Lithium-ion battery separators based-on nanolayer co-extrusion prepared polypropylene nanobelts reinforced cellulose

Low-dimensional nanomaterial separators are considered prime candidates for next-generation lithium-ion battery separators due to their higher porosity and thinner thickness. For polyolefin materials, there is no suitable solvent for solution electrospinning, the low yield of melt electrospinning, and the large size of melt-blown fibers make it challenging to efficiently prepare polyolefin low-dimensional nanomaterials. Moreover, polyolefin ma-terials have been criticized for poor electrolyte wettability and insufficient thermal stability. Herein, poly-propylene (PP) nanobelts (NBs) are prepared via a high-efficient nanolayer co-extrusion technique as supporting skeleton to suppress the shrinkage of natural cellulose separators during dehydration effectively, and the cel-lulose fibers have optimized pore size to prevent internal short circuits. The results indicate that the as-prepared PPNBs/cellulose composite separator (PPNBs/CS) with sandwich structure has superior porosity (78.4%) and ionic conductivity (1.04 mS cm-1). Meanwhile, the thermal stability, electrolyte uptake, and tensile strength are all significantly improved due to the synergies between PPNBs and cellulose fibers. More importantly, the LiFePO4||PPNBs/CSs||LM half cells exhibit better rate-performance and cycling durability than Celgard (R) 2400. Similarly, the NCM811||LM half cells and NCM811||graphite full cells assembled from PPNBs/CS-1/2 also exhibit good electrochemical performance. This work opens a new approach for easy batch preparation of high-performance lithium-ion battery separators.

Automated summary

Polypropylene nanobelts (PPNBs) are prepared using a high-efficient nanolayer co-extrusion technique as supporting skeleton, which effectively suppresses the shrinkage of natural cellulose separators during dehydration. The cellulose fibers have optimized pore size to prevent internal short circuits. The PPNBs/cellulose composite separator (PPNBs/CS) exhibits superior porosity, ionic conductivity, thermal stability, electrolyte uptake, and tensile strength due to the synergies between PPNBs and cellulose fibers. The PPNBs/CS separator also shows better rate-performance and cycling durability in lithium-ion battery half cells.