Size-dependent stress retardation effect on the activation behavior of high-capacity lithium-ion anodes

Activation is commonly observed in high-capacity lithium-ion anodes that undergo conversion and/or alloying reactions, compromising structural integrity and delaying full capacity utilization in battery systems. However, the origin of this process and its underlying mechanism remain elusive. In this work, we choose the alloying-type Sn-based material as a research model to systematically investigate the activation process. We discover that electrodes with different particle sizes exhibit markedly different cycling behaviors, with large particles (~500 nm) showing pronounced activation, while small ones (65 nm) display little to no activation. By tracking signature elements over different cycling stages, we show that lithiation in small-particle electrodes is rapidly facilitated by fast electrolyte transport, whereas large-particle electrodes require more time to fully access the electrolyte. Finite-element simulations and electrochemical kinetic analyses further reveal that this size-dependent kinetic behavior originates from stress-induced retardation associated with a “core-shell” lithiation mode, giving rise to the observed size-dependent activation. These results clarify the origin of activation mechanism for high-capacity materials, providing possibilities to control the activation process and enabling rational design of these materials for battery applications.