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.