Amorphous Modulation of Atomic Nb‐O/N Clusters with Asymmetric Coordination in Carbon Shells for Advanced Sodium‐Ion Hybrid Capacitors

Abstract

Anode materials with excellent properties have become the key to develop sodium‐ion hybrid capacitors (SIHCs) that combine the advantages of both batteries and capacitors. Amorphous modulation is an effective strategy to realize high energy/power density in SIHCs. Herein, atomically amorphous Nb‐O/N clusters with asymmetric coordination are in situ created in N‐doped hollow carbon shells (Nb‐O/N@C). The amorphous clusters with asymmetric Nb‐O3/N1 configurations have abundant charge density and low diffusion energy barriers, which effectively modulate the charge transport paths and improve the reaction kinetics. The clusters are also enriched with unsaturated vacancy defects and isotropic ion‐transport channels, and their atomic disordering exhibits high structural stress buffering, which are strong impetuses for realizing bulk‐phase‐indifferent ion storage and enhancing the storage properties of the composite. Based on these features, Nb‐O/N@C achieves notably improved sodium‐ion storage properties (reversible capacity of 240.1 mAh g−1 at 10.0 A g−1 after 8000 cycles), and has great potential for SIHCs (230 Wh Kg−1 at 4001.5 W Kg−1). This study sheds new light on developing high‐performance electrodes for sodium‐ion batteries and SIHCs by designing amorphous clusters and asymmetric coordination.

Pyridine N‐Modulated Adsorption Equilibrium of Highly Dispersed Atomic W‐P Clusters toward Advanced Potassium‐Ion Hybrid Capacitors

“…The additional peak at 33.7 eV may belong to the W─N bonds, indicating that the W atoms of W-N/P@C have been successfully N-coordinated. [35] In addition to the characteristic peaks of oxidized N, graphitized N, pyrrole N and pyridine N, [13,36] the W─N bonds at 397.8 eV in the N 1s spectra of W-N/P@C (Figure 2e) also confirm the W-N coordi-nation. In comparison (W-O/P@C), the remarkably enhanced pyridine N in W-N/P@C indicates that the composite after nitriding has high edge-dangling bonds and creates additional W-N coordination with W-P clusters.…”

“…In addition, W-N/P@C exhibits a strong electron paramagnetic resonance (EPR) signal compared to W-O/P@C (Figure 2b), meaning that the pyridine N-modulated clusters acquire abundant unsaturated vacancy defects and edge-dangling bonds, which help to provide additional storage sites and improve the charge transfer efficiency. [13,30] Figure 2c displays the thermogravimetric (TG) analyses of the composites in air. The mass loss after 300 °C can be ascribed to the oxidation of the W-N/P clusters to WO 3 as well as the pyrolysis of N-C.…”

“…[9,10] Atomically disordered clusters rich in vacancy defects and edge-dangling bonds have isotropic charge transport paths, which can create additional storage sites for efficient and fast ion storage, as well as intrinsically improve atomic utilization and decipher structure-activity relationships in amorphous clusters, These are important for improving the ion storage and kinetic behaviors of electrodes. [11][12][13] In addition, in situ encapsulation of heteroatom-doped carbon materials provides stable structural support for atomic clusters, thereby facilitating ion storage and electron transfer and improving cycling stability. [14,15] Coordination modulation of metal atoms can further improve the K + storage properties of amorphous clusters.…”