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Page 4 of 32 Yan et al. Energy Mater 2023;3:300002 https://dx.doi.org/10.20517/energymater.2022.60

-
Li - e ↔ Li (1)

As an electrode, Li has the most negative electrochemical potential (-3.040 V vs. a standard hydrogen
electrode) among all anodes, which endows LMBs with high discharge voltage and energy density.
Furthermore, Li metal anodes are able to provide an energy-dense Li-ion source, which enables the anode to
be compatible with extensive cathode materials, including non-lithiated cathodes, leading to the versatility
of battery design. For LMBs, the electrochemical deposition/dissolution of Li metal takes place on the
anodic side. Simultaneously, Li ions are consumed/accumulated at the cathodic side. According to the
+
paired cathode materials (e.g., intercalation cathode materials, O and S), LMBs can be divided into three
2
primary categories, namely, lithium-lithium intercalation compound, Li-O and Li-S batteries. The reaction
2
principle of LMBs during the charge/discharge processes is described as follows [9-11] :
Lithium-lithium intercalation compound batteries (taking Li MO as an example):
1-x
2
+
Anodic reaction: xLi = xLi + xe (3)
-
Cathodic reaction: Li MO + xLi + xe = LiMO (4)
+
-
2
2
1-x
Li-O battery:
2
+
-
Anodic reaction: 2Li = 2Li + 2e (5)
Cathodic reaction: 1∕2O + H O + 2e = 2OH (6)
-
-
2
2
+
-
Or 2Li + 2e + O = Li O (7)
2
2
2
Li-S battery:
Anodic reaction: 16Li = 16Li + 16e (8)
-
+
Cathodic reaction: S + 16Li + 16e = 8Li S (9)
+
-
8
2
Challenges facing Li metal anodes
Despite the tremendous potential of next-generation secondary battery applications, the Li anode still faces
a multitude of challenges to overcome: (i) electrolyte depletion due to the continuous reaction with Li metal
and mechanical instability of the SEI layer; (ii) dendrite formation deriving from initial uneven Li
nucleation and the subsequent selective deposition; and (iii) infinite relative volume change. These
shortcomings inevitably lead to unsatisfactory Coulombic efficiency (CE), short lifetimes and even safety
problems, such as thermal runaway and explosion hazards.