Redox-active polypyrrole/bacterial cellulose bilayer separator for lithium-ion batteries

Separator is one of the important elements of lithium-ion batteries, which affects both the capacity and safety performance of the batteries. In this paper, polypyrrole (PPy) was grown on bacterial cellulose (BC) nanofibers using in situ polymerization. A bilayered composite separator with PPy-coated BC conductive upper layer and BC insulating lower layer was prepared by paper-making method. The redox-active PPy could contribute to a specific discharge capacity of 119 mAh g-1 at 2C current density for the battery with the bilayered separator, which is significantly superior to the device with the polyolefin separator (73 mAh g-1). Moreover, the redox layer provided a low overpotential in the Li//Li symmetric cell cycle, which played an important role for the cycle stability of the lithium-ion batteries.