Amorphous shear band formation in crystalline Si-anodes governs lithiation and capacity fading in Li-ion batteries

The cycling stability of Li-ion batteries is commonly attributed to the formation of the solid electrolyte interphase (SEI) layer, which is generated on the active material surface during electrochemical reactions in battery operation. Silicon experiences large volume changes upon the Li-insertion and extraction, leading to the amorphization of the silicon-interface due to the permeation of the Li-ions into the silicon. Here, we discover how generated non-hydrostatic strain upon electrochemical cycling further triggers dislocation and eventually shear band formation within the crystalline silicon core. The latter boosts the non-uniform lithiation at the silicon interface affecting the SEI reformation process and ultimately the capacity. Our findings are based on a comprehensive multiscale structural and chemical experimental characterization, complemented by molecular dynamics modelling. This approach highlights the importance of considering electrochemical, microstructural and mechanical mechanisms, offering a strategy for developing improved anode materials with enhanced cycling stability and reduced capacity loss. Silicon undergoes large volume changes during lithium insertion and extraction, affecting the internal lithium-ion battery structure. Here, the mechanisms of how non-hydrostatic strain upon electrochemical cycling affects the crystalline silicon core was investigated.