Replacing conventional liquid electrolytes with solid electrolytes has been recognized as a promising strategy to overcome the safety issues of Li-based batteries in terms of reactivity, flammability, and toxicity. An ideal solid electrolyte should meet high ionic conductivity (10-4 -10-3 S·cm-1 at R.T.), high cationic transference number, excellent electrode compatibility, and high cyclability (Barbosa et al., 2022).

In the present work new polymer-based hybrid electrolytes have been developed to be used in Li-ion batteries. The electrolyte consists on: (i) a crosslinked system from blends of (poly(ethylene glycol) methyl ether methacrylate (PEGMA) and poly(ethylene glycol) dimethacrylate) (PEG1000DMA) acting as a polymer backbone, and (ii) lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) or/and a porous ceramic with Nasicon-type structure (Li 1.3 Al 0.3 Ti 1.7 (PO4)3 (LATP) which contributes to increase the number of charge carriers and, consequently, the ionic conductivity. These polymer electrolytes are characterized by their outstanding flexibility and processability, while the addition of inorganic loads can also be performed without the need for any additional solvent.

A series of hybrid electrolytes containing lithium salt (O/Li = 20), LATP (loads of 15- 60 %wt.), or a mixture of both were prepared and characterized. These materials showed high mechanical stability and flexibility, which also improves electrode/electrolyte contact. Regarding their electrochemical behavior, an ionic conductivity of 10-5 S·cm-1 was achieved at room temperature. This value is of the same order of magnitude as those observed for solid electrolytes containing also PEO functionality (Maia et al., 2022). However, this ionic conductivity is still low for the targeted applications, limiting the functional performance of Li-ion batteries. To solve this drawback metal organic frameworks (MOFs), as an emerging type of solid fillers, were added into the polymer matrix. Specifically, a MOF containing  phosphonate ligands is incorporated into the polymeric solution (0.05-20 %wt). The porosity of MOFs, together with their ability to disorder the arrangement of polymer chain, contributed to increase the ionic conductivity of the electrolyte (Xu et al, 2022). The objectives addressed under this research present a significant, feasible and applied value, so it is expected that the obtained results have a high knowledge transfer potential towards the design and configuration of the emerging new generations of solid state batteries.
 
Barbosa, J. C. et al., Toward Sustainable Solid Polymer Electrolytes for Lithium-Ion Batteries. ACS Omega 2022, 7, 14457−14464.
Maia B. A. et al., Designing Versatile Polymers for Lithium-Ion Battery Applications: A Review. Polymers 2022, 14, 403.
Xu Y. et al., Metalorganic framework (MOF)-incorporated polymeric electrolyte realizing fast lithium-ion transportation with high Li+ transference number for solidstate batteries. Front. Chem. 2022, 10:1013965.