Solid polymer electrolytes based on poly(lithium carboxylate) salts

The ionic conductivity, lithium ion transference number, electrochemical stability, and thermal property of solid polymer electrolytes composed of poly(ethylene oxide) (PEO) and poly(lithium carboxylate)s, (poly(lithium acrylate) (Poly(Li-A)) or poly(lithium fumarate) (Poly(Li-F)), with and without BF₃·OEt₂ were investigated. The ionic conductivities of all solid polymer electrolytes were enhanced by one to two orders of magnitude with addition of BF₃·OEt₂ because the dissociation of lithium ion and carboxylate anion was promoted by the complexation with BF₃. The lithium ion transference number in the solid polymer electrolytes based on poly(lithium carboxylate)s showed relatively high values of 0.41–0.70, due to the suppression of the transport of counter anion by the use of a polymeric anion. The solid polymer electrolytes with addition of BF₃·OEt₂ showed good electrochemical stability.     

Performance of ferrite fillers on electrical behavior of polymer nanocomposite electrolyte

Dispersal of nanofillers in polymer electrolytes have shown to improve the ionic properties of Polyethylene oxide (PEO)-based polymer electrolytes in recent times. The effects of different nanoferrite fillers (i.e., Al–Zn ferrite, Mg–Zn ferrite, and Zn ferrite) on the electrical transport properties have been studied here on the composite polymer electrolyte system. The interaction of salt/filler with electrolyte has been investigated by XRD studies. SEM image and infrared spectral studies give an indication of nanocomposite formation. In conductivity studies, all electrolyte systems are seen to follow universal power law. Composition dependence (with ferrite filler) gives the maximum conductivity in [93PEO–7NH₄SCN]: X ferrite (where X?=?2% in Al–Zn ferrite, 1% Mg–Zn ferrite, and 1% Zn ferrite) system.     

Effect of silane-functionalized mesoporous silica SBA-15 on performance of PEO-based composite polymer electrolytes

Silane-functionalized mesoporous silica SBA-15 particles with ultra-high specific surface area and large pore size were used as fillers in PEO-based solid electrolytes. FT-IR results confirmed the silane functionalization of SBA-15. Ionic conductivity and lithium ion transference number of the composite polymer electrolytes were found to simultaneously reach a high value of 5 wt.% silane-functionalized SBA-15 introduced in the matrix. It may be due to the combination effects of the unique structure of SBA-15 (i.e., ultra-high specific surface area and large pore size), the particularly functionalized surface of SBA-15 to promote fast ion transfer, and the good dispersion and compatibility of silane-functionalized SBA-15 in the composite polymer electrolytes. The results suggest an alternative way to improve the performance of solid polymer electrolytes.     

Vibrational,electrical, and structural properties of PVDF–LiBOB solid polymer electrolyte with high electrochemical potential window

Polyvinylidene difluoride (PVDF)–lithium bis(oxalato)borate (LiBOB) solid polymer electrolytes (SPEs) have been prepared by solution casting. The highest ionic conductivity achieved is 3.4610^?3 S cm^?1. Electrochemical potential window of the SPEs is found around 4.7 V. Interaction between PVDF and LiBOB is studied systematically. The changes of C–C, CF₂, and CH₂ vibration modes with an emerging shoulder are analyzed. At higher salt content, this shoulder becomes more prominent peak at the expense of CF₂ vibration mode. This suggests the possible Li⁺?F coordination. Deconvolution of IR spectra region from 1750 to 1850 cm^?1 has been carried out to estimate the relative percentage of free ions and contact ions. The finding is in good agreement with conductivity and XRD results. When more salt is present, the number of free ions percentage increases and the Full width at half-maximum (FWHM) of (110) plane is broadening. The Li⁺?F interaction breaks the folding patterns of polymer chain and enhances amorphousness domain.     

Electrochemical and thermal properties of hyperbranched polymer electrolytes for batteries

Terminal-acetylated hyperbranched poly(ethylene glycol) derivatives containing diethylene, triethylene, and hexaethylene and 3,5-dioxybenzoate branching units (poly-Ac1a, poly-Ac1b, and poly-Ac1c) were synthesized. Electrochemical and thermal properties of the hyperbranched polymer electrolytes with lithium salts such as LiCF₃SO₃ and LiN(CF₃SO₂)₂, the composite hyperbranched polymer electrolytes with LiN(CF₃SO₂)₂ containing α-LiAlO₂ and γ-LiAlO₂ fillers, and the hyperbranched polymer blended poly(ethylene oxide) electrolytes with LiN(CF₃SO₂)₂ were investigated and discussed. Paper presented at the 8th EuroConference on Ionics, Carvoeire, Algarve, Portugal, Sept. 16–22, 2001.     

Electric double layer capacitor based on activated carbon electrode and biodegradable composite polymer electrolyte

A series of polymer electrolyte based on poly(vinyl alcohol), lithium perchlorate (LiClO₄), and antimony trioxide (Sb₂O₃) was prepared via solution casting technique with distilled water as solvent. The dielectric behavior study reveals the non-Debye properties of the polymer electrolytes. In frequency dependence conductivity measurement, dispersion at low frequency was due to the interfacial resistance and space charge polarization inside the polymer electrolytes. The linear sweep voltammetry has proven that the incorporation of Sb₂O₃ into polymer matrix increases the maximum operational potential region. Electric double-layer capacitors (EDLCs) based on activated carbon electrode assembled with solid polymer electrolyte and composite polymer electrolyte has been evaluated by cyclic voltammetry (CV) and galvanostatic charge–discharge technique. CV test disclosed rectangular shapes with slight distortion, and there is no evidence for any redox currents on both anodic and cathodic sweeps, which indicates the typical behavior of EDLC. Both EDLC cells demonstrate good cyclability throughout 200 cycles with specific capacitance retention more than 90 %.     

Electrical and structural studies of a LiBOB-based gel polymer electrolyte

A series of gel polymer electrolytes (GPEs) containing lithium bis(oxalato)borate (LiBOB), propylene carbonate (PC), and ethylene carbonate (EC) have been investigated. Poly(ethylene oxide) (PEO) was used as the polymer. First, a series of liquid electrolytes was prepared by varying the Li:O ratio and obtained the best composition giving the highest conductivity of 7.1?×?10^?3 S cm^?1 at room temperature. Then, the PEO-based GPEs were prepared by adding different amounts of LiBOB and PEO into a mixture of equal weights of EC and PC (40 % of each from the total weight). The gel electrolyte comprises of 12.5 % of LiBOB, 7.5 % of PEO, 40 % of EC, and 40 % of PC gave the highest ionic conductivity of 5.8?×?10^?3 S cm^?1 at room temperature. From the DC polarization measurements, ionic nature of the gel electrolyte was confirmed. Fourier transform infrared (FTIR) spectra of electrolytes showed the Li⁺ ion coordination with EC and PC molecules. These interactions were exhibited in the peaks corresponding to ring breathing of EC at 893 cm^?1 and ring bending of EC and symmetric ring deformation of PC at 712 and 716 cm^?1 respectively. The presence of free Li⁺ ions and ion aggregates is evident in the peaks due to the symmetric stretching of O–B–O at 985 cm^?1.     

Influence of solid electrolyte particles size on ionic transport in model composite system (PVdF-HFP–Li1.3Al0.3Ti1.7(PO4)3)

The influence of filler particles size on lithium ion conductivity of composite polymer electrolytes was issued on model system vinylidenefluoride with hexafluoropropylene (PVdF-HFP)–Li_1.3Al_0.3Ti_1.7(PO₄)₃. Model electrolyte objects with filler grains of different sizes were prepared using a modified solvent casting method from a mixture of PVdF-HFP solution in dimethylformamide and Li_1.3Al_0.3Ti_1.7(PO₄)₃ solid electrolyte particles. The percolation threshold was defined and the transport properties of composite polymer electrolytes at different volume concentrations of the solid electrolyte investigated. A significant decrease in conductivity compared to that of ceramic solid electrolytes was observed. The size of the filler particles was found to affect the structure and transport properties of the prepared composite polymer electrolytes. The conductivity of the composite polymer electrolyte at 100 °C was found to increase by two orders of magnitude with the tenfold increase of the size of the filler particles.     

Raising the softening temperature of poly(vinylidene fluoride) gel electrolytes

Factors affecting the softening temperature of polymer gel electrolytes (PGEs) made from poly(vinylidene fluoride) (PVDF) have been investigated. The melting temperature transition has been found to rise with increased polymer concentration and salt concentration but reduced by solvent dielectric constant. The solvent dielectric constant was reduced by mixing propylene carbonate (PC) with the non-solvent phenyl propanol (PhP). The use of lithium salt bis(oxalate)borate (LiBOB) in place of lithium tetrafluroborote (LiBF₄) gives further enhancement to the softening temperature of PGEs. In all of those cases, there is an eventual trade-off between increased softening temperature and reduced ionic conductivity, in this fabricated gel electrolyte. Here, a variety of ways to tailor the properties of PGEs for different applications has been shown.     

Electrochemical performance of plasticized PEO-LiTf complex-based composite gel polymer electrolytes with the addition of barium titanate

Gel electrolytes and solid electrolytes have been reported as a potential element to slow down the polysulfide shuttle by reducing its mobility in the electrolytes. The preparation of sulfur-conductive polymer composites, or sulfur-carbon composites, has been reported as softening the impact of the shuttle effects. Unlike Li-ion batteries so far, no electrolyte is found to be optimal for Li–S batteries at all conditions. Taking into account all these factors, in the present study, an attempt has been made to develop solid polymer electrolytes in conjunction with non-aqueous liquid electrolytes along with inert fillers for Li–S batteries. Poly-ethylene oxide (PEO)-based composite gel polymer electrolytes (CGPE) comprising a combination of plasticizers, namely 1,3-dioxolane (DIOX)/tetraethylene glycol dimethylether (TEGDME) and a lithium salt (LiTf) with the addition of ceramic filler, barium titanate (BaTiO₃) have been prepared using a simple solution casting technique in an argon atmosphere. The as-prepared polymer electrolyte films were subjected to SEM, ionic conductivity, TG/DTA, and FTIR analyses. A symmetric cell composed of Li/CGPE/Li was assembled, and the variation of interfacial resistance as a function of time was also measured. The ionic conductivity was found to be increased as a function of temperature. The lithium transference number (Li_t ⁺) was measured, and the value was calculated as 0.7 which is sufficient for battery applications. The electrochemical stability window of the sample was studied by linear sweep voltammetry, and the polymer electrolyte film was found to be stable up to 5.7 V. The TG/DTA analysis reveals that this CGPE is thermally stable up to 350 °C. The compatibility studies exhibited that CGPE has better interracial properties with lithium metal anode. The interaction between the PEO and salt has been identified by an FTIR analysis.     

Preparation and ionic conductivity of composite polymer electrolytes based on hyperbranched star polymer

Hyperbranched star polymer HBPS-(PPEGMA) _x was synthesized by atom transfer radical polymerization (ATRP) using hyperbranched polystyrene (HBPS) as macroinitiator and poly(ethylene glycol) methyl ether methacrylate (PEGMA) as monomer. The structure of the prepared hyperbranched star polymer was characterized by ¹H NMR, ATR-FTIR, and GPC. Polymer electrolytes based on HBPS-(PPEGMA) _x , lithium salt, and/or nano-TiO₂ were prepared. The influences of lithium salt concentration and type, nano-TiO₂ content, and size on ionic conductivity of the obtained polymer electrolytes were investigated. The results showed that the low crystallinity of the prepared polymer electrolyte was caused by the interaction between lithium salt and polymer. The addition of TiO₂ into HBPS-(PPEGMA) _x /LiTFSI improved the ionic conductivity at low temperature. The prepared composite polymer electrolyte showed the highest ionic conductivity of 9?×?10^?5 S cm^?1 at 30 °C when the content of TiO₂ was 15 wt% and the size of TiO₂ was 20 nm.     

Performance evaluation of PVdF gel polymer electrolytes

A series of gel polymer electrolytes containing PVdF as homo polymer, a mixture of 1:1 Ethylene Carbonate (EC) : Propylene Carbonate (PC) as plasticizer and lithium-bistrifluoromethane sulphone imide [imide — LiN (CF₃SO₂)₂] has been developed. Amounts of polymer (PVdF), plasticizer and the imide lithium salt have been varied as a function of their weight ratio composition in this regard. Dimensionally stable films possessing appreciable room temperature conductivity values have been obtained with respect to certain weight ratio compositions. However, conductivity data have been recorded at different possible temperatures, i.e., from 20 °C to 65 °C. XRD and DSC studies were carried out to characterize the polymer films for better amorphicity and reduced glass transition temperature, respectively. The electrochemical interface stability of the PVdF based gel polymer electrolytes over a range of storage period (24 h – 10 days) have been investigated using A.C. impedance studies. Test cells containing Li/gel polymer electrolyte (GPE)/Li have been subjected to undergo 50 charge-discharge cycles in order to understand the electrochemical performance behaviour of the dimensionally stable films of superior conductivity. The observed capacity fade of less than 20% even after 50 cycles is in favour of the electrochemical stability of the gel polymer electrolyte containing 27.5% PVdF −67.5 % EC+PC −5% imide salt. Cyclic voltammetry studies establish the possibility of a reversible intercalation — deintercalation process involving Li⁺ ions through the gel polymer electrolyte.     

Electrochemical characterization of a composite polymer electrolyte with improved lithium metal electrode interfacial properties

In the development of rechargeable lithium polymer batteries it is of paramount importance to control the passivation phenomena occurring at the lithium electrode interface. It is well estabilished that the type and the growth of the lithium passivation layer is unpredictably influenced by the presence of liquid components and/or impurities in the electrolyte. Therefore, one approach to improve the stability of the lithium interface is the use of liquid-free, highly pure electrolytes. The electrochemical properties of a composite polymer electrolyte obtained by hot pressing a mixture of polyethylene oxide (PEO), a lithium salt (lithium tetrafluoroborate, LiBF₄) and a powdered ceramic additive (γ-LiAlO₂), will be presented and discussed. The electrochemical characterization included the determination of the ionic conductivity, the anodic break-down voltage and, most importantly, the stability of the lithium metal electrode interface and the lithium stripping-plating process efficiency. The main feature of this dry, true solid-state electrolyte is a very good compatibility with the lithium metal electrode, demonstrated by a very high lithium cycling efficiency, which approaches a value of 99%. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998.     

Conduction mechanism of lithium bis(oxalato)borate–cellulose acetate polymer gel electrolytes

Polymer gel electrolytes (PGE) belonging to salt–solvent–polymer hybrid systems are prepared using a mixture of lithium bis(oxalato)borate (LiBOB), γ-butyrolactone (γ-BL), and cellulose acetate (CA). The increase in ionic conductivity of PGE is due to the dissociation of ion aggregates, as confirmed by Fourier transform infrared analysis. The highest conductivity attained by the PGE is 7.05 mS cm^?1 at 2.4 wt.% CA. The plots of conductivity–temperature show a classical Arrhenius relationship. The electrical properties of the sample with the highest conductivity are analyzed using electrical permittivity and electric modulus formalism studies. Meanwhile, the frequency-dependent conductivity of the polymer gel electrolyte adheres to Jonscher’s power law. Conduction mechanism study also shows that the 2.4 wt.% CA PGE is in agreement with the small polaron hopping model.     

Reactivity of natural and synthesized FeS2 relative to the components of polymer electrolytes

Iron disulfide reactivity relative to the components of composite polymer electrolytes based on chlorinated polyvinylchloride has been studied by taking differential infrared (IR) spectra. It has been shown that iron-containing admixtures on iron disulfide surface can initiate the decomposition processes of polymer systems. Possibility of diffusion to the volume of liquid electrolyte of surface iron—comprising compounds of different composition—has been shown. In the presence of lithium salts, these admixtures initiate the destruction processes of plasticizing additives and polymer matrix. The disclosed effects of interaction enable optimization of polymer electrolyte composition for the further use in the power source of Li–FeS₂ system and to develop a complex of procedures connected with the preliminary treatment (thermal or chemical) of pyrite aimed at the modification of its surface properties.     

Infrared and conductivity studies on blends of PMMA/PEO based polymer electrolytes

Poly(methylmetacrylate)/poly(ethylene oxide) (PMMA/PEO) based polymer electrolytes were synthesized using the solution cast technique. Four systems of PMMA/PEO blends based polymer electrolytes films were investigated:

1. PMMA/PEO system,
2. PMMA/PEO + ethylene carbonate (EC) system,
3. PMMA/PEO + lithium hexafluorophosphate (LiPF₆) system and
4. PMMA/PEO + EC + LiPF₆ system.

The polymer electrolytes films were characterized by Impedance Spectroscopy and Fourier Transform Infrared Spectroscopy (FTIR). The FTIR spectra show the complexation occurring between the polymers, plasticizer and lithium salt. The FTIR results give further insight in the conductivity enhancement of PMMA/PEO blends based polymer electrolytes.     

On dielectrics of polymer electrolytes studied by impedance spectroscopy

We present a phenomenological view on dielectric relaxation in polymer electrolytes in the frequency range where conductivity is independent of frequency. Polymer electrolytes are seen as molecular mixtures of an organic polymer and an inorganic salt. The discussion applies also to ionic liquids. The following is based on systems with poly(ethylene oxide) (PEO) comprising the lithium perchlorate salt (LiClO₄) and also pure low-molecular PEO. In those systems, dipole-dipole interactions form an association/dissociation equilibrium which rules properties of the system in the low-frequency region. It turns out that effective concentration, c _S, of relaxing species provides a suitable variable for discussing electrochemical behavior of the electrolytes. Quantity c _S is proportional to the ratio of DC conductivity and mobility. Polymer salt mixtures form weak electrolytes. However, diffusion coefficient and corresponding molar conductivity display the typical (c _S)^1/2 dependence as well known from strong electrolytes, due to the low effective concentration c _S.     

A free-standing and thermostable polymer/plastic crystal electrolyte for all-solid-state lithium batteries

All-solid-state lithium batteries using flexible solid electrolytes instead of combustible organic liquid electrolytes are the ultimate solution to address the safety problem of commercialized lithium ion batteries. In this study, a free-standing and thermostable polymer/plastic crystal composite electrolyte (PPCE) based on polymerized trimethylolpropane trimethacrylate (TMPTMA)-1, 6-hexanediol diacrylate (HDDA) matrix, and plastic crystal electrolyte was prepared for all-solid-state lithium batteries. The polymerized TMPTMA-HDDA-based matrix of a porous network structure coupled with plastic crystal electrolyte (PCE) in the pores reveals good compatibility. The as-synthesized PPCE possesses excellent flexible performance, thermostability, and high conductivity, showing that PPCE can reach 8.53 × 10^?4 S cm^?1 with 7.5 wt% monomers (PPCE-7.5%) at 25 °C under a stability electrochemical window above 5.2 V. The assembled lithium batteries Li|PPCE|LiFePO₄ exhibit high capacity and highly cycling stability at room temperature, indicating great potential of all-solid-state lithium batteries.     

Polymer electrolytes plasticized with hyperbranched polymer for lithium polymer batteries

Hyperbranched polymers (HBPs) with different terminal groups and different ethylene oxide (EO) chain lengths were prepared, and the influence of the HBP structures including molecular weights and molecular weight distribution on the ionic conductivity and the mechanical property of the composite polymer electrolytes composed of poly (ethylene oxide) (PEO), HBP, BaTiO₃ as a ceramic filler, and LiN(CF₃SO₂)₂ as a lithium salt were investigated. It was found that the molecular weights of the HBP do not affect significantly the ionic conductivity, but the molecular weight distribution might affect it, and also further branching at the terminals of the HBP led to a decrease in the ionic conductivity. The HBP with longer EO chain length was effective for enhancement of the ionic conductivity in comparison with the HBP with shorter one. The increase in cross-linkable groups (acryloyl group) at the terminals of the HBP improved the tensile strength, but caused the ionic conductivity to decrease. Loosely cross-linked composite polymer electrolyte showed higher ionic conductivity and higher tensile strength than no cross-linked one. Paper presented at the Patras Conference on Solid State Ionics — Transport Properties, Patras, Greece, Sept. 14 – 18, 2004.     

Thermal and electrochemical properties of poly(butylene sulfite)-based polymer electrolyte

Poly(butylene sulfite) (poly-1) was synthesized by cationic ring-opening polymerization of butylene sulfite (1), which was prepared by the reaction of 1,4-butanediol and thionyl chloride, with trifluoromethanesulfonic acid (TfOH) in bulk. The polymer electrolytes composed of poly-1 with lithium salts such as bis(trifluoromethanesulfonyl)imide (LiN(SO₂CF₃)₂, LiTFSI) and bis(fluorosulfonyl)imide (LiN(SO₂F)₂, LiFSI) were prepared, and their ionic conductivities, thermal, and electrochemical properties were investigated. Ionic conductivities of the polymer electrolytes for the poly-1/LiTFSI system increased with lithium salt concentrations, reached maximum values at the [LiTFSI]/[repeating unit] ratio of 1/10, and then decreased in further more salt concentrations. The highest ionic conductivity values at the [LiTFSI]/[repeating unit] ratio of 1/10 were 2.36?×?10^?4 S/cm at 80 °C and 1.01?×?10^?5 S/cm at 20 °C. On the other hand, ionic conductivities of the polymer electrolytes for the poly-1/LiFSI system increased with an increase in lithium salt concentrations, and ionic conductivity values at the [LiFSI]/[repeating unit] ratio of 1/1 were 1.25?×?10^?3 S/cm at 80 °C and 5.93?×?10^?5 S/cm at 20 °C. Glass transition temperature (T _g) increased with lithium salt concentrations for the poly-1/LiTFSI system, but T _g for the poly-1/LiFSI system was almost constant regardless of lithium salt concentrations. Both polymer electrolytes showed high transference number of lithium ion: 0.57 for the poly-1/LiTFSI system and 0.56 for the poly-1/LiFSI system, respectively. The polymer electrolytes for the poly-1/LiTFSI system were thermally more stable than those for the poly-1/LiFSI system.