Ultrathin and Mechanically Robust Polyacrylonitrile-Based Solid Polymer Electrolytes Enabling Long-Cycle-Life Lithium Metal Batteries

Abstract

Polyacrylonitrile-based solid polymer electrolytes (PAN-SPEs) have emerged as promising candidates for lithium-metal batteries owing to their advantages of safety, processability, and oxidative stability. However, ultrathin PAN-SPEs (<30 μm) still suffer from low ionic conductivity and poor mechanical strength. Herein, a strategy combining dipole-dipole interactions and doping with inorganic particles is proposed to construct continuous lithium ion (Li⁺) transport channels. The nitrile groups in PAN facilitate Li⁺ transport via Lewis acid-base interactions while inhibiting anion migration. Additionally, a soft exterior/rigid interior architecture was constructed through hot pressing and solution casting, achieving an ultrathin thickness of 27.8 μm with outstanding mechanical robustness. As a result, the designed PAN-SPEs demonstrate high ionic conductivity (4.42×10^-4 S cm^-1) together with a large elongation at break (168.5%). Leveraging these synergistic advantages, the symmetric cell exhibits excellent dendrite suppression for over 1200 hours, and the Li||SPEs||LiFePO₄ cells deliver capacity retentions of 81.0% at 0.5C and 73.3% at 2C. This work provides a design paradigm for developing high-performance PAN-SPEs for lithium metal batteries.

Graphical abstract