http://www.pnas.org/content/early/2018/05/08/1803634115 Significance Lithium metal is considered as the ultimate choice of anode for high-energy batteries, but the existing Li metal electrodes are usually limited to shallow cycling conditions (1 mAh cm−2) and thus inefficient utilization (<1%). We achieve Li metal electrodes deeply and stably cyclable to capacities >10 mAh cm−2, enabled by slow release of LiNO3 into carbonate electrolyte and its subsequent decomposition to form a protective layer for reversible, dendrite-free, and highly dense Li metal deposition. Based on that, we demonstrate a Li-MoS3(in close-to-stoichiometric ratio) cell showing high areal and specific capacity and energy. Abstract Discovering new chemistry and materials to enable rechargeable batteries with higher capacity and energy density is of paramount importance. While Li metal is the ultimate choice of a battery anode, its low efficiency is still yet to be overcome. Many strategies have been developed to improve the reversibility and cycle life of Li metal electrodes. However, almost all of the results are limited to shallow cycling conditions (e.g., 1 mAh cm−2) and thus inefficient utilization (<1%). Here we achieve Li metal electrodes that can be deeply cycled at high capacities of 10 and 20 mAh cm−2 with average Coulombic efficiency >98% in a commercial LiPF6/carbonate electrolyte. The high performance is enabled by slow release of LiNO3 into the electrolyte and its subsequent decomposition to form a Li3N and lithium oxynitrides (LiNxOy)-containing protective layer which renders reversible, dendrite-free, and highly dense Li metal deposition. Using the developed Li metal electrodes, we construct a Li-MoS3 full cell with the anode and cathode materials in a close-to-stoichiometric amount ratio. In terms of both capacity and energy, normalized to either the electrode area or the total mass of the electrode materials, our cell significantly outperforms other laboratory-scale battery cells as well as the state-of-the-art Li ion batteries on the market. What do we think? Significant, or not?