Abstract
Over the last decades, the widespread diffusion of energy storage systems, related to a global rethinking of the energy sources used for mobility, for industrial and household use, has been witnessed. In this framework, energy storage systems based on lithium-ion batteries will play a fundamental role in the transition towards green electricity production and use. However, the mass production of batteries based on inorganic materials, the reference materials for Li-ion technology, has shown various problems related to supply and recyclability: the abundance of these resources is very limited and characterized by an unfavorable geolocation, their extraction and processing costs are high and the materials are poorly recyclable1,2.
To overcome these limitations, in recent decades scientists have focused on the study of organic-based materials: these compounds are capable of storing energy through redox reactions and are mainly composed of carbon, nitrogen, sulfur, oxygen and hydrogen atoms. Furthermore, they are characterized by low production costs and high recyclability, as well as the possibility of being obtained from natural sources, for an overall lower environmental impact3. Together with their high electrochemical performance, organic materials are excellent candidates to replace the inorganics-based electrodes.
Organic materials can be categorized into two groups, based on the energy storage mechanism: the former uses a cation insertion ("n-type"), which involves an exchange of lithium ions with the electrolyte such as carbonyl-based molecule (as quinone compounds), organodisulfides, azocompounds and nitriles4, the latter is based on anion insertion in the redox process (p-type) such as aromatic amines (phenothiazine and phenoxazine), together with nitroxides (as TEMPO)5. In recent years, several studies on a new p-type functional group, based on carbazole moieties, have been reported in the literature6: it shows high average potentials (3.7 V vs. Li), one of the highest among organic molecules, and a good reversible capacity around 125 mAh g-1. The overall performances are comparable, both in terms of potential and capacity, to those obtained with conventional positive-electrode materials such as LiCoO2 or LiFePO47.
Herein we would like to report on the design, the preparation and the electrochemical performance of a new set of carbazole-based molecules, cable of reversibly intercalating anions (p-type mechanism) with a high redox potential (4.0 V vs. Li+/Li0) as organic positive electrodes for energy storage applications.
Two new N-substituted carbazole molecules, lithium carbazole acetate (LiCZA) and lithium carbazole benzoate (Li-4-BACZ), were synthesized with a carboxyl functionality, in order to avoid the dissolution of the active material in the liquid electrolyte solvent. Both molecules showed an improvement in cycling stability, and in the case of Li-4-BACZ, an increase in the redox potential of 100 mV was also observed. Moreover, several different types of electrolytes were tested in order to evaluate the impact of the anion type on the p-type insertion mechanism8. Two different electrolytes were tested, LiPF6 and LiClO4, dissolved both in a 1:1 EC/DMC mixtures and in propylene carbonate.
Keywords: Carbazole, lithium batteries, organic electrode, organic batteries.
References
Scrosati, B.; Garche, J. J. Power Sources 2010, 195, 2419−2430.
Poizot, P.; Dolhem, F. Energy Environ. Sci. 2011, 4, 2003−2019.
Poizot P., Gaubicher J., Renault S., Dubois L., Liang Y., Yao Y., Chem. Rev.2020, 120, 14, 6490–6557
Bhosale M. E., Chae S., Kim J. M., Choi J.-Y., J. Mater. Chem. A, 2018, 6, 19885–19911
Esser B., Dolhem F., Becuwe M., Poizot P., Vlad A., Brandell D., J. of Power Sources 2021, 482, 228814
Yao M., Senoh H., Skai T., Kiyobayashi T., J. of Power Sources 2012, 202, 364-368
Goodenough J. B., Park K.-S., J. Am. Soc. 2013, 135, 1167−1176
Murugesan R., Dolhem F., Davoisne C., Becuwe M., ChemSusChem 2020, 13, 2364 – 2370