In recent decades

gel polymer electrolytes (GPEs) have received renewed attention in several areas such as lithium-ion batteries

solar cells and super capacitors due to their promising application.GPEs

swollen in a liquid electrolyte becoming plasticized or a gelled polymer electrolyte

have attracted particular attention because they may provide lighter and safer batteries with longer shelf life

leak proof construction and easy fabrication into desired shape and size.However

GPEs still show poor mechanical strength due to the need for impregnation with the liquid electrolytes.This significant drawback of GPEs hinders their practical application.To overcome these problems

in this review

the up-to-date technologies such as composite gel polymer electrolyte (CGPEs) and porous polymer electrolytes (PPEs) based on the gel concept have been summarized.In the CGPEs

the role of a filler in the membrane is to provide surface groups as physical cross-linking centers for the polymer segments

and thus reduce the polymer reorganization tendency which establishes additional conducting pathways on the filler surface.As a result

the nanosized particles not only lead to better ionic conductivity but also interact with the polymer hosts to enhance the mechanical strength.In PGPEs

due to the existence of the porous structure

the lithium ions can migrate not only in gel electrolyte but also in liquid electrolyte stored in the pores

leading to higher ionic conductivity.In addition

the main characteristics of these gel polymer electrolytes were mentioned.Finally

the future directions are also pointed out.