Ultrafast Na Transport into Crystalline Sn via Dislocation-Pipe Diffusion for Rapid Battery Charging

Abstract

The charging process of secondary batteries is always associated with a large volume expansion (>300%) of the alloying anodes, and in many cases, high compressive residual stresses develop near the propagating interface. This phenomenon causes a significant reduction in the rate performance of the anodes and is detrimental to the development of fast-charging batteries. However, for the Na-Sn battery system, the residual stresses that develop near the interface are not stored, but are relieved by the generation of high-density dislocations in crystalline Sn. The results of direct-contact diffusion experiments show that these dislocations facilitate the preferential transport of Na and accelerate the diffusion of these ions into crystalline Sn at ultrafast rates via “dislocation-pipe diffusion”. Advanced analyses were performed to observe the evolution of atomic-scale structures while measuring the distribution and magnitude of residual stresses near the interface. In addition, multi-scale simulations that combined classical molecular dynamics and first-principles calculations were also performed to explain the structural origins of the ultrafast diffusion rates observed in the Na-Sn system. Our findings not only address the knowledge gaps regarding the relationship between pipe diffusion and the diffusivity of carrier ions but also provide guidelines for the appropriate selection of anode materials for use in fast-charging batteries.