Structural Degradation of Cu Current Collector During Electrochemical Cycling of Sn-Based Lithium-Ion Batteries

It is an open question whether there exists structural degradation of current collectors, which likely can lead to the capacity loss of lithium-ion batteries. In this work, we investigate the cycling-induced structural degradation/damage of the Cu current collector used in Sn-based lithium half cells. Electrochemical cycling causes the formation of a layer of porous structure even after the first cycle and the formation of Li₂SnCu. The thickness of the porous structure increases with the increase of the cycle number, and local separation between the porous layer and the “solid” Cu layer occurs after prolonged cycling. The nominal contact moduli of the porous layers formed after one and five electrochemical cycles are slightly larger than the pristine Cu current collector. For the porous layers formed after twenty or more electrochemical cycles, the normal contact modulus is generally less than the pristine Cu. The indentation hardnesses of the porous structures are generally less than the pristine Cu except for the porous structure formed after five electrochemical cycles.