Advances in lithium—sulfur batteries

TLDR: In this paper, the authors present a review of the state-of-the-art of lithium-sulfur batteries, focusing on the cathode, separator, and the electrolyte.

Abstract: This review is focused on the state-of-the-art of lithium-sulfur batteries. The great advantage of these energy storage devices in view of their theoretical specific capacity (2500 Wh kg −1 , 2800 Wh L −1 , assuming complete reaction to Li 2 S) has been the motivation for a huge amount of works. However, these batteries suffer of disadvantages that have restricted their applications such as high electrical resistance, capacity fading, self-discharge, mainly due to the so-called shuttle effect. Strategies have been developed with the recent modifications that have been proposed as a remedy to the shuttle effect, and the insulating nature of the polysulfides. All the elements of the battery are concerned and the solution, as we present herewith, is a combination of modification of the cathode, of the separator, of the electrolyte, including the choice of binder, even though few binder-free architectures have now been proposed.

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Advances in lithium-sulfur batteries
X. Zhang, H. Xie, C.-S. Kim, K. Zaghib, A. Mauger, C.M. Julien
To cite this version:
X. Zhang, H. Xie, C.-S. Kim, K. Zaghib, A. Mauger, et al.. Advances in lithium-sulfur batteries. Mate-
rials Science and Engineering: R: Reports, Elsevier, 2017, 121, pp.1 - 29. �10.1016/j.mser.2017.09.001�.
�hal-01612077�

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Advances in Lithium–Sulfur Batteries
X. Zhang
1
, H. Xie
2,*
, C.-S. Kim
3
, K. Zaghib
3
, A. Mauger
4
, C.M. Julien
4,*
1
SynPLi Consulting, 17300 Rochefort, France
2
Northeast Normal University, National and Local United Engineering, Laboratory for Power
Batteries, 5268 Renmin Str., Changchun, P.R. China
3
Institut de Recherche d'Hydro-Québec (IREQ), 1800 Lionel-Boulet, Varennes, Québec, J3X 1S1,
Canada
4
Sorbonne Universités, UPMC Univ Paris 06, Institut de Minéralogie, de Physique des Matériaux
et de Cosmochimie (IMPMC), CNRS UMR 7590, 4 place Jussieu, 75005 Paris, France
*Corresponding authors: E-mail: xiehm136@nenu.edu.cn; Christian.Julien@upmc.fr
Keywords: Lithium-sulfur batteries; Polysulfides; Composite electrodes; Electrolyte;
Separators; Mesopore structure

2
Abstract
This review is focused on the state-of-the-art of lithium-sulfur batteries. The great advantage of
these energy storage devices in view of their theoretical specific capacity (2500 Wh kg
-1
, 2800 Wh
L
-1
, assuming complete reaction to Li
2
S) has been the motivation for a huge amount of works.
However, these batteries suffer of disadvantages that have restricted their applications such as high
electrical resistance, capacity fading, self-discharge, mainly due to the so-called shuttle effect.
Strategies have been developed with the recent modifications that have been proposed as a remedy
to the shuttle effect, and the insulating nature of the polysulfides. All the elements of the battery
are concerned and the solution, as we present herewith, is a combination of modification of the
cathode, of the separator, of the electrolyte, including the choice of binder, even though few
binder-free architectures have now been proposed.

3
1. Introduction
Due to the rapid development in our societies, energy storage has become critical. In this context,
lithium-ion batteries (LIBs) have enabled the commercialization of electric and plug-in hybrid cars.
They are also used for current regulation and leveling, solving the intermittence problems of
sustainable energy supply (windmills, photovoltaic plants) and integration on smart grids [1]. The huge
advantage of the Li-S battery in view of its theoretical capacity (2500 Wh kg
-1
, 2800 Wh L
-1
, assuming
complete reaction to Li
2
S) [2] has been the motivation for a huge amount of works since its discovery.
In addition, sulfur is very cheap. The concept of the Li-S battery dates from 1962 [3]. The first
promising results were obtained in the late sixties with the use of organic electrolyte [4]. Unfortunately,
this battery also suffers of disadvantages that have restricted its applications: high electrical resistance
[5], capacity fading, self-discharge, mainly due to the so-called shuttle effect. All the reviews on Li-S
batteries through the years have repeatedly reported these difficulties with which the community of
researchers in electrochemistry struggle [6-10]. In addition, the problem of high resistance of the sulfur
and the polysulfides has been solved by adding conductive elements, like carbon under different forms
[11] in the cathode, at the expense of the amount of active material available for the electrochemical
process [12]. Actually, if we add 40% of conductive carbon to the product, a figure that was still
commonly met few years ago, the advantage with the lithium-ion batteries (LIBs) is small in terms of
energy density and the volume density is even in favor of the LIBs [13]. Although these problems have
never been completely solved, constant progress has been made, in particular in the recent years, giving
hope today that these challenges will be met in the near future. It is the purpose of this work to review
the results that have been obtained, mostly in the two last years, which justify this reasonable optimism.
To limit the length of the review, attention is focused on the structural aspects and the electrochemical
properties, but not on the synthesis aspects, which are detailed in the publications we have cited. In
addition, we recommend the reading of a pertinent review on the atomic layer deposition applied to
Li-S batteries that has been recently published [14].
In most cases, the capacities reported in the papers are reported by gram of sulfur (g
sulfur
).
However, this is not a value for a battery, not even for an electrode, but just for one component of an
electrode. Such values are absolutely useless for a comparison between different composite concepts.
Any useful comparison needs to refer to the energy density on cell level, and this information is rarely
available. When available, we report it in this review; otherwise we do not mention the capacities in the
original works since they are useless for a comparison between different composite concepts, and we

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put the focus on the collection of the different approaches. Exceptions are results on which we wish to
attract attention for their outstanding performance. Even though it does not permit any comparison with
the performance at the cell level, the information available per gram of sulfur gives some insight on the
ability of the composite to use all or a part of the sulfur in the cycling process.
The electrochemical reaction during the discharge proceeds approximately in three steps [15-16]
illustrated in Fig. 1: (I) a reversible conversion of sulfur through stepwise reduction up to the formation
of S
0
→ S
4
2-
. These polysulfides are soluble, so that the reaction kinetics are fast. (II) a conversion of
S
4
2-
-polysulfides to solid Li
2
S
2
. This S
0.5-
→
S
-
reduction is more difficult, because of the energy needed
to nucleate the solid phase. (III) a conversion of solid Li
2
S
2
to solid Li
2
S. This is the most difficult step
because of the sluggish diffusion of lithium in this solid environment [15, 17]. This decomposition in
three steps is an approximation. In particular, electrochemical impedance spectroscopy [18] and in situ
X-ray diffraction spectra [19] revealed that Li
2
S appear immediately at the beginning of the lower
plateau.
Figure 1. Discharge–charge profiles of a Li–S cell, illustrating regions (I) conversion of solid
sulfur to soluble polysulfides; (II) conversion of polysulfides to solid Li
2
S
2
; (III) conversion of
solid Li
2
S
2
to solid Li
2
S.
On the other hand, the charge process is such that all the polysulfides transform via charge

Frequently asked questions

Q1. What have the authors contributed in "Advances in lithium-sulfur batteries" ?

In this paper, the authors present a review of the state-of-the-art performance of lithium-sulfur batteries, focusing on the structural aspects and the electrochemical properties. 

Q2. What are the future works mentioned in the paper "Advances in lithium-sulfur batteries" ?

It is also the only way to make a true comparison with respect to other chemistries such as Li-ion cells and prove that the hope the authors put in the future of the Li-S battery is justified. This is indeed encouraging, since this is sufficient to electric vehicles, provided the cycle life extends to thousands of cycles ( only 100 cycles have been tested in this particular case ).