Chemically driven conformational rearrangement of PVDF-based polymer electrolyte to improve ionic conductivity for long-cycling lithium metal batteries

Abstract

Poly(vinylidene fluoride) (PVDF)-based solid polymer electrolytes (SPEs) have garnered widespread attention owing to their excellent thermal stability and film-forming ability. However, low ionic conductivity and interfacial side reactions limit their practical applications. Herein, we propose a chemically driven approach to induce molecular chain conformational rearrangement of PVDF, which possesses the more highly polar β-phase to promote Li salt dissociation. An interchain Li⁺ transportation pathway with a low energy barrier was designed through the synergy of strongly coordinated Li⁺⋯–SO₃⁻ (in Nafion) and weak dipole –C–F⋯Li⁺ interaction. Thereby, the ionic conductivity was enhanced to 1.81 mS cm⁻¹. The transportation process was traced by ⁶Li and a two-dimensional ¹H spectroscopy, demonstrating that the proportion of Li⁺ transportation through the designed low-energy-barrier pathway increased from 44% to 79%. The strongly coordinated Li⁺⋯–SO₃⁻ also promoted uniform Li⁺ diffusion and surface inorganic-rich interphase formation. The Li‖Li symmetric cell achieved stable cycling for 7800 h at 0.1 mA cm⁻². The LFP‖Li batteries underwent more than 2000 and 1400 cycles at 1 and 5 C, respectively, and the NCM811‖Li battery maintained a discharge capacity of 152 mAh g⁻¹ at 500 cycles. Additionally, a 1.3 Ah pouch cell passed the nail penetration test with high safety, which provides a novel strategy for designing SPEs.