Ionic conductivities of solid polymer electrolyte/salt systems for lithium secondary battery

We establish a new ionic conductivity model based on the Nernst-Einstein equation in which the diffusion coefficient is derived from modified double lattice-nonrandom-Pitzer-Debye-Hückel (MDL-NR-PDH) model. The proposed model takes into account the mobility of the salt and the motion of the polymer host simultaneously by expressing the effective chemical potential as the sum of chemical potentials of the salt and the polymer. To describe the segmental motion of the polymer chain, which is the well-known conduction mechanism for solid polymer electrolyte (SPE) systems, the effective co-ordinated unit parameter is introduced. The obtained co-ordinated unit parameter for each state is used to describe the behavior of the ionic conductivities of the given systems. Good agreement is obtained upon comparison with experimental data of various PEO and salt systems in the interested ranges.     

Synthesis,sintering and characterization of ceria-based solid electrolytes codoped with samaria and gadolinium using the Pechini method

Studies on fuel cell components have attracted interest due to the growing demand for sustainable energy sources. In the present study, synthesis of nanometric powders of the Ce_0.8Sm_0.2−xGd_xO_1.9 system (x = 0; 0.05; 0.1) system was carried out using the polymeric precursor method (Pechini), followed by calcination at 600 °C for 1 h and pressureless sintering. Characterizations were carried out with differential thermal analysis (DTA), thermogravimetric analysis (TG), infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The grain and grain boundary contributions to the ionic conductivity of the ceramic disks obtained were assessed by complex impedance spectroscopy (CIS). Microstructural characterization was conducted by SEM. Electrical characterization showed greater grain conductivity for samples that were codoped with increasing levels of gadolinium, likely due to less deformation in the crystalline lattice with the addition of an element that contains an ionic radius closer to that of the host matrix of ceria (Ce < Gd < Sm). Grain boundary conductivity was lower than grain conductivity with a gradual rise in the same codoping element. This results from changes in microstructural characteristics due to increased codoping, including a reduction in relative density.     

Complicated phase behavior and ionic conductivities of PVP-co-PMMA-based polymer electrolytes

We have used DSC, FTIR spectroscopy, and ac impedance techniques to investigate the interactions that occur within complexes of poly(vinylpyrrolidone-co-methyl methacrylate) (PVP-co-PMMA) and lithium perchlorate (LiClO₄) as well as these systems' phase behavior and ionic conductivities. The presence of MMA moieties in the PVP-co-PMMA random copolymer has an inert diluent effect that reduces the degree of self-association of the PVP molecules and causes a negative deviation in the glass transition temperature (T_g). In the binary LiClO₄/PVP blends, the presence of a small amount of LiClO₄ reduces the strong dipole-dipole interactions within PVP and leads to a lower T_g. Further addition of LiClO₄ increases T_g as a result of ion-dipole interactions between LiClO₄ and PVP. In LiClO₄/PVP-co-PMMA blend systems, for which the three individual systems—the PVP-co-PMMA copolymer and the LiClO₄/PVP and LiClO₄/PMMA blends—are miscible at all compositional ratios, a phase-separated loop exists at certain compositions due to a complicated series of interactions among the LiClO₄, PVP and PMMA units. The PMMA-rich component in the PVP-co-PMMA copolymer tends to be excluded, and this phenomenon results in phase separation. At a LiClO₄ content of 20 wt% salt, the maximum ionic conductivity occurred for a LiClO₄/VP57 blend (i.e., 57 mol% VP units in the PVP-co-PMMA copolymer).     

Influence of cold sintering process on the structure and properties of garnet-type solid electrolytes

Li-stuffed garnet oxides are one of the most promising solid electrolytes for Li batteries, but their development is impeded by the overly high sintering temperature (above 1000 °C), which causes uncontrollable Li evaporation and poor repeatability of synthesis. The present study evaluates the possibility of addressing this issue using a recently developed technique called cold sintering process (CSP). We demonstrates that CSP can easily realize a high density of 87.7% at an extremely low temperature of 350 °C. However, the material becomes air sensitive after CSP, and the conductivity is degraded. Detailed structural and chemical analyses reveal that such detrimental effects arise from the inter-granular phase induced by the preferential dissolution of Al and Li. Therefore, in order to take full advantage of CSP during solid-electrolyte fabrication, the incongruent dissolution issue must be the focal point of improvement. Our results suggest that CSP is a promising solution to the overly high sintering temperature of garnet electrolytes, and deserves more attention in future studies.     

Ionic conduction,colossal permittivity and dielectric relaxation behavior of solid electrolyte Li3xLa2/3-xTiO3 ceramics

Perovskite-type solid electrolyte lanthanum lithium titanate (LLTO), exhibiting high intrinsic ionic conductivity, has been attracting interests because of its potential use in all solid-state lithium-ion batteries. In this work, we prepared LLTO ceramics by solid state reaction method and studied their conductivity and dielectric properties systematically. It is found that the bulk conductivity of LLTO is several orders of magnitude higher than the grain boundary conductivity. In addition, colossal permittivity was observed in LLTO ceramics in wide frequency/temperature ranges. Two non-Debye type relaxation peaks were observed in the imaginary part of permittivity, resulting from Li⁺ ions motion and accumulation near interfaces of grains/grain boundaries/electrodes. It is suggested that colossal permittivity may originate from the lithium ion dipoles inside the samples and the interfacial polarization of lithium ion accumulation near the grain boundaries. These results clarify the relations among colossal permittivity, relaxation behavior and ionic conduction in solid ion conductor ceramics.     

Electrical conductivity of Al-doped Li2ZrO3 ceramics for Li-ion conductor electrolytes

All-solid-state Li-ion batteries (LIBs) have recently attracted widespread attention for their high energy density and safety. Some research have conducted on the Li₂ZrO₃-based Li-ion conductor electrolytes, while there is little work on the conductivity below 100 °C, although it is very important for LIBs work around room temperature. Here, monoclinic Li₂ZrO₃-based ceramics are prepared via a wet chemistry method, and the conductivities of Li₂ZrO₃ ceramics are tuned by defect engineering of Al³⁺ ions introduction. The conductivity of Al-doped Li₂ZrO₃ reaches up to 3.06 × 10^-4 S cm^-1 at 25 °C, the related activation energy of conduction is less than 0.1 eV. Simulation calculation using bond valence site energy reveals that there is a two-dimensional Li-ion migration network in the crystal structure of Li₂ZrO₃.     

Preparation and infiltration of NASICON-type solid electrolytes with microporous channels

A lithium-ion conductor with microporous channels (p-LATP) was prepared by using templates from a hydrothermal-assisted sol-gel method, and the as-prepared p-LATP was infiltrated to obtain p-LATP and d-LATPs composites in this work. SEM photos showed that the morphologies of p-LATP, d-LATP, and p-LATP and d-LATP composites were quite similar. XRD analysis showed that the crystallographic structures were also similar. TEM examinations revealed that microporous channels existed in the pure p-LATP and the p-LATP and d-LATP composites but not in the pure d-LATP. The total conductivities of the composites were higher than those of the pure p-LATP and pure d-LATP. The enhancement of the total conductivity of the composites was ascribed to the interaction of microporous channels and dense lithium-ion conducting areas. The promising results obtained in this work provide a new way to prepare solid lithium-ion conductors.     

Novel chemically cross-linked solid state electrolyte for dye-sensitized solar cells

Poly(vinylpyridine-co-ethylene glycol methyl ether methacrylate) (P(VP-co-MEOMA)) and α,ω-diiodo poly(ethylene oxide-co-propylene oxide) (I[(EO)_0.8-co-(PO)_0.2]_yI) were synthesized and used as chemically cross-linked precursors of the electrolyte for dye-sensitized solar cells. Meanwhile, α-iodo poly(ethylene oxide-co-propylene oxide) methyl ether (CH₃O[(EO)_0.8-co-(PO)_0.2]_xI) was synthesized and added into the electrolyte as an internal plasticizer. Novel polymer electrolyte resulting from chemically cross-linked precursors was obtained by the quaterisation at 90 °C for 30 min. The characteristics for this kind of electrolyte were investigated by means of ionic conductivity, thermogravimetric and photocurrent-voltage. The ambient ionic conductivity was significantly enhanced to 2.3 × 10⁻⁴ S cm⁻¹ after introducing plasticizer, modified-ionic liquid. The weight loss of the solid state electrolyte at 200 °C was 1.8%, and its decomposition temperature was 287 °C. Solid state dye-sensitized solar cell based on chemically cross-linked electrolyte presented an overall conversion efficiency of 2.35% under AM1.5 irradiation (100 mW cm⁻²). The as-fabricated device maintained 88% of its initial performance at room temperature even without sealing for 30 days, showing a good stability.     

High frequency impedance measurements of sodium solid electrolytes

Solid-state sodium batteries are currently gaining enormous interest as a lower-cost and more environmentally friendly alternative to lithium batteries. They contain significantly less critical rare elements in both the electrolyte and the active material. However, to date, there is no efficient material combination of metallic anode, cathode, and solid electrolyte for room temperature applications that does not require an additional liquid electrolyte while maintaining high energy density. NaPSiO-based glass-ceramics show high ionic conductivity at room temperature, good corrosion resistance against ambient humidity and CO₂, and stability against metallic sodium. However, the conductivity mechanisms of this promising class of materials are currently poorly understood. Herein, high frequency impedance measurements up to 10⁸ Hz shed light on the contributions of grains and grain boundaries to the total impedance, including the distribution of relaxation time constants of the fully crystallized material. In addition, analysis of the temperature dependence allows separation of electrode contributions and determination of activation energies for grain and grain boundary conductivities. Our study provides the basis for fine-tuning the stoichiometry of NaPSiO-based glass-ceramics in terms of maximizing the conductive phase fraction to optimize the performance of future solid-state sodium batteries.     

Synthesis and characterization of lithium holmium silicate solid electrolyte for high temperature lithium batteries

A new Li-ion conducting holmium based solid electrolyte by the sol–gel method was synthesized. The synthesis was carried out at low temperature compared to conventional methods by which lanthanoid silicates are synthesized. The formation temperature of the compound was found through differential thermal analysis and thermogravimetric analysis (DTA-TG). The sintered samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and ac impedance spectroscopy. The temperature dependence of conductivity was analysed. The experimental results show that the formation temperature of the lithium holmium silicate was found to be above 500 °C. Highest conductivity obtained was in the order of 10⁻⁴ S cm⁻¹ at 750 °C.     

Ceria-based solid electrolyte exhibits superior mechanical and electric properties compared to zirconia-based solid electrolyte

The mechanical strength and electrical characteristics of 10 mol% gadolinium (Gd)-doped ceria (10GDC) and gadolinium-samarium (Gd–Sm) co-doped ceria ceramics treated by contact reduction were investigated. The observed increased strength of 10GDC was similar to the strength previously reported for ceria with and without Sm doping. X-ray photoelectron spectroscopy revealed that only the surface was reduced in the strengthened material. In addition, the strengthened ceramic displayed improved hardness at low test loads, which suggested the formation of a surface compression layer. The reducing conditions did not affect the electrical conductivity of the 10GDC material. Co-doping with 10 mol% each of Gd and Sm improved strength and conductivity compared with 10GDC and 20GDC. When the co-doped material was reduced, the electric conductivity remained identical; however, the mechanical strength improved, exceeding the strength of zirconia.     

Improving ionic conductivity of polymer-based solid electrolytes for lithium metal batteries

Because of its superior safety and excellent processability, solid polymer electrolytes (SPEs) have attracted widespread attention. In lithium based batteries, SPEs have great prospects in replacing leaky and flammable liquid electrolytes. However, the low ionic conductivity of SPEs cannot meet the requirements of high energy density systems, which is also an important obstacle to its practical application. In this respect, escalating charge carriers (i.e. Li⁺) and Li⁺ transport paths are two major aspects of improving the ionic conductivity of SPEs. This article reviews recent advances from the two perspectives, and the underlying mechanism of these proposed strategies is discussed, including increasing the Li⁺ number and optimizing the Li⁺ transport paths through increasing the types and shortening the distance of Li⁺ transport path. It is hoped that this article can enlighten profound thinking and open up new ways to improve the ionic conductivity of SPEs.     

Preparation and ionic conduction of Li1.5Al0.5Ge1.5(PO4)3 solid electrolyte using inorganic germanium as precursor

NASION-type Li_1.5Al_0.5Ge_1.5(PO₄)₃(LAGP) is prepared by a novel sol-gel method using low cost inorganic germanium (GeO₂) as the precursor. The composition and phase transformation during the heating of the LAGP precursors are analyzed using thermogravimetric-differential scanning calorimetry (TG-DSC) and X-ray diffraction (XRD). The structures and morphologies of the LAGP are characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that the LAGP annealed at 900 ℃ is partially crystallized and consists of a large number of nanoscale grains surrounded by amorphous regions. The LAGP particles present an irregular morphology with a large size distribution over a range of 0.2–1 μm. In addition, ionic conductivities of the prepared LAGP first increase and then decrease with an increase in the sintering temperature and time. A high ionic conductivity (4.18 × 10⁻⁴Scm^-1) with an activation energy of 0.30 eV are obtained for the LAGP sample sintered at 900 °C for 8 h.     

Synthesis,structure and electrochemical properties of Al doped high entropy perovskite Lix(LiLaCaSrBa)Ti1-xAlxO3

In this work, the Al doped high entropy perovskite Li_0.2La_0.2Ca_0.2Sr_0.2Ba_0.2TiO₃ ceramic is synthesized by using a solid state reaction method, and the effect of different doping amount on the crystal structures and conductivity are also studied. The result proves that doping leads to a positive influence on the conductivity of ceramic. The material of Li_0.1(LiLaCaSrBa)Ti_0.9Al_0.1O₃ (LLCSBTA-0.1) exhibits a high total conductivity with approximately 3.92 × 10^-7 S cm^-1 at 30 °C and an activation energy of 0.39 eV. The beneficial result can be ascribed to the increase of Li ⁺ concentration. The Li_0.2La_0.2Ca_0.2Sr_0.2Ba_0.2TiO₃ presents a pure cubic perovskite structure, but with partial tetragonal structure due to the addition of Al₂O₃. However, these high entropy perovskite ceramics showed porous structures which are unfavourable for lithium ion conduction. The electrochemical property of the Li_0.1(LiLaCaSrBa)Ti_0.9Al_0.1O₃ as electrode is investigated as well. The results show that the Li_0.1(LiLaCaSrBa)Ti_0.9Al_0.1O₃ electrode exhibits good cyclability and stability for the insert-extraction of lithium ions with the specific capacity of 58.6 mA h g^?1.     

Conductivity enhancement of Al- and Ta-substituted Li7La3Zr2O7 solid electrolytes by nanoparticles

A nanopowder consisting of La₂Zr₂O₇ particles with lithium containing species on their surface was prepared by spray flame synthesis and subsequently added to Li₇La₃Zr₂O₁₂ powder obtained by a conventional solid-state reaction. The spray flame synthesis method utilized in this work yields nanoparticles with a small size of approximately 5 nm, which is unprecedented within the scope of oxide-based ionic conductors for solid-state batteries. Remarkably, the addition of nanoparticles for sintering at a relatively low temperature of 1000 °C significantly improved the ionic conductivity by 50 %. In contrast, there was no influence of incorporating nanoparticles on the conductivity at sintering temperatures at or above 1100 °C, which is the typical temperature range applied for conventional sintering of Li₇La₃Zr₂O₁₂. Compared to prior published work with analogous materials, a more than twofold improvement in conductivity was demonstrated while the sintering temperature was decreased by 100 °C.     

Characteristics of Li–P–W–O–N electrolyte for all solid state electrochromic devices

A LiPON–WO₃ composite thin film (LPWON) was evaluated for use as a solid electrolyte in solid state electrochromic (EC) devices. LiPO₄ and a WO₃ (2 wt%) composite sputtering target was synthesized by a ball milling process. The LPWON thin films were deposited by RF magnetron sputtering in Ar + N₂ and N₂ atmospheres. The structural, electrochemical, and optical properties of the LPWON electrolytes were characterized by X-ray diffraction (XRD), UV–visible spectroscopy, and an impedance analyzer. EC mirrors with WO₃ (coloring layer), LPWON (solid electrolyte), and stainless steel (mirror electrode) on ITO (transparent electrode) glass were fabricated to analyze the improved EC properties due to the LPWON electrolyte. The LPWON may lead to electrolytes with more stable potential cycle properties.     

Mechanical and electrochemical behavior of novel electrolytes based on partially stabilized zirconia for solid oxide fuel cells

In this study, 3 mol% yttria stabilized zirconia (3YSZ) is investigated as a SOFC electrolyte alternative to 8 mol% yttria stabilized zirconia (8YSZ). The mechanical and electrochemical properties of both materials are compared. The mechanical tests indicate that the thickness of 3YSZ can be reduced to half without sacrificing the strength compared to 8YSZ. By reducing the thickness of 3YSZ from 150 µm to 75 µm, the peak power density is shown to increase by around 80%. The performance is further enhanced by around 22% by designing of novel electrode structure with regular cut-off patterns previously optimized. However, the cell with novel designed 3YSZ electrolyte exhibits 30% lower maximum power density than that of the cell with 150 µm-thick standard 8YSZ electrolyte. Nevertheless, the loss in the performance may be tolerated by decreasing the fabrication cost revealing that 3YSZ electrolyte with cut-off patterns can be employed as SOFC electrolyte alternative to 8YSZ.