Li metal anode materials are the most promising anodes for next-generation high-energy-density Li batteries. The poor interfacial stability in the battery has been the primary issue hindering their practical application. In this talk, I will present progresses in my group in the development of Li protection techniques, particularly using a chemically and electrochemically active polymer materials along with electrolyte engineering. First, the polymer coated on the Li surface can generate the SEI by preferentially chemically occupying the Li surface site and subsequently electrochemically self-decomposing at the interface. The polymer-derived SEI presented desirable ionic conductivity, density, homogeneity, and mechanical strength. Second, by tuning the electrolyte composition, the electrochemical and mechanical properties of the polymeric SEI can be further regulated. A comprehensive characterization including electrochemical evaluation, XPS, SEM, TEM, and quantitative NMR to illustrate the role of each component in the polymeric SEI formation on Li metal anode. The understanding of decomposition product and polymeric SEI structures contributed from both the polymer coating and additives in electrolytes can help to design new high-performance Li protection for next-generation Li metal batteries.