Nitrogen-Rich W-N Clusters with Atomic Disorders and Non-Grain Boundaries Confined in Carbon Nanosheets Boosting Sodium-Ion Storage

Abstract

Sodium-ion batteries (SIBs) as economic candidates have received considerable attention for large-scale energy storage applications. However, crystalline metal compounds with specific transport routes and rigid structures restrict their practical applications. Herein, the atomically dispersed N-rich amorphous W-N clusters confined in the carbon nanosheets (W-N/CNSs) are reported. Through advanced tests and calculations, the structural advantages, reaction mechanisms, and kinetic behaviors of the clusters are systematically analyzed. Compared with the crystalline W2N with low theoretical capacity (only 209.3 mAh g−1), the amorphous W-N clusters have the advantages of atomic disorders and non-grain boundaries and can afford abundant active sites (unsaturated dangling bonds) and isotropic charge transfer channels, which can be further enhanced by the N-rich characteristics and high electronegativity of the clusters. The encapsulation of CNSs has high conductivity and structural stability, which promotes electron transfer and effectively buffers volume expansions. As a SIB anode, the reversible capacity of W-N/CNSs reaches 421.2 mAh g−1 at 0.1 A g−1. Even at 20 A g−1, the reversible capacity of 170.7 mAh g−1 is maintained after 8000 cycles. This study focuses on the advantages of amorphous nitrides, which have important guiding significance for the design of atomic clusters for high-performance metal ion batteries.