Page 69 - Read Online

Page 2 of 32 Yan et al. Energy Mater 2023;3:300002 https://dx.doi.org/10.20517/energymater.2022.60

comprehensively summarized and categorized to generate an overview of the respective superiorities and
limitations of the various strategies. Furthermore, this review concludes the remaining obstacles and potential
research directions for inspiring the innovation of Li metal anodes and endeavors to accomplish the practical
application of next-generation Li-based batteries.

Keywords: Next-generation batteries, Li metal anodes, high energy density, advanced protection strategy, practical
application

INTRODUCTION
Possessing a number of desirable features, including high round-trip efficiency, long cycling life, flexible
power and energy characteristics to meet different grid functions, pollution-free operation and low
maintenance, state-of-the-art commercial lithium-ion batteries (LIBs) based on the rocking chair concept
have produced spectacular advances in transportation and communication diversification since their
introduction in the early 1990s . Unfortunately, this type of electrical energy storage device cannot keep
[1,2]
[3]
pace with the progress in the cutting-edge electronics industry . By its nature, the working principle of LIBs
+
is based on the intercalation of Li ions into layered electrode materials, such as graphite anodes and Li
metal oxide cathodes, leading to the fact that Li ions can only be intercalated topotactically into certain
+
specific sites. The drawback of capacity limitation (372 mAh g ) for the aforementioned conventional
-1
anodes can no longer meet the rapidly growing demands for power and energy density (the theoretical
-1
-1
energy density of LIBs is typically limited to 420 Wh kg or 1400 Wh L ), which stimulates the pursuit of
alternative anodes with high energy density . With an extremely high theoretical specific capacity
[4]
(3860 mAh g ) and the most negative electrochemical potential (-3.040 V vs. a standard hydrogen
-1
[3]
electrode), Li metal is strongly deemed as the ultimate anode for secondary batteries [Figure 1A and B] .
Different from intercalation chemistry, Li metal batteries (LMBs), such as lithium-oxygen (Li-O ) and
2
lithium-sulfur (Li-S) batteries, operate based on metal plating and stripping at the Li anode side and
conversion reactions at the cathode side. The non-topotactic nature of these reactions endows Li-O 2
-1
batteries (3505 Wh Kg ) and Li-S batteries (2600 Wh Kg ) with high theoretical energy density, thereby
-1
making them become the optimal choices for next-generation secondary batteries.
In fact, Li metal anodes were employed in the infancy of Li battery research, including the assembly of
primary Li cells in digital watches, calculators and implantable medical devices by Whittingham at Exxon in
[5,6]
the 1970s . Nevertheless, these non-rechargeable primary batteries led to serious waste, high costs and
environmental pollution. In the 1980s, the first generation of commercially rechargeable LMBs, assembled
with an excess amount of Li, was proposed by Moli Energy . However, due to the intrinsic chemical and
[7]
electrochemical activity of Li, the use of Li metal anodes triggers a series of notorious dilemmas during the
charge/discharge processes, including dendrite formation and growth, Li corrosion, the formation of dead
Li, unstable solid electrolyte interfaces (SEI) and volume expansion, yielding fatal short circuits, severe
lifespan attenuation and capacity loss in LMBs. Safety concerns, including inflammation and even
explosion, resulting from the short circuit of batteries, render the recall of all the cells, ultimately making
LMBs noncompetitive in the commercial market. In subsequent years, the progress regarding Li metal
anodes has been limited. In particular, with the first LIBs commercialized by Sony Corporation in the 1990s,
the commercialization of Li metal anodes was almost completely halted. Nowadays, the energy density
limitation of traditional LIBs based on graphite anodes has brought about a gradual revival of LMBs and
there has been a recent global blooming in terms of the number of publications [Figure 1C] and citations
[Figure 1D] in designing batteries where Li metal is used as the anode. Based on data from the Web of
Science, more than 500 publications dealing with the above challenges have been published from 2014 to
2016. Remarkably, an average of 15 articles have come out per month since 2016, indicating a roaring
expansion in this field.