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

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 W 2 N 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.