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Being widely considered a powerful tool for improving the capacity retention and rate capability of cathode materials for lithium-ion batteries, surface modification has never been applied for obtaining truly high-rate spinels. The stoichiometric LiMn2O4 and a material containing the LiMn2O4 core and LiNi0.5Mn1.5O4 shell with the shell/core mass ratio of 0.1:1 have been synthesized by means of a citric acid aided route. The samples studied have been characterized using thermal analysis, X-ray diffraction and scanning electron microscopy. The specific discharge capacities of LiMn2O4/LiNi0.5Mn1.5O4 and LiMn2O4 at I = 0.5C equal to 107 and 110 mAh g−1, respectively. The surface coated LiMn2O4/LiNi0.5Mn1.5O4 shows up an exceptional high-rate ability being able to retain ca. 25 mAh g−1 at the current load of 9620 mA g−1 (65C), which is 1.625 times higher than for the unmodified LiMn2O4. Such exceptional high-rate properties and better cycling ability of the core-shell LiMn2O4/LiNi0.5Mn1.5O4 compared to parent compounds prove good prospects of surface modification techniques in improving rate capabilities of spinel materials.

Еlectrochemical performance of Co 3 O 4 in lithium-ion batteries is briefly reviewed. Co 3 O 4 samples are synthesized via microwave-assisted solid state and citric acid aided methods. It is shown that the latter method leads to disperse nanosized materials having discharge capacity close to the theoretical value. Several electrolytes are probed so as to minimize capacity losses upon cycling, and the one containing lithium bis(trifluoromethane)sulfonimide in a mixture of fluoroethylene carbonate and dimethyl carbonate is selected. High-rate tests reveal that capacity retention of the samples obtained is well comparable with the best existing data, and at the current load of 5340 mA g −1 (6C) all materials studied retain more than 50% of initial capacity.

Phase diagrams of lithium salt systems in dimethyl sulfoxide, propylene carbonate and dimethyl carbonate have been obtained and conductivity measurements have been performed in the concentration range up to 0.25 mole fraction of a salt. The shape of the phase diagrams has been analyzed thermodynamically and the following order of anions for decreasing association of salts with DMSO at cLiX = 0.2 has been suggested, ClO4− > CF3SO3− > BF4− > NO3−. The eutectic-type phase diagrams of the LiClO4-PC and LiClO4-DMC systems correspond to ideal, non-interacting solutions. The conductivity isotherms for the DMSO solutions at cLiX = 0.2 are arranged in the order of increasing conductivity as CF3SO3− c LiClO 4 = 0.5–1 mole fraction of the salt, the order of solvents for increasing conductivity is DMC

Raman study of cation and anion solvation in dimethyl sulfoxide, propylene carbonate and dimethyl carbonate solutions of six lithium salts has been performed in the concentration range from 0.05 to 0.25 molar fraction of a salt. The dependences of the amount of the solvent particles involved in dimerization, hydrogen bonding, and solvation have been determined, and the mean solvation numbers have been found. It is concluded that in all solutions studied, notwithstanding the differences in the physical properties of the solvent and in the structure of the anion, both the lithium cation and the anion solvation equilibria are quantitatively similar. In all cases, solvation numbers of cations are close to two and do not vary with the growth of concentration. In particular, in molten LiX·4S solvates, LiS 4 + entities expected from the phase diagrams do not exist. It has been found that for the solvent molecules in dimers and in solvation spheres, non-coincidences between vibrational frequencies of isotropic and anisotropic lines, Δ ν NCE = ν aniso − ν iso are of opposite signs signifying that the mutual orientation of molecules is different. In all systems studied, solvation numbers of anions decrease if the salt content is growing and are close to four in concentrated solutions. These striking similarities in the structure and concentration of solvated entities clearly signify that solvation phenomena have no decisive importance in determining the properties of salt systems.

In order to successively compete with supercapacitors, an ability of fast discharge is a must for lithium-ion batteries. From this point of view, stoichiometric and substituted lithium manganese spinels as cathode materials are one of the most prospective candidates, especially in their nanosized form. In this article, an overview of the most recent data regarding physico-chemical and electrochemical properties of lithium manganese spinels, especially, LiMn 2 O 4 and LiNi 0.5 Mn 1.5 O 4 , synthesized by means of various methods is presented, with special emphasis of their use in high-rate electrochemical applications. In particular, specific capacities and rate capabilities of spinel materials are analyzed. It is suggested that reduced specific capacity is determined primarily by the aggregation of material particles, whereas good high-rate capability is governed not only by the size of crystallites but also by the perfectness of crystals. The most technologically advantageous solutions are described, existing gaps in the knowledge of spinel materials are outlined, and the ways of their filling are suggested, in a hope to be helpful in keeping lithium batteries afloat in the struggle for a worthy place among electrochemical energy systems of the 21st century.

The citric acid aided synthesis, physico-chemical and electrochemical characterization of the nanosized nickel-doped lithium manganese spinel, LiNi 0.5 Mn 1.5 O 4 having excellent high-rate properties is described. An optimal electrode material represented by perfectly shaped, well-faceted particles of 100-400 nm size containing crystallites of the 15-22 nm size could be obtained upon the thermal treatment at 700 °C. In spite of a reduced specific capacity (102 mAh·g −1 ) it is able to retain a half of it upon the discharge current of 4400 mA·g −1 (30 C) and to endure the current load of 5870 mAh·g −1 (40 C) delivering the reversible specific capacity of 25 mAh·g −1 . It is suggested that the reduced specific capacity is determined primarily by the aggregation of material's particles, whereas the good high-rate capability is governed not only by the size of crystallites but also by the perfectness of crystals, and imperfections in big, well-shaped crystals (like dislocations, grain boundaries, etc.) less retard the diffusion of lithium ions than particle boundaries in small, randomly oriented, accreted crystals.

The oxidation of aqueous solutions of manganese (II) chloride by hydrogen peroxide leads to the mixture of hausmannite (Mn3O4) with manganite (MnOOH). Being air dried, this mixture undergoes slow oxidation at room temperature during which the content of manganite is rising, and an equilibrium molar ratio Mn3O4:MnOOH reaches 1:3 in approx. 1 year of storage. In terms of reversible first order reactions, rate constants for the forward and reverse reactions are 2.62 × 10−1 and 8.75 × 10−2 month−1, respectively. In the course of oxidation, additional IR adsorption bands emerge in the region of vibrations of physisorbed water molecules at 3160 and 3300 cm−1. These bands are absent in IR spectra of equilibrium mixtures and disappear after treatment of samples with Sr2+ ions as a result of ion exchange. This finding enables one to suggest that adsorbed water forms cation exchangeable surface groups Mn (OH)2 whose transformation into MnOOH is a step determining the oxidation rate. On the other hand, these data may be considered as the first spectroscopic evidence of sorption of spherical cations onto the surface of hydrous oxides.

Size-dependent properties of colloidal and nanoscale systems could be evaluated in only two limiting approximations: supposing particles to be free or employing random dense packing models and their quantitative versions. However, real colloidal and nanoscale systems are formed by neither free nor densely packed particles, and the methods enabling one to calculate their properties at intermediate densities remain unknown. In this paper, simple relations between the particle radius R , surface area A s , pore volume V p , and packing fraction ρ are constructed in terms of the gapped gapless packing model. Calculations using recent data on A s and V p reveal that the particle radii predicted by the model are in good agreement with experimental measurements, and the ρ values evaluated for the first time depend on the pre-history of the system studied. Finally, conclusions are drawn that any dispersed solid of the specific surface area exceeding 30 m 2 /g must be constituted of nano-sized particles, and that assemblages of nano-sized particles of R > 2.6 nm are inevitably mesoporous.

Possible relations between several characteristic times, viz. the vibrational dephasing time τ V , the vibrational frequency modulation time τ ω , the time between collisions in a liquid τ BC , the collision duration time τ d , and the half-period of vibration T /2 are considered. It is found that for instantaneous collision complexes the following relations hold: τ ω ≈ T /2 or τ V ≈ T /2. For short-lived complexes τ ω ≤ τ d or τ V ≤ τ d , and 0.5≤ τ ω / T ≤2 or 0.5≤ τ V / T ≤2, whereas for long-lived species τ ω ≤ τ d or τ V ≤ τ d , and τ ω ,/ T ≥2 or τ V / T ≥2.

In this paper we employ a new method, which enables one to calculate time correlation functions of vibrational relaxation by fits in the frequency domain, in the study of picosecond vibrational dynamics, that is, vibrational dephasing and vibrational frequency modulation. This method is applied to the molecular glass former salol in bulk, in a dilute CCl4 solution and in restricted geometries after confining it in nanoporous silica glasses of various pore sizes. The important finding is that the vibrational dynamics of the confined molecules becomes faster with decreasing the pore size. An attempt is made to rationalize this effect by invoking the cooperativity issue related to the sluggish dynamics as the glass transition is approached. The removal of many-body effects by trapping the molecules in less-crowded environments seems to be the key factor. The obtained results are described in the light of recent spectroscopic, X-ray diffraction and molecular dynamics studies performed on this liquid.

Polarised and depolarised low-frequency Raman spectra of liquid formamide have been analysed. The employed fitting procedure shows convincingly that the Boson peak contribution to the overall low-frequency Raman pattern is present even in this ordinary, low-viscous liquid.

Based on a model correlation function which covers spatial correlations from Gaussian to exponential, we have arrived at an exact analytic solution of the problem of the Boson peak profile in amorphous media. Probe fits made for polyisoprene and triacetin prove the working ability of the formulae obtained.

Spatial disorder in amorphous solids inevitably leads to the violation of the ordered arrangement of atoms if compared with respective crystals, and to the probability distribution of the activation energy of transport processes. Based on the probability description of the relaxation of structural defects, the temperature dependence of the quasi-elastic line width, ΩQE, is explained. An analytical expression for the Boson peak profile covering spatial correlation from Gaussian to exponential is presented. The relation between ΩQE and the frequency of the Boson peak, ΩBoson, is elucidated; it is shown that ΩQE/ΩBoson=1/πZ where Z is the number of escape channels accessible to relaxators.

A fitting method is described which enables one to model real line profiles intermediate between Lorentzian and Gaussian by an analytical function which has an analytical counterpart in the time domain. The applications of this method comprise: (1) finding time correlation functions and correlation times by fits in the frequency domain without Fourier transforms; and (2) the decomposition of overlap lines obtaining dynamic parameters at the same time.

A computational approach was elaborated to explicitly account for the Rayleigh line wing, the Boson peak and vibrational contributions to the low-frequency Raman spectra of amorphous solids and viscous liquids. It was shown that the low-frequency Raman spectra of glycerol and polystyrene consist of the Rayleigh contribution of Lorentzian form and the Boson peak which profile follows the predictions of the theory by Martin and Brenig in the version by Malinovsky and Sokolov. In the case of triacetin, the Boson peaks decay faster in their high-frequency side than the above theory predicts. Their form can be successfully modeled with a newly introduced empirical function intermediate between the Martin–Brenig and Malinovsky–Sokolov predictions.

Distinguishing features of spectroscopy of interparticle interactions in ionic liquids are pointed out. Studies of interactions and picosecond dynamics in molten salts using this approach are reviewed. Similarities and differences between molecular and ionic liquids which manifest themselves in spectroscopic experiments are compared and discussed.

In terms of the theory which describes the instantaneous frequency shifts in liquids as a purely discrete Markovian process, an approximate analytical expression for the time correlation functions of vibrational dephasing is given, and its fit to experimental data is tested. A comparison with the (non-Markovian) stretched exponential model is made. Within the two theories, the static correlation function being transformed by molecular motion are shown to tend to the same Kubo limiting low, but the Markovian process tends from above and non-Markovian from below.

A quick method of determining the parameters of a stretched exponential fit to an experimental time correlation function of vibrational dephasing is proposed and tested.

The usual assumption that the reorientational and vibrational motions of the molecules under study are statistically uncorrelated and that the vibrational band profiles in IR, isotropic and anisotropic Raman are identical for the same vibrational mode leads to contradictory results in studies of molten salt dynamics. The conclusion was made that inconsistency of these data may be eliminated when the coupling of vibrational and rotational dephasing is taken into account.

A novel fitting method implemented recently in vibrational spectroscopy of disordered systems is briefly overviewed. It enables modelling of real line profiles intermediate between Lorentzian and Gaussian by an analytical function which has an analytical counterpart in the time domain. Numerous applications of this theoretical approach are discussed.

A method enabling one to separate the contributions of repulsion and attraction forces resulting in frequency non-coincidences in liquids is presented.

A comparison of the behaviour of commercial electrochemical manganese dioxide (γ-MnO 2 ) and non-stoichiometric anodic Mn x O y (OH) z was made. Anodic oxide proves to be composed mainly by MnO 2 (ramsdellite) and MnOOH (manganite), and contains more water and OH − than γ-MnO 2 . Hydroxide ions were shown to determine the ionic conductivity of Mn x O y (OH) z which, in turn, strongly affects the rate of electroreduction.

A comparison of the ESR spectral parameters of 14 N and 15 N nitroxide radicals in various viscous media in the region of rapid rotational motion is presented. It is shown that is viscous media, such as vaseline oil, polymers, etc., the radical reorientation has a complicated nature which cannot be described by a diffusional process with an anisotropic diffusion tensor.