Page 114 - Read Online

Page 2 of 14 Liang et al. Energy Mater 2023;3:300006 https://dx.doi.org/10.20517/energymater.2022.63

retention rate of the Li-S batteries is 72.9% after 400 cycles at 2 C. This simple preparation method and high-
performance bilayer membrane structure provide a new route for commercial application.

Keywords: Gelatin-based, electrostatic spinning, modified separator, Li-S battery

INTRODUCTION
Li-S batteries have attracted much more attention recently because of their high theoretical capacity (1675
-1
-1 [1]
mAh g ) and high energy density (2600 Wh kg ) , although several problems for Li-S batteries still must be
solved: (1) insulation and volume change of the charging and discharging products of the Li-S battery ; (2)
[2]
[3]
the “shuttle effect” during charging and discharging processes ; and (3) lithium dendrites on the lithium
anode surface . Among these problems, the “shuttle effect” is the reason for the serious capacity decay of
[4]
[5]
Li-S batteries .
Many efforts have been made to solve the problems of Li-S batteries. From the aspect of the sulfur cathode,
a common approach is designing a catalytic carbon material to load sulfur so that it encapsulates and traps
[6,7]
lithium polysulfide before it dissolves in the electrolyte . However, the structural design of cathode
materials is complicated, the cost is high, the yield is low, and this method is difficult to apply on a large
scale . From the aspect of the lithium anode, the design of multifunctional electrolyte additives can
[8,9]
effectively prevent the longitudinal growth of lithium dendrites . Nonetheless, the amount of additive is
[10]
necessarily limited. It will be consumed in repeated charge-discharge cycles and cannot guarantee long-term
effective protection of the lithium anode [11,12] . From the aspect of solid electrolytes, the shuttling of lithium
polysulfides can be completely suppressed by some solid electrolytes, etc., but their large interfacial
[13]
resistance limits the development of batteries . The separator plays the role of isolating the positive and
negative electrodes while acting as the channel of lithium-ion transmission . Modification of the separator
[14]
is a simple and effective method to inhibit the “shuttle effect”. Therefore, more and more researchers have
paid much more attention to modifying the separator in Li-S batteries to inhibit lithium polysulfide
[15]
shuttling to the negative electrode . HY Xiang et al. prepared a nanofiber membrane 3, 4-ethylene
dioxyethiophene/ F co-doped poly-m-phenyleneisophthalamide (EDOT-5/F-PMIA) by electrospinning
[16]
technology . The pore size of the nanofiber membrane was reduced after the addition of a fluorine-
containing emulsion and the EDOT. The elements S and O in the EDOT can bind to lithium polysulfide,
inhibiting the “shuttle effect” of lithium polysulfide through physical constraints and chemical binding. As a
result, Li-S batteries assembled with EDOT/F-PMIA separators exhibited excellent electrochemical
properties. It is not enough, however, to adsorb lithium polysulfides on the surface of the separator only
through physical/chemical interactions, so it is necessary to convert long-chain lithium polysulfides to
prevent the accumulation of lithium polysulfides on the separator. C. Zhou et al. prepared a double-layer
metal-organic framework - polyacrylonitrile (MOF-PAN)/rGO-PAN multifunctional nanofiber film, where
rGO is reduced graphene oxide, by electrospinning, from which the MOF particles facing the S cathode
were tightly adsorbed on the surfaces of PAN nanofibers and captured by chemical adsorption . The rGO-
[17]
PAN layer facing the Li anode side can maximize the uniform deposition of lithium ions to control the
structural changes of the Li anode. The blocking effect alone, however, cannot prevent the consumption of
the active substance, so adding a conductive component on the positive side will enable the conversion of
the lithium polysulfide on the positive side, as well as reducing the interface resistance between the
diaphragm and the positive electrode, and improving the utilization rate of the active material [18-23] .
Therefore, it will be an effective strategy to design a functional separator with physical adsorption, chemical
adsorption, and catalytic conversion, where polysulfides are adsorbed on the surface of the material by
physical/chemical action and then catalytically reduced on the surface of the separetor [24-28] . It is well known
that gelatin has high ionic conductivity and a high ion migration number, so it can trap lithium polysulfide