Lithium nitrate has been widely used to improve the interfacial stability of Li metal anode in ether electrolyte. However, the low solubility limits its application in carbonate electrolytes for high-voltage Li metal batteries. Herein, nitrated polycaprolactone (PCL-ONO2 ), which is prepared via the acylation of polycaprolactone diol (PCL-diol) followed by the grafting of nitrate group, has been proposed as an electrolyte additive to introduce high-concentration NO3 - into carbonate electrolytes for the first time. The theoretical calculations and X-ray photoelectron spectroscopy depth profiling demonstrate that the PCL-ONO2 additive preferentially reacts with Li metal and in situ constructs a stable dual-layered solid electrolyte interphase film, presenting an inner nitride-rich layer and an outer flexible PCL-based layer on the surface of Li metal anode. As a result, the Li metal anode delivers an impressive long-term cycling performance over 1400h at an elevated area capacity of 10.0mAhcm-2 and an ultrahigh current density of 10.0mAcm-2 in the Li symmetrical cells. Moreover, the PCL-ONO2 additive enables the full cells constructed by coupling high-loading LiFePO4 (20.0mgcm-2 ) or LiNi0.5 Co0.2 Mn0.3 (16.5mgcm-2 ) cathode and thin Li metal anode (≈50µm) to demonstrate greatly improved cycling stability and rate capability.