Impact of Aromatic Extension on the Electrochemical Properties of Lithium Carboxylates As Negative Organic Electrode for Lithium-Ion Battery

aLaboratoire de Réactivité et Chimie des Solides (LRCS), Université de Picardie Jules Verne CNRS UMR7314, 80039 Amiens Cedex b Institut de Chimie de Picardie (ICP), Université de Picardie Jules Verne CNRS FR3085, 80039 Amiens Cedex c Réseau sur le Stockage Electrochimique de l’Energie (RS2E), FR CNRS 3459 The integration of organic-based electrode materials in lithium-ion batteries has aroused keen interest for the last years as it combines a set of advantages against inorganic as lower toxicity, easier recyclability or it takes the advantage of the rich versatility offered by the organic chemistry. This latter can give the promise for tunable redox potentials and kinetic properties1 , 2 , 3. As recently developed, a lot of questions are still pending about the reactivity of these organic compounds, in particular the relationship between the structure and the electrochemical properties. The most promising electroactive function as negative electrode is currently the lithium carboxylate, proposed first by our lab through the di-lithiated terephthalic acid4. Although the different electrochemical tests vs lithium and integration of the materials in batteries testify of the credibility of using organic electrodes, less is placed on the understanding of the structure/reactivity relationship for which it is nonetheless crucial to guide the experimentalist towards the synthesis of higher performance organic electrodes. With this aim, we will carefully expose our recent findings on the role of the spacer between the two carboxylates. For this, a new series of molecules have been developed in our group by changing the extent of π conjugation in the aromatic core unit separating the two electroactive functions. The first in the list is the di-lithium-2,6-Naphthalene dicarboxylate (Li2-NDC) which has a theoretical capacity of 235 mAh.g-1 (Fig. 1)5. Compared to the simpler phenyl core unit (Li2-BDC)with same textural properties, we showed a greater electrochemical performances in terms of power rate capability (Fig. 2). Based on this first result, we have developed a hyper-conjugated organic compound based on the tetralithium perylen-3,4,9,10-tetracarboxylate (Li4-PTC). This perylen core unit with high extended π conjugation offers a remarkable high rate capability to the carboxylate redox active functions as a result from the greater stabilization of the radical anion state. More than 120 mAh.g-1 gravimetric capacity over one hundred cycles at 5C rate was achieved without engineering any electrode formulation (Fig.3)6 This contribution will contain more details about the development of our materials and will give an insight about the relationship between structure of the core unit and electrochemical properties of the electrode material (eg. redox potential, power, capacity retention…). References 1. Armand, M.; Tarascon, J. M., Nature, 2008, 451, 652-7; 2. Liang, Y.; Tao, Z.; Chen, J., Adv Energy Mater., 2012, 2(7), 742-769. 3. Song, Z.; Zhou, H., Energy Environ. Sci., 2013, 6(8), 2280-2301. 4. Armand, M.; Grugeon, S.; Vezin, H.; Laruelle, S.; Ribiere, P.; Poizot, P.; Tarascon, J. M., Nat. Mater., 2009, 8, 120-125. 5. Fédèle, L.; Sauvage, F.; Bois, J.; Tarascon, J.-M.; Bécuwe, M., J. Electrochem. Soc., 2014, 161(1), A46-A52. 6. Fédèle, L.; Sauvage, F.; Becuwe, M. J. Mater. Chem. A, 2014,2 (43), 18225 - 18228. Figure 1