Design of inorganic/organic bi-layered Li protection layer enabled dendrite-free practical Li metal battery

In this work, we report an inorganic/organic bi-layered, composed LiF, Li3N, Li2S, and porous polymer layer (LiFNS-PPL), Li protection layer for practical Li metal application toward high energy density Li metal batteries. The LiFNS-PPL layer, formed by a facile and scalable roll-pressing between Li metal and LiTFSI and PTFE complex film, is composed of an inside (lithium side) robust inorganic layer with 200 nm thick and outside (electrolyte side) porous polymer layer with over 20 μm thick. The robust inorganic layer prohibits dendritic Li growth. The flexible and porous polymer layer retains the protection layer structure with high Li-ion flux. This novel LiFNS-PPL protection layer enables in-plane Li growth underneath the protection layer without Li dendrites, resulting in high electrochemical performance. Even in the carbonate-based electrolyte and high areal capacity, cycle retention showed over 600 h under 1 mA∙cm−2 with 5 mAh∙cm−2 condition in the Li||Li symmetric cell. Full cells paired with high-nickel contented nickel manganese oxide (NCM811) are prepared with a high areal capacity of 5 mA h·cm−2 NCM cathode and a limited Li reservoir of 4.1 mA h·cm−2 (20 μm-thick) with 0.8 N/P ratios. The Li||NCM full cell with the protection layer presents stable cycle performance over 200 cycles with the Li anode efficiency of 99.6% calculated by average Coulombic efficiency. Our facile and scalable process for introducing multi-functional Li protection layer delivers good insight into the practical implementation of high energy density Li metal batteries.