Enhance charge capacity by the swelling of the binder utilizing ionic liquids electrolyte for lithium titanate as negative material for LIBs

SUSANA CHAUQUE; FABIANA Y. OLIVA ; OSVALDO R. CÁMARA; ROBERTO M. TORRESI.

San Pablo

Congreso; 46th World Chemistry Congress; 2017

IUPAC

The use of renewable energy and efficient storage systems are topics of current interest. LIBs have the advantage of lower weight, higher energy density, and faster charge and discharge rates, compared to other similar technologies. The lithium titanate Li4Ti5O12 (LTO) is currently one of the best candidates for anode materials of safer LIB for many reasons: the lithium insertion process takes place at a higher potential than graphite, thereby minimizing the decomposition of the solvent employed and consequently avoiding the formation of a solid electrolyte interface. In addition, LTO is a ?zero-strain? material with only a 0.2% of change in unit cell volume when Li+ ions are intercalated or de-intercalated and has a prolonged lifetime in charge/discharge cycling [1]. LIBs are also the most promising option for the next generation of the hybrid electric vehicles. For this purpose, extensive studies focused on increasing their safety. Indeed, current systems are not safe enough as they use flammable organic carbonate electrolytes, which can cause cracks, ignition, or explosion when cells are exposed to high temperatures or short-circuited. To increase the safety and stability of LIBs, the development of more suitable electrolytes is ongoing subject. Electrolytes derived from ionic liquids (IL) have gained a lot of attention due to their thermal and electrochemical stability, flame retardant performance and negligible vapor pressure [2]. In this work, LTO was synthesized by a solid-state method, and tested as negative electrode using two different kinds of electrolytes: ethylene carbonate (EC) and dimethyl-carbonate (DMC) solvent mixture (1:1 by mass) and N-n-butyl-N-methylpiperidinium (BMP) using (CF3SO2)2N− (TFSI) as anion containing 1 M of LiTFSI as lithium salt. From the results obtained, we found that the response of LTO using IL as electrolyte depend of the nature of the binder employed. Therefore, we have studied three different kind of binder, in the first place polyvinylidene fluoride (PVDF) using N-methy-2-pirrolydinone as solvent, then carboxymethylcelulose (CMC) dispersed in water and finally it was synthesized a poli(ionic liquid), which is a polymer containing one or more ionic group from ILs associated with its monomeric unit [3]. The figure insert, shows the cyclic voltammetry (CV) for this negative material using the same electrolyte (BMPTFSI) performed at 1.0 mV/s comparing each binder employed described before. It is possible to notice that the CV response for the electrode using poli(ionic liquid) as binder, is better and the charge involved is bigger than the others binders tested. This behavior it can be explained because this poli(ionic liquid) it is a ionic conductor, prepared with a 5% of the lithium salt (LiTFSI), which has a better interaction with the IL of the electrolyte; therefore allow a favorable lithium ion diffusion.[1] M. Armand, J. M. Tarascon, Nature, 451, 652 (2008).[2] H. Srour, L. Chancelier, E. Bolimowska, T. Gutel, S. Mailley, H. Rouault, C.C. Santini, J Appl Electrochem 46,149?155 (2016).[3] T.M. Benedetti, R.M Torresi, Langmuir 29, 15589-15595 (2013).