Due to the extremely high energy density, lithium metal has become an important negative electrode material.However, the reaction of lithium metal with a liquid electrolyte results in the formation of a solid electrolyte membrane (SEI), which produces dendrites, resulting in a decrease of coulombic efficiency.Due to the lower solubility of LiF in the electrolyte and its high shear modulus, it is a candidate for SEI films to protect lithium metal anodes. However, creating a uniform layer of LiF film on the surface of lithium metal remains a huge challenge. Here, we used a simple method to synthesize a LiF film on the surface of the Li sheet. According to the principle that fluorinated graphite can react with Li to form a galvanic cell and produce a product LiF, we form a primary battery on the surface of metallic lithium to manufacture a LiF film.The modified lithium sheets were assembled into symmetrical batteries, and the batteries were subjected to constant current charge and discharge tests at different current densities. The results showed that they have better cycle performance. The LiF-modified lithium electrode was cycled for 400 cycles at a high current density of 3 mA cm^-2. And in the cycle, the formation of lithium dendrites is reduced to stabilize the lithium metal anode. Therefore, this simple method brings great prospects for the safety of lithium metal batteries and the construction of high-energy lithium metal batteries.