Effect of Substrates on the Physicochemical Properties of Li7La3Zr2O12 Films Obtained by Electrophoretic Deposition.

Thin film technology of lithium-ion solid electrolytes should be developed for the creation of all-solid-state power sources. Solid electrolytes of the Li7La3Zr2O12 (LLZ) family are one of the promising membranes for all-solid-state batteries. LLZ films were obtained by electrophoretic deposition on Ti, Ni and steel substrates. The influence of different metal substrates on microstructure, phase composition and conductivity of the LLZ films after their heat treatment was studied. It was shown that the annealing of dried LLZ films in an Ar atmosphere leads to the transition from tetragonal modification to a low-temperature cubic structure. It was established that an impurity phase (Li2CO3) was not observed for LLZ films deposited on Ti foil after heat treatment, in contrast to films deposited on Ni and steel substrates. The highest lithium-ion conductivity values were achieved for the LLZ films annealed at 300 °C, 1.1 × 10-8 S cm-1 (at 100 °C) and 1.0 × 10-6 S cm-1 (at 200 °C).

Recent Strategies for Lithium-Ion Conductivity Improvement in Li7La3Zr2O12 Solid Electrolytes.

The development of solid electrolytes with high conductivity is one of the key factors in the creation of new power-generation sources. Lithium-ion solid electrolytes based on Li7La3Zr2O12 (LLZ) with a garnet structure are in great demand for all-solid-state battery production. Li7La3Zr2O12 has two structural modifications: tetragonal (I41/acd) and cubic (Ia3d). A doping strategy is proposed for the stabilization of highly conductive cubic Li7La3Zr2O12. The structure features, density, and microstructure of the ceramic membrane are caused by the doping strategy and synthesis method of the solid electrolyte. The influence of different dopants on the stabilization of the cubic phase and conductivity improvement of solid electrolytes based on Li7La3Zr2O12 is discussed in the presented review. For mono-doping, the highest values of lithium-ion conductivity (~10-3 S/cm at room temperature) are achieved for solid electrolytes with the partial substitution of Li+ by Ga3+, and Zr4+ by Te6+. Moreover, the positive effect of double elements doping on the Zr site in Li7La3Zr2O12 is established. There is an increase in the popularity of dual- and multi-doping on several Li7La3Zr2O12 sublattices. Such a strategy leads not only to lithium-ion conductivity improvement but also to the reduction of annealing temperature and the amount of some high-cost dopant. Al and Ga proved to be effective co-doping elements for the simultaneous substitution in Li/Zr and Li/La sublattices of Li7La3Zr2O12 for improving the lithium-ion conductivity of solid electrolytes.

Electrophoretic Deposition and Characterization of Thin-Film Membranes Li7La3Zr2O12.

In the presented study, films from tetragonal Li7La3Zr2O12 were obtained by electrophoretic deposition (EPD) for the first time. To obtain a continuous and homogeneous coating on Ni and Ti substrates, iodine was added to the Li7La3Zr2O12 suspension. The EPD regime was developed to carry out the stable process of deposition. The influence of annealing temperature on phase composition, microstructure, and conductivity of membranes obtained was studied. It was established that the phase transition from tetragonal to low-temperature cubic modification of solid electrolyte was observed after its heat treatment at 400 °C. This phase transition was also confirmed by high-temperature X-ray diffraction analysis of Li7La3Zr2O12 powder. Increasing the annealing temperature leads to the formation of additional phases in the form of fibers and their growth from 32 (dried film) to 104 µm (annealed at 500 °C). The formation of this phase occurred due to the chemical reaction of Li7La3Zr2O12 films obtained by electrophoretic deposition with air components during heat treatment. The total conductivity of Li7La3Zr2O12 films obtained has values of ~10-10 and ~10-7 S cm-1 at 100 and 200 °C, respectively. The method of EPD can be used to obtain solid electrolyte membranes based on Li7La3Zr2O12 for all-solid-state batteries.

Thermal Conductivity of FLiNaK in a Molten State.

Although the thermal conductivity of molten salt mixtures is of interest for many potential technological applications, precise values are often hard to obtain. In this study, the thermal diffusivity of FliNaK was studied in a molten state using the laser flash method and found to be very slightly dependent on temperature. The heat capacity of FliNaK was measured using the DSC method. There was a minor difference between our results and data from the literature. From calculations based on thermal diffusivity, density and heat capacity values, thermal conductivity was shown to decrease with temperature.

Impact of Li3BO3 Addition on Solid Electrode-Solid Electrolyte Interface in All-Solid-State Batteries.

All-solid-state lithium-ion batteries raise the issue of high resistance at the interface between solid electrolyte and electrode materials that needs to be addressed. The article investigates the effect of a low-melting Li3BO3 additive introduced into LiCoO2- and Li4Ti5O12-based composite electrodes on the interface resistance with a Li7La3Zr2O12 solid electrolyte. According to DSC analysis, interaction in the studied mixtures with Li3BO3 begins at 768 and 725 °C for LiCoO2 and Li4Ti5O12, respectively. The resistance of half-cells with different contents of Li3BO3 additive after heating at 700 and 720 °C was studied by impedance spectroscopy in the temperature range of 25-340 °C. It was established that the introduction of 5 wt% Li3BO3 into LiCoO2 and heat treatment at 720 °C led to the greatest decrease in the interface resistance from 260 to 40 Ω cm2 at 300 °C in comparison with pure LiCoO2. An SEM study demonstrated that the addition of the low-melting component to electrode mass gave better contact with ceramics. It was shown that an increase in the annealing temperature of unmodified cells with Li4Ti5O12 led to a decrease in the interface resistance. It was found that the interface resistance between composite anodes and solid electrolyte had lower values compared to Li4Ti5O12|Li7La3Zr2O12 half-cells. It was established that the resistance of cells with the Li4Ti5O12/Li3BO3 composite anode annealed at 720 °C decreased from 97.2 (x = 0) to 7.0 kΩ cm2 (x = 5 wt% Li3BO3) at 150 °C.