Synthesis of polypropylene nanofiber separators for lithium-ion batteries via nanolayer coextrusion

PP nanofibers are prepared via efficient nanolayer co-extrusion technology and directly incorporated into lithium-ion battery separators. The bonding force among the PP nanofibers is enhanced through hot pressing treatment at 120 °C, resulting in significantly improved mechanical properties of the separators. In addition, the higher porosity of PPNFS-120 effectively improves the originally poor electrolyte uptake of PP material, reduces the ion transfer impedance, and shows excellent ionic conductivity. More importantly, the NCM811 and LFP/graphite full cells assembled with PPNFS-120 demonstrate superior rate performance and cycling stability compared to commercial polyolefin separators. Additionally, the simple preparation process with low cost and high yield has great potential for scale-up production. [Display omitted] •PP nanofibers are prepared via efficient nanolayer co-extrusion.•Mechanical properties of PPNFS are improved by hot press treatment.•PPNFS-120 exhibits high porosity and electrolyte uptake.•The full cell assembled with PPNFS-120 shows excellent battery performance.•Promising large-scale production of PPNFS. Nanofiber separators are becoming increasingly popular in high-performance lithium-ion batteries (LIBs) due to their high porosity, high electrolyte uptake, and thinner thickness. So far, polypropylene (PP) materials occupy a large share of the LIB separator market due to their low cost and stable electrochemical properties. However, it is difficult to realize the preparation of PP nanofibers by solution electrospinning because there is no corresponding solvent for PP materials. Moreover, the large size of melt-blown PP fibers cannot reach the nanoscale. PP nanofibers produced by nanolayer coextrusion technology at mass can be processed into LIB separators. The tensile strength of PP nanofiber separators (PPNFS) treated with hot pressing at 120 °C (PPNFS-120) increases by 423%. PPNFS-120 has low interfacial impedance and high ionic conductivity (1.5 mS cm−1) and exhibits satisfactory thermal stability at 160 °C. In addition, the electrolyte uptake of PPNFS-120 (265%) is significantly enhanced due to the higher porosity (71.7%). More importantly, the PPNFS-120-based NCM811/graphite and LFP/graphite full cells exhibit excellent rate-performance and cycling stability. This work provides a new idea for the large-scale preparation of high-performance polyolefin nanofiber separators.