Functional carbon materials processed by NH3 plasma for advanced full-carbon sodium-ion capacitors

High-performance sodium-ion capacitors (SICs) are regarded as new-generation electrochemical energy-storage systems that are critically restricted due to the kinetic and capacity mismatch between the capacitor-type cathode and battery-type anode derived from the low capacity of carbon cathodes and the weak charge transfer kinetics of the anodes. In this study, for the first time, we investigate the pseudocapacitive storage mechanism of both ClO4- and Na ions in carbon cathode/anode with a novel NH3 plasma strategy at room temperature. Interestingly, the implementation of pseudocapacitance greatly enhances the capacity in cathodes and the kinetics in anodes, effectively reducing the mismatch between two electrodes. With the ingenious NH3 plasma strategy, which breaks the barriers of conventional methods of synthesizing N-functional carbon materials, various types and substances of N/O pseudocapacitive sites can be controlled directionally and accurately. The time-sensitive NH3 plasma treatment utilized in this work has been demonstrated to be a state-of-art method for producing high content of pyridinic-N/C=O bond and introducing ultrafast pseudocapacitance on the surface of the samples. Impressively, in-situ/ex-situ characterizations demonstrate the highly reversible evolution of Pyridinic-N and C=O during the charging/discharging processes in cathodes/anodes, which is well consistent with electrochemical results and DFT calculations, presenting the "adsorption-pseudocapacitive reactions" and "adsorption-pseudocapacitive reactions-intercalation" mechanisms for cathodes and anodes respectively. Furthermore, the SICs deliver an energy density of 107 W h kg(-1) at a power density of 200 W kg(-1). The current results are expected to be a powerful tool and an exciting opportunity to accelerate the practical application of SICs and achieve high-performance cathodes and anode materials.