Interface Controls Large-Volume Change Anodes Pulverization

Micron sized alloys have been considered as the most attractive candidates for advanced lithium or sodium ion battery anodes due to their high capacity, cost effectiveness, and ease of mass production. However, their large volume variation during (de)alloying reaction with Li or Na ions causes severe mechanical degradation of anode materials, resulting in particle pulverization and loss of electrical interparticle contact. In addition, this substantial volumetric fluctuation leads to newly exposed anode surface to electrolyte and instability of solid-electrolyte interphase (SEI), which can bring about continuously formation of SEI layers. To mitigate the large volume change issues of micron sized alloys, various approaches have been studied such as introducing various electrolytes and additives for stabilizing the SEI layers. However, these modified SEI layers are still not enough to suppress the large volume fluctuation of micron sized alloys. Here, we demonstrate that the effect of interface between electrolyte and anode surface on anode pulverization. With micron sized alloying anodes for sodium-ion batteries (Bi and Sn), we observed substantially different pulverization behavior as a choice of electrolyte solvents leading to different anode-electrolyte interface. This different interface reactivity between solvents has a big impact on not only pulverization behavior of alloying anodes but also formation and growth of SEI layers on the surface of anode. Thus, the electrochemical performances of the alloying anodes also can be influenced by its interface characteristics. We thoroughly analyzed the effect of interface of alloying anode from electrode-level to nanoscale by various characterization tools such as Scanning electron microscopy (SEM), X-ray computed tomography (X-ray CT), X-ray photoelectron spectroscopy (XPS), Atom probe tomography (APT), and cryo-transmission electron microscopy (TEM). Moreover, we clarified the mechanism of the interface reaction and pulverization pathway by theoretical simulations. We believe this study can help researchers to understand the degradation behavior of large volume change alloy anodes.