Литиевые электрохимические системы

The results of the design of a fully-tight Ni-MH battery of the NMG type are presented. The authors have developed a spread technique of making both negative and positive electrodes with sheet foam nickel as a conducting support. The influence of the density of both charging and discharging current and the discharge temperature on the discharging characteristics of the power source was studied.

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.

On basis of analysis of literature data as well as of own experimental results we suggest some regularity for degradation of silicon electrodes upon cycling. It was shown that an electrode capacity Q at n-th cycle can be calculated from equation Q = Q₀ exp(kn+?n²/2), where Q₀ is initial capacity value, k и ? are empiric constants.

Samples having the chemical formula Li_0.5 Fe_{2.5 – x} Mg_xO₄ (0 ? x ? 1) were prepared by the standard ceramic method. The parts of the dielectric constant ?', ?'' and A.C. conductivity ?(?) are measured at different frequencies from 10 ^{– 2} to 10⁵ Hz in the room temperature and different cooling velocity, and then the dielectric loss tangent tg ? was calculated. The sample with x = 0.1 what was cooled quickly showed the greatest values of ?₀ as compared with the other samples.

Electrochemical behavior of Li in the systems with PE based on polymers of chlorinated polyvinylchloride and polyvinylidene fluoride were investigated by the method of cyclic voltammetry and galvanostatic cycling. Potentiodynamic investigations have shown that on lithium electrode even in the systems with polymer electrolyte the high current densities up to 5 mA/cm² are realized. Influence of polymer electrolyte composition on the properties of the interface Li/electrolyte and rechargeable work of lithium electrode has been shown.

It was studied an influence of prior carbon treatment (temperature and gas conditions, mass content of waterproofing agent) on activity of platinum catalyst, synthesized on disperse carbon carrier. It was shown that characteristics of anodic processes depend on quantity of solid polymer electrolyte in catalytic composition. Optimal content of ion exchange polymer under varied degree of carbon carrier waterproofing (used for synthesis of platinum catalyst) is not equal.

There were investigated the self-discharge dynamics in two homogeneous groups («A» and «B») of the coin lithium cells ВR2325 on the basis of superstoichiometric fluorocarbon CF1.20, selected from the uniform experimental batch of 10000 pieces. The reason of two different groups («A» and «B») appearance through 3–6 months of storage is connected with the origin of hydrogen fluoride in cathodes of group «A» cells, which will be derivated at auto catalytic hydrolysis of C-F-bonds by a moisture tracers (0.1–0.5%).

Comparative characteristic of natural and synthesized iron disulfide has been carried out. Physical, chemical and macrostructure characteristics of pyrite powders have been shown. By the methods of cyclic Vtammetry the electrochemical properties of FeS₂ – based cathodes have been investigated in non-aqueous liquid (1М LiClO₄; PC+DME) and polymer (CPVC; 1М LiClO₄; PC) electrolytes.

Major trends in cathode active material development for lithium-ion batteries have been reviewed. Statistics on all publications in «Journal of Power Sources» (from 03.2006 till 04.2007) is summarized in order to point out that the main effort in secondary batteries development is concentrated on lithium-ion batteries, especially on positive electrode study. Based on these publications the main routes for LiCoO₂ modification as well as for novel materials research have been reviewed.

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 ?-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.