LITHIUM METAL SECONDARY BATTERY HAVING IMPROVED LIFE CHARACTERISTICS

A lithium metal secondary battery including a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and a protective layer interposed between the negative electrode and the separator. The protective layer includes an additive, wherein the additive comprises a mixture of hexagonal boron nitride (BN) flakes with an ionomer having a sulfur (S)-containing anionic group and fluorine (F).