Pb 7 Bi 3 Intermetallic Anode With Dynamic Self‐Reinforcing Bifunctional Effect for Advanced Sodium‐Ion Batteries

ABSTRACT Alloy‐type metal anodes are promising candidates for sodium‐ion batteries (SIBs) due to their favorable sodiation potentials and high theoretical capacities. However, substantial volume expansion during cycling severely hinders their practical application. Herein, we synthesized a structurally integrated Pb 7 Bi 3 intermetallic anode featuring a decoupled multi‐step alloying mechanism for high‐performance sodium storage. Upon initial sodiation, Pb 7 Bi 3 undergoes structural adjustment to generate metallic Pb and NaBi, which constructs continuous conductive networks to facilitate fast electron transport and maintain integral electrode architecture. Subsequent sodiation of Na 3 Bi with open crystal framework serves as rapid Na + diffusion channel and ion‐buffering matrix prior to the full sodiation of Pb into NaPb, Na 9 Pb 4 , and Na 15 Pb 4 . This sequential reaction homogenizes sodium insertion, alleviates internal mechanical stress, and drastically suppresses volumetric expansion. Benefiting from this unique structural evolution, the Pb 7 Bi 3 electrode delivers an initial discharge/charge capacity of 459.7/441.2 mAh g −1 at 0.05 A g −1 and remains 268.3 mAh g −1 after 4500 cycles at 0.5 A g −1 with a nearly 81% capacity retention. This work identifies the dynamic self‐reinforcing bifunctional effect of Pb 7 Bi 3 that synchronously boosts charge transport and structural stability, delivering outstanding rate and cycling performance and guiding the design of durable alloy anodes for practical SIBs.