CONICET | Buscador de Institutos y Recursos Humanos

Within electrochemical batteries, lithium-containing batteries are being used in various electronic devices such as electric cars, hybrid motors, laptops, cell phones, etc. Due to the diversity of materials that can be used as electrodes1-4 the spectrum of applications of these devices is in constant increase. However, current commercial batteries still present operational problems that limit their application, for example the low capacity. This is why new materials constantly come up that try to overcome such problems.5,6 Lithium?sulfur batteries are especially promising electrochemical systems because of their high theoretical capacity of 1672 mAh/g and energy density of 2600 Wh/kg. The high energy density is due to the phase transitions undergone by sulfur which allows capturing more lithium ions than the transition metal based materials currently used. In a charge/discharge cycle two plateaus can be seen: one at 2.3 V vs. Li/Li+ which corresponds to reduction from S8 solid to Li2S4 and the other at 1.9 V vs. Li/Li+ which corresponds to reduction of Li2S4 to yield Li2S with the corresponding formation of intermediate products. The active material is sulfur, which is economical, abundant, and non toxic.7-10 Nevertheless this material has several problems that need solution. Some of these problems are: Li2S and S8 are insulating, so it is necessary to cover them with some conductive material; the material has a change of volume of 80% between lithiated and delithiated phase; polysulfides formed as intermediates are very soluble in the electrolyte, causing a loss of active material; shuttle effects takes place, where the efficiency of the lithium anode can be lowered due the passivation with insoluble sulfides; metallic lithium is used as anode, generating degradation of the electrolyte; degradation of electrolyte by the polysulfides.One of the strategies used to improve the cyclability of the material, avoiding shuttle effects, is the modification of the separator with some materials like TiO211, or carboneaus materials12, etc., that trap the polysulfides avoiding diffusion and suppressing the shuttle effect. In this work we study the cyclability of S/C composites as cathodic materials. We used modified separators with different quantities of hard carbon oxidized prepared in the laboratory. Two kinds of separators were used: Celgard and ceramic impregnated separators. It can be seen than when modified separators are used, the retention of the initial capacity with the number of cycles is improved whith respect to the separator without modification. We also studied the effect of the quantity and the oxidation degree of hard carbon in the separator on the cyclability of the system. All samples were characterized physically and electrochemically using techniques as Scanning Electron Microscopy, Energy-dispersive X-ray spectroscopy, Cyclic voltammetric, Galvanostatic charging/discharging test, etc.