 to 1.0) so as to minimise/avoid the formation of hydroxo-products of Cr in the electrolyte for deposition of alloy coatings decreases the current efficiency for the Zn reaction, but the rate of the cathode reaction increases significantly due to intense hydrogen evolution. The results of the investigations in Zn electrolytes with pH 1.0–1.6 indicate that Zn bulk deposition is preceded by hydrogen evolution, stepwise Zn underpotential deposition (UPD) and formation of a Zn–Pt alloy. Hydrogen evolution from H₂O starts in the potential range of Zn bulk deposition. Data obtained from the electrochemical quartz crystal microbalance (EQCM) measurements support the assumption that electrochemical deposition of Zn proceeds at potentials more positive than the reversible potential of Zn. Anodic potentiodynamic curves for galvanostatically and potentiostatically deposited Zn layers provide indirect evidence about the dissolution of Zn from an alloy with the Pt substrate. The presumed potential of co-deposition of Cr (−1.9 V vs. Hg/Hg₂SO₄) is reached at a current density of about 300 mA cm⁻².     

Enhanced electrochemical properties of polyethylene oxide-based composite solid polymer electrolytes with porous inorganic–organic hybrid polyphosphazene nanotubes as fillers

Solid composite polymer electrolytes consisting of polyethylene oxide (PEO), LiClO₄, and porous inorganic–organic hybrid poly (cyclotriphosphazene-co-4, 4′-sulfonyldiphenol) (PZS) nanotubes were prepared using the solvent casting method. Differential scanning calorimetry and scanning electron microscopy were used to determine the characteristics of the composite polymer electrolytes. The ionic conductivity, lithium ion transference number, and electrochemical stability window can be enhanced after the addition of PZS nanotubes. The electrochemical impedance showed that the conductivity was improved significantly. Maximum ionic conductivity values of 1.5 × 10⁻⁵ S cm⁻¹ at ambient temperature and 7.8 × 10⁻⁴ S cm⁻¹ at 80 °C were obtained with 10 wt.% content of PZS nanotubes, and the lithium ion transference number was 0.35. The good electrochemical properties of the solid-state composite polymer electrolytes suggested that the porous inorganic–organic hybrid polyphosphazene nanotubes had a promising use as fillers in SPEs and the PEO₁₀–LiClO₄–PZS nanotube solid composite polymer electrolyte might be used as a candidate material for lithium polymer batteries.     

Electrochemical properties of LiFePO4/C synthesized using polypyrrole as carbon source

LiFePO₄/C composites were synthesized by pyrolysis of LiFePO₄/polypyrrole (PPy), which was obtained by an in situ chemical polymerization involving pyrrole monomer and hydrothermal synthesis LiFePO₄. All samples were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy, cyclic voltammetry, and galvanostatic charge–discharge techniques. The results showed the LiFePO₄/C sintered at 800 °C containing 2.8 wt.% carbon exhibited a higher discharge capacity of 49.6 mAh·g⁻¹ at 0.1 C, and bare LiFePO₄ only delivered 11.6 mAh·g⁻¹ in 2 M LiNO₃ aqueous electrolyte. The possible reason for the improvement of electrochemical performance was discussed and could be attributed to the formation of aromatic compounds during the carbonization of PPy.     

Porous inorganic filler Li4.7Ag1.63GeS4.8 in PEO electrolyte effectively inhibits Li dendrites for all-solid-state Li metal batteries

The newly created porous inorganic particles Li_4.7Ag_1.63GeS_4.8 as filler are added into poly (ethylene oxide) (PEO) with LiTFSI salt, which greatly improves the electrochemical stability of solid-state PEO-based electrolytes against Li metal in a working battery. Due to many pores and channels in the filler, Li dendrites would grow along these channels thereby effectively inhibiting their fast spread in PEO matrix and retarding the short circuit on account of the penetration of Li dendrite. The Li⁺ conductivity of this solid-state electrolyte membrane could be 1.36 × 10^-4 S/cm at 40 °C. The fabricated symmetrical Li metal cells could cycle above 550 h at 0.05 mA/cm² and corresponding LiFePO₄/Li all-solid-state cells have an excellent cycling stability of 160.65 mAh g^-1 specific capacity after 200 cycles with 99.93% columbic efficiency at 50 °C environment.     

Synthesis and characterization of submicron size particles of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> by microemulsion route

Among the various positive electrode materials investigated for Li-ion batteries, spinel LiMn₂O₄ is one of the most important materials. Small particles of the active materials facilitate high-rate capability due to large surface to mass ratio and small diffusion path length. The present work involves the synthesis of submicron size particles of LiMn₂O₄ in a quaternary microemulsion medium. The precursor obtained from the reaction is heated at different temperatures in the range from 400 to 900 °C. The samples heated at 800 and 900 °C are found to possess pure spinel phase with particle size <200 nm, as evidenced from XRD, SEM, and TEM studies. The electrochemical characterization studies provide discharge capacity values of about 100 mAh g⁻¹ at C/5 rate, and there is a moderate decrease in capacity by increasing the rate of charge–discharge cycling. Studies also include charge–discharge cycling and ac impedance studies in temperature range from −10 to 40 °C. Impedance data are analyzed with the help of an equivalent circuit and a nonlinear least squares fitting program. From temperature dependence of charge-transfer resistance, a value of 0.62 eV is obtained for the activation energy of Mn³⁺/Mn⁴⁺ redox process, which accompanies the intercalation/deintercalation of the Li⁺ ion in LiMn₂O₄.     

Magnesium ion-conducting gel polymer electrolytes dispersed with fumed silica for rechargeable magnesium battery application

Effect of fumed silica dispersion on poly(vinylidene fluoride-co-hexafluoropropylene)-based magnesium ion-conducting gel polymer electrolyte has been studied using various physical and electrochemical techniques. The composite gel electrolytes are free-standing and flexible films with enough mechanical strength. The optimized composition with 3 wt.% filler offers a maximum ionic conductivity of ∼1.1 × 10⁻² S cm⁻¹ at ∼25 °C with good thermal and electrochemical stabilities. The Mg²⁺ ion conduction in the gel nanocomposite film is confirmed from the cyclic voltammetry, impedance spectroscopy, and transport number measurements. The space-charge layers formed between filler particles and gel electrolyte are responsible for the enhancement in ionic conductivity. The applicability of the gel nanocomposite to a rechargeable battery is examined by fabricating a prototype cell consisting of Mg [or Mg-multiwalled carbon nanotube (MWCNT) composite] and MoO₃ as negative and positive electrodes, respectively. The discharge capacity and the rechargeability of the cell have been improved when Mg metal is substituted by Mg-MWCNT composite. The discharge capacity of the optimized cell has found to be ∼175 mAh g⁻¹ of MoO₃ for an initial ten charge–discharge cycles.     

Optimising organic ionic plastic crystal electrolyte for all solid-state and higher than ambient temperature lithium batteries

Organic ionic plastic crystal (OIPC) electrolytes are among the key enabling materials for solid-state and higher than ambient temperature lithium batteries. This work overviews some of the parameter studies on the Li|OIPC interface using lithium symmetrical cells as well as the optimisation and performance of Li|OIPC|LiFePO₄ cells. The effects of temperature and electrolyte thickness on the cycle performance of the lithium symmetrical cell, particularly with respect to the interfacial and bulk resistances, are demonstrated. Whilst temperature change substantially alters both the interfacial and bulk resistance, changing the electrolyte thickness predominantly changes the bulk resistance only. In addition, an upper limit of the current density is demonstrated, above which irreversible processes related to electrolyte decomposition take place. Here, we demonstrate an excellent discharge capacity attained on LiFePO₄|10 mol% LiNTf₂-doped [C₂mpyr][NTf₂]|Li cell, reaching 126 mAh g^-1 at 50 °C (when the electrolyte is in its solid form) and 153 mAh g^-1 at 80 °C (when the electrolyte is in its liquid form). Most remarkably, at high temperature operation, the capacity retention at long cycles and high current is excellent with only a slight (3%) drop in discharge capacity upon increasing the current from 0.2 C to 0.5 C. These results highlight the real prospects for developing a lithium battery with high temperature performance that easily surpasses that achievable with even the best contemporary lithium-ion technology.     

Effect of heat treatment on electrochromic properties of TiO<Subscript>2</Subscript> thin films

Electrochromic titanium oxide (TiO₂) films were deposited on ITO/glass substrates by chemical solution deposition (CSD). The stock solutions were spin-coated onto substrates and then heated at various temperatures (200–500 °C) in various oxygen concentrations (0–80%) for 10 min. The effects of the processing parameters on the electrochromic properties of TiO₂ films were investigated. X-ray diffraction measurements demonstrated that the amorphous TiO₂ films were crystallized to form anatase films above 400 °C. The electrochromic properties and transmittance of TiO₂ films were measured in 1 M LiClO₄–propylene carbonate (PC) non-aqueous electrolyte. An amorphous 350 nm-thick TiO₂ film that was heated at 300°C in 60% ambient oxygen exhibited the maximum transmittance variation (ΔT%), 14.2%, between the bleached state and the colored state, with a ΔOD of 0.087, Q of 10.9 mC/cm², η of 7.98 cm²/C and x in Li _x ClO₄ of 0.076 at a wavelength (λ) of 550 nm.     

Development of activated carbon from vine shoots by physical and?chemical activation methods. Some insight into activation mechanisms

Activated carbons (ACs) are prepared from vine shoots (VS) by the method of physical activation in air, CO₂ and steam atmospheres and by the method of chemical activation with H₃PO₄, ZnCl₂ and KOH aqueous solutions. The ACs were characterized texturally by N₂ adsorption at −196 °C, mercury porosimetry, and density measurements. The method of chemical activation has been proved to be more effective than the method of physical activation to prepare ACs with a well-developed porosity. ACs with high micro- and mesopore volumes are prepared with ZnCl₂ and H₃PO₄. Using ZnCl₂, the volume of micropores is 0.62 cm³ g⁻¹ and the volume of mesopores is 0.81 cm³ g⁻¹. A greater development of macroporosity is obtained by KOH activation. The volume of macropores is as high as 1.13 cm³ g⁻¹ for the resulting AC. Yield of the process of preparation of the ACs is low for the method of chemical activation. Some insights into the performance of the activating agents in the activation process are provided.     

Effects of humidity and temperature on the electrochemical activities of H2/O2 PEMFCs using hybrid membrane electrolytes

Electrochemical characteristics of single cell performances at various humidity conditions and constant temperatures of 40?100 °C using membrane electrode assemblies (MEAs) were studied. The MEAs consist of alternative proton-conducting hybrid membrane electrolyte and noble Pt/C catalyst for the H₂/O₂ proton exchange membrane fuel cells (PEMFCs). The function of humidity on the cell performances was investigated at larger current density values of 501 mA cm^?2 and constant cell temperatures of 80 and 90 °C and the relative humidity of 100 %. The power density value of 400 mW cm^?2 was obtained when the same MEA at similar operating conditions was used. The effects of temperature on the single cell performances were investigated at various temperature ranges of 40–100 °C and constant relative humidity of 50, 70, and 100 %. The maximum current density and power density values of about 600 mA cm^?2 and 160 mW cm^?2, respectively, were obtained at 90 °C with 100 % RH. The results were compared with the reported results of Nafion membrane and similar hybrid membranes operating at low temperatures for H₂/O₂ fuel cells. Finally, the results provided an alternative proton-conducting electrolyte as promising candidate for low/intermediate temperature operating H₂/O₂ fuel cells.     

Preparation of solutions of amidomagnesium chlorides in poly(ethylene oxide) and their characterization by conductivity measurements

Polymer electrolyte systems were prepared for the first time by dissolution of amidomagnesium chlorides in poly(ethylene oxide), (PEO). For the preparation, solutions of (hexamethyldisilylamido)magnesium chloride, (dimethylpyrrolyl)magnesium chloride, (diisopropylamido)magnesium chloride, piperidinomagnesium chloride and morpholinomagnesium chloride were chosen. The composition of these polymer electrolyte systems corresponds to the general formula R₂NMgCl·P(EO)_n·THF. Most work has been done with the system (hexamethyldisilylamido)magnesium chloride in PEO, (Me₃Si)₂NMgCl·P(EO)_n·THF, with n= 3, 4, 5, or 7. The electrolytes have a soft rubber-like consistency. At 30 °C, electrical conductivities of 10⁻⁶–10⁻⁵ S/cm were found. The conductivities were measured in the temperature range 20–60 °C. Within this temperature range a linear dependence of the logarithms of the conductivity on the inverse temperature was found and activation energies for the conducting process of 30–60 kJ/mol were calculated. Using those polymer electrolytes with a high content of the amidomagnesium compound, a reversible magnesium deposition takes place by cathodic reduction at potentials below −1.9 V vs. a Ag/AgCl reference electrode. These polymer electrolytes were found to be stable against oxidation up to about −0.3 V vs. Ag/AgCl. Electronic Publication     

Activity coefficient measurements of the system HCl−ZnCl2−H2O at 25 and 35°C

Electromotive force measurements were carried out on the HCl–ZnCl₂–H₂O system at constant total ionic strengths of 0.1, 0.2, 0.5, 1.0 and 2.0 mol-kg^–1 at 25 and 35°C using a cell consisting of Pt, H₂(g, 1 atm)|HCl(m_A), ZnCl₂(m_B)|AgCl/Ag. The data were interpreted by the mixed electrolyte equations of Pitzer and Kim in order to evaluate mixing ion-interaction parameters. The activity coefficients of ZnCl₂ and the Gibbs excess free energies of mixing are calculated and presented at I=2.0 mol-kg^–1 and compared with similar systems containing transition metal chlorides.     

One-step hydrothermal synthesis of LiMn2O4 cathode materials for rechargeable lithium batteries

LiMn₂O₄ cathode materials with high discharge capacity and good cyclic stability were prepared by a simple one-step hydrothermal treatment of KMnO₄, aniline and LiOH solutions at 120–180 °C for 24 h. The aniline/KMnO₄ molar ratio (R) and hydrothermal temperature exhibited an obvious influence on the component and phase structures of the resulting product. The precursor KMnO₄ was firstly reduced to birnessite when R was less than 0.2:1 at 120–150 °C. Pure-phased LiMn₂O₄ was formed when R was 0.2:1, and the LiMn₂O₄ was further reduced to Mn₃O₄ when R was kept in the range of 0.2–0.3 at 120–150 °C. Moreover, LiMn₂O₄ was fabricated when R was 0.15:1 at 180 °C. Octahedron-like LiMn₂O₄ about 300 nm was prepared at 120 °C, and particle size decreased with an increase in hydrothermal temperature. Especially, LiMn₂O₄ synthesized at 150 °C exhibited the best electrochemical performance with the highest initial discharge capacity of 127.4 mAh g⁻¹ and cycling capacity of 106.1 mAh g⁻¹ after 100 cycles. The high discharge capacity and cycling stability of the as-prepared LiMn₂O₄ cathode for rechargeable lithium batteries were ascribed to the appropriate particle size and larger cell volume.