Lithium-ion batteries with solid electrolytes offer safety, higher energy density and higher long-term performance, which are promising alternatives to conventional liquid electrolyte batteries. Lithium aluminum titanium phosphate (LATP) is one potential solid electrolyte candidate due to its high Li-ion conductivity. To evaluate its performance, influences of the experimental factors on the materials design need to be investigated systematically. In this work, a materials design strategy based on machine learning (ML) is employed to design experimental conditions for the synthesis of LATP. In the variation of parameters, we focus on the tolerance against the possible deviations in the concentration of the precursors, as well as the influence of sintering temperature and holding time. Specifically, models built with different design selection strategies are compared based on the training data assembled from previous laboratory experiments. The best one is then chosen to design new experiment parameters, followed by measuring the corresponding properties of the newly synthesized samples. A previously unknown sample with ionic conductivity of 1.09 × 10−3 S cm−1 is discovered within several iterations. In order to further understand the mechanisms governing the high ionic conductivity of these samples, the resulting phase compositions and crystal structures are studied with X-ray diffraction, while the microstructures of sintered pellets are investigated by scanning electron microscopy. Our studies demonstrate the advantages of applying machine learning in designing experimental conditions by the synthesis of desired materials, which can effectively help researchers to reduce the number of required experiments.

An evaluation of the environmental impact of manufacturing an oxide all-solid-state lithium battery with economic cell design.

Lithium aluminum titanium phosphate (LATP) is known to have a high Li-ion conductivity and is therefore a potential candidate as a solid electrolyte. Via sol-gel route, it is already possible to prepare the material at laboratory scale in high purity and with a maximum Li-ion conductivity in the order of 1·10 −3 s/cm at room temperature. However, for potential use in a commercial, battery-cell upscaling of the synthesis is required. As a first step towards this goal, we investigated whether the sol-gel route is tolerant against possible deviations in the concentration of the precursors. In order to establish a possible process window for sintering, the temperature interval from 800 °C to 1100 °C and holding times of 10 to 480 min were evaluated. The resulting phase compositions and crystal structures were examined by X-ray diffraction. Impedance spectroscopy was performed to determine the electrical properties. The microstructure of sintered pellets was analyzed by scanning electron microscopy and correlated to both density and ionic conductivity. It is shown that the initial concentration of the precursors strongly influences the formation of secondary phases like AlPO 4 and LiTiOPO 4 , which in turn have an influence on ionic conductivity, densification behavior, and microstructure evolution.

In this study, tape casting has been used to produce thin electrolyte and electrode sheets which were then assembled as half-cells by co-sintering. As a solid electrolyte, Li0.33La0.557TiO3 (LLTO), which features a high ionic conductivity between 10(-5)S/cm and 10(-3)S/cm at room temperature, was used. The spinel Li4Ti5O12 (LTO) was selected as electrode material, since it is chemically similar to the electrolyte and therefore no undesired foreign phases are expected to occur at the interface. The key challenge was to adjust the processing parameters such that a clean and homogeneous interface forms between LTO and LLTO, even though these materials have different densification properties. Our results demonstrate that it is possible to produce co-sintered crack-free half-cells from LTO and LLTO green tapes. With a thickness of only 25 mu m, a very thin electrolyte was realised, maximizing the ionic conductivity of the electrolyte. High co-sintering temperatures, needed to obtain a dense electrolyte, lead to a phase transition in LTO, which causes a drop in ionic conductivity. However, the even at high temperatures still open porosity of the anode offers void for additives, that could provide the necessary electronic and ionic conductivity.

Phase-pure solid electrolyte Lithium-Lanthanum-Titanate (LLTO) has been prepared by solid-state-synthesis. Thin sheets of LLTO have been successfully prepared via tape casting and subsequent sintering. A tape casting slurry composition has been developed. The influencing parameters in slurry composition are presented. These are dispersant concentration, ratio of binder to plasticizer and total amount of binder and plasticizer. Furthermore it was found that drying conditions significantly influence tape casting results. Sintered tapes were compared to massive reference samples regarding density, phase-purity, microstructure and conductivity. Our results show that sintered tapes and massive samples exhibit comparable properties.