Motivations of the research theme
Li-ion technology is based on the reversible insertion of lithium into the active material structure. In the electrode, the active material must be associated with various additives, such as the conductive agent and the polymeric binder, which give the electrode the properties suitable for its proper functioning.
The quantity of these additives (electrochemically inactive) in the electrode must remain low in order to not plague the total capacity due to a decrease in the quantity of active material per unit mass or volume of electrode.From these considerations comes the topic of the electrode formulation which consists in determining the most appropriate combination of additives and the proportions which will guarantee the best compromise between a good electrode operation and a minimum additive content, while ensuring the mechanical and electrical properties of the electrode acceptable for subsequent assembling in the accumulator and its operation. Moreover, the action of these additives will depend on the mode of elaboration of the electrode and in particular on the phase of homogenization of the electrode precursor ink or paste or slurry. The formulation work is therefore coupled with a study on the process of implementation, which must remain as simple as possible to ensure good reproducibility and to facilitate developments on a larger scale.
At the academic level, it is a fundamental approach complementary to the more empirical one carried out in industrial environments in the manufacture of batteries or active materials and additives. It, which goes beyond the objectives of performance optimization at the device level, brings a better understanding of the reaction mechanisms of the active material. This approach requires the development of methodology and analysis tools, both experimental and theoretical, and requires to consider the composite electrode as a whole, that is, to fully understand all the interactions between the different constituents though the measurement of their response to different stimuli (mechanical, chemical, electrical). This approach must be multidisciplinary and multi-scale, as the electrodes are complex composite materials.
Formulation of negative electrode with high capacity - Over the last few years, intense research has been carried out internationally on silicon as a negative electrode material, due to its specific capacity 10 times higher than graphite. Using silicon instead of graphite could significantly increase the Energy density of Li-ion batteries. We have contributed to several projects with 4 theses and several post-doctorates. Our major results are: (i) identification of the relationship between the surface composition of silicon, its reactivity with the polymer binder and subsequent cycling; (ii) explaining the mechanisms of failure in cycling by invalidating the hypothesis of lithium trapped in the form of a LixSi alloy and, on the other hand, by showing the accumulation of organic species produced by the parasitic reactions of degradation the electrolyte solvents; (iii) the mechano-synthesis of a nanostructured micrometric silicon powder, the advantage of which is the obtaining of low-cost electrodes (e.g. from waste from the silicon industry); (iv) the design of formulations for the cycling of electrodes with surface capacities 10 times superior to the state of the art; (v) extrapolation / transfer to the industrial pilot scale of efficient electrode formulations. As part of the European ALISTORE network, we have also significantly improved the Li-ion battery performance of new FeSn2, NiSb2, and TiSnSb negative electrode materials proposed by ICG-AIME (Montpellier). These results have led to a renewed interest in these materials, which today are among the most promising for sodium-ion batteries. All these studies were coupled with NMR interface characterizations.
Multiscale characterizations of transport properties - The energy density and power performance of the batteries are also limited by the transport of charges (ions and electrons) in the composite electrodes. We undertook a fundamental study of these properties at the various scales of electrode based on LiFePO4 and LiNi1/3Mn1/3Co1/3O2 by broadband dielectric spectroscopy (SDLB). The transport properties are related to the analysis of the architecture at the different scales of the composite electrodes by computed X-Ray and FIB-SEM tomography techniques in collaboration with MATEIS. In order to reduce the limitations associated with electronic transport, we use redox polymers both as an electronic conductive additive and as a binder. Our main results are: (i) the design and development of a cell to make operando measurements of SDLB, a new characterization tool in this field of research; (Ii) the identification of the electronic transport mechanisms at the various scales as well as their evolutions when the electrode is impregnated by the liquid electrolyte.
All solid-state and printable microbatteries - We are working on the development of solid and flexible micro-batteries by printing, a faster and cheaper manufacturing process than traditional ultra-vacuum deposits. Specially formulated LiFePO4 electrode inks make it possible to obtain by ink-jet printing porous electrodes which are then impregnated and covered with a printable electrolyte based on ionic liquid.  The solid character is obtained after depositing the electrolyte by the in situ formation of a silica (ionogel) or polymer (sol-gel, UV or thermal polymerization) confinement matrix. The development of all-solid (macro) batteries of improved safety is the subject of work with Solvay. We have developed solid electrolyte films based on ionic liquids confined in a polymer-silica hybrid matrix, called ionobrids.15 LiFePO4 and LiNi1/3Mn1/3Co1/3O2/ionobrid/lithium metal batteries assemblies of 1mAh/cm² have done more than 500 cycles at 60°C.
Solid/liquid electrodes for redox-flow batteries - As part of an RS2E project to revisit and increase the performance of redox-flow batteries for the stationary storage of intermittent renewable energies,, we have: (i) optimized theformulation of based electrode inks based on Li4Ti5O12 and carbonaceous conductive additives dispersed in an organic liquid electrolyte; (ii) correlated their rheological properties, electrical properties, and electrochemical performance.
- Thèses : M. Gauthier (2010-13), B.P.N. Nguyen (2011-14), N. Delpuech (2011-14, Cifre Umicore), Z. Karkar (2013-16). Post-doctorats : Y. Oumellal (2009-10), D. Mazouzi (2008-10). Projets : ANR Basilic (2010-12), FP7 EuroLiion (2011-15), FP7 Baccara (2014-16). Collaborateurs : L. Roué à l’INRSCanada, W. Porcher au CEA/LITEN, B. Humbert de PMN/IMN.
- Post-doctorat : H. Wilhelm. ANR ICARES. Collaborateur : L. Monconduit
- Collaboration avec Chimie ParisTech, l’ICMMO (Orsay) et le LGEP/GeePs (Gif/Yvette). Collaborateurs : J.-C. Badot, S. Franger, et O. Dubrunfaut. Thèses : K. Seid (2009-11), N. Besnard (2012-15, Cifre RENAULT), Projet ANR CALICE (2009-12).
- Collaborateurs : E. Maire, A. Etiemble.
- Collaboration avec le LRCS (Amiens) et Moltech Anjou (Angers). Collaborateurs : J.-P. Bonnet, P. Blanchard & P. Leriche.
- Thèses : P.-E. Delannoy (2010-12, Cifre STM) et D. Aidoud (2013-16). Projet : PIA TOURS 2015 (2012-17)
- Collaborateur : J. Le Bideau, équipe PMN/IMN.
- Réseau sur le Stockage Électrochimique de l’Énergie
- Post-doctorats: M. Youssry puis L. Madec (2012-13). Collaborateurs: J.-M. Tarascon, P. Barboux.