Electrospun-nanofibrous Redox-active separator for enhancing the capacity of Lithium-ion batteries

Separator is a key component of lithium-ion battery (LIB), and a redox-active separator can enhance the capacity of LIB by participating in battery reactions. This paper reports a redox-active separator based on Fe(CN)6 4- doped polypyrrole (PPy) composite nanofibers fabricated by electrospinning and in-situ polymerization. The separator is composed of one layer of Polyacrylonitrile (PAN)@doped-PPy core–shell structured nanofibers and another layer of PAN nanofibers. The porosity, electrolyte uptake, and ionic conductivity of the optimized redox-active separator are 79.3 ± 7.1%, 294.6 ± 31.5%, and 1.57 ± 0.06 mS∙cm−1, respectively. These values are greater than those of a commercial PP separator, 41%, 81.5 ± 17.4%, and 0.75 ± 0.02 mS∙cm−1, respectively. Accordingly, the discharge capacity of the battery cell with the redox-active separator is up to 158.7–227.0 mAh∙g−1 at the current rates of 2.0–0.2C, outperforming conventional inert separators. The enhanced battery capacity is stemmed from the redox activity of the doped-PPy polymer, as evidenced by the wider cathodic and anodic peaks in the cyclic voltammetry. In addition, the battery cells tested with redox-active separators show gravimetric energy densities of up to 103.0 mAh∙g−1, which is 56.1% and 27.2% greater than those of a commercial PP separator and the redox-active separator reported in the literature.