Total Ionic Conductivity Research Articles

Synthesis, Structure and Ionic Conductivity of Garnet Like Lithium Ion Conductor Li6.25+xGa0.25La3-xSrxZr2O12

Lithium ionic conductors which exhibit high ionic conductivity and are stable to lithium metal are demanded as solid electrolytes of all solid-state lithium batteries. Garnet-type lithium ionic conductor, Li6.25+xGa0.25La3-xSrxZr2O12 (LLZ-GaSr) has been synthesized at 1000°C by a solid-state reaction. Its phase relation, sinterability, structure and ionic conductivities have been investigated. LLZ-GaSr forms cubic phase in x = 0-0.2 as main phase, while it forms tetragonal phase with impurities in x = 0.3-0.5. XRD studies indicate the solubility limit in cubic phase of LLZ-GaSr is around x = 0.1. Sinterability is improved by Sr substitution. The total ionic conductivity of LLZ-GaSr with x = 0.1 at 25°C exhibits 1.3 × 10−3 S cm−1. The symmetrical cell with Li electrodes demonstrates that LLZ-GaSr is stable in Li metal at room temperature for 1.5 month. The Sr-substitution is effective in improvements of sinterability and ionic conductivity of Li6.25Ga0.25La3Zr2O12 (LLZ-Ga).

High-Pressure Synthesis, Crystal Chemistry, and Ionic Conductivity of a Structural Polymorph of Li3BP2O8.

A new structural polymorph of Li3BP2O8 has been successfully synthesized via a solid-state reaction between Li3PO4 and BPO4 at 4 GPa and 600 °C. The high-pressure phase of Li3BP2O8 (HP-Li3BP2O8) was found to crystallize in monoclinic symmetry with the cell parameters of a = 8.57010(4) Å, b = 11.11812(5) Å, c = 5.55380(3) Å, and β = 97.7269(3)° [space group P21/ a (No. 14)]. HP-Li3BP2O8 has a new crystal structure that has not been reported so far. The total ionic conductivities measured for the polycrystalline sample by alternating-currrent impedance were 3.4 × 10-7 and 2.1 × 10-6 S/cm at 399 and 456 K, respectively. The lithium ionic conductivity of HP-Li3BP2O8 was higher than that of the low-pressure phase Li3BP2O8 in the temperature range of 375-456 K. This is caused by the difference in the dimensions of the lithium arrangements between LP- and HP-Li3BP2O8.

Fabrication and electrochemical characteristics of NCM-based all-solid lithium batteries using nano-grade garnet Al-LLZO powder

Garnet-related Li6.25Al0.25La3Zr2O12 (Al-LLZO) powder was prepared by calcination the precursor synthesized a Couette–Taylor reactor. The powder comprised regular blocks (1–2μm) and consisted of fine particles (average particle size: D50=600nm, specific surface area: 2.42m2g−1) that adopted a highly crystalline nanoscale cubic structure (lattice parameter: a=13.07769Å; crystallite size: 41.4nm). A composite electrolyte (CE) sheet in which the Al-LLZO nanopowder was finely dispersed was prepared by casting a slurry comprising 70wt% Al-LLZO, polyethylene oxide (PEO), and lithium salt (LiClO4). The total ionic conductivity of the CE sheet was 7.59×10−6Scm−1 at 25°C and 1.93×10−3Scm−1 at 70°C, compared with 3.03×10−4Scm−1 at 25°C for the Al-LLZO pellet. Cyclic voltammetry showed that the electrochemical potential of the CE sheet was superior to that of PEO sheet. For application of the CE in all-solid lithium batteries (ASLBs), a composite NCM-based cathode composed of Al-LLZO, PEO, Super-P, and VGCF was also prepared. The discharge capacity of the cell was ∼122mAhg−1 at 0.1C & 70°C in voltages of 3.0–4.1V, and ∼80% of the initial capacity was maintained over 100 cycles with high rate characteristics.

Effect of grain boundary and Ar–H2 atmosphere on electrical conductivity of bulk a-La2Mo2O9 studied by impedance and x-ray photoelectron spectroscopy

The effect of grain boundary on electrical conductivity of α-La2Mo2O9 (LAMOX) over the temperature range of 300 °C to 400 °C has been investigated in this paper. Grain boundary effect characterisation for the mentioned temperature range has been done by electrochemical impedance spectroscopy (EIS). The calculated values of grain boundary width and specific grain boundary conductivity for α- La2Mo2O9 are 14.6 nm and 0.0146 μS/cm respectively. Total ionic conductivity calculated by EIS for α-La2Mo2O9 at 300 °C is 1 μS/cm. Resulting electrical conductivity of grain boundary comes out to be two orders less than the total electrical conductivity suggesting high activation energy requirement for grain boundary conduction. The electrical conductivity of α-La2Mo2O9 treated in Ar-H2 atmosphere (2.5 mS cm−1 at 200 °C) is approximately three orders higher than the electrical conductivity of LAMOX treated in air atmosphere. This may be attributed to reduction of Mo6+ to lower valance states in LAMOX as confirmed by x-ray photoelectron spectroscopy (XPS). Therefore, the low ionic conductivity nature of monoclinic phase of La2Mo2O9 has been explained on the basis of grain boundary conduction mechanism in the present study.

Synthesis and understanding of Na11Sn2PSe12 with enhanced ionic conductivity for all-solid-state Na-ion battery

All-solid-state Na-ion batteries (NIBs) that incorporate nonflammable solid-state electrolytes and an inexhaustible alkali metal offer a potential solution to the safety and cost concerns associated with conventional Li-ion batteries that use liquid electrolytes. Na-ion solid-state electrolytes (SSEs) with high ionic conductivity are the key to success for all-solid-state NIBs. Here, we report a new Na-ion SSE, Na11Sn2PSe12, with a superior grain conductivity of 3.04 mS cm−1 and a total ionic conductivity of 2.15 mS cm−1 at 25 °C. Single-crystal X-ray diffraction, first-principles phonon calculations, and the proposed bonding energy model indicate that its superior ionic conductivity stems from the presence of a high density of dispersive Na+ vacancies, three-dimensional Na-ion conduction pathways, and a low bonding energy of the Na+ ion with its neighboring atoms. Na11Sn2PSe12 is used for the first time as the electrolyte in all-solid-state Na-Sn/TiS2 battery cell, which shows excellent rate performance and delivers a high reversible capacity of 66.2 mAh (g of TiS2)−1 after 100 cycles with cycling retention of 88.3% at a rate of 0.1 C at room temperature.

Changes in structure and electrical conductivity of some rare-earth-doped ceria induced by strontium addition

In order to investigate the effect of strontium addition on the structure and ionic conductivity of rare-earth-doped ceria, powders with composition Ce0.85Dy0.15-xSrxO2-δ (x = 0, 0.05, 0.075) and Ce0.85Yb0.15-xSrxO2-δ (x = 0, 0.05, 0.075) are synthesized using a Pechini method. X-ray diffraction (XRD) and Raman spectroscopy analysis evidence the formation of single-phase solid solutions for all investigated powders and their corresponding sinters. An increase in grain size with strontium content is evidenced by scanning electron microscopy (SEM). Electrochemical impedance spectroscopy allows only the determination of total ionic conductivity of the investigated samples. The sample with stoichiometry Ce0.85Yb0.10Sr0.05O2-δ exhibits the highest ionic conductivity (8.6 × 10−4 S/cm at 500 °C) and the lowest activation energy of conduction (0.71 eV) among all investigated samples. The activation energy of conduction has a dominating effect on ionic conductivity for Ce–Yb system.

Preparation of a Li7La3Zr1.5Nb0.5O12 Garnet Solid Electrolyte Ceramic by using Sol-gel Powder Synthesis and Hot Pressing and Its Characterization

In this study, we prepared and characterized Nb-doped Li7La3Zr2−xO12 (LLZNO) powder and pellets with a cubic garnet structure by using a modified sol-gel synthesis and hot pressing. LLZNO powder with a very small grain size and cubic structure without secondary phases could be obtained by using a synthesis method in which Li and La sources in a propanol solvent were mixed together with Zr and Nb sources in 2-methoxy ethanol. A pure cubic phase LLZNO pellet could be fabricated from the prepared LLZNO and an additional 6-wt% of Li2CO3 powder by hot pressing at 1050 °C and 15.8 MPa. The hot-pressed LLZNO pellet with a relative density of 99% exhibited a very dense surface morphology. The total Li ionic conductivity of the hot-pressed LLZNO was 7.4×10 −4 S/cm at room temperature, which is very high level compared to other reported values. The activation energy for ionic conduction was estimated to be 0.40 eV.

Fabrication and charge-discharge reaction of all solid-state lithium battery using Li4-2xGe1-xSxO4 electrolyte

Bulk-type solid-state batteries using a LIthium Super Ionic CONductor (LISICON)-based oxide electrolyte, Li4-2xGe1-xSxO4, were assembled by spark plasma sintering (SPS) and electric furnace sintering (FS), and their charge-discharge performances were investigated. Li4-2xGe1-xSxO4, which has a γ-Li3PO4-type structure, was synthesized by conventional solid-state reaction. The total ionic conductivity of the Li3.6Ge0.8S0.2O4 sample sintered at 600 °C by SPS was 2 × 10−5 S cm−1 at room temperature, which is comparable to the bulk conductivity of the material sintered at 800–1100 °C by FS. No impurity peaks were observed in the X-ray diffraction patterns of the LiNi1/3Mn1/3Co1/3O2-Li3.6Ge0.8S0.2O4 mixture even after high-temperature sintering at 900 °C by FS. The solid-state cells of laminated LiNi1/3Mn1/3Co1/3O2 cathode and Li3.6Ge0.8S0.2O4 electrolyte co-sintered by SPS at 600 °C and FS at 900 °C exhibited first discharge capacities of 130 and 92 mAh g−1, respectively, at 60 °C. These experimental results confirm that the LISICON-based material, Li4-2xGe1-xSxO4, exhibits thermal compatibility to the active material and relatively high lithium ion conductivity, which lead to the high charge-discharge performance of the bulk-type all-solid-state cell.

Oxide ionic conductivity and microstructures of Pr and Sm co-doped CeO2-based systems

AbstractThe compositions Ce0.80Sm0.2-xPrxO2-δ (x=0-0.12) were prepared through the citrate-nitrate method. The synthesized Pr3+ and Sm3+ co-doped ceria powders with different compositions were calcined at 600°C for 3 h. Phase structure of the calcined powders was characterized by X-Ray diffraction (XRD) analysis.All the calcined samples were found to be ceria based solid solutions of fluorite type structures. The morphology examinations were carried out by scanning electron microscopy (SEM) analysis. Relative density of more than 91% of the theoretical can be achieved by sintering the Ce0.80Sm0.2-xPrxO2-δ pellets at 1400°C for 6 h. The two-probe a.c. impedance spectroscopy was used to study the ionic conductivity of the doped ceria samples. The Ce0.80Sm0.80Pr0.12O1.90 composition showed the highest total ionic conductivity value which is 2.39 × 10−2 S/cm at 600°C.

Garnet-like Li7-xLa3Zr2-xNbxO12 (x = 0−0.7) solid state electrolytes enhanced by self-consolidation strategy

Garnet-like Li7La3Zr2O12 electrolytes with Nb doping are synthesized by self-consolidation method. Different from conventional methods such as cold or hot isostatic pressing, not any pressing assistance is employed throughout the preparation process. Although the preparation process is dramatically simplified, both density and ionic conductivity of the obtained samples are enhanced. Nb-doped content plays a key role in the sintering of the packed precursor powders and in the structure stabilization of the obtained bulk samples. The optimized 0.60 mol Nb-doped sample with relative density of 94%, fine particle boundaries, and solitary cubic structure possesses the maximum total ionic conductivity of 5.22 × 10−4 S cm−1 at 30 °C, which is comparable to the highest reported value of the samples prepared by conventional pressing methods. This work verifies that self-consolidation strategy is effective, reliable, and productive for the preparation of cubic Li7La3Zr2O12 electrolyte, which would significantly facilitate the development of ceramic electrolyte membrane technology.

High lithium ionic conductivity of garnet-type oxide Li7+xLa3Zr2-xSmxO12 (x = 0–0.1) ceramics

Li7La3Zr2O12 (LLZO) garnet is one of the most promising Lithium-ion solid electrolytes in all-solid-state Lithium-ion batteries, due to its higher chemical stability to Li metal and relatively higher lithium-ion conductivity. To further increase the electrical conductivity of LLZO, Sm3+ is doped into the Zr4+ site of LLZO so that excess Li occupies the position of the octahedral. Thereby lithium ion transport and increasing ionic conductivity are promoted. The optimal addition of Sm3+ is 0.06. Li7+xLa3Zr2-xSmxO12 (LLZSO, x = 0.06) electrolyte with cubic phase is obtained with sintering at 1200 °C for only 3 h. It has higher relative density and better ionic conductivity than the pristine LLZO. Its bulk and total ionic conductivity are ∼6.4 × 10−4 S·cm−1 and 2.46 × 10−4 S·cm−1 at 20 °C, respectively.

Structural, electrical and thermal studies on microwave sintered Dy and Pr co-doped ceria ceramics as electrolytes for intermediate temperature solid oxide fuel cells

The present study was focused on the effects of co-doping on the conductivity enhancement of CeO2-based solid ceramics for application as electrolytes in intermediate temperature solid oxide fuel cells (IT-SOFCs) and the correlation of ionic conductivity variations with micro structural alterations resulting from the addition of co-dopants. Nano-crystalline Dy and Pr co-doped ceria Ce0.8Pr0.2−xDyxO2−δ solid solutions were successfully synthesized by sol–gel auto-combustion and innovative densification by energy efficient microwave sintering (MS) at 1300 °C. The XRD results in concurrence with Raman studies ascertained the formation of cubic fluorite structure in the entire range of composition. The lattice parameters obtained by Rietveld refinement showed lattice contraction with increased dysprosium content. MS has resulted in improved densification and the relative densities of all the samples were noticed above 96% of the theoretical density. TEM images confirmed the nano-crystalline character in the as-prepared samples with the particle sizes measured around 20 nm. SEM micrographs showed spherical faceted near-uniform grains (average grain sizes around 225 nm) with distinct grain boundaries and negligible porosity. Formation of oxygen vacancies and their concentration in all the samples was assessed with the help of Raman spectroscopy. Total ionic conductivity values and activation energies were measured depending on the Dy content. The ionic conductivity of the best composition was found to be 6.8 mS cm−1 at 500 °C. Thermal expansion co-efficient of the samples was matched with that of the commonly used electrode materials. These results gave rise to the firm conclusion that the investigated co-doped ceria has the potential to be utilized as an electrolyte for IT-SOFC applications.

Effect of La3+ and Pr3+ co-doping on structural, thermal and electrical properties of ceria ceramics as solid electrolytes for IT-SOFC applications

In the present investigation, the effect of La3+ and Pr3+ co-doping on structural, thermal and electrical properties of ceria ceramics useful as solid electrolytes in intermediate temperature solid oxide fuel cells (IT-SOFCs) has been studied. The co-doped ceria Ce0.8Pr0.2–xLaxO2-δ samples have been prepared successfully via sol-gel auto-combustion synthesis. The high dense ceramic samples have been achieved by carry out an optimized conventional sintering at 1300 °C for 4 h. The powder X-ray diffraction analysis of all the co-doped ceria ceramics revealed the single phase with cubic-fluorite structure formation. Crystallographic information has been carried out from the powder X-ray diffraction and Rietveld refinement analysis. The scanning electron microscope and energy dispersive spectroscopy analysis revealed the smaller grain size with high density in microstructure and stoichiometric elemental confirmations. Raman spectra of prepared ceramics revealed the information of phase and oxygen vacancy formation in the entire compositions. The dilatometric studies of prepared co-doped ceria ceramics revealed the moderate coefficients of thermal expansion. The electrical parameters such as total conductivities and activation energies have been studied with the help of impedance spectroscopy. Among all these co-doped ceria ceramic samples, Ce0.80Pr0.10La0.10O2−δ found to exhibit the highest value of total ionic conductivity with minimum activation energy and this makes it could be a promising electrolyte material for IT-SOFC applications.

The Li+ conducting composite based on LiTi2(PO4)3 and Li3BO3 glass

The LiTi2(PO4)3 based composites containing amorphous Li3BO3 were formed and investigated by means of X–ray diffractometry, thermogravimetry, scanning electron microscopy, impedance spectroscopy and density methods. The study shows that when a polycrystalline LiTi2(PO4)3 material is sintered with Li3BO3 glass, the resultant ceramics exhibit very high total ion conductivity. The maximum conductivity of 1.43 × 10−4 S cm−1 at 30 °C was achieved for the LTP–0.3LBO material sintered at 900 °C compared to 5.15 × 10−8 S cm−1 of the ceramic LiTi2(PO4)3.

Non-equilibrium microstructure of Li1.4Al0.4Ti1.6(PO4)3 superionic conductor by spark plasma sintering for enhanced ionic conductivity

In solid-state electrolytes, the large resistance at grain boundaries remains the bottleneck for high ionic conductivity. Here we develop an alternative and somewhat counterintuitive strategy to enhance their ionic conductivity via non-equilibrium microstructure. Using Li1.4Al0.4Ti1.6(PO4)3 as an example, we demonstrate that semi-crystalline interphase between well crystallized ceramic phase and amorphous glass phase can be induced by spark plasma sintering, resulting in total ionic conductivity of 1.3 × 10−3 S cm−1 without any doping, which is 2 orders of magnitude higher than that derived by the conventional method. It is further demonstrated that the non-equilibrium structure is stable in ambient condition, yet can be converted into equilibrium structure by annealing with higher crystallinity but much lower ionic conductivity, proving that the non-equilibrium structure is indeed the key to the high performance. This opens door for its applications in electric vehicles, and the strategy is applicable to other ionic systems as well.

Ionic conduction and dielectric properties of yttrium doped LiZr2(PO4)3 obtained by a Pechini-type polymerizable complex route

We report on the ion transport properties of Li1+xZr2-xYx(PO4)3 (0.05 ≤ x ≤ 0.2) NASICON type nanocrystalline compounds prepared through a Pechini-type polymerizable complex method. Structural properties were characterized by means of powder X-ray diffraction, Raman spectroscopy and electron microscopy with selected area electron diffraction. Impedance spectroscopy was utilised to investigate the lithium ion transport properties. Y3+ doped LiZr2(PO4)3 compounds showed stabilized rhombohedral structure with enhanced total ionic conductivity at 30 °C from 2.87 × 10−7 S cm−1 to 0.65 × 10−5 S cm−1 for x=0.05 to 0.20 respectively. The activation energies of Li1+xZr2-xYx(PO4)3 show a decreasing trend from 0.45 eV to 0.35 eV with increasing x from 0.05 to 0.20. The total conductivity of these compounds is thermally activated, with activation energies and pre-exponential factors following the Meyer-Neldel rule. The tanδ peak position shifts to the high-frequency side with increasing yttrium content. Scaling in AC conductivity spectra shows that the electrical relaxation mechanisms are independent of temperature.

Sr- and Nb-co-doped Li7La3Zr2O12 solid electrolyte with Al2O3 addition towards high ionic conductivity

In the present study, series of garnet-type Li6.75+xLa3−xSr x Zr1.75Nb0.25O12 solid electrolytes [LLSZN with various Sr contents (x = 0.05–0.25)] have been prepared via conventional solid-state method. The effects of Sr contents on their phase structure and ionic conductivity have been systematically investigated on the combined measurements of X-ray diffraction and scanning electron microscopy and alter current impedance spectroscopy. Our results reveal that a phase transition from tetragonal to cubic structure occurs when both Sr and Nb elements is introduced, and such a cubic structure can be stable over the whole Sr contents variation, which is suggested to provide a beneficial impact on the performance of LLSZN. Accordingly, both relative density and total ionic conductivity exhibit a favorable tendency of increasing first and then decreasing with increased Sr contents, wherein a peak value at 93.46% and 5.09 × 10−4 S cm−1, respectively, can be well achieved. Particularly, the maximum ionic conductivity is almost twice that of the compared sample (2.93 × 10−4 S cm−1), and possess the minimum activation energy ~ 0.30 eV. Such a modification method, featured with higher efficiency and lower cost, is expected to be helpful for the development of solid electrolyte.

Synthesis and characterization of Y and Dy co-doped ceria solid electrolytes for IT-SOFCs: a microwave sintering

In this communication, the electrical conductivities and thermal expansion studies of microwave sintered co-doped ceria Ce0.8Y0.2−xDy x O2−δ (x = 0, 0.05, 0.10, 0.15 and 0.20) solid electrolyte materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) synthesized by sol–gel auto-combustion method were discussed. Microwave sintering at 1300 °C for 30 min was used for making dense powder compacts. The relative densities of all the samples are noticed above 95%. Raman spectrum was characterized by the presence of a very strong band near 460 cm−1, which along with X-ray diffraction (XRD) analysis ascertain the sample formation with a single-phase cubic fluorite structure. The lattice parameter values were calculated from XRD patterns. SEM images show nearly uniform grains with distinct grain boundaries. The thermal expansion coefficients (TECs) are found to vary linearly with temperature and were measured in the range from 14.15 to 13.20 × 10−6 °C−1. The investigation on total ionic conductivity (TIC) was executed with variation in dopant concentration and relative oxygen vacancies. The impedance analysis reveals that the sample Ce0.80Y0.10Dy0.10O2−δ displays the highest TIC, i.e., 7.5 × 10−3 S·cm−1 at 500 °C and minimum activation energy 0.90 eV compared to others. With the highest TIC and minimum activation energy, the Ce0.80Y0.10Dy0.10O2−δ might be the possible material as the solid electrolyte in intermediate temperature SOFCs.

Solid lithium ion conducting composites based on LiTi2(PO4)3 and Li2.9B0.9S0.1O3.1 glass

The LiTi2(PO4)3–based ceramic composites with addition of Li2.9B0.9S0.1O3.1 (LBSO) were formed and investigated by means of X–ray diffractometry, thermogravimetry, scanning electron microscopy, impedance spectroscopy and density methods. Significant enhancement of total ionic conductivity of the formed composites could be observed after sintering the material at high temperatures. The maximum conductivity of 1.79 × 10−4 S·cm−1 at 30 °C was achieved for the LTP–0.3LBSO material sintered at 900 °C compared to 5.15 × 10−8 S·cm−1 of the ceramic LTP.

Synthesis of Fast Fluoride-Ion-Conductive Fluorite-Type Ba1- xSb xF2+ x (0.1 ≤ x ≤ 0.4): A Potential Solid Electrolyte for Fluoride-Ion Batteries.

Toward the development of high-performance solid electrolytes for fluoride-ion batteries, fluorite-type nanostructured solid solutions of Ba1- xSb xF2+ x ( x ≤ 0.4) were synthesized by high-energy ball-milling method. Substitution of divalent Ba2+ by trivalent Sb3+ leads to an increase in interstitial fluoride-ion concentration, which enhances the ionic conductivity of the Ba1- xSb xF2+ x (0.1 ≤ x ≤ 0.4) system. Total ionic conductivities of 4.4 × 10-4 and 3.9 × 10-4 S cm-1 were obtained for Ba0.7Sb0.3F2.3 and Ba0.6Sb0.4F2.4 compositions at 160 °C, respectively. In comparison to isostructural Ba0.3La0.7F2.3, the ionic conductivity of Ba0.7Sb0.3F2.3 is significantly higher, which is attributed to the presence of an electron lone pair on Sb3+. Introduction of such lone pairs seems to increase fluoride-ion mobility in solid solutions. In addition, Ba0.7Sb0.3F2.3 was tested as a cathode material against Ce and Zn anode using La0.9Ba0.1F2.9 as the electrolyte. Ba0.3Sb0.7F2.3/La0.9Ba0.1F2.9/Ce cell showed high discharge and charge capacities of 301 and 170 mA h g-1, respectively, in the first cycle at 150 °C.