**Composite Gel Polymer Electrolytes Based on Organo-Modified Nanoclays: Investigation on Lithium-Ion Transport and Mechanical Properties**

#### **Cataldo Simari \*, Ernestino Lufrano, Luigi Coppola and Isabella Nicotera \***

Department of Chemistry and Chemical Technologies, University of Calabria, 87036 Rende, CS, Italy; ernestino.lufrano@unical.it (E.L.); luigi.coppola@unical.it (L.C.)

**\*** Correspondence: cataldo.simari@unical.it (C.S.); isabella.nicotera@unical.it (I.N.)

Received: 26 July 2018; Accepted: 21 August 2018; Published: 24 August 2018

**Abstract:** Composite gel polymer electrolytes (GPEs) based on organo-modified montmorillonite clays have been prepared and investigated. The organo-clay was prepared by intercalation of CTAB molecules in the interlamellar space of sodium smectite clay (SWy) through a cation-exchange reaction. This was used as nanoadditive in polyacrylonitrile/polyethylene-oxide blend polymer, lithium trifluoromethanesulphonate (LiTr) as salt and a mixture of ethylene carbonate/propylene carbonate as plasticizer. GPEs were widely characterized by DSC, SEM, and DMA, while the ion transport properties were investigated by AC impedance spectroscopy and multinuclear NMR spectroscopy. In particular, 7Li and 19F self-diffusion coefficients were measured by the pulse field gradient (PFG) method, and the spin-lattice relaxation times (T1) by the inversion recovery sequence. A complete description of the ions dynamics in so complex systems was achieved, as well as the ion transport number and ionicity index were estimated, proving that the smectite clay surfaces are able to "solvatate" both lithium and triflate ions and to create a preferential pathway for ion conduction.

**Keywords:** gel polymer electrolytes; composites; montmorillonite clays; lithium batteries; PFG-NMR; self-diffusion coefficient; blend polymers
