1,720,977 research outputs found
LI/LI1+XV3O8 SECONDARY BUTTON CELLS - DEPENDENCE OF CYCLE LIFE ON ELECTROLYTE NATURE AND CYCLING REGIME
No full textThe behaviour of the Li/Li1+xV3O8 system in a secondary button cell has been investigated. it is shown that when using electrolytes based on LiAsF6 (without stabilizing additives) the best result are achieved with cyclic esters. It is established that the charging conditions influence significantly the cell cyclability, while the discharge conditions have a limited effect. It is also demonstrated that mixtures of ethylene and propylene carbonate lead to a considerably better reversibility of the system. A satisfactory electrode performance has been obtained: 180 Ahkg-1 at the 100th cycle for the positive electrode material and over 95% utilization of the Li electrod
Improvement of potassium vanadates performance by preliminary water intercalation in their structure.
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Li/ Li1+xV3O8 secondary batteries. III°. Further characterization of the mechanism of Li+ insertion and of the cycling behaviour.
No full textThe 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
A new approach for the improvement of Li1+xV3O8 performance in rechargeable Li batteries.
No full textA method for the improvement of the electrochemical properties of Li1+xV3O8 is presented based on the partial modification of its crystal structure by the introduction of small amounts of inorganic compounds, such as H2O, CO2 and NH3. The modification is performed by preliminary insertion of these molecules at high (H2O) or ambient pressure (CO2) or by use of appropriate method of synthesis (NH3). A remarkable specific capacity of about 280 mAh/g has been achieved corresponding to the reversible intercalation of 3 equivalents of Li per mol Li1+xV3O8. The high capacity performance and the good reversibility observed is assigned to the preliminary expansion of the interlayer spacing by the inorganic compounds inserted into it, this leading to an increased mobility and enhanced distribution of the Li+ ions in the Li1+xV3O8 layers
Li/ Li1+xV3O8 batteries. V°. Comparison with other secondary cells and influence of micro- and macro-structural alteration on the cathode performance.
No full textLi/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.
No full textWith 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
Potassium vanadate - Promising materials for secondary Li batteries.
No full textThe electrochemical performance of the phases K3V5O14, KV3O8, K2V8O21 and KV5O13, in view of their use as positive electrodes for secondary lithium cells, has been investigated. While the two potassium richer compounds showed very low recharge efficiency, a good revesibility and high capacity performance have been observed for the K2V8O21 and KV5O13 compounds. The remarkable specific capacity of KV5O13, which is about 210 mA h g−1 at 2 h discharge rate, and its excellent cycleability proves it as a promising alternative for a positive electrode of secondary lithium batteries
Small particle-size lihium-vanadium oxide: an improved cathode material for high rate rechargeable Li batteries.
No full textA 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
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