US Patent 8980474 Lithium secondary battery

A lithium secondary battery includes a positive electrode, a negative electrode, and an electrolyte. The negative electrode includes a current collector, an active material layer on the current collector and including an amorphous silicon oxide represented by SiOx (0.95<x<1.7), and an SEI layer on the active material layer and including about 70 area % or more of protrusion parts having a size of about 5 nm to 300 nm during charging of the battery.