The development of new electrolytes is a crucial target to devise secondary batteries running on alkaline- and alkaline-earth elements characterized by a high specific energy and power and an extensive cyclability, able to provide power for a wide range of applications ranging from portable electronic devices to electric vehicles. The electrolytes must satisfy very demanding requirements, including: (a) easy migration of the alkaline- and alkaline-earth cations between the electrodes of the battery; (b) high compatibility with all the other functional materials used in the assembly of the device; (c) wide potential window and excellent chemical stability.

This report summarizes the preparation and characterization of innovative families of electrolytes meant to address these issues and opens the way for future research trends in this field. The investigated materials comprise: (i) single-ion-conducting nanocomposite polymer electrolytes; (ii) solid-state single-ion-conducting polymers; and (iii) conventional polymer electrolytes.

In detail, the first approach comprises the study of nanocomposite polymer electrolytes (nCPEs) consisting of PEG400 and innovative lithiated fluorinated nanofillers (e.g., titanium or iron oxide) whose surface anion groups are neutralized with Li⁺ cations. These materials are single-ion conductors, and at room temperature they exhibit a Li⁺ conductivity higher than 10^-5 S/cm. The second approach includes the investigation of Poly(vinyl alcohol)-based solid polymer electrolytes which are obtained by direct lithiation of partially hydrolyzed poly(vinyl alcohol), forming a lithium-poly(vinyl alkoxide) macromolecular salt. In this case it is possible to demonstrate a conductivity higher than 10^-5 S/cm at RT upon plasticization with EMImTFSI ionic liquid.

Finally, Broadband Electrical Spectroscopy (BES) studies of classic polymer electrolytes and innovative Magnesium salts for secondary Mg batteries will be presented. This technique will allow for the detailed elucidation of the interplay taking place between structure and conductivity of in these systems, thus tailoring the design of future polymer electrolytes.

The chemical composition of the studied materials is analyzed by ICP-AES and microanalysis. The thermal properties are investigated by HR-TG and DSC measurements. The structure and the interactions in the materials are studied by vibrational spectroscopies (FT-MIR and –FIR). The electric response is elucidated by Broadband Electrical Spectroscopy (BES). Results allow to propose a conduction mechanism and to define the interplay existing between structural, thermal transitions and electrochemical properties of proposed innovative electrolytes.

Acknowledgement

This project has received funding from the BIRD 2016 program of UNIPD.