Effective Stress Dissipation by Surface Engineering to Achieve Ultrafast and Ultra‐Stable Sodium‐Ion Batteries

ABSTRACT Stress accumulation is the primary cause of structural degradation and performance failure in FeSe 2 ‐based anodes. Therefore, suppressing stress accumulation during cycling is critical for achieving long‐term stability in FeSe 2 ‐based anodes for sodium‐ion batteries (SIBs). In this work, guided by (density functional theory) DFT calculations and Finite‐element simulations, a stress dissipation strategy and successfully implemented it by fabricating a Co 3 B 2 O 6 coating on the FeSe 2 surface is designed. Unlike conventional coating materials, Co 3 B 2 O 6 exhibits superior mechanical strength and stress‐buffering capability to maintain structural stability, effectively dissipating the stress from volume expansion during cycling. Therefore, the modified Co 3 B 2 O 6 @FeSe 2 exhibits a significantly reduced maximum Von Mises stress (72.66 MPa) compared to pristine FeSe 2 (116.83 MPa) at a high current density of 300 mA cm − 2 . In addition, the Co 3 B 2 O 6 coating facilitates fast reaction kinetics by providing multiple migration pathways through its topological structure. As a result, the Co 3 B 2 O 6 ‐3 wt.%@FeSe 2 (Co3@FeSe 2 ) exhibits a superior rate capacity of 578 mAh g − 1 at 20 A g − 1 . Moreover, the assembled NaNi 1/3 Fe 1/3 Mn 1/3 O 2 (NFM)//Co3@FeSe 2 full‐cell exhibits excellent cycling stability without noticeable capacity fading after 900 cycles. This work provides a useful insight into stress dissipation by surface modification for the design of high‐performance FeSe 2 ‐based anode materials for SIBs.