Thermodynamics-driven interfacial engineering of alloy-type anode materials

Alloy-type anodes can enable high specific capacity for Li-ion batteries, but the large volume change during cycling often causes fastcapacity fading. Here, we report a thermodynamically driven grain boundary engineering method to improve alloy-type anodes via the spontaneous formation of 2D interfacial phases (complexions). Notably, the 2.8 at% Bi-doped SnSb achieves improved cycling stability and rate capability, even though it is 99% dense and has a mean crystallite size 2.73 larger than the undoped SnSb reference sample. Cryogenic transmission electron microscopy reveals Bi segregation at grain boundaries. Thermodynamic modeling further suggests the stabilization of a nanoscale liquid-like interfacial phase. Synchrotron transmission X-ray microscopy shows the suppressed intergranular cracking upon cycling with Bi addition. It suggests that the liquid-like interfacial phase serves as a stress relief mechanism for the high volumetric expansion anode via improved grain boundary sliding and Coble creep, akin to room-temperature superplasticity observed in Sn-Bi.