Pb₇Bi₃ Intermetallic Anode With Dynamic Self-Reinforcing Bifunctional Effect for Advanced Sodium-Ion Batteries

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 Pb₇Bi₃ intermetallic anode featuring a decoupled multi-step alloying mechanism for high-performance sodium storage. Upon initial sodiation, Pb₇Bi₃ 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 Na₃Bi with open crystal framework serves as rapid Na⁺ diffusion channel and ion-buffering matrix prior to the full sodiation of Pb into NaPb, Na₉Pb₄, and Na₁₅Pb₄. This sequential reaction homogenizes sodium insertion, alleviates internal mechanical stress, and drastically suppresses volumetric expansion. Benefiting from this unique structural evolution, the Pb₇Bi₃ 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 Pb₇Bi₃ 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.