INTRODUCTION
Lithium metal is a promising anode candidate for developing
high-energy-density Li-based batteries due to its ultrahigh specific
capacity (3860 mA h g-1) and low redox potential
(-3.040 V versus the standard hydrogen electrode).[1-3] Unfortunately, uncontrollable lithium
dendrite growth during the electrochemical process and the unstable
electrode/electrolyte interface result in poor cycle life, low Coulombic
efficiency (CE), and even explosion. [4-6]
Among various strategies attempted to tackle the aforementioned
problems, [7-12] constructing a three-dimensional
(3D) current collector is an efficient method to mitigate dendrite
growth as the 3D configuration with a high specific surface area and the
porous structure can reduce the local current density and accommodate
the volume change upon repeated stripping/plating.[13,14] A number of successful demonstrations of
uniform Li deposition by adopting the 3D strategy can be found in the
literature, such as porous metal-based foams and 3D carbon-based
frameworks.[15-18] However, the high specific
surface area of a 3D host is double-bladed, as it also leads to an
increased interfacial reaction between the Li metal and electrolyte,
making the already unstable interface (between Li and existing
electrolytes) worse, and serving as a major contributor to the low
Coulombic efficiency commonly associated with the 3D configuration.[19,20] To improve the CE, constructing artificial
solid-electrolyte interphase (SEI) to reduce the irreversible reaction
between electrolyte and lithium metal is a commonly adopted method.[21,22] To date, most of the artificial SEI layers
are constructed either on lithium metal or planar current collectors,[23-25] although interfacial stability is a
particularly critical issue in the 3D configuration and building an
efficient artificial SEI layer on the 3D host may represent a most
promising solution to simultaneously achieving long cycle stability and
high CE. Recently, a couple of attempts have been made to build SEI on
3D electrode hosts. For example, Zhai et al. designed a 3D
g-C3N4/G/g-C3N4architecture, and a high average CE (99.1%) was achieved for 500 cycles
at 1 mA cm-2/1 mA h cm-2.[26] Liu et al. reported a LiBr-LiF-rich SEI on
the surface of 3D sponge nickel, and the assembled cell exhibited a good
cycle life (over 800 cycles at 1 mA cm-2/1 mA h
cm-2). [27] Carbon cloth is an
important 3D substrate in constructing composite lithium metal anode
because of its good chemical stability, excellent mechanical
performance, and electrical conductivity. Its 3D architecture has been
found to effectively reduce the local current density and accommodate
lithium. However, the commercial carbon cloth is lithiophobic, and the
existing modification strategies mainly focused on functional groups
grafting (-C=O, -COOH), heteroatom doping (N/S/P co-doping, O doping),
and lithiophilic material decorating. [28-31] Most
recently, Cao et al. reported CoSe2 anchored carbon
fiber cloth to enhance lithiophilicity by forming
Co/Li2Se, and the system exhibited excellent cycle
performance.[32]
Herein, we demonstrated uniform surface decoration of carbon cloth by
ZnS/ZnO nanotubes (ZSONT/CC), serving as a multifunctional skeleton to
host lithium metal for anode applications. The formed nanotube uniformly
covers the entire surface of the individual carbon fiber. Most
importantly, during the electrochemical pre-lithiation process, ZnS and
ZnO serve as precursors for in situ generations of SEI containing
Li2S, Li2O, and LiZn, which materials
are most desirable for SEI functionality. More specifically, it is known
that Li-Zn alloy enhances the affinity of the 3D host to lithium and
thus guides the uniform lithium deposition.[33]Li2S possesses a low Li diffusion energy barrier (0.28
eV) and a high ionic conductivity (10-5 S
cm-1), which enable fast Li+transport kinetics.[34] Li2O has
an affinity for lithium and can also reduce the elastic strain energy
between the plated lithium and the substrate because of the lower
crystalline mismatch.[35] As a result, the
Li/ZSONT/CC half-cell can last for 700 hours at 4 mA
cm-2 / 4 mA h cm-2. A stable CE of
99.2% is achieved over 400 cycles at 1 mA cm-2/ 1 mA
h cm-2. When assembled with LiFePO4cathode, the full cell exhibits an excellent cycle performance (with
71% capacity retention after 4000 cycles) and improved rate
performance. The present work provides an effective strategy in forming
SEI on 3D electrode host with possible control on the SEI content.