A. M. Skundin

Electrode nanomaterials for lithium-ion batteries

The state-of-the-art in the field of cathode and anode nanomaterials for lithium-ion batteries is considered. The use of these nanomaterials provides higher charge and discharge rates, reduces the adverse effect of degradation processes caused by volume variations in electrode materials upon lithium intercalation and deintercalation and enhances the power and working capacity of lithium-ion batteries. In discussing the cathode materials, attention is focused on double phosphates and silicates of lithium and transition metals and also on vanadium oxides. The anode materials based on nanodispersions of carbon, silicon, certain metals, oxides and on nanocomposites are also described. The bibliography includes 714 references.

Temperature effect on the lithium diffusion rate in graphite

The temperature influence on the diffusion coefficient for lithium in graphite is investigated. The activation energy for lithium diffusion in graphite is calculated. Its value is 35 kJ mol−1.

Lithium intercalation and deintercalation processes in Li4Ti5O12 and LiFePO4

We have studied the kinetics of electrochemical lithium intercalation and deintercalation processes at different currents in lithium iron phosphate and lithium titanate based composite materials containing fine carbon particles. The results demonstrate that lithium intercalation and deintercalation processes in the electrode materials are characterized by an overvoltage: 4 and 2 mV, respectively, for a cell with a lithium titanate based electrode and 4 and 24 mV for a lithium iron phosphate based cell. Li4Ti5O12 solubility in Li7Ti5O12 is 1.1% (the limit of the solid solution at Li4.03Ti5O12), and Li7Ti5O12 solubility in Li4Ti5O12 is 2.5% (the limit of the solid solution at Li6.93Ti5O12). The conductivity of the phosphate and titanate solid solutions involved in the lithium intercalation and deintercalation processes has been determined.

Sol–gel fabrication and lithium insertion kinetics of the Mo-doped lithium vanadium oxide thin films Li1+xMoyV3−yO8

Abstract Thin films of molybdenum-doped vanadium oxide bronzes Li 1+ x Mo y V 3− y O 8 (0≤ y ≤0.20) were synthesized by sol–gel process in metal alkoxides solution. The influence of the applied hydrolysis ratio on the particles shape and size, their location and orientation on the substrate has been investigated. The variation of both material morphology and unit cell geometry changes the lithium galvanostatic discharge capacity significantly. There are two factors resulted in increasing of material capacity: decreasing of (100) crystallite faces contribution to the whole particle surface and increasing of Mo-doping level y . Lithium chemical diffusion coefficient and exchange current density on the interface “film/aprotic Li + -conducting electrolyte” were determined on materials having optimized Mo-doping level and particle morphology at various Li concentrations in the host structure by electrochemical impedance spectroscopy.

Influence of chemical prehistory on the phase formation and electrochemical performance of LiCoO2 materials

Abstract Thermal decomposition of freeze-dried salt precursors leads to the formation of low-temperature (LT) modification of LiCoO 2 at 350–450 °C. The conversion rate of LT into high-temperature (HT) modification at 850 °C depends greatly on the anion composition of salt precursors and correlates quite well with the appearance of second step at thermogravimetric curves of their thermal decomposition related to the solid-state reaction between Li 2 CO 3 and Co 3 O 4 . Relationship between the appearance of Co 3 O 4 and preferential formation of LT/HT polymorphs at reduced temperatures is discussed. The consecutive formation of LT and HT modifications during solid-state reaction between Li 2 CO 3 and Co 3 O 4 at T >800 °C was observed. LiCoO 2 cathode materials with the domination of LT polymorph demonstrated a better initial discharge capacity while a greater amount of HT modification is accompanied by better reversibility of charge–discharge processes.

Products of lithium interaction with nanostructured oxides SnO2-TiO2 and mechanism of charge-discharge of electrodes in a lithium-ion battery

Products of lithium interaction with thin-film nanostructured SnO2-TiO2 (ST) oxides are studied with the aid of x-ray diffraction analysis and Moessbauer spectroscopy on the 119Sn nuclei. Electrochemical properties of a series of the ST electrodes with different concentrations of TiO2 varied from 0 to 20 mol % are also examined. It is concluded that the specific feature of the charge-discharge mechanism of the ST electrodes is a significant participation of oxygen in reversible reactions during insertion and extraction of lithium as compared with an alloying mechanism of operation of tin-containing anodes. The leading role in this is played by titanium oxide. Remaining stable towards reduction by lithium, it facilitates the holding of the neighboring layers of SnO2 in a nanodisperse state and in an oxidized state. The effect of a decrease in the capacity degradation in modified TiO2 electrodes, which is discovered in this work, is attributed to the hampering of the growth of nanocrystallites of β-Sn by interlayers of tin and titanium oxides mentioned above.

Kinetics of lithium deintercalation from LiFePO 4

We have studied the kinetics of lithium deintercalation from lithium iron phosphate in a cathode material for batteries. The main contribution to the resistance of the cell is made by interfaces and the resistance of LiFePO4 grains. The FePO4 solubility in LiFePO4 is 4.0%. The lithium deintercalation process can be described in terms of a heterogeneous grain model and its rate is controlled by the lithium diffusion across the layer of the forming product (FePO4).

Tolerant-to-methanol cathodic electrocatalysts based on organometallic clusters

A new approach to the fabrication of catalytic systems based on hetero-and homometal-chalcogenide clusters of Pt-M-X type (M: Fe, Mn; X: S, Se, Te), which provides the reproducibility of catalyst composition and uniform distribution of catalyst over the carbon support, is proposed. Thus obtained catalysts are characterized using the XRD, TEM, and EDAX methods. The electrocatalytic activity of these systems in the oxygen reduction reaction, the role of the nature of chalcogenide atom and the atom of the second metal, which is the platinum partner, and the electrochemical behavior of nonplatinum chalcogenide systems are studied.

Nanostructured catalysts for cathodes of oxygen-hydrogen fuel cells

Bimetallic catalysts platinum-cobalt, platinum-chromium, and platinum-tungsten, deposited onto highly dispersed carbon black from complex cluster-type compounds of corresponding metals with a 1: 1 atomic ratio of metals are developed. The catalysts are characterized by methods of x-ray diffraction analysis and energy dispersive analysis of x-rays. The procedure involving use of a thin-film rotating disk electrode is employed to probe kinetic parameters of the oxygen reduction reaction on the catalysts developed. The investigated binary catalysts exhibit specific electrochemical characteristics that are not inferior and, in some cases, are superior to the characteristics intrinsic to the commercial platinum catalyst E-TEK, when tested in the composition of a gas-diffusion electrode under conditions that are close to real conditions in which cathodes of oxygen-hydrogen fuel cells operate.

Electrode materials for lithium-ion batteries of new generation

The studies of fundamentally new electrochemical systems for lithium-ion batteries of new generation, which were performed at the Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, are briefly reviewed. The results of investigation of lithium insertion into negative electrodes based on silicon and silicon-carbon composites and operation of positive electrodes of nano-structured materials based on vanadium oxides are described.