Thermally stable 3D cross-linked fluorinated polyimide/PVDF-HFP hybrid separator for lithium battery applications

Commercial Celgard 2325 separators suffer from poor flexibility, poor electrolyte wettability, and thermal instability, which can cause internal short circuits and thermal runaway in lithium rechargeable batteries. A novel 3D cross-linked and thermotolerant fluorinated polyimide (PI) / PVDF-HFP (PV) hybrid nanofiber sepa-rator rich in polar functional groups was fabricated using an electrospinning technique. PI and PV polymers are joined by a hydrogen bond through their exposed amide (-NH) and fluorinated (-CF) functional groups to build a supramolecular polymer cross-linked system. The separator exhibited high porosity (75 %), outstanding elec-trolyte uptake ability (775 %), strong mechanical properties (15.7 MPa), excellent thermal stability, and flexi-bility. As a result, the separator showed excellent Li+-conductivity (3.3 mS cm-1) and high Li+-transference number (tLi+ = 0.7) and maintained a proper-contacted electrolyte/electrode interaction for stable Li plating/ stripping. Furthermore, when the PI/PV hybrid separator was applied in anode-free Li-metal batteries (a protocol of Cu/NMC cell), or Li-ion (MCMB /NMC) batteries, the cells achieved a high capacity and long lifetime. Remarkably, the Cu/NMC cell fabricated with a PI/PV hybrid separator is more robust and continues to function even after being heated at a high temperature of 140 degrees C for 1 h.

Automated summary

A novel 3D cross-linked and thermotolerant fluorinated polyimide/polyvinylidene fluoride-hexafluoropropylene hybrid nanofiber separator with high porosity, excellent thermal stability, and flexibility was developed. The separator exhibited outstanding electrolyte uptake ability, strong mechanical properties, and achieved stable Li plating/stripping. When applied in anode-free Li-metal batteries or Li-ion batteries, the cells showed high capacity and long lifetime. The hybrid separator also demonstrated robust functionality even after being heated at a high temperature.