Gel polymer electrolyte with improved adhesion property based on poly(4-hydroxybutyl acrylate) for lithium-ion batteries

Gel polymer electrolytes (GPEs) have emerged as a promising candidate in lithium-ion batteries (LIBs) to address safety issues of liquid electrolytes and to realize flexible batteries. For GPEs, good adhesion between electrolyte and electrodes is highly important to secure performance and stability of the LIBs. Here, new GPEs based on the poly(4-hydroxybutyl acrylate) network are presented. The 4-hydroxybutyl acrylate is a versatile monomer providing excellent adhesion characteristics for various applications, however, there have been no studies for GPEs. We investigated from GPE materials design to their gelation, adhesion, rheology, electrochemical stability, and ion conductivities. In materials design, we gradually controlled liquid content (80–95 vol%) and monomer:crosslinker ratio (99:1–80:20), simultaneously. From the investigation of 16 GPE candidates, we categorized the GPEs based on tanδ change during photopolymerization, into no gelation, viscous gel formation, and stable gel formation. The mechanical properties of the GPEs can be efficiently controlled based on GPE materials design, by showing range of storage modulus from 0.92 kPa to 19.01 kPa. From adhesion characterization, the prepared GPEs indeed present up to 10.92 times higher lap shear strength compared to reference GPEs with conventional ethylene oxide linkage. Also, the GPEs exhibit excellent electrochemical stabilities without significant electrochemical current generation compared to liquid electrolyte, and show reasonable ion conductivities above 10⁻³ S∙cm⁻¹. We applied GPE8 in half-cell LIB to investigate the electrochemical performance. The initial Coulombic efficiency and discharge capacity were 99.69% and 212.37 mAh∙g⁻¹, and exhibited capacity retention of 87.43% upon varied C rate from 0.1 C to 1 C.