Failure Mechanisms of Metallic Lithium Anodes

Before introducing the practical applications of lithium alloy in present metal lithium batteries, it is necessary to understand the failure mechanisms of lithium anode. Actually, during the past 10 years, deep and fundamental understanding on the failure mechanisms of the Li metal anode has been extensively discussed. No matter in LIBs, Li-S, Li-O2 or solid-state electrolyte Li-metal batteries, generally, these issues will cause the failure of Li anode[29-31]:
i) Uncontrolled interfacial reactions: the uncontrolled interfacial reaction also called the side reactions that happen on the Li-metal surface with the organic electrolytes. As the high reactivity of Li-metal in the organic electrolyte, it easily appears corrosive reactions to deplete the electrolytes and generate thick SEI layers, which will lead to increasing resistance and low Coulombic efficiency[29].
ii) Uncontrollable Li dendrite growth: the Li dendrites could penetrate through the separator and cause cell short circuit, resulting in a series of safety concerns[32]. Meanwhile, the dendritic Li could also produce so-called “dead Li” via electrical detachment of Li from the current collector; significantly affect the cycle life of the Li-metal battery[32]. And now it is widely accepted that unstable and inhomogeneous SEI films, inhomogeneous electric fields, and inordinate lithium-ion flux are the origination of the dendrite growth[2, 18].
iii) Infinite relative volume changes: as the “hostless” nature of Li, during repeated stripping/plating process, the relative volume change of Li anode is virtually infinite, which will initiate cracks on the SEI, leading high structural instability for the Li anode[2]. As the specific example illustrated in the previous report[2, 33], a single-sided commercial electrode needs to reach an areal capacity of 3 mA·h·cm–2, indicating a huge change in thickness of ~14.6 μm for Li. In terms of future applications, this value could be even higher, really a formidable challenge on the SEI stability.