CsAg4Br3-xI2+x solid solutions, which are isomorphic to the well-known alpha-RbAg4I5 superionic conductor, exhibit very similar conductivity by Ag+ ions. However, the CsAg4Br3-xI2+x electrolytes, promising low-temperature superionic conductors, have been little studied. Therefore, the present work set out to clarify their thermodynamic stability, define an existence region, and characterise the crystal structure parameters as a function of x. CsAg4Br3-xI2+x samples were prepared by solid-phase synthesis over a wide range from x = -0.25 to x = 2.00. The phase composition of the samples was specified by X-ray diffraction and thermal analysis. Single-phase CsAg4Br3xI2+x was observed for freshly synthesised samples within the composition range of 0.25 < x <= 1.35; however, all solid solutions CsAg4Br3-xI2+x (with the exception of x = 0.38) were found to be metastable at room temperature. Although the research samples can be easily prepared, they gradually decomposed when stored at 25 degrees C over a period of months. Solid solutions having a predominance of iodine decomposed most rapidly, while samples with a predominance of bromine decomposed much more slowly. Only one of the studied samples, having x = 0.38, underwent no changes; this sample remained single-phase throughout the entire storage period of up to >3 years. The occupancy of different crystallographic positions of Ag in freshly prepared samples as a function of x was established. The polythermal cross-section of the four-component system Cs - Ag - Br - I along the line between two non-existent compounds "CsAg4Br5" - "CsAg4I5" was used to represent the CsAg4Br3-xI2+x solid solution field.

The degree of swelling of the lithium form of the perfluorosulfonic acid membrane Nafion in alcohols (ethanol, 2-propanol), water-alcohol mixtures, and highly polar aprotic solvents (N,N-dimethylformamide (DMF) and N-methyl-2-pyrrolidone (NMP)) was studied, as well as the thermodynamics of membrane-solvent interaction using microcalorimetry. It was shown that the equilibrium swelling degree of the membrane correlates with the donor number of the solvent and the enthalpy of polymer swelling. The enthalpy of membrane swelling in all studied solvents is negative, indicating polymer solvation. Concentration dependences of the swelling and mixing enthalpies in DMF and NMP were studied in greater detail. The negative values of the swelling enthalpy across the entire concentration range of the solvents indicate good thermodynamic compatibility of the membrane with the solvent and highlight the advantage of using these solvents to produce Nafion dispersions due to their strong solvating properties.

A set of computational and experimental methods is used in the study of chemical side interactions in the LiMn2O4-based lithium-ion cathodic half-cell over the 25–60°C temperature range. The degradation of LiMn2O4-spinel-based electrodes is shown to start upon the LiMn2O4 granules contacting the standard (basic) electrolyte solution (1 m LiPF6 in a mixture of ethylene carbonate and dimethyl carbonate (1 : 1, by wt)). It is established that under current-less conditions, the degradation of the LiMn2O4-based electrode is caused by the mutual thermodynamic instability between LiMn2O4 and the LiPF6 lithium salt. The equilibrium interaction products are determined, and the mechanism of the critical temperature influence on the degradation of lithium-ion batteries with lithium–manganese spinel is refined. A model is proposed for the primary surface layer at the LiMn2O4/electrolyte interface formation and evolution, which explains the distinctive features of the degradation processes in this system.

CsAg4Br3–хI2+х solid solutions with x=0.38; 0.50; 0.63 were prepared by solid-phase synthesis; the single-phase of the products was confirmed by X-ray diffraction and differential scanning calorimetry. Studies of the electrical transport characteristics of CsAg4Br3–хI2+х included measurements of the ionic conductivity by the four-probe method in the range of –50…+120°C and an evaluation of the electronic component of the conductivity by the Hebb-Wagner method. It was shown that the ionic conductivity of CsAg4Br3–хI2+х solid solutions in the studied range of compositions is practically independent of x and is very close to that of the well-known superionic conductor RbAg4I5. The activation energy of conduction for all studied compounds is about 10 kJ mol–1. The oxidation potential determined by the stepwise polarization technique for CsAg4Br3–хI2+х solid solutions is noticeably higher than that of RbAg4I5, and is in the range of 0.75–0.78 V (vs. Ag0/Ag+). The high electrochemical characteristics of CsAg4Br3–хI2+х (0.38≤x≤0.63) and the absence of polymorphic transitions in the studied range from –160°C to the melting point (175 – 178°С) make these materials promising for use in electrochemical devices based on solid electrolytes, especially for low temperature applications.

Solid solutions CsAg4Br3 – хI2 + х (x = 0.38; 0.50; 0.68) are prepared by solid-state synthesis; the single phase of the products is confirmed using the methods of X-ray diffraction and differential scanning calorimetry. The studies of electrotransport characteristics of CsAg4Br3 – хI2 + х involve measuring the ionic conductivity by the four-probe method in the temperature interval from –50 to +120°C and estimating its electronic component by the Hebb–Wagner method. It is shown that in the studied interval of compositions, the ionic conductivity of CsAg4Br3 – хI2 + х solid solutions is practically independent of x, approaching the conductivity of the well-known superionic conductor RbAg4I5. The activation energy of conduction is found to be about 10 kJ mol–1 for all compounds studied. The oxidation potential determined by the method of stepwise polarization for CsAg4Br3 – хI2 + х solid solutions is considerably higher as compared with RbAg4I5, being in the range of 0.75–0.78 V (vs. Ag0/Ag+). The high electrochemical characteristics of CsAg4Br3 – хI2 + х (0.38 ≤ x ≤ 0.63) and the absence of polymorphic transitions in the considered interval from –160°С to the melting point (175–178°С) make these materials promising for the use in electrochemical devices, especially in low-temperature applications.

Determining the oxidation potential (OP) of lithium-ion battery (LIB) electrolytes using theoretical methods will significantly speed up and simplify the process of creating a new generation high-voltage battery. The algorithm for calculating OP should be not only accurate but also fast. Our work proposes theoretical principles for evaluating the OP of LIB electrolytes by considering LiDFOB solutions with different salt concentrations in EC/DMC solvent mixtures. The advantage of the new algorithm compared to previous versions of the theoretical determination of the oxidation potential of electrolyte solutions used in lithium-ion batteries for calculations of statistically significant complexes, the structure of which was determined by the molecular dynamics method. This approach significantly reduces the number of atomic–molecular systems whose geometric parameters need to be optimized using quantum chemical methods. Due to this, it is possible to increase the speed of calculations and reduce the power requirements of the computer performing the calculations. The theoretical calculations included a set of approaches based on the methods of classical molecular mechanics and quantum chemistry. To select statistically significant complexes that can make a significant contribution to the stability of the electrochemical system, a thorough analysis of molecular dynamics simulation trajectories was performed. Their geometric parameters (including oxidized forms) were optimized by QM methods. As a result, oxidation potentials were assessed, and their dependence on salt concentration was described. Here, we once again emphasize that it is difficult to obtain, by calculation methods, the absolute OP values that would be equal (or close) to the OP values estimated by experimental methods. Nevertheless, a trend can be identified. The results of theoretical calculations are in full agreement with the experimental ones.

Методами изотермической сорбции и микрокалориметрии исследована термодинамика взаимодействия полиперфторсульфоновой кислоты Nafion с водой. Определены концентрационные зависимости энергетических и энтропийных параметров смешения водных растворов Nafion и показано, что энергия Гиббса и энтальпия смешения отрицательны, а энтропия смешения положительна во всем диапазоне составов раствора. Экспериментальные изотермы сорбции воды и концентрационные зависимости энтальпии разбавления водных растворов проанализированы с использованием термодинамической модели, учитывающей парные невалентные взаимодействия в растворе, неравновесную стеклообразную структуру полимера и эффекты диссоциации ионогенных сульфогрупп Nafion. Расчетное значение параметра Флори–Хаггинса составило 1.48, а значение его энтальпийной компоненты близко к нулю.

The thermodynamics of interaction between poly(perfluorosulfonic acid) Nafion and water is studied by isothermal sorption and microcalorimetry. The concentration dependences of energy and entropy parameters of mixing of Nafion aqueous solutions are determined. It is shown that the Gibbs energy and the enthalpy of mixing are negative while the entropy of mixing is positive over the entire range of solution compositions. The experimental water sorption isotherms and the concentration dependences of the enthalpy of dilution of aqueous solutions are analyzed in terms of the thermodynamic model allowing for pair nonvalence interactions in solution, nonequilibrium glassy structure of the polymer, and effects of the dissociation of ionic sulfo groups of Nafion. The calculated value of the Flory–Huggins parameter is 1.48, and the value of its enthalpy component is close to zero.

A new method for the solid-phase synthesis of the superionic conductor CsAg 4 Br 2.5 I 2.5 is proposed, which facilitates the preparation of a single-phase product. The thermal behavior of CsAg 4 Br 2.5 I 2.5 in the temperature range from –160 to +190°С was studied by differential scanning calorimetry, and the absence of polymorphous transitions was confirmed; the only first-order phase transition is observed near 177°C and corresponds to the incongruent melting of the solid electrolyte. It is shown that the dense ceramics can be obtained from CsAg 4 Br 2.5 I 2.5 powder by pressing at room temperature; the optimal value of pressure is determined. Studies of the electrical transport characteristics of CsAg 4 Br 2.5 I 2.5 included measurements of the ionic conductivity by the four-probe method in the range of –60…+120°C and an assessment of the electronic component of the conductivity by the Hebb–Wagner method. The contribution of electron transfer is shown to be negligibly small (~10 –9 S cm –1 ), and the ionic conductivity is close to that of the well-known superionic conductor RbAg 4 I 5 and is characterized by a low activation energy (10.3 kJ mol –1 ). The oxidation potential determined by the stepwise polarization method is 0.78 V, which is noticeably higher than that of RbAg 4 I 5 . The absence of first-order phase transitions at temperatures below the melting point, combined with high ionic conductivity, makes the CsAg 4 Br 2.5 I 2.5 compound more attractive for low-temperature applications, and the increased electrochemical stability makes it more attractive for use in chemical power sources as compared to RbAg 4 I 5 .

A new method for the solid-phase synthesis of the superionic conductor CsAg4Br2.5I2.5 is proposed, which facilitates the preparation of a single-phase product. The thermal behavior of CsAg4Br2.5I2.5 in the temperature range from –160 to +190°С was studied by differential scanning calorimetry, and the absence of polymorphous transitions was confirmed; the only first-order phase transition is observed near 177°C and corresponds to the incongruent melting of the solid electrolyte. It is shown that the dense ceramics can be obtained from CsAg4Br2.5I2.5 powder by pressing at room temperature; the optimal value of pressure is determined. Studies of the electrical transport characteristics of CsAg4Br2.5I2.5 included measurements of the ionic conductivity by the four-probe method in the range of –60…+120°C and an assessment of the electronic component of the conductivity by the Hebb–Wagner method. The contribution of electron transfer is shown to be negligibly small (~10–9 S cm–1), and the ionic conductivity is close to that of the well-known superionic conductor RbAg4I5 and is characterized by a low activation energy (10.3 kJ mol–1). The oxidation potential determined by the stepwise polarization method is 0.78 V, which is noticeably higher than that of RbAg4I5. The absence of first-order phase transitions at temperatures below the melting point, combined with high ionic conductivity, makes the CsAg4Br2.5I2.5 compound more attractive for low-temperature applications, and the increased electrochemical stability makes it more attractive for use in chemical power sources as compared to RbAg4I5.

The electrolyte is an important component of lithium-ion batteries, especially when it comes to cycling high-voltage cathode materials. In this paper, we propose an algorithm for estimating both the oxidising and reducing potential of electrolytes using molecular dynamics and quantum chemistry techniques. This algorithm can help to determine the composition and structure of the solvate complexes formed when a salt is dissolved in a mixture of solvents. To develop and confirm the efficiency of the algorithm, LiBF4 solutions in binary mixtures of ethylene carbonate (EC)/dimethyl carbonate (DMC) and sulfolane (SL)/dimethyl carbonate (DMC) were studied. The structure and composition of the complexes formed in these systems were determined according to molecular dynamics. Quantum chemical estimation of the thermodynamic and oxidative stability of solvate complexes made it possible to establish which complexes make the most significant contribution to the electrochemical stability of the electrolyte system. This method can also be used to determine the additive value of the oxidation and reduction potentials of the electrolyte, along with the contribution of each complex to the overall stability of the electrolyte. Theoretical calculations were confirmed experimentally in the course of studying electrolytes by step-by-step polarisation using inert electrodes. Thus, the main aim of the study is to demonstrate the possibility of using the developed algorithm to select the optimal composition and solvent ratio to achieve predicted redox stability.

The review analyzes and summarizes the results of investgations of lithium-conducting polymer electrolytes obtained via ion exchange from the initial H + form of perfluorinated sulfonic cation-exchange membranes of the Nafion family. Salt forms of membranes not only retain the high strength and chemical stability inherent in the parent materials, but also have increased thermal stability (compared to the protonated form). The introduction of plasticizers (dipolar aprotic solvents and their mixtures) and modifying additives makes it possible to achieve a conductivity of 10 −5 –10 −3 S/cm in the ambient temperature range. This makes polymer electrolytes based on lithiated Nafion membranes (Li-Nafion) very attractive for practical use instead of liquid nonaqueous electrolytes in electrochemical power sources. Such research is actively conducted in the field of lithium–oxygen, lithium−sulfur, and lithium-ion batteries, as well as batteries with a lithium metal negative electrode. It is proposed to use Li-Nafion not only as an electrolyte/separator, but also as a functional binder of electrode materials, as a thin barrier layer on a positive electrode or a microporous separator, as an artificial protective layer on the surface of a lithium metal electrode, etc. For all types of considered power sources, the results confirming the prospects for the development of electrochemical systems using Li-Nafion have been obtained.

The resistance of electrolytes to oxidative decomposition on the positive electrode surface is one of barriers that complicate the development of rechargeable batteries with the high energy density. The electrochemical stability of electrolytes is directly related to the composition and structure of solvate complexes formed at salt dissolution. Based on a combination of methods of molecular dynamics and quantum chemistry it is possible to develop the algorithm for theoretical assessment of the electrolyte resistance to anodic oxidation as a function of its composition. This algorithm can be used for selecting versions among the studied mixtures of solvents and lithium salts with the aim of developing new electrolytes stable up to 5 and 6 V. In this study, the methods of classical molecular dynamics and quantum chemistry are used for finding the structure of solvate complexes formed in LiBF4 solutions in the binary mixture ethylene carbonate (EC)/dimethylcarbonate (DMC). The quantum-chemical assessment of the thermodynamic and oxidation stability of solvate complexes makes it possible to find which complexes make the most considerable contribution to the electrochemical stability of the electrolyte system and calculate the additive potential of electrolyte oxidation.

A composite consisting of silicon nanoparticles and reduced graphene oxide nanosheets (Si/RGO) was studied as a promising material for the negative electrode of lithium-ion batteries. Commonly used polyvinylidene fluoride (PVdF) and carboxymethyl cellulose (CMC) served as a binder. To reveal the influence of the binder on the electrochemical behaviour of the Si/RGO composite, binder-free electrodes were also prepared and examined. Anode half-cells with composites comprising CMC as a binder demonstrated the best properties: capacity over 1200 mAh∙g-1, excellent cycling performance and good rate capability up to 1.0C.

Two types of treatment of the initial mechanical mixture [silicon nanopowder and graphene oxide (GO)] for obtaining Si/RGO nanocomposites were used: reduction in hydrazine vapor and heat treatment at 550°C in an argon atmosphere. It was shown that the type of reduction has an influence on the morphological and electrochemical characteristics of the composites due to the formation of defects and the presence of nitrogen in the graphene network. Less defective and nitrogen doped Si/RGO composites have a better electrochemical behavior as an active material of negative electrode for lithium-ion batteries. The discharge capacity of electrodes based on Si/RGO nanocomposites amounted to 437 mA h g–1 without polymer binder and 1192 mA h g–1 with CMC as a binder.

The use of dipolar aprotic solvents to swell lithiated Nafion ionomer membranes simultaneously serving as electrolyte and separator is of great interest for lithium battery applications. This work attempts to gain an insight into the physicochemical nature of a Li-Nafion ionomer material whose phase-separated nanostructure has been enhanced with a binary plasticiser comprising non-volatile high-boiling ethylene carbonate (EC) and sulfolane (SL). Gravimetric studies evaluating the influence both of mixing temperature (25 to 80 °C) and plasticiser composition (EC/SL ratio) on the solvent uptake of Li-Nafion revealed a hysteresis between heating and cooling modes. Differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) revealed that the saturation of a Nafion membrane with such a plasticiser led to a re-organisation of its amorphous structure, with crystalline regions remaining practically unchanged. Regardless of mixing temperature, the preservation of crystallites upon swelling is critical due to ionomer crosslinking provided by crystalline regions, which ensures membrane integrity even at very high solvent uptake (≈200% at a mixing temperature of 80 °C). The physicochemical properties of a swollen membrane have much in common with those of a chemically crosslinked polymer gel. The conductivity of ≈10−4 S cm−1 demonstrated by Li-Nafion membranes saturated with EC/SL at room temperature is promising for various practical applications.

The electrotransport characteristics of the polymer electrolyte based on lithiated Nafion-115 membrane plasticized by high-boiling dipolar aprotic solvents—sulfolane (SL), ethylene carbonate (EC), and diglyme (G2) and also by their binary and ternary mixtures are studied in a wide temperature interval (from –60 to +80°C). The best transport properties (conductivity 10–5–10–4 S cm–1 in the interval from –20 to +70°C) are demonstrated by samples plasticized with binary mixtures EC/G2 and EC/SL in certain ratios. The ternary plasticizer provides low activation energy (10–20 kJ mol–1) and sufficiently high conductivity in the temperature region not lower than –10°C.

The electrochemical behavior of layer-structure LiNi1/3Mn1/3Сo1/3O2 solid solution, a positive electrode material of lithium-ion battery, with surface protective layer of amorphous lithium borate is studied. The protective coating is prepared by the eutectic incongruent melting at 750°C of a pre-synthesized compound Li3BO3, mechanically mixed with LiNi1/3Mn1/3Сo1/3O2 powder. The glassy lithium borate 3Li2O∙B2O3 is found to form island-like structures presumably localized in electrochemically active regions of the active-material particles’ surface. The optimal lithium borate content, which makes possible the LiNi1/3Mn1/3Сo1/3O2 stable cycling at 0.5 C rate with the maximum discharge capacity, is found to be equal to 1 wt %.