Synergistic Enhancement of Pyridinic N-B and Nano-Sandwich Structure on the High Energy Density and Long Cycle Life of Symmetrical Carbon-Based Lithium-Ion Capacitors

Abstract

Carbon-based Lithium-ion capacitors (LICs) are considered as promising energy storages devices with high energy density and power density. However, the mismatch of charge-storage capacity and electrode kinetics between cathode and anode electrodes remains a challenge. In this research, we propose a “Self-assembly-Template” method to prepare B, N co-doped porous carbon (BN-C) with nano-sandwich structure and abundant pyridinic N-B species. The nano-sandwich structure can increase powder density and cycle stability by constructing stable solid electrolyte interphase film, shortening Li+ diffusion pathway and accommodating volume expansion during repeated charging/discharging. The abundant pyridinic N-B species can simultaneously promote the adsorption/desorption of Li+/PF6- and reduce diffusion barrier. The BN-C used as the anode/cathode material promotes the matching of charge-storage capacity and results into high capacity. Owing to the synergistic effect of nano-sandwich structure and pyridinic N-B species, the assembled symmetrical BN-C//BN-C LICs exhibit high energy density of 234.7 W h kg−1, high power density of 39.38 kW kg−1, and excellent cycling stability (91% capacitance retention after 10000 cycles), superior to most of the reported carbon-based LICs. As Density functional theory simulation demonstrated, the pyridinic N-B shows the enhanced adsorption activity for Li+ and PF6-, which is beneficial to increase the capacity of anode and cathode, respectively. Meanwhile, the relatively lower diffusion barrier of pyridinic N-B promote the Li+ migration resulting into good rate performance. Therefore, this work provides a new approach for the synergistic modulation of nano-structure and active site simultaneously to fabricate the cathode/anode dual-appliable electrode material in the LICs application.

Keywords: sandwich structure carbon nanosheet, pyridinic N-B species, high energy density, high cycling stability, Li-ion capacitors