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Author: Barghamadi, Marzieh; Kapoor, Ajay; Wen, CuieTitle: A review on li-s batteries as a high efficiency
rechargeable lithium batteryYear: 2013Journal: Journal of The Electrochemical SocietyVolume: 160Issue: 8Pages: A1256-A1263URL: http://hdl.handle.net/1959.3/351310
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*Corresponding author. Tel.: +61 3 92145651; Fax: +61 3 92145050 E-mail address: [email protected] (C. Wen).
A review on Li-S batteries as a high efficiency rechargeable lithium battery
Marzieh Barghamadi, Ajay Kapoor, Cuie Wen*
Faculty of Engineering and Industrial Sciences, Swinburne University of Technology
Hawthorn, Victoria, 3122, Australia
Abstract
Energy production and storage are critical research domains where the demands for improved
energy devices and the requirement for greener energy resources are increasing. There is
particularly intense interest in Lithium (Li)-ion batteries for all kinds of electrochemical
energy storage. Li-ion batteries are currently the primary energy storage devices in the
communications, transportation and renewable-energy sectors. However, scaling up the Li-
ion battery technology to meet current increasing demands is still problematic and issues such
as safety, costs, and electrode materials with higher performance are under intense
investigation. The Li-sulphur (S) battery is a promising electrochemical system as a high-
energy secondary battery, particularly for large-scale applications, due to its low cost,
theoretically large specific capacity, theoretically high specific energy, and its ecofriendly
footprint. The Li-S battery exhibits excellent potential and has attracted the attention of
battery developers in large scale production in recent years. This review aims to highlight
recent advances in the Li-S battery, providing an overview of the Li-ion battery applications
in energy storage, then detailing the challenges facing Li-S battery and current applied
strategies for improvement in its efficiency.
Keywords: Energy Storage; Li-ion Batteries; Li-S Batteries; Advances and Improvements in
Cathode
*Corresponding author. Tel.: +61 3 92145651; Fax: +61 3 92145050 E-mail address: [email protected] (C. Wen).
Contents
1. Introduction ............................................................................................................................ 3
2. Current Li-ion batteries .......................................................................................................... 4
3. Li-S battery ............................................................................................................................ 8
3.1. Fundamental aspects of the Li-S battery ......................................................................... 8
3.2. Challenges for the Li-S battery ..................................................................................... 10
3.3. Advances in Li-S battery ............................................................................................... 12
3.3.1. Advances in cathode ............................................................................................... 12
3.3.2. Advances in anode .................................................................................................. 17
3.3.3. Development in electrolyte ..................................................................................... 19
3.4. Application of Li-S battery in electric vehicles ............................................................ 21
4. Conclusions and outlook ...................................................................................................... 22
Acknowledgements ............................................................................................................ 23
References .......................................................................................................................... 24
3
1. Introduction
An energy economy based on fossil fuels is at a serious risk due to the continued increase
in demand for oil, the depletion of non-renewable resources, and with the rate of CO2
emissions showing a dramatic increase in the last 30 years. This increase has also resulted in
a rise in global temperature and a series of associated climate changes.1 Energy is, therefore,
a vital global issue and attempts are being made to rectify current problems by utilizing new
energy resources. In this regard, electrical energy storage is recognized as an essential
element for both stationary and mobile power equipment.2, 3
Electrical energy storage systems play a crucial role in managing the gap between energy
generation and demand, especially for electricity generation from renewable and sustainable
sources, such as solar and wind, and in portable electronics such as personal computers,
cordless tools, and electric vehicles. There are several technologies available such as
flywheels and compressed air, but batteries are at the forefront of energy storage systems,
especially for electricity.4
Battery Energy Storage Systems (BESSs) have appeared as promising storage
technologies for power applications, offering a wide range of power system applications. The
batteries are made from cells that convert chemical energy to electrical energy and vice versa.
They are rated in terms of their energy and power capacities. The amount of energy per mass
or volume that a battery can deliver is a function of the cell’s voltage and capacity.
Significant development is going on in the battery technology. Different types of batteries
have been commercially developed, while some are still in the experimental stage.5, 6 Safe,
low-cost, high-energy-density and long-lasting rechargeable batteries are urgently needed to
address important issues in energy generation, such as the increased energy consumption of
portable devices.7 Rechargeable batteries are used in portable electronics, power tools,
4
electric vehicles (EVs), and in stationary electrical energy storage (EES) for a grid supplied
by wind, radiant-solar, and nuclear power.8 Among all the types of batteries, lithium batteries
have attracted the most attention because the theoretical energy density (both gravimetric and
volumetric) of lithium metal is the highest for all solid electrodes.4 Lithium-ion batteries have
been under intense scrutiny over the past 20 years because of their advantages, such as high
energy density, high operating voltage and low rate of self-discharge.9-11
2. Current Li-ion batteries
Lithium-ion batteries employ lithium storage compounds as the positive and negative
electrode materials. During the battery’s cycling, lithium ions (Li+) exchange between the
positive and negative electrodes. Li-ion batteries have been discussed as rocking chair
batteries because the lithium ions “rock” back and forth between the positive and negative
electrodes as the cell is charged and discharged.12 The working mechanism of a typical Li-ion
battery is presented in Figure 1.
Sony commercialized the lithium ion battery (LIB) first in the early 1990s. Until now,
lithium-ion batteries have offered the most practical solutions to a wide variety of electrical
energy storage applications, such as mobile phones, lap-top computers, MP3s, due to their
high voltage, high energy density, light weight and good environmental compatibility in
comparison to other kind of batteries.9, 13 Lithium ion batteries have also found applications
in satellites14 and in biomedical device clinical trials, such as Neurostimulator, Ventricular
Assist, Artificial Heart.15-17 However, the maximum energy density of current lithium ion
batteries is too low to satisfy the demands of key markets such as transport and they need to
be improved.18 Some of the major challenges facing this kind of battery are as follows: (i)
The obtainable or usable capacity is inadequate (and much lower than the theoretical limit)
and diminishes with the rate of cycling; (ii) The power density is insufficient for the intended
applications, especially in EVs; (iii) The energy efficiency is too low due to large polarization
5
losses for charge and discharge, with the situation worse at higher cycling rates; (iv) The
cycling life is limited due to capacity fading with cycling; and (v) The price is high. Overall,
the existing Li-ion batteries often suffer from deterioration in their microstructure or the
architecture of the electrodes accompanied by volume expansion or contraction, phase
transformation, and morphology changes of the active electrode materials during cycling.4 In
addition, safety of lithium metal oxide cathodes is an issue because of their intrinsic thermal
properties. The thermal runaway is caused by the exothermic reactions between the
electrolyte, anode and cathode, with temperature and pressure increasing in the battery.19 For
example, a fully charged lithium cobalt oxide can release oxygen, which oxidizes the solvent
and causes the battery thermal runaway.
In order to improve the energy and power density of LIB, the use of anode materials with
larger capacity and higher Li diffusion rate is required. Different materials such as nano
carbon, alloys and metal oxides have been developed. Nano carbons like graphite can
effectively store Li and improve storage ability due to their high surface area and
morphology. Li anode can be alloyed with some elements such as Sn, Si, Al to improve the
capacity and safety. But this will result in large volume change which causes cracking of the
electrode and capacity fading. Metal oxides like Fe3O4, SnO2 and CuO have been proposed as
potential materials for LIB anode, but their capacity decrease rapidly because of large volume
changes.20 SnO2-nanofiber carbon composite21 and Fe3O4 /reduced graphene oxide
nanocomposite22 were applied as anode to deal with this issue.
The main LIB cathode materials are lithium metal oxides like LiCoO2 which have high
energy density, but they suffer from some intrinsic and safety issues in addition to high cost.
Although using nanostructured lithium metal oxides can solve some problems like low
conductivity, it causes more safety issues due to higher surface area.23 Better stability has
6
been achieved by coating the cathode LiCoO2 with ZnO, which suppresses the cobalt
dissolution.24
Li-ion materials are currently the subject of intense research.25 Several countries,
including Japan, United States and European countries, are supporting R&D programs aimed
at solving these problems in order to develop advanced and efficient LIB.26 Indeed
identifying new materials offering a better performance than those offered by the current
common anode and cathode used in rechargeable Li battery is necessary. In general, the
performance of any device depends on the properties of its materials; this is also true for
lithium batteries. Thus, a new generation of rechargeable lithium batteries can only be
achieved by a breakthrough in electrode and electrolyte materials.1
Introducing positive electrode materials that offer higher capacity and improved safety
properties, as well as negative electrode materials with improved specific energy, energy
density, rate capability, and longevity are the main research and development goals in the
lithium battery area. Adopting new electrolytes, additives and electrode material coatings to
improve both the cycle life and calendar life of lithium batteries are also receiving increased
attention.27
Reaching beyond the horizon of rechargeable lithium batteries requires an exploration of
new chemistry, especially electrochemistry, and new materials. Non-lithiated cathode
materials not only exhibit higher specific capacities than lithiated cathode materials, but also
provide enhanced safety as they cannot be overcharged. Rechargeable Li-S is highly efficient
lithium rechargeable battery. Sulphur has one of the highest theoretical capacities for the
cathode of lithium batteries in comparison with all other cathode materials in this kind of
battery. Based on complete reactions with metal lithium to form Li2S, it has a theoretical
specific capacity of 1675 mA h g-1.28-30 Table I compares the different kinds of lithium
batteries.
7
Table I. Comparison of lithium batteries.
a The molecular mass of O2 is not included in these calculations. b Based on the sum of the volumes of Li at the beginning and Li2S at the end of discharge. c Based on the sum of the volumes of Li at the beginning and Li2O2 at the end of discharge. d Assuming the product is anhydrous LiOH and alkaline conditions. e Based on volume of ZnO at the end of discharge.
Battery Cell voltage (V)
Theoretical capacity (mAhg-1)
Theoretical specific energy (Wh kg−1)
Theoretical energy density (Wh l−1)
Overall reaction References
Conventional Li-ion 3.80 155 387 1,015 Li(C) + CoO2 ↔LiCoO2 15, 31
Li-S 2.20 1672 2,567 2,199b 2Li + S ↔ Li2S 31, 32
Li–air (non-aqueous) 3.00 3862 11,248a 3,436c 2Li + O2 ↔ Li2O2 31, 33
Li–air (aqueous) 3.20 1861 5,789a 2,234d 2Li + ½O2 + H2O ↔ 2LiOH 31, 33
Zn–air 1.65 820 1,086 6,091e Zn + ½O2 ↔ ZnO 31, 34
Al-air 2.70 2980 8100 NA 4Al + 3O2 + 6H2O → 4Al(OH)3 34, 35
Mg-air 3.10 2200 6800 NA Mg + ½O2 + H2O → Mg(OH)2 34
8
3. Li-S battery
The lithium–sulphur (Li-S) battery, which is composed of a sulphur composite cathode, a
polymer or liquid electrolyte, and a lithium anode, is a promising candidate for high energy
systems. Figure 2 presents a schematic configuration of a Li-S battery. It is based on the
lithium/sulphur redox reaction, given by:
16 Li + S8 → 8Li2S [1]
Assuming complete conversion, it has a high theoretical specific capacity of 1675mA h
g−1 and a high theoretical specific energy of 2600 Wh kg-1.36, 37
3.1. Fundamental aspects of the Li-S battery
Sulphur is a promising positive electrode material for lithium batteries due to its high
theoretical specific capacity of approximately 1675 mA h g-1. The Gibbs energy of the Li/S
reaction is more than five times the theoretical energy of a Li-ion system, ~ 2600 Wh kg-1.
The concept of electrochemical energy conversion and storage utilizing sulphur as the
positive electrode in an alkali metal anode battery dates back to the 1960s.38 During recent
decades, there has been strong incentive to develop a rechargeable Li/S battery.39, 40 Many
articles regarding the electrochemical properties of the Li–S cell, such as discharge
capacity,36, 41, 42 cycling,42-44 and self-discharge45 have been published.
Among the various types of rechargeable batteries, this system is a very attractive
candidate, because of its high theoretical capacity, high theoretical power density and wide
temperature range of operation. Moreover, elemental sulphur benefits from advantages such
as natural abundance, low cost, excellent safety due to its intrinsic protection mechanism
from overcharge, and its non-toxicity.46-48
In the nature sulphur exists in more than 30 allotropes, and ring-structural
cyclooctasulphur (S8) is the most stable form.28 In the discharge process of a fresh Li-S
battery, an S–S covalent bond of S8 is first broken to form a chain-structural polysulphide
9
(PS) anion (Sx2−, x = 8), and then it is further reduced into Li2S through multistage
reactions.49, 50
The reaction mechanism of a Li-S battery is different from that of commercial secondary
lithium batteries with an intercalation-deintercalation mechanism in lithium metal oxide and
graphite. Reduction of sulphur in a Li-S battery is a multistep electrochemical process that
can be composed of different intermediate species. In general lithium metal reacts with
sulphur (S8) to produce lithium polysulphides with a formula of Li 2Sn. Long chain
polysulphides are produced first, such as Li2S8 and Li2S6, which are shortened during further
reduction of sulphur. The final product of discharge is lithium sulphide (Li2S) and the overall
reaction is given by Eq. 1.39, 51 In this process, sulphur accepts electrons from an open-circuit
voltage (OCV) to 2.1V, forming lithium polysulphide and then lithium polysulphide is
reduced. From the viewpoint of phase transitions, the discharge can be divided into four
stages, as follows:
I: Reaction of elemental sulphur with Li is given by:
S8+ 2Li+ + 2e− → Li2S8 [2]
II: A reaction between dissolved Li2S8 and lithium is described as:
Li 2S8+ 2Li+ + 2e−→ 2Li2S4 [3]
III: A transition from the dissolved Li2S4 to insoluble Li2S2 or Li2S by the coexistence of Eqs.
4 and 5:
Li 2S4+ 2Li+ + 2e−→ 2Li2S2 [4]
Li 2S4+ 6Li+ + 6e- → 4Li2S [5]
IV: An equilibrium reaction of insoluble Li2S2 and Li2S is described as:
Li 2S2+ 2Li+ + 2e− → 2Li2S [6]
Eq. 3, is the most complicated of the four stages because it is affected by both the
solubility of the polysulphides in the electrolyte and the chemical equilibrium between each
10
type of polysulphide in the solution. Therefore, this reaction is affected strongly by the type
of electrolyte solvents. The outcome of stage III depends on the competition of Eqs. 4 and 5.
The final discharge products are mainly a mixture of Li 2S2 and Li2S. As Eq. 5, is the
predominant reaction, the Li-S cell has high capacity with slightly lower discharge voltages
and a shorter stage IV. Stage IV is kinetically slow and suffers from high polarization
because of the non-conductive nature of Li2S2 and Li2S. Figure 3 shows the voltage profile of
the first discharge of a sample of Li-S cell.52, 53
As the current density increases, both the discharge capacity and the plateau voltage
decrease. X-ray diffraction analysis of discharged sulphur electrodes proves that at low
current density, only Li2S peaks are displayed while at high current density, both elemental
sulphur and Li2S peaks can be observed. The discharge capacity of the sulphur electrode
greatly decreases after discharging at high current density due to under-utilization of the
active material.54
3.2. Challenges for the Li-S battery
Although the Li-S battery has considerable advantages, it still suffers from a series of
problems that have hindered its practical application. The discharge products precipitate
during the second discharge step, covering the positive electrode surface and causing poor
electrode rechargeability and capacity limitation. This is mainly linked to the passivation of
the positive electrode. In fact the discharge stops when the surface is fully covered by these
insulating species.39, 55 The long-chain lithium polysulfides dissolve into the electrolyte and
migrate to the anode to form lower-order polysulfides by reacting with lithium, and then they
diffuse back to cathode to be deoxidized to a longer-chain. This causes the so-called internal
“shuttle” effect, which leads to the corrosion of the lithium anode and consequently causes
poor efficiency and a short cycle life in rechargeable Li-S batteries. Additionally, the
continuous reaction of the soluble polysulfide to the Li anode leads to significant self-
11
discharge and the deposition of solid Li2S2 and Li2S on the cathode, which results in active
mass loss and capacity fading. Some amount of the insoluble Li2S and Li2S2 accumulate on
the Li anode. Another challenge is the volume change accompanied by morphology change
which occurs in the electrode upon the active sulphur dissolution and the final products
precipitation. These problems contribute to the fast aging of electrodes and a quick fading of
the practical specific charge of the battery.56-58
Therefore, the Li-S battery is unsuitable for a high energy density primary battery that is
required to have a long calendar life and service time. Another problem is the very poor
electronic conductivity of sulphur, which causes poor electrochemical contact of the sulphur
and leads to low utilization of active materials in the cathode.3 Thus, a large quantity of
conductive agents is needed when making the sulphur cathode. Compositing elemental
sulphur with carbon50, 59 and conducting polymers60-62 can significantly improve the electrical
conductivity of a sulphur cathode.
The successful development of a Li-S battery, regarded as a candidate for the next
generation of batteries, requires extensive research on the electrochemical behavior under
various operating conditions.36, 63 A lot of research has been conducted to mitigate the
negative effect of the polysulphide shuttle. Much of this work has focused on either the
protection of the lithium anode42 or on the restriction of the ionic mobility of the polysulphide
anions.64, 65 However, since protection of the lithium anode causes a slow reaction rate at the
anode during the discharge cycle due to passivation of the anode, this leads to a loss of power
density in the battery. Gel electrolytes and solid electrolytes have been reported as a means of
slowing down the polysulphide shuttle by reducing the ionic mobility of the electrolytes.64, 66,
67 It is also necessary to introduce conductive additives and strong adsorbent agents with a
large surface area to the cathode. The preparation of the sulphur-conductive polymer
12
composites, or sulphur-carbon composites, has been reported as softening the impact of the
shuttle effects.52
3.3. Advances in Li-S battery
3.3.1. Advances in cathode
Based on studies reported in the literature over the last few years, the ideal structure for a
sulphur electrode requires the following characteristics: a closed structure for efficient
polysulphide containment, a limited surface area for sulphur electrolyte contact, sufficient
space to accommodate sulphur volumetric expansion and the small characteristic dimensions
of a sulphur electrode to avoid pulverization, a short pathway for both electrons and Li ions
to achieve high capacity at a high power rate, a large conductive surface area on which to
deposit the insulating Li2S2 and Li2S in order to preserve the morphology of the electrodes,
and suitable electrolyte additives to passivate the lithium surface and so minimize the shuttle
effect.68
The literature reports on different strategies that have been considered to improve Li-S
battery electrochemical performance, mainly focused on the combination of a conductive
matrix with sulphur to form a highly conductive composite. In recent years, carbon-based
nanomaterials, including 0-D fullerene, 1-D carbon nanotube and 3-D graphite, have attracted
a great deal of interest.69, 70
Several research attempts have focused on the development of carbon/sulphur
nanocomposites, in which sulphur particles were embedded in the nanopores of the
conductive carbon matrix. They can increase both the electrical and ionic conductivity of the
sulphur cathode while at the same time suppressing the polysulphide shuttle phenomenon.40,
55, 71 Using nanostructured sulphur-carbon composite cathodes can considerably improve both
the cyclability of the battery and the utilization of sulphur in the battery cycles. The pores in
this structure not only act as micro-containers for the elemental sulphur that provides
13
sufficient contact to the insulating sulphur and promotes the electrical conductivity, but also
facilitates the transport of Li ions during the electrochemical cycling and accommodates the
produced polysulphides and sulphide ions during the electrochemical reactions.3 Preparing a
uniform mixture of carbon and sulphur or obtaining a composite of carbon-encapsulated
sulphur requires multiple processing steps. Some related works will now be discussed.
Researchers have investigated the use of a sulphur cathode containing carbon nanotube
(CNT) in a Li-S battery, and this has demonstrated great cycling stability and coulombic
efficiency.72
Composite cathodes containing a sulphur/acetylene black (AB) composite, in which the
sulphur was embedded inside the nano-pores of the acetylene black, showed a high discharge
capacity and good cycle performance.73
A nano-sized S/PPyA (poly(pyrrole-co-aniline) ) composite delivered a high initial
discharge capacity and acted as a good conductive matrix, a strong adsorbing agent, and as a
firm reaction chamber for the sulphur cathode materials, and it improved both the capacity
and cycling stability of the cathode.60 It has been observed that the cycling life and specific
capacity of the battery are improved when carbon nanofiber (CNF) is added into the sulphur
electrode because CNF provides a good electrical connection and structural stability.68, 74 Ji et
al.75 showed that loading S in to the porous CNF improves the battery performance. It
provides both high conductivity and high surface area for S and reduces the PS solubility.
Also this structure can accommodate Sulphur volume changes. Figure 4 shows the SEM
images for bare Sulphur and CNF-encapsulated sulphur electrodes. Figure 4(a) shows CNF
formed inside the AAO template and Figure 4(b) shows CNF after sulphur infusion and AAO
etching with a weight ratio of 3:1 (sulphur to carbon). The energy-dispersive X-ray
spectroscopy (EDS) images in Figures 4(d) and (e) confirm the presence of carbon and
sulphur in the electrode.
14
Zhang et al.76 introduced a novel polymer, polyaniline polysulfide (SPAn), which can
hold an appropriate amount of sulphur. The polymer has polyanilline as the backbone chain
and 2 four-member rings with S-S bonds as the side chains of aniline. An ordered
mesoporous carbon (OMC) sphere with uniform channels is applied as the conductive agent
in the sulphur cathode. Sulphur filled the holes of the OMCs by a co heating method. The S-
OMC composite exhibits excellent cycling performance compared to the bare S cathode.46, 77
Applying spherical OMC-S as a cathode material provides a battery with high initial
discharge capacity and cyclability.78 Wang et al.79 used microporous–mesoporous carbon
which has a high adsorption capacity and conductivity as the sulphur immobilizer to provide
a stable cathode and consequently a battery with good cyclability. Also cycle life of Li-S
battery extends with encapsulated sulphur in mesoporous hollow carbon capsules. It showed
91% capacity retention after 100 cycles.58
Recent reports suggest that a multi-wall carbon nanotube (MWCNT) is a promising
conductive material that could improve the cycling performance of the Li-S battery. It
provides the electrochemical reaction sites with a large interface area, between the MWCNTs
and the lithium polysulphides, on which the electrochemical reaction can take place, and
accommodates Li2S and Li2S2 without clogging the pores in the cathode.80-82 Choi et al.50
reported an improved discharge capacity and cycle performance of a Li-S battery with a
carbon coating on the surface of the sulphur, which enhanced the electrical contact and
adsorption of the lithium polysulphide.
A breakthrough for Li-S batteries is the application of a Graphene-S cathode in the
battery.83-88 Graphene is a material that could not be imagined 70 years ago. Research on
graphene is very new, having explosively started in 2004 following the development of a
simple technique to prepare a single-layer graphene sheet.89
15
Graphene is single layer of sp2-hybridized carbon atoms found in graphite, known for its
unusual electronic properties and possible applications.90-92 In recent reports, two-
dimensional graphene has been considered as a potential electrode material for battery
applications, due to its superior electrical conductivity, high surface area, and broad
electrochemical window. In comparison to CNT and CNF, it is typically impurity-free and
much cheaper. They have many applications in a variety of industries and research.93-96 An
early example of an improvement achieved with graphene was the production of sulphur–
graphene nano sheets (S-GNS) by heating a mixture of elemental sulphur and synthesized
graphene nanosheets. The S-GNS composite showed a significantly improved capacity and
cycle life compared to the pristine S cathode.83 The use of graphene-wrapped sulphur
particles as the cathode material in a Li- S battery has also been reported.85
A functionalized graphene sheet-sulphur nanocomposite (FGSS) with sandwich-type
architecture has been synthesized and studied as a possible cathode material for Li-S
batteries. The unique composite structure and good conductivity of graphene contributes to
the observed good cycling stability.97. Ji et al.84 investigated on the graphene oxide-sulphur
(GO-S) nanocomposite cathode that displays good reversibility and excellent capacity
stability. This improved performance may be related to the reduction of GO by incorporation
of S which improves the conductivity of the GO, and diminution of Li polysulfides
dissolution due to mild interaction between GO and S.98
The design and synthesis of sulphur cathode coated with reduced graphene oxide (RGO)
has been reported where the carbon framework serves as a conductive layer and
nanoelectrochemical reaction chamber.99 A layer-structured sulphur-expanded graphite (EG)
composite has been employed as a cathode in Li-S batteries to improve the electrochemical
performance.100 The EG maintains a layered structure similar to natural flake graphite with a
higher surface area that provides sufficient contact to the insulating sulphur and improves the
16
conductivity. Each layer of EG could be considered as a micro current collector to provide
sufficient electrons for a reaction between the cathode materials and lithium ions. The
development of graphene materials, and their applications in the electrochemical energy
fields, is still in its infancy and many challenges remain.
A cathode should have uniform combination of active sulphur and conductive materials
for better performance. Among the components in the sulphur cathode, the binder plays an
important role in improving cell performance, especially in regards to the cycle life. A binder
should not only have high adhesion between the electrode materials and the current collector,
but should also facilitate electron transport and lithium ion diffusion because of the ability to
form a good electric network between the active material and conductive carbon.37
Kim et al.101 investigated PTFE +CMC and PTFE + PVA as binder in Li-S battery. These
cathodes have larger specific surface area with more contact area between the cathode
materials and the electrolyte, leading to decreased interfacial resistance and consequently
improved capacity. Jung et al.51 studied the mixed polymer binder system of PVP and PEI in
order to maintain the initial morphology of cathode during charge–discharge cycles to
improve the cycle performance of battery. The cycling property of polyethylene oxide (PEO)
and polyvinylidene fluoride (PVdF) binder with a carbon nanofiber is also investigated and
proved that the capacity increased by applying binders.74 Gelatine has been used as a binder
in the sulphur cathode, which is electrochemically stable and functions as a highly adhesive
which stabilize the structure of the cathode and effective dispersion agent for the cathode
materials.37 Table II lists the discharge capacity of improved Li-S batteries by applying
different cathode materials.
17
Table II. Comparison the discharge capacity of cathode’s materials used in Li-S battery.
Cathode materials Discharge current rate
Initial discharge capacity (mAhg-1)
Cycle number
Residual reversible capacity (mAhg-1)
Electrolyte References
Sulphur 0.4 mAcm-2 710 50 230 LiCF3SO3-DME-DOL 102
Sulphur 0.1 mAcm−2 400 50 100 LiTFSI in Tetraglyme 103
Sulphur 160 mAg-1 1094 80 <150 LiPF6- EC-DMC 88
S-MPCa 250 mAg-1 1584.56 30 804.94 LiTFSI-DOL-DME 3
S-Carbon 100 mAg−1 1232.5 50 800 LiClO4-DEGDME–DOX 25
S-PPyb 50 mAg−1 1280 20 800 LiTFSI-PEGDME 104
S-Carbon 50 mA g-1 1300 30 700 LiTFSI-EMITFSI 46
S-PEGc-CMK-3d 168 mAg-1 1320 20 1,100 LiPF6-TEGDME 7
S-PANe 0.3 mAcm−2 893 50 600 PVDF Gel Electrolyte 59
S- MWCNT 168 mAg-1 734.7 100 491.5 LiPF6 -EC/DMC 82
SPAn 0.2 mAcm−2 980 20 403 LiCF3SO3 /DOL-DME 76
S-MWCNT 0.1 mAcm−2 485 50 300 LiTFSI in Tetraglyme 103
S-CNF 100 mAg-1 1191 20 700 LiCF3SO3-TEGDME 74
S/PPy–MWCNT 0.1 mAcm−2 1309 100 725.8 LiCF3SO3-TEGDME 80
S–PPy Nanowire 0.1 mAcm-2 1222 20 570 LiCF3SO3-DOL-DME 61
S/T-PPyf 0.1 mAcm-2 1151.7 80 650 LiCF3SO3-TEGDME 69
S-OMC 168 mAg-1 1138 80 800 LiTFSI-DOL-DME 71
S-AB 40 mAg-1 934.9 50 500 LiPF6/ PC-EC-DEC 73
S-PPyA 0.1 mAcm−2 1285 40 866 LiCF3SO3-DOL-DME 60
S-CNF 335 mAg-1 1200 150 730 LiTFSI-DOL-DME 68
S-OMC 0.1 mAcm−2 1265.5 25 800 PEO18Li(CF3SO2)2N–SiO2 77
S-MWCNT 60 mAg−1 700 60 482 LiPF6-EC-DMC-EMC 81
S-GNS 50 mAg-1 1611 40 700 LiTFSI-PEGDME 83
S-GO 168 mAg-1 1320 50 735 PYR14TFSI-LiTFSI- PEGDME
84
S- EG 280 mAg-1 1210.4 50 957.9 LITFSI- DME/ DOL 86
S-FGS 168 mAg-1 950 50 800 LiTFSI-DME-DOL 97
TGg-S-RGO 200 mAg−1 1290 100 928 NA 99
S- EG 25 mAg-1 1588 50 1200 LiClO4-DME-DOL 100
S- GNS 160 mA g-1
1598 80 670 LiPF6-EC-DMC 88
a Mesoporous Carbon b Polypyrrole c Polyethylene glycol d The most well-known member of the mesoporous carbon family e Polyacrylonitrile f Tubular polypyrrole g Thermally exfoliated graphene nanosheet 3.3.2. Advances in anode
The use of elemental lithium as the anode in Li-S batteries remains a major issue due to
safety concerns arising from the formation of lithium dendrites during cycling, which can
penetrate the separator and lead to thermal runaway. One way to avoid this safety problem in
the Li-S system is to use a high-capacity anode material other than elemental lithium. Some
18
researchers have investigated this possibility. A novel lithium metal-free battery consisting of
a silicon nanowire anode and a Li2S/mesoporous carbon composite cathode, with high
theoretical specific energy, has been reported.105 He et al.30 designed a Li-S cell with non-
lithiated electrode materials. They used graphite anodes and a non-lithiated sulphur
composite cathode (Sulphur- acetylene black- PTFE) by incorporating lithium metal foil to
provide lithium and so enhanced the performance of the cells.
Li negative electrodes have also been replaced by a Sn–C–Li alloy which demonstrated
higher chemical stability towards sulphides.106 Since lithium is so reactive, the protected Li
anode was introduced to the Li-S battery to enhance the charge/discharge performance by
reducing the growth of the solid electrolyte interface (SEI) layer and suppressing the reaction
between the Li and soluble polysulphides.
A Li negative electrode with a Li–Al alloy layer can increase the cycle life of a battery.107
The protection layer on the Li anode can be prepared using a UV cured polymerization
method42 It can be seen the protected anode has a smoother and denser surface morphology.
The protected anode can suppress the overcharge during the charge process and form a stable
SEI layer which causes stable discharge capacity up to 100 cycles in battery. Liu et al.108 used
an anode of lithium-rich multiphase Li2.6BMg0.05 alloy foil for Li-S battery. This alloy is
composed of Li5B4, Li, and Li3Mg7 and provides a battery with lower polarization and longer
cycle life than the pure Li anode based battery due to its improved morphology. Figure 5
compares the surface morphology of a pure and alloyed anode. As shown in Figure 5, lots of
dendrites are detected on the pure Li surface after 70 cycles, while Li2.6BMg0.05 anode
inhibits the formation and growth of Li dendrites and shows a more homogeneous
morphology.
19
3.3.3. Development in electrolyte
For the successful operation of a Li-S battery, the electrolyte should have high ionic
conductivity and enough PS solubility, electrochemical stability, chemical stability regarding
the lithium, and safety. Also it should stabilize the chemical composition and structure of the
sulphur cathode by suppressing dissolution of polysulphide. The capacity of a sulphur
electrode is insufficient when using conventional organic liquid electrolytes due to the high
solubility of polysulphides during both the charge and discharge processes.109 A number of
strategies have been explored to address the polysulfide solubility issue, including the design
of adjusted organic liquid electrolytes,110 the use of ionic liquid-based electrolytes,111 and the
application of polymer electrolytes.112
Choi et al.113 studied the effect of different liquid electrolyte combinations based on
DME, DEGDME, TEGDME and DIOX on Li-S battery efficiency; and Chang et al.43
researched on a mixed electrolyte of TEGDME and DOXL. It is found that a mixture of
electrolytes is more suitable because of the lower viscosity and the better wetting of the
electrodes which facilitate ion transportation. The electrochemical performance of Li-S
battery has also been investigated using LiClO4 DOL/DME as electrolyte and proved that an
optimum mixture of these solvents led to better cycle performance. DME offers higher PS
solubility and faster PS reaction kinetic, but high content of DME could increase the
resistance of the battery due to the high solubility of polysulfide, whereas DOL could
improve the interfacial contact between the electrodes and electrolyte.114
Polymer electrolytes have attracted a great deal of research interest for use in the Li-S
battery due to higher safety because of both the absence of flammable organic solvents and
the much lower reactivity toward lithium; also they can control the dissolution of
polysulphides. These electrolytes are divided into two groups: (i) Solid polymer electrolyte
(SPE) in which polymer acts as both mechanical matrix and solvent to dissolve lithium salts;
20
(ii) Gel polymer electrolyte (GPE) in which a polymer is gelled by conventional electrolyte
solutions. Here polymer only provides dimensional stability. GPE has been more attention-
grabbing due to higher ion conductivity and major manufacturers of Li-ion batteries have
incorporated this electrolyte.115 It has been reported that PEO with ceramic filler and lithium
salts in the Li-S battery possesses good mechanical properties and ionic conductivity. This
polymer electrolyte postpones diffusion of the lithium polysulphides and sulphur dissolution,
leading to decreasing self-discharge, also the polar groups in the polymer chains can dissolve
the ionic salts.116, 117 Scrosati et al.106 improved the overall operation and safety of the battery
by replacing the common liquid organic solutions by a gel-type polymer membrane, with
trapping (EC: DMC/LiPF6) solution saturated with lithium sulfide in a (PEO/LiCF3SO3)
polymer. In another work the discharge process of Li-S with PVdF gel polymer electrolyte
has been investigated.118 The PVdF gel polymer electrolyte was prepared by LiCF3SO3 as
lithium-ion resource, tetraglyme as plasticizer, and PVdF as a gelling agent which shows a
high first discharge capacity of 1268 mAh g-1.
Another approach is using ionic liquid-based electrolytes. An ionic liquid of N-methyl-N-
butyl-piperidinium (PP14) was synthesized as an electrolyte in the Li-S battery and showed
good chemical and electrochemical stability towards lithium and sulphur. The
dischargeability and reversibility of battery were improved because of a stable structure of
sulphur due to suppressed dissolution of polysulfides in the electrolyte.111
Another efficient and economical strategy to modify electrode/electrolyte interface in Li
batteries is using an additive at small concentration in the electrolyte. LiNO3 is mentioned as
an additive in electrolyte for Li-S batteries by Aurbach and his co-workers119. It this case,
solvents, polysulphide and LiNO3 additives reacted with lithium to form a protective surface
film (SEI) on the surface of the Li anode; this layer not only protected the lithium anode from
chemical reaction with the dissolved polysulphide but also prevented PS from
21
electrochemical reduction on the Li anode surface and inhibited the loss of active materials.53,
120. Although the cycle life and discharge capacity of the Li-S batteries improved, the safety
was reduced because of the strong oxidation of LiNO3. Thus, a new additive to the electrolyte
for Li-S batteries has been explored, LiBOB (lithium bis(oxalato) borate).121 This is thermally
more stable, and since its hydrolytic decomposition products are less toxic and corrosive, it is
more environmentally friendly. In batteries with LiBOB, a passivating surface film on is
formed on the lithium anode giving a higher discharge capacity, and a better cycle
performance.
3.4. Application of Li-S battery in electric vehicles
Currently, the transportation sector is the main consumer of fossil fuels that are a
contributing factor in global greenhouse gas (GHG) emissions. Over recent decades,
extensive effort have been devoted to the development and introduction of electric drive
vehicles, including both electric and hybrid vehicles (HEV), as a fundamental solution to the
serious emission and pollution problems, to the benefit of society.46, 122 In 1996 General
Motors released the EV-1, the first all-electric car from a major manufacturer.26 EVs
eliminate or reduce toxic exhaust emissions from automobiles, especially in urban areas of
high air pollution and consequently reduce carbon dioxide emissions, addressing concerns
over global climate change. This generation of vehicles is considered to promise a saving of
non-renewable energy sources by reducing dependence on oil and gas for transportation.
Hybrid electric vehicles are now commercially available and growing in market share and
there is increased interest internationally in the development and commercialization of
modern battery-powered electric vehicles. Leading companies in this industry, such as BMW,
Ford, Nissan, Tesla and Daimler Benz, use lithium-ion batteries as the energy supplier for the
EVs they have produced.123, 124 However, in order to develop Li-ion batteries of adequate
energy density for EVs to have an efficient driving range, it will be necessary to go beyond
22
present strategies and develop cells with higher energy density and lower costs. Li-S batteries
are good candidates for this.125, 126 Sion Power Corporation127 is working on the application of
the Li-S system for EV applications. They have developed a cell that can demonstrate 350
Wh kg-1 in unmanned aerial vehicle flights. High efficiency Li-S batteries could provide
appropriate energetic and environmental performance. Applying the Li-S battery in EV’s can
reduce the charge time and increase the cycle life of the EV batteries. It is predicted that Li-S
batteries will be commercially available between 2020 and 2025.122
4. Conclusions and outlook
In recent years, significant effort has been made to improve the performance of Li-S
batteries as an electrochemical energy storage device with high power output/input, excellent
cycle life and a low cost, for use in a number of applications ranging from portable
electronics to electric vehicles. Although theoretically the energy density of Li-S cell is high,
there are many challenges to be addressed before theory becomes practice. As highlighted in
this review, such challenges are frequently rooted in materials discovery and optimization
because the efficiency of a battery depends on the electrode and electrolyte performance.
This review presents the current status of the Li-S battery and discusses its challenges
and its electrochemical reaction mechanism. Generally, one of the main problems of the Li-S
battery is its poor cycle life, mainly caused by PS dissolving into the electrolyte. To
overcome this hurdle, all cathodes, anodes and electrolytes should be modified. Research has
demonstrated that applying a sulphur/carbon-based composite as the cathode has opened up a
new way to Li-S batteries with high efficiency. Among of the many carbon-based materials,
graphene provides hope because of its high electrical conductivity, high surface area and low
cost. The Li metal anode can cause some safety problems. However, promising results have
been achieved recently in Li/S battery efficiency by using a non-lithium metal anode such as
silicon, or by applying protected anode technologies. As mentioned in this review, electrolyte
23
has a direct effect on cell performance and various electrolytes have been investigated for the
Li-S battery and, among these, polymer electrolytes have been regarded as good candidate for
future researches on Li-S battery because of their safety and easy design and fabrication.
Although there has been promising progress, many aspects of Li-S batteries are not fully
understood, and will require additional investigation. High initial capacities above 1000 mA h
g-1 can be achieved with an improved cell, but maintenance of the initial cathode morphology
is difficult. To overcome these issues, researchers are explore more profound mechanisms
and reasons of the capacity fading in Li-S batteries after cycling. These issues will be solved
when all the problems are identified. In addition, Li-S batteries have to compete with other
energy conversion and storage technologies, such as fuel cells, which are promising energy
devices for the transport, mobile and stationary sectors. Meanwhile, Sion Power Corporation
is focusing on developing the commercial Li-S battery and claims that the Sion Power's Li-S
will be the next rechargeable power source for a wide variety of applications, including
unmanned vehicle systems, military communications and electric vehicles.
The ultimate goal is to develop a low-cost, high-throughput, environmentally friendly
battery. In order to reach this ambitious goal, there must be a better understanding of the
current situation with Li-S batteries. This review may provide some new insights and
opportunities into the challenges in this area, and so help move towards a commercially
available Li-S battery.
Acknowledgements
This research is financially supported by the Australian Research Council (ARC) through
ARC Discovery Project DP110101974.
24
References
[1] B. Scrosati and J. Garche, J. Power Sources, 195, 2419 (2010).
[2] D. A. C. Brownson, D . K. Kampouris, and C. E. Banks, J. Power Sources, 196, 4873
(2011).
[3] C. Liang, N. J. Dudney, and J.Y. Howe, Chem. Mater., 21, 4724 (2009).
[4] M. K. Song, S. Park, F. M. Alamgir, J. Cho, and M. Liu, Mater. Sci. Eng., R, 72, 203
(2011).
[5] M. Mirzaeian and P.J. Hall, Electrochim. Acta, 54, 7444 (2009).
[6] K. C. Divya and J. Østergaard, Electr. Pow. Syst. Res., 79, 511 (2009).
[7] X. L. Ji, K.T. Lee, and L. F. Nazar, Nat. Mater., 8, 500 (2009).
[8] J. B. Goodenough and Y. Kim, J. Power Sources, 196, 6688-6694.
[9] J. M. Tarascon and M. Armand, Nature, 414, 359 (2001).
[10] J. B. Goodenough, J. Solid State Electrochem., 16, 2019 (2012).
[11] D. Aurbach, Y. Talyosef, B. Markovsky, E. Markevich, E. Zinigrad, L. Asraf, J. S.
Gnanaraj, and H. J. Kim, Electrochim. Acta, 50, 247 (2004).
[12] T. B. Reddy, Linden's handbook of batteries, 4th ed., p.26.1, McGraw-Hill, New York,
(2011).
[13] A. S. Arico, P. Bruce, B. Scrosati, J. M. Tarascon, and W. V. Schalkwijk, Nat. Mater., 4,
366 (2005).
[14] F. Santoni, P. Tortora, F. Alessandrini, and S. Passerini, in: European Space Agency, p.
653 (2002).
[15] D.C. Bock, A.C. Marschilok, K.J. Takeuchi, and E.S. Takeuchi, Electrochim. Acta, 84,
155 (2012).
[16] M. Nagata, A. Saraswat, H. Nakahara, H. Yumoto, D. M. Skinlo, K. Takeya, and H.
Tsukamoto, J. Power Sources, 146, 762 (2005).
25
[17] T. B. Reddy, Linden's handbook of batteries, 4th ed., p.31.2, McGraw-Hill, New York,
(2011).
[18] J. S. Lee, S. Tai Kim, R. Cao, N. S. Choi, M. Liu, K. T. Lee, and J. Cho, Adv. Energy
Mater., 1, 34 (2011).
[19] Q. Wang, P. Ping, X. Zhao, G. Chu, J. Sun, and C. Chen, J. Power Sources, 208, 210
(2012).
[20] L. Ji, Z. Lin, M. Alcoutlabi, and X. Zhang, Energy Environ. Sci., 4, 2682 (2011).
[21] L. Ji, Z. Lin, B. Guo, A. J. Medford, and X. Zhang, Chemistry, 16, 11543 (2010).
[22] L. Ji, Z. Tan, T. R. Kuykendall, S. Aloni, S. Xun, E. Lin, V. Battaglia, and Y. Zhang,
Phys. Chem. Chem. Phys., 13, 7170 (2011).
[23] Y. Wang and G. Cao, Adv. Mater., 20, 2251 (2008).
[24] T. Fang, J. G. Duh, and S. R. Sheen, J. Electrochem. Soc., 152, A1701 (2005).
[25] C. Wang, J. j. Chen, Y. N. Shi, M. S. Zheng, and Q. F. Dong, Electrochim. Acta, 55,
7010 (2010).
[26] J. Tellefson, Nature, 456, 436 (2008).
[27] T. B. Reddy, Linden's handbook of batteries, 4th ed., p.26.75, McGraw-Hill, New York,
(2011).
[28] S.S. Zhang, D. Foster, and J. Read, J. Power Sources, 195, 3684 (2010).
[29] P.G. Bruce, Solid State Ionics, 179, 752 (2008).
[30] X. He, J. Ren, L. Wang, W. Pu, C. Wan, and C. Jiang, ECS Trans., 2, 47 (2007).
[31] P. G. Bruce, S. A. Freunberger, L. J. Hardwick, and J. M. Tarascon, Nat. Mater., 11, 19
(2012).
[32] X. Ji and L. F. Nazar, J. Mater. Chem., 20, 9821 (2010).
[33] O. Crowther, B. Meyer, M. Morgan, and M. Salomon, J. Power Sources, 196, 1498
(2011).
26
[34] T. B. Reddy, Linden's handbook of batteries, 4th ed., p.33.2, McGraw-Hill, New York,
(2011).
[35] Y. Shaohua and K. Harold, J. Power Sources, 112, 162 (2002).
[36] D. Marmorstein, T.H. Yu , K.A. Striebel, F.R. McLarnon, J. Hou , and E. J. Cairns, J.
Power Sources, 89, 219 (2000).
[37] J. Sun, Y. Huang, W. Wang, Z. Yu, A. Wang, and K. Yuan, Electrochim. Acta, 53, 7084
(2008).
[38] D. Herbert, and J. Ulam, in “U.S. Patent”, patent No.3,043,896 (1962).
[39] C. Barchasz, J. C. Leprêtre, F. Alloin, and S. Patoux, J. Power Sources, 199, 322 (2012).
[40] Y. V. Mikhaylik and J. R. Akridge, J. Electrochem. Soc., 151, A1969 (2004).
[41] J. H. Shin, S. S. Jung, K. W. Kim, and H. J. Ahn, J. Mater. Sci. Mater. Electron., 13, 727
(2002).
[42] Y. M. Lee, N. S. Choi, J. H. Park, and J. K. Park, J. Power Sources, 119-121, 964
(2003).
[43] D. R. Chang, S. H. Lee, S. W. Kim, and H. T. Kim, J. Power Sources, 112 , 452 (2002).
[44] H. Ryu, H. Ahn, K. Kim, J. Ahn, J. Lee, and E. Cairns, J. Power Sources, 140, 365
(2005).
[45] S. E. Cheon, K. S. Ko, J. H. Cho, S. W. Kim, E. Y. Chin, and H. T. Kim, J. Electrochem.
Soc., 150 (6), A800 (2003).
[46] J. Wang, S. Y. Chew, Z. W. Zhao, S. Ashraf, D. Wexler, J. Chen, S. H. Ng, S. L. Chou,
and H. K. Liu, Carbon, 46, 229 (2008).
[47] B. H. Jeon, J. H. Yeon, and I. J. Chung, J. Mater. Process. Technol., 143-144, 93 (2003).
[48] Y. Zhang, Y. Zhao, K. E. Sun, and P. Chen, The Open Materials Science Journal, 5, 215
(2011).
[49] V. S. Kolosnitsyn and E. V. Karaseva, J. Electrochem., 44, 506 (2008).
27
[50] Y. J. Choi, Y. D. Chung, C. Y. Baek, K. W. Kim, H. J. Ahn, and J. H. Ahn, J. Power
Sources, 184, 548 (2008).
[51] Y. Jung and S. Kim, Electrochem. Commun., 9, 249 (2007).
[52] C. Lai, X. P. Gao, B. Zhang, T. Y. Yan, and Z. Zhou, J. Phys. Chem. C, 113, 4712
(2009).
[53] S.S. Zhang, Electrochim. Acta, 70, 344 (2012).
[54] H. S. Ryu, Z. Guo, H. J. Ahn, G. B. Cho, and H. Liu, J. Power Sources, 189, 1179
(2009).
[55] S. E. Cheon, K. S. Ko, J. H. Cho, S. W. Kim, E. Y. Chin, and H. T. Kim, J. Electrochem.
Soc., 150 (6), A796 (2003).
[56] H. Schneider, A. Garsuch, A. Panchenko, O. Gronwald, N. Janssen, and P. Novák, J.
Power Sources, 205, 420 (2012).
[57] P. G. Bruce, L. J. Hardwick, and K. M. Abraham, MRS Bull., 36, 506 (2011).
[58] N. Jayaprakash, J. Shen, S. S. Moganty, A. Corona, and L. A. Archer, Angew. Chem.
Int. Ed. Engl., 50, 5904 (2011).
[59] J.Wang, J. Yang, C. Wan, K. Du, J. Xie, and N. Xu, Adv. Funct. Mater., 13, 487 (2003).
[60] L. Qiu, S. Zhang, L. Zhang, M. Sun, and W. Wang, Electrochim. Acta, 55, 4632 (2010).
[61] M. Sun, S. Zhang, T. Jiang, L. Zhang, and J. Yu, Electrochem. Commun., 10, 1819
(2008).
[62] Y. Yang, G. Yu, J. J. Cha, H. Wu, M. Vosgueritchian, Y. Yao, Z. Bao, and Y. Cui, ACS
Nano, 5, 9187–9193 (2011).
[63] E. Strauss, D. Golodnitsky, and E. Peled, Electrochim.Acta, 45, 1519 (2000).
[64] X. He, Q. Shi, X. Zhou, C. Wan, and C. Jiang, Electrochim. Acta, 51, 1069 (2005).
[65] J. L. Wang, J. Yang, J.Y. Xie, N. X. Xu, and Y. Li, Electrochem. Commun. 4, 499
(2002).
28
[66] H. S. Ryu, H. J. Ahn, K. W. Kim, J. H. Ahn, K. K. Cho, and T. H. Nam, Electrochim.
Acta, 52, 1563 (2006).
[67] R. A. Huggins, J. Power Sources, 153, 365 (2006).
[68] G. Zheng, Y. Yang, J. J. Cha, S. S. Hong, and Y. Cui, Nano Lett., 11, 4462 (2011).
[69] X. Liang, Y. Liu, Z. Wen, L. Huang, X. Wang, and H. Zhang, J. Power Sources, 196,
6951 (2011).
[70] H. P. Huang and J. J. Zhu, Chin. J. Anal. Chem., 39, 963 (2011).
[71] S. R. Chen, Y. P. Zhai, G. L. Xu, Y. X. Jiang, D.Y. Zhao, J. T. Li, L. Huang, and S. G.
Sun, Electrochim. Acta, 56, 9549 (2011).
[72] J. Guo, Y. Xu, and C. Wang, Nano Lett., 11, 4288 (2011).
[73] B. Zhang, C. Lai, Z. Zhou, and X. P. Gao, Electrochim. Acta, 54, 3708 (2009).
[74] Y. J. Choi, K. W. Kim, H. J. Ahn, and J. H. Ahn, J. Alloys Compd., 449, 313 (2008).
[75] L. Ji, M. Rao, S. Aloni, L. Wang, E. Cairns, and Y. Zhang, Energy Environ. Sci., 4, 5053
(2011).
[76] S. c. Zhang, L. Zhang, W. k. Wang, and W. j. Xue, Synth. Met., 160, 2041 (2010).
[77] X. Liang, Z. Wen, Y. Liu, H. Zhang, L. Huang, and J. Jin, J. Power Sources, 196, 3655
(2011).
[78] J. Schuster, G. He, B. Mandlmeier, T. Yim, K. T. Lee, T. Bein, and L. F. Nazar, Angew.
Chem. Int. Ed. Engl., 51, 3591 (2012).
[79] D. W. Wang, G. Zhou, F. Li, K. H. Wu, G. Q. Lu, H. M. Cheng, and I. R. Gentle, Phys.
Chem. Chem. Phys., 14, 8703 (2012).
[80] X. Liang, Z. Wen, Y. Liu, H. Zhang, J. Jin, M. Wu, and X. Wu, J. Power Sources, 206,
409 (2012).
[81] W. Zheng, Y. W. Liu, X. G. Hu, and C. F. Zhang, Electrochim. Acta, 51, 1330 (2006).
29
[82] W. Wei, J. Wang, L. Zhou, J. Yang, B. Schumann, and Y. NuLi, Electrochem.
Commun., 13, 399 (2011).
[83] J. Z. Wang, L. Lu, M. Choucair, J. A. Stride, X. Xu, and H. K. Liu, J. Power Sources,
196, 7030 (2011).
[84] L. Ji, M. Rao, H. Zheng, L. Zhang, Y. Li, W. Duan, J. Guo, E. J. Cairns, and Y. Zhang,
J. Am. Chem. Soc., 133, 18522 (2011).
[85] H. Wang, Y. Yang, Y. Liang, J. T. Robinson, Y. Li, A. Jackson, Y. Cui, and H. Dai,
Nano Lett., 11, 2644 (2011).
[86] Y. X. Wang, L. Huang, L. C. Sun, S. Y. Xie, G. L. Xu, S. R. Chen, Y. F. Xu, J. T. Li, S.
L. Chou, S. X. Dou, and S. G. Sun, J. Mater. Chem., 22, 4744 (2012).
[87] M. S. Park, J. S. Yu, K. J. Kim, G. Jeong, J. H. Kim, Y. N. Jo, U. Hwang, S. Kang, T.
Woo, and Y. J. Kim, Phys. Chem. Chem. Phys., 14, 6796 (2012).
[88] F. Zhang, Y. Dong, Y. Huang, G. Huang, X. Zhang, and L. Wang, J. Phys. Conf. Ser.,
339, 012003 (2012).
[89] M. Pumera, Chem. Rec., 9, 211 (2009).
[90] W. Gao, L. B. Alemany, L. Ci, and P. M. Ajayan, Nat. Chem., 1, 403 (2009).
[91] Y. Zhang, H. Li, L. Pan, T. Lu, and Z. Sun, J. Electroanal. Chem., 634, 68 (2009).
[92] H. Wang, Q. Hao, X. Yang, L. Lu, and X. Wang, Electrochem. Commun., 11, 1158
(2009).
[93] D. Wang, C. Wang, D. Choi, J. Li, L. V. Saraf, Z. Yang, J. Zhang, Z. Nie, R. Kou, I. A.
Aksay, J. Liu, and D. Hu, ACS Nano, 3, 907 (2009).
[94] C. Wang, D. Li, C. O. Too, and G. G. Wallace, Chem. Mater., 21, 2604 (2009).
[95] S. m. Paek, E. Yoo, and I. Honm, Nano Lett., 9, 72 (2009).
[96] A. L. M. Reddy, A. Srivastava, S. R. Gowda, H. Gullapalli, M. Dubey, and P. M.
Ajayan, ACS Nano, 4, 6337 (2010).
30
[97] Y. Cao, X. Li, I. A. Aksay, J. Lemmon, Z. Nie, Z. Yang, and J. Liu, Phys. Chem. Chem.
Phys., 13, 7660 (2011).
[98] L. Zhang, L. Ji, P. A. Glans, Y. Zhang, J. Zhu, and J. Guo, Phys. Chem. Chem. Phys.,
14, 13670 (2012).
[99] N. Li, M. Zheng, H. lu, Z. Hu, C. Shen, X. Chang, G. Ji, J. Cao, and Y. Shi, Chem.
Commun., 48, 4106 (2012).
[100] S. Li, M. Xie, J. Liu, H. Wang, and H. Yan, Electrochem. Solid-State Lett., 14 (7),
A105 (2011).
[101] N. I. Kim, C. B. Lee, J. M. Seo, W. J. Lee, and Y. B. Roh, J. Power Sources, 132, 209
(2004).
[102] S. E. Cheon, S. S. Choi, J. S. Han, Y. S. Choi, B. H. Jung, and H. S. Lim, J.
Electrochem. Soc., 151 (12), A2067 (2004).
[103] S. C. Han, M. S. Song, H. Lee, H. S. Kim, H. J. Ahn, and J. Y. Lee, J. Electrochem.
Soc., 150 (7), A889 (2003).
[104] J. Wang, J. Chen, K. Konstantinov, L. Zhao, S. H. Ng, G. X. Wang, Z. P. Guo, and H.
K. Liu, Electrochim. Acta, 51, 4634 (2006).
[105] Y. Yang, M. T. McDowell, A. Jackson, J. J. Cha, S. S. Hong, and Y. Cui, Nano Lett.,
10, 1486 (2010).
[106] J. Hassoun and B. Scrosati, Angew. Chem. Int. Ed., 49, 2371 (2010).
[107] Y.S. Nimon, M.Y. Chu, and S.J. Visco, in “U.S patent” , Patent No. 6,537,701 (2003).
[108] S. Liu, J. Yang, L. Yin, Z. Li, J. Wang, and Y. Nuli, Electrochim. Acta, 56, 8900
(2011).
[109] M. Nagao, A. Hayashi, and M. Tatsumisago, Electrochim. Acta, 56, 6055 (2011).
[110] J. H. Shin and E. J. Cairns, J. Electrochem. Soc., 155 (5), A368 (2008).
31
[111] L. X. Yuan, J. K. Feng, X. P. Ai, Y. L. Cao, S. L. Chen, and H. X. Yang, Electrochem.
Commun., 8, 610 (2006).
[112] S. S. Jeong, Y. T. Lim, Y. J. Choi, G. B. Cho, K. W. Kim, H. J. Ahn, and K. K. Cho, J.
Power Sources, 174, 745 (2007).
[113] J. W. Choi, J. K. Kim, G. Cheruvally, J. H. Ahn, H. J. Ahn, and K. W. Kim,
Electrochim. Acta, 52, 2075 (2007).
[114] W. Wang, Y. Wang, Y. Huang, C. Huang, Z. Yu, H. Zhang, A. Wang, and K. Yuan, J.
Appl. Electrochem., 40, 321 (2010)
[115] X. Kang, Chem. Rev., 104, 4303 (2004).
[116] X. Zhu, Z. Wen, Z. Gu, and Z. Lin, J. Power Sources, 139, 269 (2005).
[117] Y. Zhao, Y. Zhang, D. Gosselink, T. N. L. Doan, M. Sadhu, H. J. Cheang, and P. Chen,
Membranes, 2, 553 (2012).
[118] H. S. Ryu, H. J. Ahn, K. W. Kim, J. H. Ahn, and J. Y. Lee, J. Power Sources, 153, 360
(2006).
[119] D. Aurbach, E. Pollak, R. Elazari, G. Salitra, C. S. Kelley, and J. Affinito, J.
Electrochem. Soc., 156 (8), A694 (2009).
[120] S.S. Zhang, J. Electrochem. Soc., 159 (7), A920 (2012).
[121] S. Xiong, X. Kai, X. Hong, and Y. Diao, Ionics, 18, 249 (2011).
[122] S. J. Gerssen-Gondelach and A. P. C. Faaij, J. Power Sources, 212, 111 (2012).
[123] B. G. Pollet, I. Staffell, and J. L. Shang, Electrochim. Acta, 84, 235 (2012).
[124] T. B. Reddy, Linden's handbook of batteries, 4th ed., p.29.7, McGraw-Hill, New York,
(2011).
[125] Boston Consultancy Group, http://www.bcg.com/documents/file36615.pdf, (2010).
[126] B. L. Ellis, K. T. Lee, and L. F. Nazar, Chem. Mater., 22, 691 (2010).
32
[127] Y. V. Mikhaylik, I. Kovalev, R. Schock, K. Kumaresan, J. Xu, and J. Affinito, ECS
Trans., 25 (35), 23 (2010).
33
Figure Captions
Fig. 1. Schematic illustration of a typical lithium ion battery.
Fig. 2. Schematic configuration of Li-S battery based on graphene- sulphur composite (G-S)
cathode.
Fig. 3. Voltage profile of the first discharge of a Li-S cell. Reproduced from Zhang,53
(written permission has been obtained from the previous publisher).
Fig. 4. SEM characterizations of hollow carbon nanofiber-encapsulated sulphur: (a) anodic
aluminum oxide (AAO) template after carbon coating, (b) hollow carbon nanofiber-
encapsulated sulfur after etching away AAO template, (c) cross-sectional image of hollow
carbon nanofiber/S array, (d) carbon elemental mapping of (c) and (e) sulfur elemental
mapping of (c). Reproduced from Zheng et al.,68 (written permission has been obtained from
the previous publisher).
Fig. 5. SEM images of surface morphologies after 70 cycles: (a) Li anode; (b) Li2.6BMg0.05
anode. Reproduced from Liu et al.,108 (written permission has been obtained from the
previous publisher).
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