The invention discloses an electrolyte and a negative electrode structure. An example electrolyte includes a solvent, a lithium salt, and an additive selected from the group consisting of a mercaptosilane, a mercaptosiloxane, and combinations thereof. The electrolyte may be used in a method for making a solid electrolyte interface (SEI) layer on a surface of an electrode. A negative electrode structure may be formed from the method.