Cyano-Functionalized Polyimide with Li ⁺ Coordination Channels: Ultra-Stable Nanofiber Separators for High-Energy-Density Lithium Batteries

Escalating requirements for energy density, fast-charging capability, and operational safety in lithium-ion power batteries demand separators with exceptional structural stability and ion-transport efficiency. Herein, a flexible, improved-wettability polyimide membrane derived from a diamine monomer containing cyano groups is synthesized via electrospinning. The interconnected pore structure and high porosity of the cyano-based polyimide separator deliver the desired electrolyte wettability (405%) and thermal stability. Importantly, the introduction of polar cyano groups with a high dielectric constant provides a high anodic oxidation potential. The lithium-ion battery assembled with the cyano-based polyimide separator provides strong coordination with Li⁺, exhibiting elevated ion conductivity (1.04 mS cm^-1, 25 °C) and high-rate performance, delivering a capacity of 98.4% at a rate of 0.5 C after 200 cycles. Moreover, the cyano-based polyimide separator displays great cycling durability and capacity retention (99.5%, 133.6 mAh g^-1) even at 100 °C. The above-mentioned properties imply that cyano-containing polyimide nanofibrous membranes are outstanding candidates as separators in the high-capacity lithium-ion battery industry.