AbstractThe performance of the lithium (Li) metal anode in rechargeable batteries has been hampered by the formation of unstable solid‐electrolyte interphase layers, which compromise cycle life and pose significant safety concerns. Herein, for the first time, the anodizing oxidation of pure Li in a liquid electrolyte is developed by using tetrahydrofuran with LiNO3. With this novel process, thickness‐controllable Li oxide films with in situ nitrogen doping during the anodizing process can be obtained. The resulting nitrogen‐doped Li oxide film (NLO) exhibits a uniform surface of the Li metal anode, effectively suppressing Li dendrite growth and simultaneously improving Li ionic conductivity. In addition, the Li metal full cells with Li/NLO anodes perform a long stable life of 1100 cycles at 5C. More importantly, this work demonstrates the great potential of NLO films as a solid‐state electrolyte in solid‐state Li metal batteries. The symmetric Li cells with NLO films perform excellent cycling stability for 300 h at 2 mA cm−2 current density and high Li+ ion conductivity of ≈3 ×10−4 S cm−1 at room temperature. This research not only provides a novel Li anodizing process and a stable Li metal anode but also opens up new possibilities for new solid‐state Li metal battery technologies.