Highly dispersible graphene oxide nanoflakes in pseudo-gel-polymer porous separators for boosting ion transportation

Gel-type polymer electrolytes have received considerable attention due to the battery explosion issue associated with volatile liquid-electrolyte-based lithium ion batteries (LIBs). However, the high ionic conductivity of gel-type polymer electrolytes originates from polymer swelling by the liquid electrolyte, and these materials inevitably have poor mechanical strength during device deformation. Here, we report structural gel-type polymer separators with highly porous and uniform morphology arising from the phase inversion of PVdF-HFP polymers with highly dispersible nanoscale graphene oxide nanoflake (GON). Via simple γ-ray irradiation of conventional graphene oxide solution, large 2D particles were cut into small 2D particles with a narrow size distribution, which in turn resulted in a dramatic change in solution transparency and particle dispersity. γ-ray-irradiated graphene oxide nanoflakes (γ-GON) with high dispersity are located inside the porous PVdF-HFP skeleton, inducing additional micron-sized pores of ∼8 μm in the composite membranes. The modified porous film showed both gel-polymer electrolyte-like (uptake of 1.7 times more liquid electrolyte than conventional polyethylene separator) and polymer separator-like behavior (maintenance of original porous structure after soaked with liquid electrolyte). As a result, this pseudo-gel-polymer separator with a tailored pore structure has uniform ion flux and enhanced interfacial properties with electrodes, contributing superior battery performance.