Failure mechanism of lithium metal anode under practical conditions

Abstract

Lithium (Li) metal is regarded as one of the most promising anodes in the next-generation high-energy-density rechargeable batteries due to its ultrahigh theoretical specific capacity and low reduction potential. Nevertheless, the unstable solid electrolyte interphase on the surface of Li metal anode and the nonuniform Li deposition seriously hinder its practical applications. Currently, mild conditions are employed in the researches of Li metal anode, which is of great significance for fundamentally understanding the physicochemical features of the anode interface and the mechanisms of Li deposition. However, practical conditions including ultrathin Li metal anode (< 50 μm), low negative/positive electrode areal capacity ratio (< 3.0), and lean electrolyte (< 3.0 g·Ah<sup>–1</sup>) are the premise to realize high energy density of Li metal batteries (> 350 W·h·kg<sup>–1</sup>). Herein, the gaps of Li metal anode under mild and practical conditions in terms of the cycling stability and surface morphology are compared and the reasons for the gaps are analyzed carefully. The total quantity of active Li metal decreases and the utilization depth of Li per cycle has been greatly improved under practical conditions. Therefore, the huge volume fluctuation and uneven Li deposition result in ceaseless destruction and regeneration of solid electrolyte interphase, and thus consuming the lean electrolyte and generating a large quantity of dead Li rapidly. Consequently, the polarization voltage of Li metal anode increases rapidly and the cycling stability of Li metal batteries deteriorates evidently under practical conditions. Moreover, the electrochemical reaction of Li metal anode is accelerated while fast charge/discharge process is employed, which further aggravates the stability of Li metal anode. This work reveals the challenges of Li metal anode under practical conditions and present the perspectives for the further researches in practical Li metal anode, which conduces to the solid development of high-energy-density Li metal batteries.