Li/ Li1+xV3O8 batteries. V°. Comparison with other secondary cells and influence of micro- and macro-structural alteration on the cathode performance.

Li/Li1+xV3O8 cells have been compared with analogous cells based on TiS2, V6O13 and β-Na0.17V2O5 cathode. The results have demonstrated thet this bronze can be ranked among the most promising cathode materials for high rate rechargeable Li cells. This has encouraged attempts aimed at improving the electrochemical performance of the bronze through substitution of V witch such transition metals as Cr and Mo, and substitution of Li with Na. None of these substituted materials performed better thet the parent compound. On the other hand, controlled H2O Intercalation within the layers resulted in an increased interlayer distance and in higher capacities. A remarkable improvement in cell performance at high rate (10 mA/Cm2) was obtained with a new technique of cathode preparation

Li/ Li1+xV3O8 secondary batteries. IV°. Evaluation of factors affecting the performance of test cells.

With the aim of optimizing the performance of Li/Li1+xV3O8 cells, several aspects of cathode preparation have been examined. The influence of synthesis technique nature and amount of conductive additive, compacting pressure, cathode loading, and particle size, has been investigated. Furthermore, the role played by the solutions on cathode efficiency has been outlined. The formulations which perform best are based on small-sized particles blended with about 20% acetylene black and compacted at very high pressures to improve the contact between particles. Such cathodes can provide high capacities at high rate and good cycling efficiencies. The Kinetic loss of capacity, observed during the first few cycles, may be alleviated by choosing solutions with high fluidity and conductivity

Solid solutions Li1+xV3O8 as cathodes for high rate secondary Li batteries

Following a preliminary investigation, Li/Li1+xV3O8 cells have been examined. Using samples of low x content, up to 3 eq Li+ could be accepted both chemically and electrochemically by one mole of active material. Li+ is accomodated in the tetrahedral sites existing between the (V3O8)(1+x)- layers. Li+ jumping from site to site is fast and permits high rate capabilities: at 10 mA/cm2, 1.1 eq Li+ per mole could still be inserted. The structure does not show irreversible alterations upon extended lithiation, allowing long cycle lives to be achieved. Kinetic constraints limit the recovery of the full capacity of the first discharge at medium-high rates, but the second-discharge capacity declines slowly with cycle numbe

Li/ Li1+xV3O8 secondary batteries. III°. Further characterization of the mechanism of Li+ insertion and of the cycling behaviour.

The reduction mechanism of the bronze Li1.2V3O8 in nonaqueous Li cells has been elucidated. Upon Li+ insertion, a solid solution is formed with an upper composition of Li3V3O8. Within this composition range, Li+ progressively fills the tetrahedral sites available in the unit cell. Four such sites are supposed to be filled at the upper composition limit. Beyond this, a new phase is nucleated to accommodate excess Li+, this resulting in a constant cell's OCV. Li+ insertions not greater than 3.0 eq/mol are reversible, as shown by the cycling behavior and the x-ray patterns. Owing to the outstanding structure stability and to the high speed of Li+ diffusion in Li1.2V3O8, extended cycling at high rates is achievable with cells based on this bronze. 445 cycles at discharge rates variable in the range of 2-10 mA/cm 2 have been obtained

Small particle-size lihium-vanadium oxide: an improved cathode material for high rate rechargeable Li batteries.

A Li rechargeable battery with a cathode based on small particle-size Li1+xV3O8 has a high cathode utilization and a long cycle life at high discharge rates. It is shown that decreasing the particle diameter from 10 to 1 μm decreases 10 times the current density really applied to the cathode. This is particularly beneficial by limiting the cathodic capacity losses and thereby increasing the life to several hundreds of cycles. The high rate capability afforded by the use of small particles results in good power energy characteristics

RECHARGEABLE COMPACT LI CELLS WITH LIXCR0.9V0.1S2 AND LI1+XV3O8 CATHODES AND ETHER-BASED ELECTROLYTES

The electrochemical parameters of compact disk cells with cathodes of Li1+xV3O8, LiCr0.9V0.1S2, and electrolytes based on cyclic ethers, are studied. It is shown that the decrease of discharge time from 10 to 1.3h has but a small effect on cathode utilization, which drops from 80% to about 70% for both cathode materials. The polarization resistance of freshly deposited Li, from electrolytes of ethers, and their mixtures with ethylene carbonate, are identical. Continuous cycling tests with maximum cathode utilization in the electrolyte of composition 1.5M LiAsF672MeTHF/THF(1:1)/0.2% 2MeF demonstrate a cycling efficiency of 96-97% for Li. A lower efficiency of about 94% is obtained in ethylene carbonate containing electrolytes. It is suggested that an increase in the thickness of the passive film formed on the Li electrode is responsible for the capacity decay at the end of the cycling life. The rate of self-discharge at room temperature for a fully charged cell is about 5-8% per month. This self-discharge is attributed to the Li electrode, which is passivated during storage in the ether-based electrolytes

Non-aqueous electrolyte solutions in chemistry and modern technology

In this paper a brief survey is given of the properties of non-aqueous electrolyte solutions and their applications in chemistry and technology without going into the details of theory. Specific solvent-solute interactions and the role of the solvent beyond its function as a homogenous isotropic medium are stressed. Taking into account Parker's statement1) ldquoScientists nowadays are under increasing pressure to consider the relevance of their research, and rightly sordquo we have included examples showing the increasing industrial interest in non-aqueous electrolyte solutions. The concepts and results are arranged in two parts. Part A concerns the fundamentals of thermodynamics, transport processes, spectroscopy and chemical kinetics of non-aqueous solutions and some applications in these fields. Part B describes their use in various technologies such as high-energy batteries, non-emissive electro-optic displays, photoelectrochemical cells, electrodeposition, electrolytic capacitors, electro-organic synthesis, metallurgic processes and others. Four Appendices are added. Appendix A gives a survey on the most important non-aqueous solvents, their physical properties and correlation parameters, and the commonly used abbreviations. Appendices B and C show the mathematical background of the general chemical model. The Symbols and abbreviations of the text are listed and explained in Appendix D