The influence of hafnium impurities on the electrochemical performance of tantalum substituted Li7La3Zr2O12 solid electrolytes

Garnet-based Li7La3Zr2O12 (LLZO) is considered one of the most promising oxide-ceramic solid electrolyte materials for inorganic all-solid-state batteries. Dopants and substituents like Al, Ta, Nb, Ga, and W were shown to have a high impact on the total ionic conductivity, increasing it from 10−6 S/cm up to 10−3 S/cm. However, natural zirconium sources always contain a small amount of hafnium which could also act as dopant, but the separation of these two elements is complicated and expensive. In this work, we investigate the influence of various Hf-impurity concentrations on the performance of tantalum-doped LLZO. We synthesised Li6.45Al0.05La3Zr1.6−xHfxTa0.4O12 (LLZHO with x = 0 – 1.6) via conventional solid-state synthesis and have demonstrated that up to x = 0.1, hafnium impurities do not have a significant impact on the performance of the material. Above this concentration, the Li-ion conductivity is steadily reduced to around 70% when zirconium is fully substituted by hafnium resulting in Li6.45Al0.05La3Hf1.6Ta0.4O12. As the purity of Zr precursors has a great impact on their price, these findings can help to reduce the price of LLZO in general, as lower grade zirconium can be used in industrial scale applications.

Electrical and Structural Properties of Li1.3Al0.3Ti1.7(PO4)3-Based Ceramics Prepared with the Addition of Li4SiO4

The currently studied materials considered as potential candidates to be solid electrolytes for Li-ion batteries usually suffer from low total ionic conductivity. One of them, the NASICON-type ceramic of the chemical formula Li1.3Al0.3Ti1.7(PO4)3, seems to be an appropriate material for the modification of its electrical properties due to its high bulk ionic conductivity of the order of 10−3 S∙cm−1. For this purpose, we propose an approach concerning modifying the grain boundary composition towards the higher conducting one. To achieve this goal, Li4SiO4 was selected and added to the LATP base matrix to support Li+ diffusion between the grains. The properties of the Li1.3Al0.3Ti1.7(PO4)3−xLi4SiO4 (0.02 ≤ x ≤ 0.1) system were studied by means of high-temperature X-ray diffractometry (HTXRD); 6Li, 27Al, 29Si, and 31P magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR); thermogravimetry (TG); scanning electron microscopy (SEM); and impedance spectroscopy (IS) techniques. Referring to the experimental results, the Li4SiO4 additive material leads to the improvement of the electrical properties and the value of the total ionic conductivity exceeds 10−4 S∙cm−1 in most studied cases. The factors affecting the enhancement of the total ionic conductivity are discussed. The highest value of σtot = 1.4 × 10−4 S∙cm−1 has been obtained for LATP–0.1LSO material sintered at 1000 °C for 6 h.

Sintering behavior and ionic conductivity of Li1.5Al0.5Ti1.5(PO4)3 synthesized with different precursors

Li1.5Al0.5Ti1.5(PO4)3 (LATP) powders were prepared from different NO x -free precursors using an aqueous-based solution-assisted solid-state reaction (SA-SSR). The sintering behavior, phase formation, microstructure and ionic conductivity of the powders were explored as a function of sintering temperature. The powders showed a relatively narrow temperature windows in which shrinkage occurred. Relative densities of 95% were reached upon heating between 900 and 960 °C. Depending on the morphological features of the primary particles, either homogeneous and intact microstructures with fine grains of about <2 µm in size or a broad grain size distribution, micro-cracks and grain cleavages were obtained, indicating the instability of the microstructure. Consequently, the ceramics with a homogeneous microstructure possessed a maximum total ionic conductivity of 0.67 mS cm−1, whereas other ceramics reached only 0.58 mS cm−1 and 0.21 mS cm−1.

Silicon Substituted Lithium Stannum Phosphate Ceramic Electrolytes: Structural, Electrical and Electrochemical Properties

Structural, electrical and electrochemical properties of silicon (Si) substituted NASICON-structured lithium stannum phosphate, Li1+ySn2P3-ySiyO12 with 0 < y < 1 that was prepared by the low-temperature water-based sol-gel method has been investigated. From the structural analysis, all samples in the system displayed rhombohedral symmetry. The total ionic conductivity, σt, and ionic mobility, µ was increased with the increase of silicon content, y. A high ionic conductivity value of 6.05 × 10-5 S cm-1 exhibited at y = 0.5 with a temperature of 500 °C. Linear sweep voltammetry analysis showed that the sample was electrochemically stable up to 5.1 V. Meanwhile, the ionic transference number value of the sample was 0.99, suggesting that the majority of mobile charge carriers were predominantly due to ions. Thus, from these results, it indicated that silicon substitution in LiSn2P3O12 ceramic electrolytes is significantly enhanced the electrical and electrochemical properties.

Submicron-Sized Nb-Doped Lithium Garnet for High Ionic Conductivity Solid Electrolyte and Performance of Quasi-Solid-State Lithium Battery

The garnet Li7La3Zr2O12 (LLZO) has been widely investigated because of its high conductivity, wide electrochemical window, and chemical stability with regards to lithium metal. However, the usual preparation process of LLZO requires high-temperature sintering for a long time and a lot of mother powder to compensate for lithium evaporation. In this study submicron Li6.6La3Zr1.6Nb0.4O12 (LLZNO) powder―which has a stable cubic phase and high sintering activity―was prepared using the conventional solid-state reaction and the attrition milling process, and Li stoichiometric LLZNO ceramics were obtained by sintering this powder―which is difficult to control under high sintering temperatures and when sintered for a long time―at a relatively low temperature or for a short amount of time. The particle-size distribution, phase structure, microstructure, distribution of elements, total ionic conductivity, relative density, and activation energy of the submicron LLZNO powder and the LLZNO ceramics were tested and analyzed using laser diffraction particle-size analyzer (LD), X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Electrochemical Impedance Spectroscopy (EIS), and the Archimedean method. The total ionic conductivity of samples sintered at 1200 °C for 30 min was 5.09 × 10−4 S·cm−1, the activation energy was 0.311 eV, and the relative density was 87.3%. When the samples were sintered at 1150 °C for 60 min the total ionic conductivity was 3.49 × 10−4 S·cm−1, the activation energy was 0.316 eV, and the relative density was 90.4%. At the same time, quasi-solid-state batteries were assembled with LiMn2O4 as the positive electrode and submicron LLZNO powder as the solid-state electrolyte. After 50 cycles, the discharge specific capacity was 105.5 mAh/g and the columbic efficiency was above 95%.

Submicron Sized Nb Doped Lithium Garnet for High Ionic Conductivity Solid Electrolyte and Performance of All Solid-State Lithium Battery

The garnet Li7La3Zr2O12 (LLZO) has been widely investigated because of its high conductivity, wide electrochemical window and chemical stability to lithium metal. However, the usual preparation process of LLZO requires a long time of high-temperature sintering and a lot of mother powders against the lithium evaporation. The submicron Li6.6La3Zr1.6Nb0.4O12 (LLZNO) powders are prepared by conventional solid-state reaction method and attrition milling process, which are stable cubic phase and have high sintering activity, and Li stoichiometric LLZNO ceramics are obtained by sintering at a relative lower temperature or for a short time by using these powders which are difficult to control under high sintering temperature and long sintering time. The particle size distribution, phase structure, microstructure, distribution of element, total ionic conductivity, relative density and activation energy of submicron LLZNO powders and LLZNO ceramics are tested and analyzed by laser diffraction particle size analyzer, XRD, SEM, EIS and Archimedean method. The total ionic conductivity of sample sintered at 1200 &deg;C for 30 min is 5.09 &times; 10-4 S&middot;cm-1, the activation energy is 0.311 eV, and the relative density is 87.3%, and sintered at 1150 &deg;C for 60 min total ionic conductivity is 3.49 &times; 10-4 S&middot;cm-1, the activation energy is 0.316 eV, and the relative density is 90.4%. At the same time, all-solid-state batteries are assembled with LiMn2O4 as positive electrode and submicron LLZNO powders as solid state electrolyte. After 50 cycles, the discharge specific capacity is 105.5 mAh/g and the columbic efficiency is above 95%.

The influence of co-doping strontium and zirconium on structure and ionic conductivities of Li6+yLa3−ySryNbZrO12 solid electrolytes

To enhance the ionic conductivity of lithium garnets, a co-doping strategy was adopted with both strontium and zirconium for [Formula: see text] ([Formula: see text], 0.25, 0.5, 0.75 and 1.0) (LLSNZO). By increasing the content of Sr, lithium garnet ceramics maintain cubic structure when [Formula: see text] is in the range of 0–0.75. A secondary phase of [Formula: see text] appeared in the ceramic when [Formula: see text]. We also studied the cross-section of lithium garnets with silver electrode. Results showed that the density of LLSNZO ceramics increased continuously against the increase of Sr content, while their total ionic conductivity enhanced initially and then reduced, with the maximum reached when [Formula: see text]. It is indicated that ionic conductivity of lithium garnets is not only decided by the density but also decided by the concentration and the mobility of [Formula: see text].

Dual Substitution and Spark Plasma Sintering to Improve Ionic Conductivity of Garnet Li7La3Zr2O12

Garnet Li7La3Zr2O12 is one of the most promising solid electrolytes used for solid-state lithium batteries. However, low ionic conductivity impedes its application. Herein, we report Ta-doping garnets with compositions of Li7-xLa3Zr2-xTaxO12 (0.1 ≤ x ≤ 0.75) obtained by solid-state reaction and free sintering, which was facilitated by graphene oxide (GO). Furthermore, to optimize Li6.6La3Zr1.6Ta0.4O12, Mg2+ was select as a second dopant. The dual substitution of Ta5+ for Zr4+ and Mg2+ for Li+ with a composition of Li6.5Mg0.05La3Zr1.6Ta0.4O12 showed an enhanced total ionic conductivity of 6.1 × 10−4 S cm−1 at room temperature. Additionally, spark plasma sintering (SPS) was applied to further densify the garnets and enhance their ionic conductivities. Both SPS specimens present higher conductivities than those produced by the conventional free sintering. At room temperature, the highest ionic conductivity of Li6.5Mg0.05La3Zr1.6Ta0.4O12 sintered at 1000 °C is 8.8 × 10−4 S cm−1, and that of Li6.6La3Zr1.6Ta0.4O12 sintered at 1050 °C is 1.18 × 10−3 S cm−1.

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

The 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.