Surface Film Formation on New Composite Anode: Impact of Electrolyte Additives
Authors: Sayah Simon , Ghamouss Fouad , Santos Pena Jesus , Lemordant Daniel , Tran-Van François 
Published: February 2020

The new composite anode Si0.32Ni0.14Sn0.17Al0.04C0.35 exhibits a high specific capacity as well as fast kinetics of charge and discharge [1].  However, due to the side reactions occurring at the electrolyte/electrode interphase, the electrode reversibility is not yet optimal. Therefore, the main objectives of this work are to examine the reactions occurring at the electrode/electrolyte interface and then to evaluate the impact of the electrolyte composition on the performances of this composite anode.

It is now well known that the performances of Li-ion intercalation electrodes are closely linked to the nature of the electrode/electrolyte interphase which depend in turn on the composition of the electrolyte. In many commercial Li-ion batteries using conventional electrolytes, such interphase is stabilised and improved by formulating electrolyte with specific additives. Such species act as SEI (Solid Electrolyte Interphase) improvers since they are easily reduced at the anode before Li+ intercalation during the first charge of the battery. This results in the formation of a thin, insoluble and Li+ conductive passivation layer which prevents further decomposition of the electrolyte and improves the reversibility of the electrode.

We have explored a series of SEI builder additives: vinylene carbonate (VC), vinyl ethylene carbonate (VEC), ethylene sulfite (ES), propylene sulfite (PS), fluoroethylene carbonate (FEC) and di-fluorethylene carbonate (F2EC). The impact of these additives on the SEI formation at the Si0.32Ni0.14Sn0.17Al0.04C0.35 has been studied as a function of their amount using electrochemical methods (CV, GCPL and EIS) and surface characterization techniques (XPS, SEM, Raman spectroscopy).

Results indicate that reversibility and stability of the composite anode can be enhanced by a careful choice of the solvent and the SEI improver additive.  Alternatively to the classical ternary EC/PC/3DMC mixture , Room Temperature Ionic liquids containing  bis(trifluoromethylsufonyl)imide  anion and di-alkyl pyrrolidium, di-alkyl piperidinium or tetra-alkylammonium cations have been used as electrolytes solvent suppressing therefore side reactions due to traditional solvent decompositions and improving the electrode reversibility [2] [3].

(1)   Z. Edfouf, F. Cuevas, M. Latroche, C. Georges, C. Jordy, G. Caillon, T. Hézèque, J.-C. Jumas, M. T. Sougrati, "Nanostructured Si/Sn–Ni/C composite as negative electrode for Li-ion batteries", J. Power Sources, 196 (2011) 4762-4768.

(2)   W. Zhang, F. Ghamouss, A. Darwiche, L. Monconduit, D. Lemordant, R. Dedryvère, H. Martinez, “Surface film formation on TiSnSb electrode : impact of electrolyte additives”, Journal of Power Sources 268 (2014) 645-657.

(3)   W. Zhang, F. Ghamouss, A. Mery, D. Lemordant, R. Dedryvère, L. Monconduit, H. Martinez, “Improvement of the stability of TiSnSb anode under lithiation using SEI forming additives and room temperature ionic liquid/DMC mixed electrolyte”, Electrochimica Acta, 170 (2015) 72-84.

Figure 1