Thickness-dependent fracture of amorphous carbon coating on SnO2 nanowire electrodes

Carbon-coated SnO2 nanowires (NWs) were fabricated and applied as electrode to study the lithiation process using in situ transmission electron microscopy. A critical coating thickness (∼9 nm) was found, above which the carbon coating is able to constrain the lithiation-induced expansion of SnO2 core without failure. Theoretical modeling and numerical simulation were performed and revealed that such thickness-dependent fracture can be attributed to the thickness-dependent maximum stress developed in the carbon coating during the lithiation of SnO2 core. Our work provides direct evidence of the mechanical robustness of thick carbon coating and offers a minimum thickness of carbon coating for constraining the deformation of anode materials with large lithiation-induced volume change.