Douaa FARHAT^a, Fouad GHAMOUSS^a, Julia MAIBACH^b, Kristina EDSTRÖM^b, Daniel LEMORDANT^a

(a) Laboratoire de Physico-Chimie des Matériaux et des Electrolytes pour l’Energie (PCM2E), EA 6299. Université François Rabelais, Parc de Grandmont, 37200 Tours, France

 (b) Ångström Laboratory, Department of Chemistry UPPSALA University, Lägerhyddsvägen1, 75120 Uppsala, Sweden

douaa.farhat@etu.univ-tours.fr , fouad.ghamouss@univ-tours.fr

Lithium-ion batteries (LiB) are now the most popular type of rechargeable batteries for portable electronics and larger scale applications, such as electric vehicles, for their high voltage, high cycling performances and high energy densities.

Large-scale applications require also safety standards. Low impact on environment, high safety and high thermal stability, are required conditions for Li-ion Batteries electrolytes. Therefore, a safe combination of solvents and lithium salt needs to be designed.

In the past decades, significant progress has been made in Li-ion batteries technology but some points remain to be solved. In particular providing alternatives to flammable solvents actually used, without any significant loss of performances, is challenging.

Due to their low vapor pressure, their large electrochemical window (exceptionally stable until 6 V vs. Li/Li⁺), their high thermal stability and the lack of toxicity and environmental impact, dinitriles (NC(CH₂)_nCN, DN) are a credible alternative to solvents like alkyl carbonate in Li-ion batteries⁽¹⁾. DN can dissolve lithium salts at relatively high concentrations, with moderate increase in viscosity. Adiponitrile (n = 4) and glutaronitrile (n = 3) have been used in the formulation of electrolytes designed to be used in Li-ion batteries and ultra-capacitors (1-4). However, using these solvents is still challenging due to theirs low electrochemical stability toward graphite negative electrode.

In this study, the behavior of DN-based electrolytes with graphite, titanate (Li₄Ti₅O₁₂) and NMC (LiNi_1/3Co_1/3Mn_1/3O₂) electrodes were investigated. The formation process of the solid electrolyte interface (SEI) in DN-based electrolytes at the graphite anode has been carefully examined using several electrochemical and surface analysis methods including EIS, CV, GCPL, SEM, EDX and XPS. The impact of SEI builder additives, such as vinylene carbonate (VC), fluoroethylene carbonate (FEC), di-fluoroethylene carbonate (F₂EC), lithium bis(oxalato)borate (LiBoB) and succinic anhydride (SA), on the rate capability and cyclability of the graphite electrode has been  studied. Moreover transport properties like ionic conductivity, viscosity, Li+ transference number in DN-based electrolytes have been determined using electrochemical methods. 

As a conclusion, results indicate that the performances of the batteries depends on the nature of the DN used as solvent as well as the nature and amount of additive.

Fig: First galvanostatique charge/discharge @C/20 of graphite electrodes cycling in ADN with and without additives. Inset: SEM images at the end of charge (delithiation).

References :

1)       Y. Abu-Lebdeh et al. Journal of the Electrochemical Society. (2009)156 1 A60

2)       A. Brandt. Journal of the Electrochemical Society. (2012)159 (12) A2053

3)       F. Ghamouss et al J Appl Electrochem (2013) 43, 375–385

4)       F. Ghamouss et al J. Phys. Chem. C, (2014) 118 (26), pp 14107