Rigid and flexible dual-network polymer electrolytes with enhanced interfacial interaction to accelerate Li+ transfer†

Abstract

Composite solid-state electrolytes with high structural strength and toughness are effective means to improve the safety and processability of solid-state batteries. However, due to the poor interface compatibility between polymers and inorganic electrolytes, the efficiency of lithium ion transport is affected. To address these issues, we utilized electrospinning technology to prepare highly tough polyacrylonitrile porous membranes. Subsequently, a rigid covalent organic framework electrolyte CPTP was polymerized in situ within the pores to fabricate a rigid and flexible dual-network polymer electrolyte (PAN/CPTP). Experimental results indicate that the carbon–hydrogen compound CPTP interacts with PAN through hydrogen bonding, thus enhancing the interface compatibility of the composite electrolyte, with a resulting mechanical strength as high as 15.5 MPa. The optimized interface eliminates the Li⁺ transport barriers between the PAN and CPTP networks, thus increasing the concentration of free lithium ions in the electrolyte and reducing the lithium ion transport barrier. The lithium ion conductivity (0.94 × 10⁻³ S cm⁻¹) and Li ion transfer selectivity (t_Li⁺ = 0.89) of the composite electrolyte were significantly improved at 30 °C, demonstrating excellent stability towards high-voltage cathodes and lithium metal. Thus, Li//PAN/CPTP//Li symmetric batteries could operate stably for 4000 hours, and NCM811//PAN/CPTP//Li full cells could be cycled stably over 200 times at 4.5 V and 30 °C with 85% capacity retention. This rigid and flexible polymer electrolyte film is easy to prepare over a large area, and the assembled flexible pouch cell has high flexibility and safety.