Lithium electrochemical systems

Possibility of ultradispersed TiO₂2 (anatase modification) using as the base of the lithium power sources cathode material obtained by chloride-acid hydrolysis of titanium tetrachloride has been studied. The researches of Li+ ions electrochemical intercalation kinetics and phasic model of the process was suggested. The cathode material phase composition changes during discharge were fixed and interpreted.

It is shown that an examination of reduced galvanostatic charge-discharge curves allows making preliminary conclusion on degradation mechanism upon cycling. If such degradation is due to loss of active material all normalized curves coincide. In the case of insulating films building up normalized curves are shifted along potential axis. Various structure changes result in qualitative change of curves shape.

The review summarizes literature data on the thermal decomposition of ferrous oxalate with the formation of Fe, FeO, Fe₂O₃, Fe₃O₄, Fe₃C, and other products. Historical evolution of views on the ways and mechanisms of oxalate thermolysis is traced. The current state of the art is analyzed from the perspective of FeC₂O₄·2Н₂O0 compound for the synthesis of lithium iron phosphate LiFePO₄, which is a promising cathode material for lithium-ion batteries.

The methods for the synthesis of lithium iron phosphate LiFePO₄ with olivine structure have been developed. New materials based on lithium iron phosphate, including doped with metals, the «LiFePO₄ + carbon» composites obtained by pyrolysis of organic compounds have been synthesized. Crystallographic characterization of the synthesized materials was carried out; their electrochemical characteristics of the extraction and intercalation of lithium have been identified. A correlation between the crystallographic and electrochemical characteristics of the materials was found. It was confirmed that an effective way to improve the electrical conductivity of LiFePO₄ is to create a carbon shell of the products of pyrolysis of organic compounds on the material's particles surface. A correlation of electrical conductivity and temperature of synthesis of the material was determined. The sequence of chemical interaction between precursors for the synthesis of LiFePO₄ is defined; the mechanism of solid-phase interaction is described.

Silicon electrodes with regular porous structure were prepared by the photoelectrochemical etching of single-crystal n-type silicon wafers, followed by the removal of the substrate. Electrodes with pores having circular and square section were studied. The porosity was increased via additional oxidation with the subsequent etching of oxide. The electrochemical characteristics of anodes were found to depend on porosity, electrodes with porosity 60-70% possessing maximal capacity for lithium reversible insertion. Electrodes thus prepared feature much higher capacity per area unit (up to 25 mA·h/cm2) than usual thin-film electrodes (about 1 mA·h/cm2).

The corrosion and electrochemical behavior of magnesium and the MA 21 magnesium-lithium alloys in solutions of moderately acidic phosphates with various additives was studied. The inhibiting effect of nitrate and fluoride ions on the anode dissolution of these objects was revealed. Features of the electrochemical dissolution of magnesium and the magnesium-lithium alloys in nitrate phosphate solutions with fluoride ions caused by their activation-passivation competition have been noted. Distinctive features of the electrochemical behavior of the magnesium-lithium alloys in comparison with pure magnesium in nitrate phosphate fluoride solutions due to their structural and phase specifics have been established.

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In modem technological processes increase used molten multicomponent solt mixtures. Determination of the composition and melting temperature are important in application of the compositions, identification of patterns processes occurring during melting and solidification of alloys, as well as the phases in equilibrium at a given thermodynamic conditions, possibly in the study of phase diagrams. In this paper we propose a graphical method of calculation and choice of salt composition on the basis of the study five-component reciprocal system Li,K||F,Cl,VO₃,MoO₄ for use as electrolytes and heat storage materials.

Possibilities for increasing efficiency of impedance spectral measurements are investigated. It is shown that for determination of linear electrochemical impedance a linearly changing input signal is preferable, and for the quantitative estimation of non-linearity of electrochemical impedance as an input signal it is expedient to use the cosine electric beats. The constructive diagrams of generators of such signals are offered.

In this paper the possibility of applying of hydrolysis lignin as the lithium battery cathode material was demonstrated for the first time. Hydrolysis lignin features have been investigated by impedance spectroscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Electrochemical characterization was carried out at room temperature using 1M LiBF4 in γ-butyrolacton electrolyte system. The chemical composition of cathode materials upon battery discharge down to 0.9 V was studied by the X-ray photoelectron spectroscopy and Infrared spectroscopy. The suggestions on possible electrochemical reactions occurring in the lithium/hydrolysis lignin system were made on the basis of the products composition analysis.