Plasma-promoted surface regulation of a novel integrative carbon network for boosting the long-cycle capability of sodium-ion storage

Abstract

In the process of Na+-storage in hard carbon materials, the sluggish (de)sodiation kinetics and irreversible reactions of surface groups with electrolytes are bottlenecks that limit the rate performance and long-term cycle stability. We successfully prepared a novel integrative carbon network material (ICN) on a large scale, and the carbon structure and surface oxygen groups were regulated to increase the rate and cycle capability using a plasma-assisted catalyst-free carbonization process. ICNs typically have ultrathin carbon nanofiber units (∼10 nm) interconnected by sp2 hybrid covalent bonds, which form an interface-free integrative conductive network and ultra-short ion/electron transport pathways. The order degree of surface carbon stacking, interlayer spacing, and the content of –CO groups can be regulated by surface plasma treating to further boost kinetics and enhance reversible reactions. Thus, the ICN exhibits all-round improvements in terms of a large reversible capacity (389.5 mAh g−1 after 100 cycles at 50 mA g−1), a superior rate capability (285 mAh g−1 at 2000 mA g−1 after 3000 cycles), and good cycling stability (retain 72.2% after 10,000 cycles at 2000 mA g−1). According to the analysis of the dynamics, the capacitive mechanism by which Na+ quickly inserts/adsorbs with the surface/subsurface atoms is primarily responsible for the excellent electrochemical performance. A full cell made up of an ICN anode and a Na3V2(PO4)3 cathode successfully lit the diode, demonstrating the ultra-high rate capability of ICN in practical application. It has a reversible capacity of 101.9 mAh g−1 at 1000 mA g−1 and maintains 76% after 2000 cycles, demonstrating the ultra-high rate capability of ICN in practical application. These results suggest a new perspective on the structure design of carbon-based materials for fast and long-life sodium-storage anodes.