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Research area 09 - ENGINEERING SCIENCES, 09-206 - Nano- and membranous technologies

Keywordshybrid membranes, composite polymer electrolytes, ion-exchange membranes, NASICON, heterovalent doping, all-solid-state lithium batteries

Annotation
The need for reliable and powerful batteries for portable electronics, electric vehicles and energy storage grids requires new solutions to improve the cyclability, energy density, safety and life of existing battery technologies. Currently, lithium-ion batteries (LIBs) are recognized as the most promising electrochemical energy storage devices on the market. The use of lithium metal as anodes allows increasing the battery charge density (~40–50%). However, in this case, lithium dendrites can grow through a separator impregnated with liquid organic electrolytes commonly used in modern LIBs, which leads to serious safety problems, incl. overheating of the battery, gas formation and even explosion. In the case of lithium-sulfur batteries (one of the promising “post-lithium-ion” energy storage devices), which also use lithium anodes and owing to this have a higher energy density, one of the main problems is the need to eliminate the migration of products of cathodic processes (polysulfides). To solve problems associated with the use of liquid organic electrolytes, one of the promising approaches is the use of solid electrolytes with significantly lower flammability, volatility, toxicity and a wider operating temperature range. It is well established that solid polymer electrolytes, as well as ceramics based on phosphates with the NASICON structure, which are resistant to moisture, safe, and stable during cycling, are of considerable interest. At the same time, low values of lithium conductivity for undoped compounds, along with high grain boundary resistance (in the case of phosphates) and low cation transfer numbers (for polymer electrolytes), noticeably limit their wide application. The creation of hybrid (organic-inorganic) composite electrolytes based on polymeric materials with ion-conducting additives can largely overcome these disadvantages, since the polymer matrix can absorb any changes in the electrode volume during cell operation and reduce the contact resistance between the electrolyte and the electrode (lithium anode). During the implementation of the project, it is planned to solve an urgent scientific problem related to the development of new electrolytes for solid-state batteries with lithium anodes. One of the important tasks in this case will be to manufacture and study the electrochemical properties of membranes of new generation, as well as new solid electrolytes based on lithium phosphates with the NASICON structure with high conductivity, selectivity and resistance to degradation, and the ability to prevent the formation of lithium dendrites. One of the new approaches will be the introduction of nanosized oxide materials into ion-conducting polymers to increase their selectivity and reduce the permeability of polysulfides. On the basis of a number of ion-conducting and inert polymers, including those first obtained by our scientific group, and phosphates with the NASICON structure, new hybrid composites of the "polymer in ceramics" and "ceramics in polymer" types will be created. The developed materials will be comparable in their characteristics to world analogues or even surpass them. With their use, prototypes of all-solid-state and lithium-sulfur batteries with improved functional characteristics will be manufactured and tested. An important task of the project will be the understanding of regularities of changes in the properties of the prepared materials depending on the nature of the introduced cations, their concentration, the type of additives used to create composites, the polymer-filler ratio, as well as their effect on the operation of energy storage devices.

Expected results
As a result of the project implementation, new promising membrane materials (solid electrolytes) based on phosphates with the NASICON structure with improved conductive properties for all-solid-state batteries with the lithium metal anode, including lithium-sulfur batteries. A number of new solid lithium-conducting electrolytes based on complex phosphates with the NASICON structure will be manufactured and studied both individually and as composites with additives designed to accelerate transport along grain boundaries. Moreover, a number of composite polymer electrolytes of various types (“polymer-in-ceramics ” and “ceramics-in-polymer”) with inorganic particles (phosphates or nanosized metal oxides) will be manufactured with a wide approbation of previously unexplored for this purpose perfluorinated sulfonic acid membranes of Nafion type and sulfonated block copolymers of styrene, ethylene and butylene, which were for the first time manufactured in our group. The expected project results will match the world level of research that is substantiated by the relevance of the scientific problem associated with the development of electrolytes for batteries with improved functional properties. During the project, the regularities of dependence of the transport properties of hybrid membrane materials on the polymers used to create them, the polymer-filler ratio, the degree of dispersion and the morphology of the filler will be established. An important outcome of the project will be recommendations on the composition and conditions for the synthesis of efficient and safe electrolytes with high conductivity, good mechanical properties and low permeability of polysulfides (in the case of the use in lithium-sulfur batteries). The prototypes of all-solid-state lithium metal and lithium-sulfur batteries with improved functional will be created. The best materials obtained in this project will be tested at RENERA LLC. Thus, the data obtained during the implementation of the project will be of high importance not only from the point of view of fundamental science, but also for practical applications.

Annotation of the results obtained in 2023
Lithium titanium phosphate with the NASICON structure was iso- and heterovalent doped with germanium/zirconium and aluminum/iron ions, respectively. The lattice parameters of the prepared compounds were refined. The crystal structure of a number of phosphates was refined using the Rietveld method. In the systems under study (Li1+yTi2-x-y(Ge, Zr)x(Al, Fe)y(PO4)3 (x = 0-0.2, y = 0-0.2)), compositions characterized by the highest lithium conductivity were determined. It was shown that the ionic conductivity of phosphates doped with iron ions is somewhat lower than that of those doped with aluminum ions. Moreover, the conductivity of materials prepared by the sol-gel technique is less than that of materials prepared by the solid-state method. The contributions of the bulk and grain-boundary conductivity of the obtained phosphates, as well as the contribution of the electronic component to the total conductivity, were determined. The resulting electrolytes were shown to be stable with respect to lithium. The synthesis techniques of the studied phosphates were optimized by varying the synthesis method (sol-gel/solid-state), the final sintering temperature and time, and intensity of mechanical processing of their precursors. It was shown that ball-milling of phosphates prepared by the sol-gel method, followed by their pelletizing and repeated sintering, allows increasing their conductivity to the conductivity of materials prepared by the solid-state method (~7.10-4 S/cm). The local environment of phosphorus atoms in some phosphates was studied using 31P MAS NMR spectroscopy. Using 7Li NMR spectroscopy with a pulsed magnetic field gradient, the diffusion coefficient of lithium in Li1.2Ti1.6Ge0.2Al0.2(PO4)3 was estimated. Polymer electrolytes based on Nafion-212 membranes and a polystyrene-based polymer functionalized with phenylsulfonylimide groups (SSEBS-Ph) were synthesized and studied. With an increase in the solvation degree of Nafion membranes, an increase in their ionic conductivity is observed. Nafion membranes in Li+ form, kept in an EC-PC mixture show maximum values of solvation and ionic conductivity (8.2 solvent molecules per 1 sulfonic acid group and 2.9∙10-4 S/cm at 25°C, respectively). Keeping Nafion membranes in the H+ form in 1 M LiTFSI in the EC-PC mixture leads to a decrease in ionic conductivity and the solvation degree by 3.7 and 2.6 times, respectively. Among SSEBS-Ph membranes, the maximum ionic conductivity values were obtained for samples kept in 1 M LiTFSI in DO-DME (3.6∙10-6 S/cm at 25°C). The mechanical properties of solvated Nafion membranes were studied. It was shown that membrane rupture occurs in the reversible deformation region. Young's modulus decreases in the order Nafion-Li-DO-DME~Nafion-H-EC-PC>Nafion-H-DO-DME>Nafion-Li-EC-PC, which correlates with increasing solvent content. Using various carbon materials, such as pyrolyzed polyaniline and commercial mesoporous and microporous carbons, the composite sulfur-carbon cathode materials were prepared. The discharge capacity of S/Smes, S/Cmicr and S/Сpani in the first cycle is 1247 and 513 and 985 mAh/g, respectively. S/Smes showed the highest discharge capacity in the first cycles and the best kinetics of electrochemical reactions in the Li-S battery. The rate of the capacity decrease decreases in the series S/Smes > S/Сpani> S/Сmicr. Using cells with S/Smes, S/Cpani cathodes and Nafion-Li-DO-DME, SSEBS-Ph-H-EC-PC membranes, it was shown that the membrane is able to suppress the polysulfide diffusion, which is the main reason for the capacity decrease of lithium-sulfur batteries. For example, after 10 cycles, the Li-S cell with the S/Cmes cathode retains 77% of the initial value of the discharge capacity if a membrane was used, while it retains only 17% of the value if a polypropylene separator was used. Nafion-Li-EC-PC electrolyte is electrochemically stable up to 6 V and is predominantly a cationic conductor. Its transfer numbers, estimated using the Bruce-Vincent method, were TLi+=0.76. The Nafion-Li-EC-PC membrane shows the stable operation of a lithium battery. Nafion-Li-EC-PC was used as an electrolyte and separator in a lithium metal battery with the LiFePO4 cathode. Symmetrical Li|Nafion-212-EC-PC|Li cells are characterized by an overvoltage of ~0.3 V at a current density of ±0.1 mA/cm2. At 25°C, LiFePO4|Nafion-212-EC-PC|Li batteries showed capacities of 141, 136, 125 and 100 mAh/g at 0.1, 0.2, 0.5 and 1C charge/discharge and a capacity of 120 mAh/g at 0°C and 0.1C with stable characteristics for 50 charge/discharge cycles.

Publications

1. Stenina I.A., Taranchenko E.O., Ilin A.B., Yaroslavtsev A.B. Синтез и ионная проводимость сложных фосфатов Li1+xTi1.8 xFexGe0.2(PO4)3 со структурой NASICON Журнал неорганической химии, Том 68, №12, С. 1683-1690 (year - 2023) https://doi.org/10.31857/S0044457X23601360

2. Voropaeva D.Y., Novikova S.A., Stenina I.A., Yaroslavtsev A.B. Nafion-212 Membrane Solvated by Ethylene and Propylene Carbonates as Electrolyte for Lithium Metal Batteries Polymers, Том 15(22), статья № 4340 (year - 2023) https://doi.org/10.3390/polym15224340

3. Stenina I.A., Novikova S.A., Voropaeva D.Y., Yaroslavtsev A.B. Solid Electrolytes Based on NASICON-Structured Phosphates for Lithium Metal Batteries Batteries, Том 9(8), статья № 407 (year - 2023) https://doi.org/10.3390/batteries9080407

4. Novikova S.A., Voropaeva D.Yu., Li S.A, Kulova T.L., Yaroslavtsev A.B Nafion-117 membrane for lithium-sulfur batteries Book of abstracts of International Conference “Ion transport in organic and inorganic membranes-2023”. Sochi, 22 – 27 May, 2023., с. 203-205 (year - 2023)

5. Novikova S.A., Voropaeva D.Yu., Li S.A, Kulova T.L., Yaroslavtsev A.B. Perfluorosulfonic acid membranes for lithium-sulfur batteries Сборник тезисов докладов Всероссийской конференции по электрохимии с международным участием, 23-27 октября 2023 Москва, С. 300-301 (year - 2023)

6. Pyrkova A.B., Stenina I.A., Yaroslavtsev A.B. Синтез и ионная проводимость фосфата лития-титана со структурой NASICON, допированного цирконием и трехвалентными элементами Сборник тезисов докладов Седьмой международной конференции стран СНГ «Золь-гель синтез и исследование неорганических соединений, гибридных функциональных материалов и дисперсных систем «Золь-гель 2023», 28 августа – 01 сентября 2023 г. Москва, с.97 (year - 2023)

7. Stenina I.A., Pyrkova A.B., Taranchenko E.O., Yaroslavtsev A.B. Твердые электролиты Li1+yAly(Zr, Ge)xTi1,8-x-y(PO4)3: синтез и ионная проводимость Физическая химия и электрохимия расплавленных и твердых электролитов: сб. материалов XIX Российской конференции, 17–21 сентября 2023 г. /, с.391-392 (year - 2023)

8. Yaroslavtsev A.B., Stenina I.A. Накопители энергии в России ЭЛЕКТРОХИМИЯ В РАСПРЕДЕЛЕННОЙ И АТОМНОЙ ЭНЕРГЕТИКЕ Сборник трудов второго Всероссийского семинара "Электрохимия в распределенной и атомной энергетике", посвященного 70‐летию профессора Хасби Биляловича Кушхова, с. 272-273 (year - 2023)