Artificial protective coatings for lithium metal anode to improve its stability

The use of lithium metal as an anode in lithium-metal batteries is desired due to its high capacity and highly negative potential but is still not achieved due to the high activity and consequent chemical and electrochemical instability of this metal. On contact with the electrolyte, a film (SEI) is formed on the lithium surface consisting of the electrolyte decomposition products. Typically, this film has a heterogeneous structure, making it unstable and it cracks during cycling, which leads to lithium local deposition in the form of outgrowths – dendrites. A short circuit can occur when the dendrites grow to the cathode, followed by a possible battery fire. To solve this problem, it was proposed to coat lithium anodes with artificial SEI with the desired properties: homogeneous structure, high ionic and low electronic conductivity, and mechanical and chemical stability. The main methods for applying such coatings are dipping, dripping, doctor blade smearing, chemical or electrochemical reaction with lithium, and techniques such as magnetron sputtering, atomic and molecular layer deposition, and plasma activation. In this review examples of artificial protective coatings of different nature on lithium, their structure and functional features are considered. The reasons for their enhancement of lithium-metal anode operation stability and the characteristics obtained as a result of anode protection by these films are also indicated. At comparison of various approaches to creation of artificial SEI the methodological problem on an estimation of their efficiency is revealed and the decision variant is offered.