Enhancement Of Ionic Conductivity Research Articles

Photo-Effect on Ion Transport in Mixed Cation and Halide Perovskites and Implications for Photo-Demixing*.

Lead halide perovskites are considered to be most promising photovoltaic materials. Highest efficiency and improved stability of perovskite solar cells have been achieved by using cation and anion mixtures. Experimental information on electronic and ionic charge carriers is key to evaluate device performance, as well as processes of photo‐decomposition and photo‐demixing which are observed in these materials. Here, we measure ionic and electronic transport properties and investigate various cation and anion substitutions with a special eye on their photo‐ionic effect, following our previous study on CH3NH3PbI3, where we found that light enhances not only electronic but also ionic conductivities. We find that this phenomenon is very sensitive to the nature of the halide, while the cationic substitutions are less relevant. Based on the observation that the ionic conductivity enhancement found for iodide perovskites is significantly weakened by bromide substitution, we provide a chemical rationale for the photo‐demixing in mixed halide compositions.

Photo‐Effect on Ion Transport in Mixed Cation and Halide Perovskites and Implications for Photo‐Demixing**

AbstractLead halide perovskites are considered to be most promising photovoltaic materials. Highest efficiency and improved stability of perovskite solar cells have been achieved by using cation and anion mixtures. Experimental information on electronic and ionic charge carriers is key to evaluate device performance, as well as processes of photo‐decomposition and photo‐demixing which are observed in these materials. Here, we measure ionic and electronic transport properties and investigate various cation and anion substitutions with a special eye on their photo‐ionic effect, following our previous study on CH3NH3PbI3, where we found that light enhances not only electronic but also ionic conductivities. We find that this phenomenon is very sensitive to the nature of the halide, while the cationic substitutions are less relevant. Based on the observation that the ionic conductivity enhancement found for iodide perovskites is significantly weakened by bromide substitution, we provide a chemical rationale for the photo‐demixing in mixed halide compositions.

Enhancement of ionic conductivity of aqueous solution by silanol groups over zeolite surface

The ionic conduction of zeolite powder in ion-exchanged water and various other solutions was investigated. H-BEA-92.5, which contained many silanol groups, showed the highest conductivity of 1.1 × 10−1 S cm−1 at 95 °C in a 10,000 ppm NaCl aqueous solution. After controlling the amount of surface silanol groups by calcination or dealumination, zeolites with a relatively large number of surface silanol groups showed the highest conductivity in water. The improvement of conductivity with zeolite in water was also observed for zeolite-related materials with surface silanol groups. Therefore, we conclude that surface silanol groups play an important role in increasing the conductivity of solution with zeolite in water. Furthermore, it was revealed that the mechanism of conduction was similar to the Grötthuss mechanism because of its apparent activation energy.

Dependence of Ionic Conductivity on the Thickness of β-AgI Thin Film Prepared on Polyethylene Terephthalate

β-AgI thin films with thicknesses of 0.09–8.9 µm were prepared on polyethylene terephthalate (PET) substrate. Dependence of ionic conductivity on the thickness of the β-AgI thin film was measured via impedance spectroscopy in the temperature range of 300–330 K. It has been confirmed that the ionic conductivity of the b-AgI thin film is several hundred times higher than the b-AgI bulk. The enhancement of ionic conductivity is considered to be due to the formation of a high ion-conducting region near the hetero-interface region of b-AgI and PET. Furthermore, it has been suggested that the activation energy and carrier density may change depending on the distance from the interface, and the thickness dependence of enhancement in ionic conductivity may be related to the film thickness dependence of crystal orientation and structural disorder of β-AgI thin films.

Synthesis of Porous Proton Ion Conducting Solid Polymer Blend Electrolytes Based on PVA: CS Polymers: Structural, Morphological and Electrochemical Properties.

In this study, porous cationic hydrogen (H+) conducting polymer blend electrolytes with an amorphous structure were prepared using a casting technique. Poly(vinyl alcohol) (PVA), chitosan (CS), and NH4SCN were used as raw materials. The peak broadening and drop in intensity of the X-ray diffraction (XRD) pattern of the electrolyte systems established the growth of the amorphous phase. The porous structure is associated with the amorphous nature, which was visualized through the field-emission scanning electron microscope (FESEM) images. The enhancement of DC ionic conductivity with increasing salt content was observed up to 40 wt.% of the added salt. The dielectric and electric modulus results were helpful in understanding the ionic conductivity behavior. The transfer number measurement (TNM) technique was used to determine the ion (tion) and electron (telec) transference numbers. The high electrochemical stability up to 2.25 V was recorded using the linear sweep voltammetry (LSV) technique.

Natural Inspired Carboxymethyl Cellulose (CMC) Doped with Ammonium Carbonate (AC) as Biopolymer Electrolyte.

Green and safer materials in energy storage technology are important right now due to increased consumption. In this study, a biopolymer electrolyte inspired from natural materials was developed by using carboxymethyl cellulose (CMC) as the core material and doped with varied ammonium carbonate (AC) composition. X-ray diffraction (XRD) shows the prepared CMC-AC electrolyte films exhibited low crystallinity content, Xc (~30%) for sample AC7. A specific wavenumber range between 900–1200 cm−1 and 1500–1800 cm−1 was emphasized in Fourier transform infrared (FTIR) testing, as this is the most probable interaction to occur. The highest ionic conductivity, σ of the electrolyte system achieved was 7.71 × 10−6 Scm−1 and appeared greatly dependent on ionic mobility, µ and diffusion coefficient, D. The number of mobile ions, η, increased up to the highest conducting sample (AC7) but it became less prominent at higher AC composition. The transference measurement, tion showed that the electrolyte system was predominantly ionic with sample AC7 having the highest value (tion = 0.98). Further assessment also proved that the H+ ion was the main conducting species in the CMC-AC electrolyte system, which presumably was due to protonation of ammonium salt onto the complexes site and contributed to the overall ionic conductivity enhancement.

Ion Transport in Solvated Sodium-Ion Conducting Gel Polymer Electrolytes

Single ion conducting gel polymer electrolytes (GPEs) are characterized as having a certain amount of ionic liquid or solvent incorporated into a single ion-conducting polymer matrix and may afford the advantages of high conductivity and low electrolyte polarization under battery operation. Single ion conducting polymers often suffer from low conductivity due to their reliance on polymer segmental motion to achieve sufficient ion mobility. However, by incorporating specific solvents into a single ion conducting matrix, mobility of the polymer can be enhanced while still maintaining the advantages of single ion conduction. Although many of the solvents used to swell GPEs are mixtures of flammable organic solvents (such as dimethyl carbonate), there are many potential non-reactive, low vapor pressure solvents that could effectively solvate alkali-ion based GPEs and plasticize the polymer matrix to enhance ion conductivity. Adipate-based solvents are a group of non-volatile plasticizers with low viscosities and low vapor pressures at room temperature derived from adipic acid. The ester groups in these solvents may effectively solvate alkali ions such as Na+, leading to higher conductivity, while circumventing issues of flammability found in current alkali-ion conducting electrolytes. This study investigates the properties of sodium-ion conducting GPEs that have been swollen with varying adipate-based solvents and the subsequent dielectric response from the solvent addition. Dielectric relaxation spectroscopy was used to characterize the Na+ conductivity, static dielectric constant, ion-conducting content, and mobility of the membranes before and after the non-volatile solvent uptake. Understanding this relationship will pave the path toward safer, more efficient solid-state polymer electrolytes for battery applications.

Resorcinol-Formaldehyde (RF) as a Novel Plasticizer for Starch-Based Solid Biopolymer Electrolyte.

A starch-resorcinol-formaldehyde (RF)-lithium triflate (LiTf) based biodegradable polymer electrolyte membrane was synthesized via the solution casting technique. The formation of RF crosslinks in the starch matrix was found to repress the starch’s crystallinity as indicated by the XRD data. Incorporation of the RF plasticizer improved the conductivity greatly, with the highest room-temperature conductivity recorded being 4.29 × 10−4 S cm−1 achieved by the starch:LiTf:RF (20 wt.%:20 wt.%:60 wt.%) composition. The enhancement in ionic conductivity was an implication of the increase in the polymeric amorphous region concurrent with the suppression of the starch’s crystallinity. Chemical complexation between the plasticizer, starch, and lithium salt components in the electrolyte was confirmed by FTIR spectra.

Hybridizing polymer electrolyte with poly(ethylene glycol) grafted polymer-like quantum dots for all-solid-state lithium batteries

Solid-state polymer electrolytes (SPEs) show great potential owing to inherent flexibility and safety but limited by the low ionic conductivity. Herein, poly (ethylene glycol) grafted polymer-like quantum dots (PPQDs) with average diameter of ~2.5 nm and abundant conduction groups are synthesized as nanofillers for hybrid polymer electrolytes. The functionalization of poly (ethylene glycol) provides abundant Li+ transfer sites and meanwhile enhances the compatibility between PPQDs and poly (ethylene oxide) (PEO). Accordingly, these PPQDs uniformly disperse and form rich networks with PEO chains to effectively reduce the crystallinity of PEO and promote the dissociation of lithium salts, different from large-size or inorganic fillers. Consequently, efficient ion-conductive networks are constructed by PPQDs and PEO for vertical Li+ conduction: 5.53 × 10−5 S cm−1 at 30 °C, 16 times higher than that of PEO electrolyte. Furthermore, the hydrogen-bonding interactions at PPQD-PEO interfaces afford excellent stability and flexibility to electrolytes. And superior cycling performance of ~146 mAh g−1 after 150 cycles at 1.0C with capacity decay of 0.046% per cycle is therefore achieved. Compared with traditional fillers, PPQDs with inherent advantages, i.e., molecular-level size and designable groups, endow hybrid electrolytes with dramatically enhanced ion conduction and stability, manifesting great potential for all-solid-state lithium batteries.

Enhanced ion conductivity of sulfonated poly(arylene ether sulfone) block copolymers linked by aliphatic chains constructing wide-range ion cluster for proton conducting electrolytes

A series of sulfonated poly(arylene ether sulfone) block copolymers with aliphatic chains (SPAES-LA) to lend structural flexibility in the polymer backbone have been synthesized to prepare proton exchange membranes (PEMs) showing improved electrochemical performance and dimensional/oxidative stabilities. The SPAES-LAs, bearing different hydrophilic/hydrophobic segment lengths, are prepared via polycondensation and sulfonation reactions. The sulfonation reaction occurs in specific fluorenylidene units by using chlorosulfonic acid. The SPAES-LA membrane, fabricated by solvent casting method, exhibits remarkable dimensional/thermal stabilities. Moreover, proton conductivity of as-prepared SPAES-LA membranes demonstrates significant improvement with expansion of ion clusters which is due to the increased hydrophilic volume ratio. In particular, the SPAES-LA-X12Y28 membrane exhibited heightened proton conductivity of 158.4 mS cm−1 as well as suitable dimensional stability and durability towards radical oxidation, due to an effective well-defined hydrophilic-hydrophobic interface. Furthermore, H2/O2 fuel cell performance using SPAES-LA-X12Y28 membrane achieves a maximum power density of 232.02 mW cm−2, a result which points out that SPAES-LA membranes show great potential for applications of polymer electrolyte membrane.

Solid Polymer Electrolytes Derived from Crosslinked Polystyrene Nanoparticles Covalently Functionalized with a Low Lattice Energy Lithium Salt Moiety

Three new crosslinked polystyrene nanoparticles covalently attached with low lattice energy lithium salt moieties were synthesized: poly(styrene lithium trifluoromethane sulphonyl imide) (PSTFSILi), poly(styrene lithium benzene sulphonyl imide) (PSPhSILi), and poly(styrene lithium sulfonyl-1,3-dithiane-1,1,3,3-tetraoxide) (PSDTTOLi). A series of solid polymer electrolytes (SPEs) were formulated by mixing these lithium salts with high molecular weight poly(ethylene oxide), poly(ethylene glycol dimethyl ether), and lithium bis(fluorosulfonyl)imide. The crosslinked nano-sized polymer salts improved film strength and decreased the glass transition temperature (Tg) of the polymer electrolyte membranes. An enhancement in both ionic conductivity and thermal stability was observed. For example, the SPE film containing PSTFSILi displayed ionic conductivity of 7.52 × 10−5 S cm−1 at room temperature and 3.0 × 10−3 S cm−1 at 70 °C, while the SPE film containing PSDTTOLi showed an even better performance of 1.54 × 10−4 S cm−1 at room temperature and 3.23 × 10−3 S cm−1 at 70 °C.

A versatile nano-TiO2 decorated gel separator with derived multi-scale nanofibers towards dendrite-blocking and polysulfide-inhibiting lithium-metal batteries

A nano-TiO 2 decorated gel PMIA separator with multi-scale structure was synthesized, which delivered a remarkable enhancement in ionic conductivity, lithium dendrites growth inhibition and “shuttle effect” obstruction, leading to predominant electrochemical performance to lithium-metal batteries. • A versatile multi-scale TiO 2 -assisted fluorine-bearing PMIA-based GPE is prepared. • The GPE shows reduced aperture, increased porosity and electrolyte uptake. • The GPE shows well-distributed Li + flux, excellent thermal and mechanical properties. • The TiO 2 -assisted GPE restrains lithium dendrites growth and “shuttle effect”. • Lithium-metal cells with the GPE separator show excellent electrochemical properties. In this study, a versatile fluorine-bearing gel membrane with multi-scale nanofibers was rationally designed and synthesized via facile one-step blend electrospinning of nano-titanium dioxide (TiO 2 ) particles and fluorinated poly-m-phenyleneisophthalamide (PMIA) polymer solution. The prepared multi-scale TiO 2 -assisted gel separator presented relatively high porosity, small aperture, giving rise to superior affinity to electrolyte and sufficient active sites to accelerate lithium ions migration. Meanwhile, the as-fabricated multifunctional GPE also rendered outstanding heat-resistance and well-distributed lithium-ions flux, and the mutual overlaps between the coarse fibers and the fine fibers within the multi-scale nanofiber membrane provided a strong skeleton support, which in turn laid a solid footing stone for high-security and dendrite-proof batteries. Particularly, the nano-TiO 2 particles within PMIA membrane acted as “gatekeepers”, which can not only resist the growth of lithium dendrites, but also intercept the dissolved polysulfide on cathode side. Based on these merits, the gel PMIA-based lithium cobalt (LCO)/lithium battery obtained the remarkably improved rate capability and cycle performances on account of superior ionic conductivity, steady anodic stability window and weakened polarization behavior. Meanwhile, the resultant lithium-sulfur cell also delivered the outstanding cycling stability with the aid of the greatly prevented “shuttle effect” of dissolved lithium polysulfides based on the physical trapping and chemical binding of the prepared GPE to polysulfides species. This work proved that the addition of functional inorganic nanoparticles similar with TiO 2 in multi-scale gel PMIA membrane can enhance the lithium ions transport capability, resist the growth of lithium dendrites as well as inhibit the shuttle effect of polysulfides, which would prompt a great development for dendrite-blocking and polysulfide-inhibiting lithium-metal cells.

Characterizing the Blocking Electron Ability of the Schottky Junction in SnO2–SDC Semiconductor–Ionic Membrane Fuel Cells

Recent research has shown that fuel cells using semiconductor–ionic conductor material (SIM) as electrolytes can achieve good performance due to the enhancement of ionic conductivity, and the Schot...

Ionic Conductivity Enhancement of Polyelectrolyte Multilayers by Variation of Charge Balance

Three different approaches to enhance the dc conductivity of poly(diallyl-dimethyl¬ammonium)/ poly(acrylic acid) (PDADMA/PAA)n polyelectrolyte multilayers (PEM) are investigated. The first two appr...

Polyaniline (PANI) mediated cation trapping effect on ionic conductivity enhancement in poly(ethylene oxide) based solid polymer electrolytes with application in solid state dye sensitized solar cells

The ionic conductivity enhancement in solid polymer electrolytes due to introduction of polyaniline (PANI) conducting polymer is demonstrated using poly(ethylene oxide) (PEO) based solid polymer electrolyte comprising tertapropylamonium iodide (Pr4NI) and iodine (I2). The electrolyte with optimized composition has been characterized by ionic conductivity measurements, DC polarization test, Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Differential Scanning Calorimetry (DSC). About eight-fold increase in the ionic conductivity from 9.33 × 10−6 Scm−1 to 8.61 × 10−5 Scm−1 at room temperature was obtained by the addition of 1.5 wt% of PANI to the PEO solid polymer host. FTIR measurements suggest that Pr4N+ cations are able to coordinate not only with oxygen atoms of PEO, but also with nitrogen atoms of the PANI polymer effectively immobilizing or “trapping” the bulky Pr4N+ cations and promoting ionic dissociation. DSC studies show that PANI, also acting as a plasticizer, reduces the crystallinity of PEO and lower it's melting temperature. The DC polarization tests confirmed the increased iodide ion conductivity evidently mediated by PANI due to the combined effect of cation trapping and plasticizing. Solid state dye sensitized solar cells fabricated with optimized electrolyte composition incorporating PANI exhibited the highest energy conversion efficiency of 5.01% compared to 3.52% for the DSSC without PANI.

Tuning semiconductor LaFe0.65Ti0.35O3-δ to fast ionic transport for advanced ceramics fuel cells

Heterostructure and their associated properties like band energy, band bending, and interface play a vital role in the conduction of charge carriers. Enhancement of ionic conductivity has been observed by the semiconductor SrTiO3 and ionic conductor heterostructure formation, such insightful effect may be beneficial for electrolyte application in solid oxide fuel cells. Herein we report the formation of semiconductor and ionic materials heterostructure of LaFe0.65Ti0.35O3-δ (LFT) and Sm and Ca co-doped cerium oxide Ce0.8Sm0.05Ca0.15O2-δ (SCDC) with three folds enhancement in the ionic conductivity. When LFT-SCDC heterostructure was applied in the fuel cell, LFT-SCDC work as a good electrolyte and achieve a maximum power output density of 0.98 W/cm2. LFT-SCDC maintains the ionic and electronic conduction, the presence of electrons, their blockage and the fast promotion of ion transport play a key role in physical interpretation in realizing outstanding performance and understanding the mechanism of semiconductor electrolyte ceramics fuel cells. The constructed heterostructure between two different constituent phases of LFT and SCDC has established strong band bending at heterointerface, leading to the fast ionic transport in the interface. The combination of UV–visible spectroscopy and ultraviolet photoelectron spectroscopy (UPS) determine the band structure of both constituents, where the creation of oxygen vacancies are supported by X-ray photoelectron spectroscopy (XPS). It is revealed by the various investigation of electrical properties of LFT-SCDC heterostructure that it has both electronic and ionic behavior, where the built-in electric field formed by band energy alignment helps to enhance the transport of ions.

Potassium Prussian blue-coated Li-rich cathode with enhanced lithium ion storage property

Abstract With high specific capacity, the layered Li-rich Mn-based oxide (LRMO) is a promising candidate cathode material for Li-ion batteries. However, the irreversible release of Li-ions during the first charging process, instability of LRMO/electrolyte interface and relatively low ion conductivity of LRMO result in low initial Coulombic efficiency (ICE), poor cycle stability and rate performance, which prohibit its further application. Interface engineering via additive coating is expected to effectively address these issues. Herein, we rely on potassium Prussian blue (KPB), a Li+ acceptor with good ion conductivity, as a new coating material on LRMO particles. The KPB coating not only forms a protective layer on the surface of LRMO against electrolyte corrosion, but also functions as a host for Li+ transport and accommodation, leading to enhanced ion conductivity and ICE of LRMO cathode. Consequently, 2 wt% KPB coated LRMO cathode achieved an initial discharge capacity of up to 281.7 mA h g−1 with an ICE of 85.69% compared to an ICE of 79.52% for the LRMO cathode without coating. The cycling and rate performance are also greatly improved as evidenced by the well maintained capacity of up to 176.8 mA h g−1 after 100 cycles at a current density of 0.5 C, compared to the limited capacity of only 135.3 mA h g−1 for the LRMO cathode without coating. This work pioneers the use of potassium Prussian blue as additive coating material to enhance performance of LRMO cathode, and we expect it to inspire the battery community with new strategies of material engineering/design toward practical application in high-energy lithium-ion batteries.

Effect of silica nanofiber dispersion on electrochemical properties of cellulose acetate composite gel electrolytes

In this article, a novel cellulose acetate (CA) based nanocomposite polymer electrolyte membranes have been successfully synthesized with SiO2 nanofibers using hot press method. SEM image shows that the synthesized nanofibers exhibit diameter in the range from 40 nm to 60 nm. The impedance spectroscopy analysis reveals a maximum ionic conductivity of 8 × 10−4 Scm−1 with 5 wt% of nanofibers at room temperature. An enhancement of ionic conductivity is attributed to the reinforcement nanofibers, which provides a longer path for Li+ ions to conduct in the polymer matrix. A detail study of FTIR and XRD show that addition of nanofibers actually help to generate more Li+ ions in the polymer matrix, which results in increase of ionic conductivity. The interfacial and electrochemical stabilities have also been found to be better after reinforcement of SiO2 nanofibers.

Phase formation and relaxor properties of lead-free perovskite ceramics on the base of sodium-bismuth titanate (Na0.5Bi0.5)(Ti,Mg)O3

Effects of cation substitutions on crystal structure parameters, microstructure, dielectric and ferroelectric properties of ceramic solid solutions (Na0.5Bi0.5)(Ti1-xMgx)O3 with x = 0 ÷ 0.1 were studied. Phase transitions near 400 K demonstrate a pronounced relaxor behavior typical for (Na0.5Bi0.5)TiO3 (NBT) based compositions conditioned by presence of polar nanoregions in nonpolar matrix. Changes in the perovskite structure parameters, microstructure, and functional properties of Mg2+ modified NBT ceramics confirmed the influence of the acceptor dopant amount on their properties. Increase in total conductivity at high temperatures and effects of dielectric relaxation were observed with increasing amount of magnesium cations indicating enhancement of ionic conductivity.

The mechanism of enhanced ionic conductivity in Li1.3Al0.3Ti1.7(PO4)3–(0.75Li2O·0.25B2O3) composites

Abstract The oxide-based Li+ conductors are considered as potential solid electrolytes for lithium-ion batteries. Among the NASICON–type materials, Li1.3Al0.3Ti1.7(PO4)3 (LATP) seems to be a promising candidate for application. Although its bulk conductivity is of the order of 10−3 S · cm−1, and seems to be sufficient for practical use, the total conductivity is considerably limited by the highly resistant grain boundaries. This shortcoming may be overcome by the formation of LATP–based ceramics with appropriate sintering aids. In this study, the 0.75Li2O·0.25B2O3 (LBO) glass with low melting point was chosen to improve the ionic conductivity of LATP. The properties of Li1.3Al0.3Ti1.7(PO4)3–y (0.75Li2O·0.25B2O3) (0 ≤ y ≤ 0.3) system were studied by means of: high temperature X-ray diffractometry (HTXRD), 6Li/7Li, 11B, 27Al and 31P magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR), thermogravimetry (TG), scanning electron microscopy (SEM), impedance spectroscopy (IS) and density methods. Based on the experimental results, it is shown that the use of LBO glass as a sintering aid results in the enhancement of the total ionic conductivity of LATP ceramics. The correlations between apparent density, microstructure, composition, sintering temperature and ionic conductivity are presented and discussed. The presumed mechanism of the conductivity enhancement is analyzed in terms of the brick-layer model (BLM). The highest value of the total ionic conductivity, equal to 1.9 × 10−4 S · cm−1, was obtained for LATP–0.1LBO sintered at 800 °C.