**The Use of Succinonitrile as an Electrolyte Additive for Composite-Fiber Membranes in Lithium-Ion Batteries**

#### **Jahaziel Villarreal 1, Roberto Orrostieta Chavez 1, Sujay A. Chopade 2, Timothy P. Lodge 2 and Mataz Alcoutlabi 1,\***


Received: 13 January 2020; Accepted: 11 March 2020; Published: 17 March 2020

**Abstract:** In the present work, the e ffect of temperature and additives on the ionic conductivity of mixed organic/ionic liquid electrolytes (MOILEs) was investigated by conducting galvanostatic charge/discharge and ionic conductivity experiments. The mixed electrolyte is based on the ionic liquid (IL) (EMI/TFSI/LiTFSI) and organic solvents EC/DMC (1:1 *v*/*v*). The e ffect of electrolyte type on the electrochemical performance of a LiCoO2 cathode and a SnO2/C composite anode in lithium anode (or cathode) half-cells was also investigated. The results demonstrated that the addition of 5 wt.% succinonitrile (SN) resulted in enhanced ionic conductivity of a 60% EMI-TFSI 40% EC/DMC MOILE from ~14 mS·cm<sup>−</sup><sup>1</sup> to ~26 mS·cm<sup>−</sup><sup>1</sup> at room temperature. Additionally, at a temperature of 100 ◦C, an increase in ionic conductivity from ~38 to ~69 mS·cm<sup>−</sup><sup>1</sup> was observed for the MOILE with 5 wt% SN. The improvement in the ionic conductivity is attributed to the high polarity of SN and its ability to dissolve various types of salts such as LiTFSI. The galvanostatic charge/discharge results showed that the LiCoO2 cathode with the MOILE (without SN) exhibited a 39% specific capacity loss at the 50th cycle while the LiCoO2 cathode in the MOILE with 5 wt.% SN showed a decrease in specific capacity of only 14%. The addition of 5 wt.% SN to the MOILE with a SnO2/C composite-fiber anode resulted in improved cycling performance and rate capability of the SnO2/C composite-membrane anode in lithium anode half-cells. Based on the results reported in this work, a new avenue and promising outcome for the future use of MOILEs with SN in lithium-ion batteries (LIBs) can be opened.

**Keywords:** ionic liquids; succinonitrile; electrolyte; lithium ion batteries; composite fibers; mixtures
