It is shown that a promising solid electrolyte is afraid of water

(ORDO NEWS) — The results of the study are published in the journal Chemistry of Materials. Renewable energy sources (RES) around the world are of great interest due to their environmental friendliness and high energy conversion efficiency, however, their implementation is associated with serious problems due to their inherent cyclical and intermittent nature of the work. Because the mode of energy generation is followed by a period of inactivity.

It is obvious that such a power source with unpredictable cycling is unlikely to interest the consumer. But this problem has a solution – energy storage. It is assumed that they will accumulate spontaneously generated energy, and then supply it in accordance with the level of consumption, thereby ensuring a stable and adaptive power supply.

Flowing redox batteries are considered the most promising among a wide range of energy storage systems due to the ease of scaling, ease of use, and the ability to control output power.

A flowing redox battery is, in fact, an ordinary battery, but the “opposite”: liquids (anolyte and catholyte) are used as electrodes in a redox battery, and a solid membrane is used as an ion-conducting electrolyte. Since it is the membrane properties that determine the final performance and battery life, scientists are considering the possibility of manufacturing membranes from various materials, including inorganic and polymeric ones.

One of these compounds is LATP – Li 1.3 Al 0.3 Ti 1.7 (PO 4) 3 . This is a well-known lithium conductor from the NASICON family, which received its name from the first Na Super Ionic CONductor, which was described in detail in detail. All conductors of this family have a similar crystalline structure, which determines the high ionic conductivity of the compounds.

Although the conductivity and structural features of LATP are described in sufficient detail, their resistance to environmental factors such as air and water remains poorly understood. Skoltech Center for Energy Technology (CEST) researcher Mariam Pogosova and her colleagues decided to find out if pure water affects the properties of LATP.

“LATP aroused our great interest: it is a well-known superionic conductor with high potential for further chemical and technological improvement. It is known that LATP has a number of disadvantages, such as high fragility and low resistance to lithium metal. Nevertheless, these shortcomings did not bother us, since we planned to compensate them by creating a composite material, and we started to work,” Pogosova explained.

In previous studies of this group of scientists, it was shown that the conductivity of ceramic LATP drops sharply when stored in air or argon. The researchers hypothesized that humidity could be the main reason for the decrease in conductivity, and decided to test how water affects LATP.

Initially, scientists synthesized LATP through an innovative two-step solid-state reaction. Then, the obtained LATP samples were placed in deionized water and kept for up to 12 hours. After that, the researchers analyzed the electrochemical, structural, chemical, and morphological properties of the samples, reinforcing the results with theoretical modeling methods.

During the experiments, it was shown that upon contact with water, the properties of LATP ceramics significantly deteriorate: after two hours of exposure to water, the total ionic conductivity decreases by 64 percent. Scientists also observed the appearance of microcracks, distortion of the grain shape, the formation of nanoparticles, changes in the chemical composition of the substance, compression of the unit cell, as well as changes in the intrastructural polyhedra. Based on these observations, scientists came to the conclusion that LATP ceramics are highly sensitive to water and probably cannot be used in aqueous flow redox batteries.

“Obviously, LATP is too exposed to water, which casts doubt on the possibility of its use in flowing redox batteries, especially water. I want to emphasize that the operating conditions of the “deionized water / LATP” system, which is the subject of this study, do not correspond to the real operating conditions of a flowing redox battery, since anolyte / catholyte solutions are more complex.

Therefore, so far I will not risk making any predictions regarding the prospects for using LATP. Nevertheless, I note that as a result of the study, important fundamental knowledge was obtained that also has practical value: we were able to show that in the presence of water in any form, one must be on guard. For example, now we know that it is possible to maintain the original characteristics of LATP ceramics with the help of simple drying and evacuation,” said Mariam Pogosova.

She also noted that this work, surprisingly, is the first such detailed and comprehensive study of the problem of the effect of water on LATP. “We plan to conduct additional studies to clarify the behavior of LATP in other environments and to check how this conductor will behave under conditions that correspond to the working conditions of flowing redox batteries,” added Pogosova.

Specialists from the Moscow State University named after M.V. Lomonosov and the N. N. Semenov Federal Research Center for Chemical Physics, Russian Academy of Sciences, took part in a joint study. The study was conducted as part of the Lithium Redox Flow Batteries for High Power and High Energy Density Energy Storage project under the Next Generation (Skoltech-MIT) project program.

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