A separator for a lithium secondary cell is provided. The separator has a separator substrate, selected from porous separators for liquid-electrolyte cells and solid-electrolyte separators having lithium ion conductivity, and has a layer of glassy carbon (GC), which is applied at least on one side of the separator substrate. A lithium secondary cell is also provided, which contains a negative electrode, a positive electrode, and a separator placed between the negative electrode and the positive electrode. The glassy carbon layer of the separator faces the negative electrode.