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.