Understanding of discharge-charge processes inside porous binder- free carbon nanotube membrane as cathode materials in non-aqueous Li-Air batteries
Résumé
New efficient energy storage devices are one of the most important challenges for researchers all over the world. Because of the growth of portable technologies on the market (automobile, mobile phones …), it is essential to develop new devices to efficiently store increasing quantities of energy. The most promising technologies, which could replace Li-ion batteries used currently in this kind of devices, operate by ion intercalation (Na-ion or all-solid-state batteries) or by electrochemical reactions (Lithium-sulfur or Metal-air batteries). The latter work by reducing small molecules, like dioxygen, to metal oxide species in Lithium-air devices, and whose main discharge product is Li2O2. Lithium-air battery is one important alternative because of its largest theoretical energy storage density. Nevertheless, the cyclability remains the main difficulty to overcome, either on the anode by the dendrimer formation of lithium particles, or in the cathode by the non-reversibility of oxygen reduction reaction (oxidation of ORR products), which occur during charge process and obstruct the oxygen and lithium cation flux. In this work, we are interested in the understanding of discharge-charge electrochemical/chemical processes inside porous cathode materials in non-aqueous Li-Air batteries. We use binder-free carbon nanotube (CNT) membranes as microporous cathode material and dimethylsulfoxyde (DMSO)/LiClO4 as electrolyte. The cathode section was analyzed by coupling electrochemical analysis using an air half-cell and post-mortem analysis using SEM to observe the product morphologies of the top, the bottom and through the thickness of CNT membranes (influence of the structure). XPS was also used to determine reaction products. Coupling these different techniques, it is possible to correlate the discharge conditions with the product morphologies and their locations inside the CNT membrane, in order to determine the key parameters that are responsible for the membrane blockage during cycling.