Fast ion conduction in solid-state matrices constitutes the foundation for a wide spectrum of electrochemical systems that use solid electrolytes (SEs), examples of which include solid-state batteries (SSBs), solid oxide fuel cells (SOFCs), and diversified gas sensors. Mixing different solid conductors to form composite solid electrolytes (CSEs) introduces unique opportunities for SEs to possess exceptional overall performance far superior to their individual parental solids, thanks to the abundant chemistry and physics at the new interfaces thus created. In this review, we provide a comprehensive and in-depth examination of the development and understanding of CSEs for SSBs, with special focus on their physiochemical properties and mechanisms of ion transport therein. The origin of the enhanced ionic conductivity in CSEs relative to their single-phase parents is discussed in the context of defect chemistry and interfacial reactions. The models/theories for ion movement in diversified composites are critically reviewed to interrogate a general strategy to the design of novel CSEs, while properties such as mechanical strength and electrochemical stability are discussed in view of their perspective applications in lithium metal batteries and beyond. As an integral component of understanding how ions interact with their composite environments, characterization techniques to probe the ion transport kinetics across different temporal and spatial time scales are also summarized.

Mobile Ions in Composite Solids.

In the present article, we have studied the effect of the salt concentration (LiPF6) on transport properties and ion dynamics of blend solid polymer electrolyte (PEO–PAN) prepared by solution cast technique. Fourier transform infrared (FTIR) spectroscopy confirms the presence of microscopic interactions such as polymer–ion and ion–ion interaction evidenced by a change in peak area of anion stretching mode. The fraction of free anions and ion pairs obtained from the analysis of FTIR implies that both influence the ionic conductivity with different salt concentration. The complex dielectric permittivity, dielectric loss, complex conductivity have been analyzed and fitted in the entire frequency range (1 Hz–1 MHz) at room temperature. The addition of salt augments the enhancement of dielectric constant and shift of relaxation peak in loss tangent plot toward high frequency indicates a decrease of relaxation time. We have implemented the Sigma representation (σ″ vs. σ′) for solid lithium ion conducting films which provide better insight regarding the dispersion region in Cole–Cole plot (e″ vs. e′) in lower frequency window. The dielectric strength, relaxation time and hopping frequency are in correlation with the conductivity which reveals the authenticity of results. Finally, the ion transport mechanism was proposed for getting the better understanding of the ion migration in the polymer matrix.

Effect of salt concentration on dielectric properties of Li-ion conducting blend polymer electrolytes

Hybridizing poly(vinylidene fluoride-co-hexafluoropropylene) with Li6.5La3Zr1.5Ta0.5O12 as a lithium-ion electrolyte for solid state lithium metal batteries

Poly(vinylidene fluoride–hexafluoropropylene) (PVdF–HFP) gel electrolytes comprising a combination of plasticizers,
ethylene carbonate (EC) and propylene carbonate (PC) and lithium salt LiX ðX ¼ BF�4 ;CF3SO�3 ; ClO�4 Þ have been
prepared using the solution casting technique in an argon atmosphere. The prepared electrolytes were subjected to ionic
conductivity, compatibility with lithium metal anode and thermogravimetric (TG)/differential thermal analysis (DTA).
The membranes, which possess lithium salt, LiBF4 exhibited maximum conductivity and on contrary it undergoes
severe passivation with lithium metal. All these membranes are found to be stable thermally about 70�C.

Characterization of poly(vinylidenefluoride–hexafluoropropylene) (PVdF–HFP) electrolytescomplexed with different lithium salts

We investigate the effect of blend host polymer on solid polymer electrolyte (SPE) films doped with ammonium iodide (NH4I) salt using a variety of experimental techniques. Structural studies on the composite SPEs show that the blending of Poly(ethylene oxide) (PEO)–Poly(vinylidene fluoride) (PVDF) polymers in a suitable ratio enhances the amorphous fraction of the polymer matrix and facilitates fast ion conduction through it. We observe that the addition of a small amount of PVDF in the PEO host polymer enhances the ion – polymer interaction leading to more ion dissociation. As a result, the effective number of mobile charge carriers within the polymer matrix increases. Systematic investigation in these blend SPEs shows that the maximum conductivity (1.01 × 10–3 S/cm) is obtained for PEO – rich (80 wt. % PEO, 20 wt. % PVDF) composites at 35 wt. % NH4I concentration at room temperature. Interestingly, at higher salt concentrations (above 35 wt. %), the conductivity is found to decrease in this system. The reduction of conductivity at higher salt concentrations is the consequence of decrease in the carrier concentration due to the formation of an ion pair and ion aggregates. PVDF–rich compositions (20 wt. % PEO and 80 wt. % PVDF), on the other hand, show a very complex porous microstructure. We also observe a much lower ionic conductivity (maximum ∼ 10–6 S/cm at 15 wt. % salt) in these composite systems relative to PEO-rich composites.

Investigation of ionic conduction in PEO-PVDF based blend polymer electrolytes

Solid polymer electrolyte membrane comprising poly(vinyl chloride) (PVC), poly(ehylene oxide) (PEO) and different lithium salts (LiClO4, LiBF4 and LiCF3SO3) were prepared by the solution casting technique. The effect of complexing salt on the ionic conductivity of the PVC/PEO host polymer is discussed. Solid polymer electrolyte films were characterized by X-ray diffraction, FTIR spectroscopy, TG/DTA and ac impedance spectroscopic studies. The conductivity studies of these solid polymer electrolyte (SPE) films are carried out as a function of frequency at various temperatures ranging from 302 K to 353 K. The maximum room temperature ionic conductivity is found to be 0·079 × 10−4 S cm−1 for the film containing LiBF4 as the complexing salt. The temperature dependence of the conductivity of polymer electrolyte films seems to obey the Vogel-Tamman-Fulcher (VTF) relation.

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Effect of complexing salt on conductivity of PVC/PEO polymer blend electrolytes

Composite polymer electrolytes comprising of polyvinyl chloride (PVC), poly(butyl methacrylate) (PBMA), lithium perchlorate (LiClO4), ethylene carbonate (EC) and with different ratios of aluminium oxide (Al2O3) are prepared by solution casting technique and characterized. Structural and complex formations are confirmed from XRD and FTIR studies. Conductivity studies were carried out and found that as the Al2O3 concentration increases the conductivity is found to increase initially and then decrease after certain concentration. The room temperature ionic conductivity of polymer electrolyte film bereft of Al2O3 is found to be 0.116 mS cm−1 which increases to 0.712 mS cm−1 in electrolyte membranes with 10 wt% of Al2O3. Dielectric behaviour (e′ and e″) for the composite polymer electrolytes was found to decreases with increase in frequency due to existence of electrode polarization effect. The high dielectric constant and low dielectric modulus are observed for 10 wt% of Al2O3 incorporated PVC–PBMA composite polymer electrolyte compared to other Al2O3 concentrations. The morphology of polymer electrolyte membranes were studied by scanning electron microscope.

Investigation on Al2O3 doped PVC-PBMA blend polymer electrolytes

Poly(vinyl chloride) (PVC)—poly(butyl methacrylate) (PBMA) blended polymer electrolytes with lithium perchlorate (LiClO4) as the complexing salts are prepared by solution casting technique. The addition of PBMA into PVC matrix is found to induce considerable changes in physical and electrical properties of the polymer electrolytes. Addition of PBMA into PVC matrix is found to increase the conductivity by two orders of magnitude (1.108 × 10−5 S cm−1) when compared with that of the pristine PVC polymer electrolyte (10−7 S cm−1). Structural, thermal, mechanical, morphological, and polymer–salt interactions are ascertained from X-ray diffraction (XRD), thermogravimetry/differential thermal analysis (TG/DTA), mechanical analysis, scanning electron microscope (SEM), and Fourier transform infrared spectroscopy (FTIR) respectively. A thermal stability upto 250 °C is asserted from the TG/DTA analysis. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44939.

Effect of PBMA on PVC‐based polymer blend electrolytes

Plasticized polymer electrolytes comprising of ethylene carbonate as the plasticizing agent in poly (vinyl chloride) [PVC]–poly (butyl methacrylate) [PBMA] blended polymer electrolytes were prepared by solution casting technique. Complex formation, structural elucidation, conductivity, dielectric parameters (Ɛ′, Ɛ″, M′, and M″), thermal stability, and surface morphology are brought out from FTIR, XRD, ac impedance analysis, dielectric studies, thermogravimetry/differential thermal analysis, and scanning electron microscopic studies, respectively. Polymer electrolytes are found to exhibit higher ionic conductivity at higher concentration of plasticizer at the cost of their mechanical stability. Conductivity of 1.879 × 10−4 S cm−1 is exhibited by the polymer electrolyte consisting of 69% of plasticizer with appreciable thermal stability up to 523 K. Temperature and frequency dependence of conductivity is found to follow Vogel Tammann Fulcher relation and Jonscher power law, respectively. Real and imaginary parts of dielectric constants are found to decrease with increase in frequency which could be due to the electrode polarization effect.

Influence of plasticizer on ionic conductivity of PVC-PBMA polymer electrolytes

https://robots.iopscience.iop.org/article/10.1088/1757-899X/263/2/022006/pdf

M. Usha Rani

Papers

Effect of complexing salt on conductivity of PVC/PEO polymer blend electrolytes

Investigation on Al2O3 doped PVC-PBMA blend polymer electrolytes

Effect of PBMA on PVC‐based polymer blend electrolytes

Influence of plasticizer on ionic conductivity of PVC-PBMA polymer electrolytes

TiO2 as conductivity enhancer in PVdF-HFP polymer electrolyte system