Real-Time Observation of Mechanical Evolution of Micro-Sized Si Anodes by In Situ Atomic Force Microscopy

Pulverization of Si particles and the subsequent loss of electrical contact is a well-known degradation mechanism in most Si-based anodes, but the underlying electrochemical–mechanical coupling behavior in actual battery cells is still poorly understood. In this work, we employed in situ atomic force microscopy (AFM) to characterize the morphological evolution of microsized Si (μSi) anode during electrochemical cycling in real time. As a result, we successfully visualized important mechanical evolution on the cross-section of μSi anode such as initial pulverization, onset of particle crack formation and its patterns, irreversible volumetric changes, fresh solid electrolyte interface (SEI) formation at cracked surfaces, and particle isolations. In addition, we revealed via in situ AFM that limiting the upper cutoff voltage (e.g., <0.7 VvsLi) can suppress the mechanical failure of a μSi anode and subsequently improve capacity retention with a reduced cell impedance. These results demonstrated the potential of the proposed in situ AFM as a powerful technique that can identify electrochemical–mechanical behaviors of various energy-storage materials at the "real-world" electrode level.