I. M. Gamayunova

Kinetics of electrochemical lithium intercalation into thin tungsten (VI) oxide layers

The methods of galvanostatic intermittent titration, cyclic voltammetry, and electrode impedance spectroscopy are used to study the behavior of tungsten (VI) oxide film electrodes free of binding and conducting additives in the course of reversible lithium intercalation from nonaqueous electrolyte at 25°C. The studies are performed for electrodes with different degrees of crystallinity at the variation of the lithium concentration in intercalate from zero to 0.017 mol/cm3. Lithium diffusion coefficient is in the range of 10−11–10−16 cm2/s. The concentration dependences of the intercalation-layer transport parameters are analyzed, the equivalent circuit versions are discussed, and results obtained by different methods are compared.

Impedance spectroscopy of lithium-carbon electrodes

The methods of coulometric titration and electrode impedance spectroscopy are used in studying the behavior of carbon film electrodes free of binding and conducting additives in the course of reversible lithium intercalation from nonaqueous electrolytes. The electrodes with the high and low degrees of graphitization are studied. The measurements are performed in the frequency range from 105 to 10−2 Hz with the lithium concentration in intercalate varied from 0.025 mol/cm3 (corresponds to LiC6) to a state free of lithium. The factors responsible for the hysteresis in charge-discharge curves, the versions of equivalent circuits (EC) suitable for modeling the impedance spectra of LixC6 electrodes, the dependence of EC parameters and the lithium diffusion coefficient on the concentration are discussed. It is shown that all experimental impedance spectra can be adequately modeled by a common general EC. The concentration dependences are consistent with the earlier data of pulse methods. The diffusion coefficient varies approximately from 10−12 to 10−13 cm2/s.

Impedance spectroscopy of lithium-tin film electrodes

A method of electrochemical impedance spectroscopy was used to study the reversible lithium intercalation from nonaqueous electrolyte into tin films with the thickness of 0.1–1 μm. The impedance spectra of lithium-tin (LixSn) electrodes have a complicated shape depending on the electrode state and prehistory; they reflect the occurrence of several consecutive and parallel processes, including the lithium migration, diffusion, and accumulation. The formation of a solid-electrolyte layer on the surface at Li intercalation into Sn is observed. Equivalent circuits are proposed that adequately model the experimental data on the LixSn electrodes both freshly prepared and after prolonged cycling. Problems associated with the choice of equivalent circuits and determination of their parameters, the accuracy of the diffusion coefficient determination, the trends in the parameters’ variation with electrode potential (composition) are discussed.

The synthesis, structure, and electrochemical properties of Li2FeSiO4-based lithium-accumulating electrode material

Different approaches to synthesis of Li2FeSiO4-based electrode materials for lithium intercalation, using low-cost and abundant Li-, Si-, and Fe-containing parent substances, are discussed. XRD, SEM, and a laser-diffraction analyzer of particle size were used for structure and morphology characterization of the composite electrode materials. Li2FeSiO4 was shown to be the main lithium-accumulating crystalline phase; minor LiFeO2 and Li2SiO3 admixtures are also present. The material microparticles’ average size was shown to vary from tenths of micrometer to 1 μm. Larger objects sized ca. 2–4 μm are the microparticles’ agglomerates. The material electrochemical properties were studied by dc chronopotentiometry (galvanostatic charging–discharging) and cyclic voltammetry with potential linear sweeping. The initial reversible cycled capacity of the best samples is 170 mA h/g. The anodic and cathodic processes manifest obvious hysteresis caused by the presence of several different lithium ion energy states in the material; the transition between the states is kinetically hindered. The dependences of the specific capacity and its stability under cycling on the current load and the conductive carbon component content in the composite were elucidated.

Photoelectrochemistry of lithium

Abstract The results of investigation of the processes occurring at the lithium/nonaqueous solution interface under the influence of light irradiation are presented. The primary step of the cathodic photoeffect revealed is photoemission of electrons from lithium into passivating layers on its surface. The electron photoemission technique has been used for obtaining information about the composition and electric characteristics of the passivating layers during lithium storage in solution under open-circuit conditions.