Highly N-doped and flexible carbon nanofiber membrane as cathode host for Li-Se batteries

Abstract

Se as an active material attracts tremendous attention because of its high volumetric capacity and better conductivity than S for rechargeable batteries. Herein, a carbon nanofiber membrane (PM-CNF) is designed and prepared as free-standing Se host by electrospinning the solution of polyacrylonitrile (PAN) and poly(styrenesulfonic acid)-melamine salt, followed by carbonization and activation process. PM-CNF shows super flexibility and high N-doping level of 8.92 % (pyrrolic-N: 2.15 % and pyridinic-N: 3.07 %), which is beneficial for ions diffusion and electrons transformation. The free-standing PM-CNF/Se cathode delivers a high reversible capacity of 570 mAh g−1 at 0.5 C, superior rate capacity of 375 mAh g−1 at 8 C, and stabile cycling over 1800 cycles. The excellent electrochemical performance can be ascribed to high Li-ion diffusion coefficient (2.99 × 10−9 cm2 s−1) and capacitance-contributed ratio (77.1 % at 0.1 mV s−1). The analysis of the charge/discharge process reveals that no polyselenide intermediates are observed during the first cycling process and thus the inhibited shuttle effect of polyselenides over cycling, which primarily contributes to the long cycling stability.