EleCtrospinned Carbon Nanotubes Network for Li/Air Cathode (ECCENTRIC) – ECCENTRIC

The first step of the project was to fabricate various structures of electrode materials based on model 1D carbon electrodes to study the influence of electrode structure on the performance. The gas diffusion electrodes (GDE) made either by using the electrospinning technique or by filtration of a suspension of 1D material have in particular different porosities, specific surface and electronic conductivities. The electrochemical charge and discharge studies were carried out in two configurations devices: in a half-cell device developed in the project and which makes it possible to exclusively study the problems related to the positive electrode and in a Li-Air battery in order to study under real operating conditions. The electrochemical characterizations were coupled with imaging analyzes obtained by scanning electron microscope (SEM) in post-discharge and/or after cycling. These studies show the influence on the structure of the electrodes and on the localization and the morphology of the deposits generated during the discharge.

Electrochemical studies coupled with SEM analyzes have shown that the deposition of lithium oxide (Li2O2) during the discharge reaction is dependent on the diameter of the 1D materials that compose the GDE. For materials of several hundreds of nanometers in diameter, the Li2O2 is deposited in the form of toroids whereas this one is conform for materials having a diameter of about ten nanometers. Thus, materials with larger diameter have the highest Li2O2/carbon ratio and with smaller diameters with conformal deposition have greater discharge capacity and better cyclability. Similarly, the deposition of an oxide on the surface of these carbonaceous materials shows an improvement in stability. Finally, the interfaces have a critical role in the viability of Li-Air batteries.

Many challenges remain to be overcome for the development for the use of carbon-based electrocatalysts for Li-Air batteries operating in non-aqueous electrolytes. However, the main obstacle remains the instability of the electrolyte and materials with the reaction products of superoxides.

Although the project is applied, the researches done within the framework of the ECCENTRIC project are at the fundamental level and the results obtained will be published in international scientific journals.

Since the revival of the Li-Air technology by K.M. Abraham in 1996 using non-aqueous electrolyte, this technology has been foreseen as the savior by the automobile industry, generating a worldwide competition at an academic level supported by private funding (Toyota or IBM for instance) and public agencies such as the Department of Energy as well as with the creation of startups such as Liox Power or PolyPlus Battery for instance. Even though considerable progresses have been made in the last years, the battery community realizes that Li-O2 cells have a long way to go before to be commercialized: a better understanding of the fundamental mechanisms at play during the cycling is necessary. Hence, international groups at the forefront of this field such as Bruce’s, Nazar’s, McCloskey’s, Shao-Horn’s, Gasteiger’s, Janek’s groups and others are currently placing a lot of efforts on understanding the effect of solvent properties on the discharge product formation as well as the use of redox mediators in solution as a way to overcome the large overpotential encountered during the charge. Our approach in ECCENTRIC project is in line with this worldwide push for knowledge creation regarding the physico-chemical processes upon cycling. Nevertheless, while other groups are largely focusing on the understanding of the solvent influence on the cycling properties, only few has been done concerning the understanding of the electroactive material functioning and this project aim to fill this gap with an in depth study of the electrode impact on the charge/discharge mechanism. Thus, the ECCENTRIC project starts with fundamental researches on air electrodes, further used to develop new materials electrodes for positive electrode for Li-Air batteries. The aim of ECCENTRIC is to demonstrate that viable metal-air battery can be developed following an innovation-through-science approach, involving the acquisition of new knowledges and understandings of the science underpinning the lithium-air batteries.
The ECCENTRIC consortium involves three well-recognized fundamental research groups that will put together their complementary skills in Surface science and Nanosciences (CEA LICSEN partner), Material science and Processing (LCMCP) and batteries testing and characterization as well as chemistry (Collège de France UMR UMR 8260) to develop new materials and study their catalytic and electronic properties from single building block to their assembly into complex 2D and 3D network. The building blocks will be assembled in interpenetrated networks or through core/shell structures thanks to electrospinning, a simple and upscalable technique. Li-Air batteries tests made in real cycling conditions will guide the finding of the most suitable parameters for the discharge/charge processes.
The project opens new avenues to other fields, such as Na-Air systems, electrode nanostructuration, as well as multiphase transport and reactivity.