The density of 2567 W h kg-1, calculated on

The growing concern about global warming and air
pollution, caused by the depletion of limited and nonrenewable fossil fuels,
are receiving increasing attention, to the development of alternative sources
of clean and renewable energy such as wind and solar energy has led to the
creation of another sustainable society. These technologies require a large
energy storage system for reliable, low cost, environmentally friendly,
intermittent energy generation. Undoubtedly, the search of advanced energy
storage devices with higher energy densities is crucial to the development of
our future society1. Among the best candidates
for the next generation of high energy storage systems, metallic sulfur
batteries, such as Li-S, Na-S and Mg-S, have high theoretical energy densities,
which makes them especially attractive. Of these, the Li-S battery has the
highest theoretical energy density of 2567 W h kg-1, calculated on
the basis of the Li anode (~ 3860mAh / g) and the S cathode (~ 1675mAh / g),
making it a promising option for the next generation of high-energy
rechargeable batteries2-4.

However, there are many complicated challenges in order
to achieve practical application for example (1)insulating
nature of sulfur and sulfides5,6, interrupt electron
transportation in the cathode, resulting low utilization of active materials;(2) dissolution of polysulfide7 grow up shuttle phenomenon
which lead to columbic efficiency decay and loss of active material;(3) the volume change of sulfur during cycling
destroys the electronic integrity of the composite electrode, induces a
continuous surface side reaction, causing a rapid capacity fading8.

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Up to now, enormous efforts have been made to solve
the above problems through the construction of advanced composite electrode
materials which have included sulfur embedding in N-doped9-11 carbon or different
morphologies carbon, including porous carbon12, porous hollow carbon13,14, Disordered carbon nanotubes, double shelled hollow carbon
spheres15,16, spherical ordered
mesoporous carbon nanoparticles17 and so on.

It is no doubt that these materials have made
substantial progress in greatly improving the specific capacity, cycle
stability and cycle life of Li – S cells. However, the fatal defect of these
processes is that they are all generally complex and not suitable for practical
use.

The binder is an important component in the battery
function for binding and holding the active material to the electrode, improves
the electrical contact between the active material and the conductive carbon,
and binds the active material to the current collector18. The selection of an
appropriate binder has been found to significantly affect battery performance19-22. For example,
polyvinylidene fluoride (PVDF) is a type of conventional binder used in
electrode preparation. Many studies indicate that PVDF binders are not suitable
for electrode materials that swell in volume, such as silicon and sulfur,
because of their relatively weak bond strength. On the other hand,
N-methyl-2-pyrrolidone (NMP), a high-boiling organic solvent, is toxic and not
conducive to industrial production and environmental protection23,24. Based on past research
experience, the appropriate lithium-sulfur battery binder should have the
following characteristics: (i) good adhesive strength21. The ideal binder should be
capable of maintaining the structural stability of the electrode material with
a large volume change during the cycle. New binders such as LA 13225, SBR + CMC26 were developed to build a
more robust network for the entire sulfur cathode. (ii)
Suitable swelling capacity22. For sulfur cathodes,
proper electrolyte absorption of the binders can improve the rate performance
of the batteries. Lacey et al22. In
addition, they demonstrate that the binder reduces the porosity of the carbon /
sulfur composite cathode, which is detrimental to electrolyte impregnation. A
swelling-sensitive binder such as PEO can contain a large amount of electrolyte
in its volume and inhibit cathode passivation upon discharge. In other words,
the swelling of the binder leads to an improved solvent system for the sulfur
species electrochemistry27. (iii) Effective adsorption of multi-lithium sulfide28. The most serious problem
limiting the development of Li – S batteries is the dissolution of Li2 Sn
(4 n 8). Cui et al29. demonstrated the strong
Li–O interaction between poly (- vinylpyrrolidone) (PVP) and Li2Sn
(1 8) with theoretical calculations. Yang30 prepared a novel
multifunctional binder. He introduced quaternary ammonium cations play an
important role in fixing polysulfides and inhibiting the shuttling effect.

From the above discussion, the binder should be
considered as the active component of the Li – S cell. However, it is difficult
to satisfy the requirement for application with a single binder. The reasonable
use of different functional binders is an effective strategy for improving the
electrochemical performance of Li – S cells.

In this work, we investigated the application of
Gelatin and PEI composite as functional binders in Li–S batteries. Gelatin is
good adhesive material provide the elastic and mechanical properties which can
buffer the volume changes during repeatable charge and discharge process and
PEI is polar in nature with abundant amine groups and hyperbranched network
structures, which provide the strong affinity to absorb polysulfide
intermediates. When we used Gelatin/PEI composite as a binder, it remarkably
improved cycling performance with good capacity retention and suppressing the
shuttling effect of the polysulfides