View
226
Download
0
Category
Preview:
Citation preview
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
1/25
59
Advanced Energy Devices: Lithium IonBattery and High Energy Capacitor
M. K. Devaraju, M. Sathish, and I. Honma
Abstract
The development of modern technology toward energy production and storage
is essential to support human life with wide impact on the environment,
human health, and worlds economy. Through the development of the advanced
energy systems, human life can be ensure in a networked society even more
conveniently. In the electric and energy field, secondary batteries will play a
critical factor in reducing the environmental hazard and enable the effective
construction of the green energy society. At present, high power density and high
energy density are required as a power sources for the hybrid electric vehicle(HEV) and electric vehicle (EV). As we know, Li-ion battery has high energy
density but low power density. The energy density of Li-ion battery decreases
with the increase in rate capability, but electric double-layer capacitor has high
power density but low energy density. So, this chapter focuses on the advanced
energy devices such as lithium-ion battery and high energy capacitors beginning
with brief introduction.
The importance of the solution process mainly including the hydrothermal
and solvothermal method as sustainable chemistry toward the processing of
the positive electrode materials for lithium-ion batteries has been discussed.
The requirement and different techniques of the carbon coating using differentcarbon sources to improve the electrochemical property of the positive electrode
materials have been focused. The electrochemical property of the olivine-
structured cathode materials affected by different particles size and morphology
has been addressed. The concept of using graphene-based compounds for
the electric double-layer capacitor applications and electrochemical capacitor
M.K. Devaraju () M. Sathish I. Honma
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Aoba-ku,Sendai, Japan
e-mail:devarajumk@rediffmail.com;marappan.sathish@gmail.com;
i.honma@tagen.tohoku.ac.jp;
J. Kauffman, K.-M. Lee (eds.), Handbook of Sustainable Engineering,
DOI 10.1007/978-1-4020-8939-8 105,
Springer Science+Business Media Dordrecht 2013
1149
mailto:devarajumk@rediffmail.commailto:devarajumk@rediffmail.commailto:marappan.sathish@gmail.commailto:marappan.sathish@gmail.commailto:i.honma@tagen.tohoku.ac.jpmailto:i.honma@tagen.tohoku.ac.jpmailto:marappan.sathish@gmail.commailto:devarajumk@rediffmail.com7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
2/25
1150 M.K. Devaraju et al.
based on pseudocapacitance has been discussed. The hybrid capacitors such
as metal oxide-doped graphene and PANI/graphene nanocomposites with their
electrochemical performances have also been discussed.
1 Introduction
The rapid growth of science and technology during the last several decades in the
world is keep changing the human life by contributing to their needs to enjoy
their living. Recently, the development of the advanced energy devices becomes
critical to global human development including the ecosystems, economic growth,
employment, and prosperity of the present and future generation. In addition, the
slow diminishing of available energy resources is an alarm to change the present
energy system to the sustainable and renewable one for a long-term energy supplyfor the mankind. Moreover, realization of the low carbon society based on
the advanced technologies for the sustainable development is one of the greatest
challenges at present.
The key technology for this challenge is to develop the next generation of clean
energy storage devices with high power density, high energy density, and high safety
for the hybrid electric vehicles (HEV), plug-in hybrid electric vehicles (PHEV), and
pure electric vehicles (PEV) (Aric-o et al.2005). The practical realization of these
applications involves the development of the advanced energy functional materials
for the high energy storage and for a long-term performance. Lithium-ion batteryand capacitors are considered as the future advanced energy storage systems for
various next generation electronic and electrical applications.
Lithium-Ion Battery: Lithium-ion (Li-ion) batteries are comprised of cells that
employ lithium intercalation compounds as the positive and negative materials. As
a battery is cycled, lithium ions (LiC) exchange between the positive and negative
electrodes. They are also referred to as rockingchair batteries as the lithium ions
rock back and forth between the positive and negative electrodes as the cell is
charged and discharged. The positive electrode material is typically a metal oxide
with a layered structure, such as lithium cobalt oxide (LiCoO2), or a material with
a tunneled structure, such as lithium manganese oxide (LiMn2O4), on a currentcollector of aluminum foil. The negative electrode material is typically a graphitic
carbon, also a layered material, on a copper current collector. In the charge/discharge
process, lithium ions are inserted or extracted from the interstitial space between
atomic layers within the active materials (Ehrlich2001).
The mechanism involved in Li-ion battery is shown in Fig. 59.1. Where the
lithium metal was substituted with other insertion compounds, such as graphite
or non-graphitic carbon, LiCoO2 was used as the cathode material. The entire
electrochemical process would involve the reversible transfer of lithium ions
between the two electrodes. During the charge process, lithium ion is de-intercalatedfrom the cathode layers, then transported and intercalated into the carbonaceous
anode. While the discharge process occurred, the lithium ions are deintercalated
from the carbonaceous anode and intercalated again to empty site between layers of
the cathode materials (Park2010).
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
3/25
59 Advanced Energy Devices: Lithium Ion Battery and High Energy Capacitor 1151
e
e e
e
e
e
e
e
A
LixC6 +Li1xCO2
Li+
charge
dischargeLi
+
Fig. 59.1 Schematic representation of Li ion battery showing discharge intercalation mechanism
(Ehrlich2001)
Among the batteries, especially secondary batteries have been essential part of
the power source for the advanced energy devices. In the future, they will become
a key factor to pursue comfortable human life. The electric power source willbe produced by the environmentally friendly wind generation and solar cell, and
the produced electric power can charge the batteries which are not harmful and
friendly to the environment. In the electric and energy field, secondary batteries
will play a critical factor in reducing the environmental hazard and enable the
effective construction of the green energy society (Park2010). After three decades
of development in battery technology, the Li-ion battery technology has emerged
as one of the most popular battery technologies (Tarascon and Armand 2001).
They are widely used in various electronic devices because of their good cycle
life, high energy density, and high capacity over any other battery technologies.
The Li-ion battery technology that now dominates much of the portable batterybusiness has matured enough over the last 5 years to be considered for the short-
term implementation in the hybrid electric vehicles (HEV) and electric vehicles
(EV) applications (Tarascon and Armand2001).
High Energy Capacitors: The discovery of a so-called condenser, now referred
to as a capacitor that electric charges could be stored on the plate, was made in
the mid-eighteenth century during the period when the phenomena associated with
static electricity were being revealed. The embodiment known as a condenser is
attributed to Musschenbroek (Encyclopedia Britannica1926) in 1746 at Leyden in
the Netherlands, hence the name Leyden jar. The electrochemical capacitor wassupposed to boost the hybrid electric vehicle to provide the high or strong power
for acceleration and additionally allow the recovery of braking energy. The electric
double-layer capacitor consisting of a single cell with a high surface area electrode
material is loaded with electrolyte (Kotz and Carlen2000). The schematic diagram
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
4/25
1152 M.K. Devaraju et al.
collectorpolarizing
electrodes
electrolyte
separator
collector
electric double layer
+
+ +
+
+
+
+
+
+
+
+
+
+
+
+
-
-
-
-
-
-
Fig. 59.2 Schematic representation showing basic structure of electric double layer (Kotz andCarlen2000)
of the double-layer electric capacitor is shown in Fig. 59.2. Electric double-layer
capacitors store the electric energy in an electrochemical double layer (Helmholtz
layer) formed at the solid/electrolyte interface. Positive and negative ionic charges
within the electrolyte accumulate at the surface of the solid electrode. The quantity
of ion removed from the electrolyte equals the charge developed on the electrodesurface. Therefore, the maximum energy stored in a capacitor is limited by the
capacitance of the capacitor, C, and the maximum operating voltage, V.
Recently, high-performance electrochemical energy storage systems are being
investigated as they are very important for the electric vehicles and hybrid electric
vehicles (Liu et al. 2010). Great efforts have been made to develop high-power
(10kWkg1) electrochemical capacitors (ECs) due to their faster charge and
discharge processes, in seconds, than those of batteries. In addition, electrochemical
capacitors have a longer cycle life as compared to batteries because no or negligibly
small chemical charge transfer reactions are involved.
When compared with those of other secondary batteries and Li-ion battery, it has
the following advantages: long cycle life, >100,000 cycles; some system up to 106;
good power density (under certain conditions, limited by IR or equivalent series
resistance (esr) complexity of equivalent circuit); simple principle and mode of
construction; cheap material (for aqueous embodiment); combines state-of-charge
indication, Q D CV; and can be combined for the rechargeable battery for the hybrid
application (electric vehicles). However, ECs suffer from a lower energy density
than batteries (Liu et al. 2010). The energy density can be improved by adopting
asymmetric (hybrid) systems; at present they have been extensively explored by
combining a battery like Faradic electrode (as energy source) and a capacitiveelectrode (as power source) to increase the operation voltage, which leads to a
notable improvement of the energy density of high-power ECs nearly to that of
batteries (Yoshino2004).
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
5/25
59 Advanced Energy Devices: Lithium Ion Battery and High Energy Capacitor 1153
In this chapter, solution-based synthesis and characterization of the olivine-
structured lithium metal phosphates (LiFePO4, LiMnPO4, and LiCoPO4) nanoma-
terials used as the positive electrode materials will be focused. The sustainable
chemistry process such as supercritical solvothermal method and solution processthat has been used for the materials synthesis is discussed. These methods can
be considered as environmentally friendly, rapid, and easy process for large-
scale synthesis or preparation of the advanced functional materials. High-energy
capacitors such as metal oxidedoped graphene, PANI/graphene nanocomposites,
and electrochemical capacitors based on pseudocapacitance have been discussed
along with their electrochemical property for the advanced energy systems.
2 Positive Electrode Materials for Li-Ion Battery
Among the battery components, the cathode materials are the one which are crucial
in determining the high power, safety, longer life, and cost of the battery that satisfies
the requirements of the larger battery system. These can be applicable to the electric
vehicles, power tools, energy storage equipment, and so on (Padhi et al. 1997).
There are various types of materials being used as the positive electrode materials
for the lithium-ion batteries as shown in Fig. 59.3 (Tarascon and Armand 2001).
The structural, chemical stability, availability of redox couples at a suitable energy,
specific capacity, operating voltage, and safety issues are the primary considerations,
and these properties are different among the positive electrode materials shownin Fig. 59.3. Lithium-based electrodes have four types of structure which have
lithium insertion voltage of above 3 V. They include layers of lithium metal oxides
such as LiCoO2, LiNiO2, LiCoNiO2, and LiMnNiO2; the zigzag layers structure
of LiMnO2; the three-dimensional spinel type, LiMn2O4 and Li1=2Mn3=2O4; and
the olivine structure of LiMPO4 (M=Fe, Mn, Co, and Ni). Recently, Li2MSiO4(M=Fe, Mn, and Co) based cathodes have been investigated, which are envisaged
as the potential cathode candidate for the high-power batteries (Dominko2010).
This is because of their overwhelming advantages such as high theoretical capacity
(>330mAhg1 which is possible while extracting more than one LiC ion per
formula unit), high thermal stability through strong SiO bonding, safety, cost-
effectiveness, eco-friendliness, and ease to synthesize. This chapter discusses the
olivine-structured LiMPO4cathode materials.
3 LiMPO4(M=Fe, Mn, Co, and Ni) as Positive Electrodes forLi-Ion Battery
In 1990s, LiCoO2 was commercialized by Sony. Since then, a series of excellent
candidates has appeared because of high cost and oxidative instability of LiCoO2foruse as the cathode material. In this regard, the layered rock salt systems, LixNiO2(0
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
6/25
1154 M.K. Devaraju et al.
Li1xMn2yMyO4
Li1xCo1yMyO2
Li1xNi1yzCoyMzO4[M=Mg,AI,...]
LixMn1yMyO2[M=Cr, Co,...]
Vanadium oxides
[V2O5, LiV3O8]MnO2
Composite alloys[Sn(M)-based]
Carbons
Graphite
0 200 400 600
Capacity (A h kg1)
800 1000 3,800 4,000
[Sn(O)-based]
3d-Metal oxidea
Li-ionpotential
Li-metalpotential
Positivematerials
Negativ
ematerials
Positive material:
Negative material:
of Li ion
limited cycling)
Li metal
of Li metal
(
of Li ion
limited RT cycling
of Li metal
Nitrides LiMyN2
Polyanionic compound [Li1xVOPO4,LixFePO4]
4
3
2
PotentialversusLi/Li+(
v)
1
0
Fig. 59.3 Voltage vs. capacity of some cathode materials (Tarascon and Armand2001)
to some degree. However, they are still problematic due to their compositions.
To overcome these disadvantages and problems, the olivine-structured lithium metal
phosphate cathode materials are considered as the attractive cathode materials
because they are in low cost, abundant in nature, exhibit high theoretical capacity
(170mAhg1) (Padhi et al.1997), high thermal stability owing to the presence of
a strong PO covalent bond, and easy to synthesize.
LiMPO4 (M=Fe, Mn, Co, and Ni) belongs to the orthorhombic structure, which
consists of the hexagonal closed packing (HCP) of the oxygen atoms with LiC and
M2C cations located in half of the octahedral sites and P5C cations in one eighth of
the tetrahedral sites(Fig.59.4). This structure may be described as chains (along the
c direction) of edge sharing MO6octahedra that are cross-linked by the PO4groupsforming a three-dimensional network. Tunnels perpendicular to the [010] and [001]
directions contain octahedrally coordinated LiC cations (along the b-axis), which
are mobile in these cavities (Jin and Jiang2009). Among the phosphates, LiFePO4is considered most stable, low cost, and high compatibility with the environments.
3.1 Synthesis of LiMPO4(M=Fe, Mn and, Co) Cathodes by theSolution Process
Since the demand for the cathode materials for lithium-ion battery is increasing
continuously, various methods have been developed to prepare lithium metal
phosphate nanoparticles, such as the solgel method (Choi and Kumta 2007),
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
7/25
59 Advanced Energy Devices: Lithium Ion Battery and High Energy Capacitor 1155
Fig. 59.4 The schematic representation of the crystal structure of LiMPO4 (M=Fe, Mn, Co, and
Ni) compounds showing the HCP oxygen array with MO6 and PO4 groups (Jin and Jiang2009)
coprecipitation (Arnold et al.2003), mechanochemical activation (Kim et al.2007),
spray technology (Konarova and Taniguchi 2009), and solid-state reaction (Padhi
et al.1997). However, all these methods have limitations in practice. Commercial
success of new cathode materials is mainly dependent on the preparation method,
which controls morphology, particle size, and cation order among other critical
experimental parameters. Although traditionally high-temperature methods have
been used, they are both energy intensive and cannot readily produce manypotentially metastable structures that might result in high lithium-ion diffusivity.
However, they do have the advantage of being hydroxyl/water-free. There are
many possible approaches for the synthesis of active materials, but in the end, a
commercially viable approach must be used (Whittingham et al. 2004). Therefore,
simple solution process could be required to overcome practical problems.
Recently, soft chemical approaches such as hydrothermal and solvothermal or
ion exchange offer several advantages and are being used on the tonnage quantities,
as such, the chemical industry considers them viable. Hydrothermal synthesis has
been extensively studied for the synthesis of simple oxides such as those of tungsten,molybdenum, and vanadium, and today many of the key parameters are understood
(Chirayil et al. 1997). Different kinds of phosphates have also been successfully
prepared by the hydrothermal method (Byrappa et al. 2008). The advantages of
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
8/25
1156 M.K. Devaraju et al.
Precursors Spheres Plates Cubes Rods
Hydrothermal and solvothermal process
Hydrothermal and solvothermal products
PrecursorsTeflonliner
AutoclaveFURNACE/OVEN
Fig. 59.5 Showing experimental scheme of hydrothermal and solvothermal process for the design
of nanoparticles with various shapes (Author unpublished work)
using the hydrothermal and solvothermal methods are shown in Fig. 59.5, where
morphology, size, and other experimental parameters can be easily controlled.
Moreover, low-temperature solution process is environmentally friendly, low energy
consuming, and easy to perform for the large-scale production.
The concept of the hydrothermal process for the preparation of LiFePO4 was
first realized by Yang et al. in (2001). However, preparation of the nanocrystalline
particles ranging from 500 to 1,500 nm was reported by Tajimi et al. (2004) under
the hydrothermal reaction condition at the reaction temperature of 150220C for
several hours using various amounts of polyethylene glycol (PEG).
Recently, monodispersed particles of LiFePO4 were prepared using a mixture ofisopropanol and aqueous solution by controlling the RH factor (Zhang et al.2009).
The monodispersed LiFePO4 particles were controlled from 1 to 4m in length
and 12m in diameter. Small particles of LiFePO4 measuring 4001m with
the shape of discrete short rods were obtained at the RH factor of 1 ( Fig. 59.6a).
However, several attempts have been made to obtain cathode materials with different
size and morphology. In this regard, the rodlike LiFePO4 particles with 100 nm
of uniform diameter and 510 nm of the aspect ratio were synthesized by the
hydrothermal reaction at 220C (Huang et al. 2010), and the rodlike morphology
can be seen inFig. 59.6b.In order to reduce the reaction time and to obtain homogeneous monodispersed
particles, a few attempts have been made to synthesize the cathode materials at a
shorter reaction period. Hence, a rapid production of the cathode materials by the
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
9/25
59 Advanced Energy Devices: Lithium Ion Battery and High Energy Capacitor 1157
Fig. 59.6 LiFePO4 cathode materials with different morphology synthesized by hydrothermalmethod (Reproduced with permission from Zhang et al. (2009), Huang et al. (2010) and Xu et al.
(2008))
continuous hydrothermal method has been adopted to synthesize LiFePO4nanopar-
ticles (Xu et al.2008) ranging from 20 to 40 nm in diameter as shown inFig. 59.6c.
This process is promising for the large-scale synthesis of high purity monodispersed
nanocrystalline electrode materials for the application in the Li-ion battery.
Recently, surface modified LiFePO4/C nanocrystals were synthesized from the
supercritical batch reactors at 400C for 30 min using inexpensive environmentally
friendly solvent such as ethanol and water (Rangappa et al. 2009). The as-
synthesized particles exhibited less than 15 nm in diameter. Morphology can also beeasily controlled by this process such as the nanoarchitectured structure of LiFePO4as shown inFig. 59.7a (Rangappa et al. 2010), and nanoplate/nanorods of LiMnPO4(Fig. 59.7b, c) were synthesized in the presence of surfactants such as oleic acid and
oleylamine at 400C for 410 min (Rangappa et al. 2010a). In addition, LiCoPO4nanoparticles were also synthesized by this method. The as-synthesized LiCoPO4particles showed 50100 nm in diameter (Fig. 59.7d). The experimental results
confirmed that using selective surfactants and solvents, morphology and size of
the cathode materials could be easily modified. Furthermore, the reaction time and
temperature can be shortened in the light of the energy savings.
The microwave-hydrothermal and microwave solvothermal methods have beenused to synthesize the positive electrode materials within a short period of reaction
time as these methods have advantage of changing the reaction kinetics while
irradiating microwave. The platelets like LiMnPO4 nanoparticles (Ji et al. 2011)
were synthesized using the microwave hydrothermal method at 120180C for
a short period of reaction time, and the as-synthesized particles are shown in
Fig. 59.8a.The size of the platelets was controlled to 150 nm thickness and 5 m
basal dimensions. The nanorods of LiFePO4 were prepared by the rapid microwave
solvothermal method (Murugan et al.2008) at 300C for 5 min. The large nanorods
of LiFePO4with a width of 40 6 nm and a length of up to 1m were successfullysynthesized in presence of tetraethylene glycol (TEG) as shown in Fig. 59.8b.
This result showed the effect of selective solvents on the morphology of the final
products.
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
10/25
1158 M.K. Devaraju et al.
Fig. 59.7 (a) Nanoarchitectured of LiFePO4 (b) and (c) nanoplate and nanorods of LiMnPO4and (d) sphere-like particles of LiCoPO4 synthesized by supercritical method (Reproduced with
permission from Rangappa et al. (2010a) and Rangappa et al. (2010b) and LiCoPO4 from authors
unpublished work)
Polyol-mediated solvothermal synthesis (Lim 2010) of LiMPO4 (M=Fe and
Mn) particles with dimensions of length and width in the range of 200350 and
200400 nm, respectively, are shown in Fig. 59.8c.The use of the polyol solvents
acts not only as a solvent but also as a reducing environmental agent and stabilizer,
thereby limiting particle growth and preventing agglomeration. Thickness of the
plate-like LiFePO4 down to 30 nm, width of 100 nm, and length of 200 nm were
synthesized by the solvothermal method at 180C for 18h (Nan et al. 2011).
Morphology and well-resolved lattice fringes of LiFePO4 can be seen inFig. 59.8d.Morphology and size have their own effects on the property of the cathode materials.
Therefore, the solution-based green synthesis methods are much beneficial in
designing the nanocrystalline electrode materials since the nanocrystalline materials
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
11/25
59 Advanced Energy Devices: Lithium Ion Battery and High Energy Capacitor 1159
Fig. 59.8 (a) Platelet like of LiMnPO4 nanoparticles synthesized by microwave hydrothermalmethod (b) large nanorods of LiFePO4 synthesized by microwave solvothermal method (c)
platelike LiFePO4 synthesized by polyol method (d) thin plate like LiFePO4 synthesized by
solvothermal method (Reproduced with permission from Ji et al. (2011), Murugan et al. (2008),
Lim et al.(2011) and Nan et al. (2011))
possessing different shape are promising to behave much differently than the
bulk materials. Hence, from the nanocrystalline materials, improved and surprising
physicochemical reaction can be expected, which could play a vital role in various
technological and chemical applications.
3.2 Conductive Coating of Cathode Materials
The practical capacity and high rate performance of the olivine-structured lithium
metal phosphates are not impressive due to its low electronic conductivity
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
12/25
1160 M.K. Devaraju et al.
(1 109 scm1 at room temperature). To improve the electronic conductivity
of these materials, the following approaches have been considered:
(a) Decreasing the particle size for shortening the ionic and electronic transport
(b) Surface modification by the conductive carbon coating(c) Doping the supervalent cations to enhance the intrinsic conductivity
(d) Designing different morphology and changing the texture and pore size
However, the expected electronic conductivity cannot be reached simply by
producing the cathode materials with different morphology, size, or doping su-
pervalent cations. Therefore, surface modification of these materials is necessary
by conductive carbon coating because carbon coating offers better electronic
conductivity. The conductive carbon coating can be done either by the in situ or
ex situcoating technique. The in situ coating involves mixing of the carbon source
during the synthesis of the cathode materials at various reaction temperatures. This
method is useful to achieve homogeneous coating around the individual particles.
However, sometimes coating may not be uniform due to inhomogeneous mixing or
improper design of the experimental conditions. Theex situcoating involves mixing
of the carbon source either by the physical mixing or by high-energy ball milling
method.
Recently, various conductive carbon sources were successfully coated on to the
cathode materials, and this chapter discusses several carbon coating techniques.
Sugar was used as the carbon source by Jeon et al. (2007), and the in situ mixing
was carried out during the synthesis of the LiFePO4 particles, and carbon was
successfully mixed with the cathode materials as shown in Fig. 59.9a. Under thesupercritical water conditions, ascorbic acid was used as the carbon source, and the
in situ coating was carried out to synthesize the LiFePO4/C particles (Rangappa
et al. 2009). Formation of the carbon layer can be seen in Fig. 59.9bfor the heat
treated LiFePO4 particles at 500C. This result shows that ascorbic acid can act as
the reducing agent to prevent the oxidation of metal ion from divalent to trivalent
and also as effective carbon source for the conductive coating.
Saravanan et al. (2009) have used D-gluconic acid lactone (C6H10O6) as the
carbon source, and the in situ coating was carried out using the solvothermal
method. Figure 59.9c shows 5-nm carbon layer formation around the particles.
This result shows that at low temperature (250C), the carbon coating can be
achieved using the selective carbon sources. The conductive polymer such as
PEDOT was used to coat LiFePO4by Murugan et al. (2008) via the rapid microwave
solvothermal method. The homogeneous conductive polymer coating can be seen
around the LiFePO4 nanorod as shown inFig. 59.9d.
Hence, better carbon coating can be made through the solution process as all of
the solution routes start from a precursor in a liquid solution which provides intimate
mixing of the carbon source with the ingredients on the atomic level, leading to
the rapid homogeneous nucleation and uniform particle formation. Moreover, when
compared with the other methods such as the carbonothermal and high-temperatureheating process used for the carbon coating and materials preparation, the solution-
based synthesis methods have advantages on the materials preparation and the
carbon coating at the low temperature with the selection of suitable organic solvents
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
13/25
59 Advanced Energy Devices: Lithium Ion Battery and High Energy Capacitor 1161
Fig. 59.9 Carbon-coated LiFePO4materials using (a) sugar, (b) ascorbic acid, (c) D-gluconic acidlactone, and (d) PEDOT polymer (Reproduced with permission from Jeon et al. (2007), Rangappa
et al.(2009), Saravanan et al. (2009) and Murugan et al.(2008))
which can contribute as carbon source during the synthesis of the cathode materials.
High-boiling point solvents like glycols can be beneficial as the carbon source and
to achieve better in situ coating at the time of synthesis.
3.3 Charge/Discharge Process ofCathodeMaterials
Specific capacitance of the potential Lithium-ion battery cathode material is usu-
ally determined by the electrochemical galvanostatic charge/discharge technique.
Specific amount of the cathode materials was mixed with the carbon additives
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
14/25
1162 M.K. Devaraju et al.
1.2
2.0
2.5
3.0
3.5
1.3 1.4
VoltageversusLi/Li+(
V)
1.5 1.6
Charge
Voltage gap resulting from hysteresis
Discharge
xin LixFeSiO4
1.7 1.8 1.9 2.0
Fig. 59.10 Typical galvanostatic chargedischarge curve of LiFeSiO4at a C/20 rate (Reproducedwith permission from Dreyer et al. (2010))
and then with the binder to make electrode paste. The electrode paste will be
pressed on Ni mesh and then cell assembled in the argon glove box. For the
charge/discharge measurement, the current rates of the cathode materials will be
calculated based on its theoretically calculated specific capacity in various timespans and considering the amount of the cathode material present in the electrode
paste. The cut-off voltages used for the measurements are adapted according to the
type of the measured cathode material. It is important to note that materials that can
be cycled at high C-rates and operating in the voltage window of commercially used
electrolytes are desirable. During the galvanostatic cycling, structural change occurs
inside the electrode material as a result of the LiC insertion/extraction (lithium metal
is used as a counter electrode anode). The results from the measurements can be
plotted in the galvanostatic charge/discharge curves (voltage vs. capacity, voltage
vs. composition as shown inFig. 59.10(Dreyer et al.2010), and capacity vs. cycle
number). Important parameters that can be determined from these curves are specificcapacity, voltage, and reversibility (e.g., polarization, voltage gap between charge
and discharge).
The LiMPO4 (M=Fe and Mn) cathode materials with similar crystal structure
synthesized by various solution routes show different electrochemical property.
The discharge capacity is not only dependent on the structure of the cathode
materials, but other facts also influence the electrochemical property of the cathode
materials, for example, crystal size, morphology, and method of carbon coating. For
example, the charge/discharge profile of the LiFePO4nanorods shown inFig.59.10a
shows the discharge capacity of 140 mAhg1
(Fig. 59.11a) for the first cycle anddecreases to 130 mAhg1 after 20 cycles (Huang et al. 2010). The potential voltage
gap between the charge and discharge profile is wide. This might be due to low
conductivity, and it can be overcome by proper conductive carbon coating to
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
15/25
59 Advanced Energy Devices: Lithium Ion Battery and High Energy Capacitor 1163
20 0
0 60 120
1
1
50
50
25
25
Capacity (mAhg1
)
a
c
b
d
CellVoltage(V
vs.
Li/Li+)
180
1.0
4.5
4.0
3.5
2.5
3.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
1.5
2.0
2.5
2.5
3.0
3.0
3.5
3.5
4.0
4.0
4.5
4.5
5.0
20 40
Voltage(V)
Voltage(V)
60 80 100 120 140
0.5C
First cycle
160 0
0
20
20 30
Charge-discharge at 0.1C
50 7010
40
40
60
60
80
Capacity (mAh/g)
Capacity (mAh/g)
Voltage(V
vs.
Li/Li+)
100 120 140 160180
Fig. 59.11 Chargedischarge curves of (a) LiFePO4 nanorods, (b) sphere-like LiFePO4/C,
(c) thin plate like LiFePO4/C, and (d) colloidal nanocrystal of LiMnPO4 (Reproduced with
permission from Huang et al. (2012), Rangappa et al.(2009), Saravanan et al.(2009)and Rangappa
et al.(2010a))
improve the electrochemical property. Discharge capacity of about 165 mAhg1
(Fig. 59.11b) for a sphere-like LiFePO4/C particle is synthesized by supercritical
water in the presence of ascorbic acid as the carbon source and reducing agent(Rangappa et al. 2009). The discharge capacity of these materials is close to the
theoretical capacity of LiFePO4 (170 mAhg1). The cyclic performance of these
material was quiet satisfactory. However, further study is necessary to reduce the
wide potential observed in the chargedischarge profile and to increase the high rate
performance.
The thin platelike LiFePO4/C (Saravanan et al. 2009) showed the discharge
capacity of around 150160mAhg1 up to 50th cycle as shown inFig. 59.11c.The
chargedischarge profile of this material shows relatively low potential gap between
the charge and discharge profile. This is due to the platelike morphology, whichcan provide short distance for the Li-ion insertion and exertion and also due to the
homogeneous coating of carbon around the platelike LiFePO4/C particles. The col-
loidal nanocrystal of LiMnPO4with rodlike morphology (Rangappa et al. (2010a))
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
16/25
1164 M.K. Devaraju et al.
shows the discharge capacity of around 70 mAhg1 (Fig. 59.11d). The development
of new strategy of conductive carbon coating can enhance the discharge capacity
of LiMnPO4 materials. The intrinsic electronic conductivity of LiMnPO4 is very
low due to the JahnTeller distortion, and it is not possible to achieve fulltheoretical capacity of LiMnPO4. However, further study is necessary to improve
the electrochemical property of the LiMnPO4cathode materials.
4 Electrochemical Capacitors
Electrochemical capacitors, also called supercapacitors, store energy using either
ion adsorption (electrochemical double-layer capacitors) or fast surface redox
reactions (pseudocapacitance). It is well known that the electrochemical double-layer capacitors (EDLC) store the opposite charge electrostatically using reversible
adsorption of ions of the electrolyte on active materials surface that is elec-
trochemically stable and has high accessible surface area (Conway 1999). As
there is no chemical reaction involved in the storage mechanism, the process is
highly reversible for millions of cycles and results long life for the capacitors.
And the specific capacitance depends on the available active specific surface
area of the active materials. Whereas, in the pseudocapacitance, surface or near
surface redox reactions occur during the charge storage mechanism, resulting high
specific capacitance with relatively short cycle life compared to EDLCs. Thus, the
development of high capacitive energy storage systems with optimum cycle life, low
cost, and environmentally friendly materials is essential to meet the energy demands
of modern society and emerging environmental concerns.
4.1 Graphene-Based Electrochemical Double-Layer Capacitors
Carbons and carbon-based composites materials are the most widely used owing
to their high surface area, moderate cost, and ecofriendly nature. A variety of
carbon morphologies with different surface area and chemical nature such as carbonnanotubes, carbon nanofibers, carbon fibres, onions, and nanohorns have been
investigated (Simon and Gogotsi 2008; Zhang et al. 2009). Similarly, activated
carbons, mesoporous carbon, template carbon, and chemically derived carbon have
been examined. The carbons used in EDLC are generally pretreated to remove
moisture, and most of the surface functional groups are present on the carbon surface
to improve stability during cycling.
The presence of functional groups will result in increased serious resistance and
capacitance fading during aging. The double-layer capacitance of activated carbon
reaches 100120 F/g in organic electrolytes; this value can exceed 150300 F/g inaqueous electrolytes, but at a lower cell voltage because the electrolyte voltage
window is limited by the water decomposition. The research on carbon materials
was directed toward increasing the pore volume by developing high surface area
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
17/25
59 Advanced Energy Devices: Lithium Ion Battery and High Energy Capacitor 1165
carbon and refining the activation process. However, the capacitance increase was
limited even for the most porous samples (Simon and Gogotsi2008). From a series
of activated carbons with different pore sizes in various electrolytes, it was shown
that there was no linear relationship between the surface area and the capacitanceowing to the inability of electrolyte access to the entire surface through smaller
pores. Also, the poor conductivity of the porous carbon materials limits the high
capacitance. Thus, high surface area carbon material with optimum pore size and
conductivity is essential to realize the high capacitance.
The key to reaching high capacitance by charging the double layer is using high
surface area carbon materials with electronically conducting electrodes. Graphitic
carbon satisfies all the requirements for this application, including high conductivity,
electrochemical stability, and open porosity that offer huge surface area (Simon
and Gogotsi 2008). Thus, graphene-based supercapacitors are under intensive
investigation as potential alternative to the activated carbon that is used in thecurrent supercapacitor electrodes. The effective surface area of graphene materials
should depend highly on the number of layers, that is, single- or few-layered
graphene sheets with less agglomeration might be expected to exhibit higher
effective surface area. The recent research reports on clean graphene materials
with specific capacitance ranging from 120 to 250 F/g. The chemical nature of the
graphene nanosheets and its purity greatly depend on the method of preparation and
subsequent processing of the resulting graphene sheets.
As mentioned earlier, the presence of functional groups on the graphene surface
greatly influences on its capacitance. In general, the presence of oxygen containingfunctional groups result diminishes the capacitance and cycle life (Pandolfo and
Hollenkamp2006). Wang et al. (2009) reported a maximum specific capacitance
of 205 F/g with an excellent long cycle life along with 90% specific capacitance
retained after 1,200 cycle tests. Also, it is confirmed that the interfacial capacitance
of the multilayer graphene sheets is found to depend on the number of layers. In
addition to the graphene quality, the fabrication of electrodes and its structure also
influences the performance of the resulting supercapacitors. Recently, P.M. Ajyan
group reported an in-plane fabrication approach for ultrathin supercapacitors
based on electrodes comprised of pristine graphene and multilayer reduced graphene
oxide (Yoo et al.2011). And this approach allows for the formation of an efficientelectrical double layer by utilization of the maximum electrochemical surface area
and results a maximum specificapacitance of 247 F/g. The research on supercapac-
itors using graphene nanosheets is under tremendous progress. Combining high-
quality graphene sheets with suitable electrode fabrication technique will lead to the
commercial production of EDLC capacitors with high capacitance in the near future.
In the row of various chemical modification processes, doping of hetero-atoms,
such as nitrogen, sulfur, and boron, into the graphene backbone is another possible
route. Also, the heteroatom doping in the carbon materials (CNTs, graphene)
and metal oxides has always created excitement in the material chemistry as thematerials property can be tuned significantly. Recently, studies have focused on
direction, and several possible routes have been identified for the effective N- or
B-doping in the graphene sheets (Hulicova et al. 2006; Kwon et al.2009).
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
18/25
1166 M.K. Devaraju et al.
Significant enhancement in capacitance has been reported for the heteroatom-
doped graphene sheets, and the following possible mechanisms have been proposed
for the enhancement: (1) the improvement of the electrode wet-ability, due to the
increase in the number of hydrophilic polar sites; (2) the decrease of equivalentseries resistance (ESR) of a capacitor cell by the increase of the carbon electric
conductivity; (3) the occurrence of space-charge-layer capacitance in carbon by the
increase of its electron density; and (4) the occurrence of that pseudocapacitance
through the Faradic charge transfer, because the nature of carbon becomes electron
donor. Though, it is difficult to point out one particular effect for the capacitance
enhancement, it is believed that the pseudocapacitance through Faradic charge
transfer is the most important factor in enhancing the capacitance of the N- or
B-doped graphene sheets. Since the research on this direction is still in infancy stage,
additional experiments and theoretical understating are necessary. Understanding of
the mechanism and further development in the preparation method is expected toplay an important role in the improvement of the supercapacitor performance in the
coming years.
4.2 Electrochemical Capacitors Based on Pseudocapacitance
The large specific pseudocapacitance of Faradaic electrodes (typically 3001,000
F/g) exceeds that of the carbon-based materials using double-layer charge storage,
resulting in great interest in these systems. Specific capacitance of more than 600 F/ghas been reported for the RuO2-based system owing to its good conductivity,
fast and reversible electron transfer together with the electroadsorption of protons
on the surface. However, the Ru-based aqueous electrochemical capacitors are
expensive, and the 1-V voltage window limits their applications to small electronic
devices (Simon and Gogotsi2008). Thus, pseudocapacitive transition-metal oxides
such as MnO2, NiO, and redox polymers such as polyanilines, polypyrroles, and
polythiophenes could be used to make electrodes, because they are predicted to
have a high capacitance for storing electrical charge, inexpensive, and not harmful
to the environment. Poor conductivity and lack of stability during cycling are
major drawbacks associated with these materials for their usage in supercapacitors.Thus, numerous efforts have been made to use these metal oxides successfully
in supercapacitors by making composite with conductive support such as carbon
and gold.
Recently, Lang et al. (2011) developed a nanoporous gold/MnO2 electrode by
combining chemical de-lloying Ag65Au35 (at %) with the electroless plating of
MnO2 (Fig. 59.12), in which nanoporous gold acts as a double-layer capacitor and
also provides good electronic/ionic conductivity to enhance the pseudocapacitive
behavior of the nanocrystalline MnO2. And the MnO2loading can be controlled by
adjusting the platting time. The gold/MnO2 hybrid material has very high specificcapacitance of 1,145 F/g at a scan rate of 50 mV/s. The obtained high specific
capacitance at a scan rate of 50 mV/s is higher (one order of magnitude) than
the reported MnO2 film electrodes at 5 mV/s (Toupin et al. 2004). This could be
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
19/25
59 Advanced Energy Devices: Lithium Ion Battery and High Energy Capacitor 1167
MnO2
nanocrystals
Growth
N2H4
N2H4Mn7+
NPG
Fig. 59.12 Schematic showing the fabrication process for nanoporous gold/MnO2 hybrid mate-rials by directly growing MnO2 onto nanoporous gold (Reproduced with permission from Lang
(2011))
attributed to the porous metal/oxide structure, in which the nanocrystalline MnO2grows epitaxially into the internal surface of the highly conductive nanoporous gold,
allowing easy and efficient access of both electrons and ions so as to afford a fast
redox reaction at high scan rates as well as good cyclic stability. The power and
energy densities of the hybrid structure increase with the loading rate of MnO2and
reach maximum of 57 Wh/kg and 16 kW/kg, respectively, with the MnO2 plating
time of 20 min. The high specific capacitances, charge/discharge rates, and good
cyclic stability offered by this hybrid structure make them promising electrodes
materials in supercapacitors.
4.2.1 GrapheneMetal Oxide NanocompositesAs the graphene nanosheets have vast surface area with excellent conductivity, it
will be an appropriate candidate to accommodate a large amount of metal oxides.
In addition, the EDLC behavior of the graphene nanosheets can also be enhanced,
which contributes to the total capacitance of the resulting composite. Recently,
graphenemetal oxide nanocomposite systems have been developed by various re-
searchers, and high specific capacitances with good cycling performance have been
reported (Zhang et al. 2009,2010; Huang et al. 2012;Simon and Gogotsi2008).
Also, layered double hydroxides (LDH) materials containing transition metals have
been reported to be promising electrode materials for supercapacitors because of
their relatively low cost, high redox activity, and environmentally friendly nature.
Gao et al. reported the preparation of graphene Ni/Al layered double hydroxide
(LDH) nanocomposite and a maximum specific capacitance of 781.5 F/g with an
excellent cycle life (Gao et al. 2011). The observed capacitance is almost 1.5 times
higher than that of the pure LDH electrodes. The larger capacitance for GNS/LDH
may be caused by the combination of electric double-layer capacitance and Faradicpseudocapacitance. At the same time, the open structure system of GNS/LDH
improves the contact between the electrode materials and the electrolyte and thus
makes full use of the electrochemical active material contribution to the overall
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
20/25
1168 M.K. Devaraju et al.
capacitance. Development of suitable GNSmetal oxide or LDH nanocomposites
with appropriate ratio will lead to high capacitance owing to the combination of
EDLC and pseudocapacitance from GNS and metal oxide or LDH, respectively.
4.2.2 GraphenePolymer NanocompositesTo exploit the potential of the graphene-based materials for the supercapacitor
applications, graphene-conducting polymer nanocomposite was prepared by several
preparation route, and electrochemical capacitance was reported in the range of
233 500 F/g (Zhang et al.2009). However, the capacitance was mainly dominated
by the pseudocapacitance from the polymer films coated on the graphene paper
surface, and the EDLC from the graphene sheet was less utilized due to the agglom-
erated layer-like structure in the graphene paper. Among the conductive polymers,
carbon (or) graphenePANI composites have been extensively studied and well
documented in the literature for supercapacitor applications (Zhang et al. 2010;Huang et al. 2012). And flexible nanoelectrodes also have been developed using
carbon nanotube/PANI or graphene/PANI nanocomposites for the supercapacitors
applications (Meng et al.2010).
Typically, in all these studies, the aniline polymerization on the graphene surface
was carried out using oxidants such as ammonium persulfate ((NH4/2S2O8) or
ferric chloride (FeCl3), and the experimental strategy plays a vital role on the
morphology of the graphene/PANI composite and their electrochemical response.
Recently, preparation of graphenepolyaniline nanocomposite electrodes via oxida-
tive polymerization of aniline by MnO2was shown. And a superior supercapacitiveperformance (641 F/g, 1540% enhancement than the reported capacitance for
graphenepolyaniline) has been observed (Sathish et al. 2011). As mentioned
earlier, the method of polymerization plays a vital role on the materials property.
GO/MnO2 composite was prepared (Sathish et al.) by mixing appropriate amount
of MnO2 nanosheets and GO nanosheets. Then, appropriate amount of aniline
was added to the above composite, and the chemical oxidation polymerization of
aniline was initiated by the reduction of Mn4C ion, and the resulting Mn2C ions
will go to the solution. This process enables the formation of slow and uniform
polyaniline nanofibers on the graphene surface with significant porosity, which
enables the impulsive peculation of electrolyte to access large surface area (authorsunpublished work). Thus, the graphene surface also has been used for EDLC
in addition to the pseudocapacitance from polyaniline. Figure 59.13 shows the
schematic representation of the polyaniline formation on the graphene sheets.
Similarly, Xu et al. (2010) introduced a facile method to construct the hierarchical
nanocomposites by combining the one-dimensional (1D) conducting polyaniline
(PANI) nanowires with the 2D graphene oxide (GO) nanosheets. It is shown
that the aniline concentration plays a key role on the PANI morphology, at
lower concentration (0.05 M); vertically aligned PANI nanowire arrays on GO
surface are observed owing to the heterogeneous nucleation on the GO nanosheets(Fig. 59.14a). When aniline concentration was increased to 0.06M, homoge-
neous nucleation will take place after the initial nucleation on the solid surface.
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
21/25
59 Advanced Energy Devices: Lithium Ion Battery and High Energy Capacitor 1169
Mn2+Graphene oxide
GO-PANI
GO-MnO2
(i) Aniline
Mn4+
MnO2nanosheets
Fig. 59.13 Schematic representation of polyaniline formation on graphene surface via oxidative
polymerization of aniline by MnO2 (Reproduced with permission from (From authors work))
Consequently, random connected PANI nanowires were produced (Fig. 59.14b).
The hierarchical nanocomposite structures of PANI/GO were further proved by the
UV-vis, FTIR, and XRD measurements. The hierarchical nanocomposite possessed
higher electrochemical capacitance of 555 F/g at a discharge current density of
0.2 A/g and better stability than each individual component as the supercapacitor
electrode materials, showing a synergistic effect of PANI and GO. Also, the
observed specific capacitance of the nanocomposite is much higher than that of the
random connected PANI nanowires (298 F/g) obtained under the same condition.
This study will further guide the preparation of functional nanocomposites by
combining different dimensional nanomaterials.
4.3 Asymmetric (or) Hybrid Capacitors
Asymmetric or hybrid systems offer an attractive alternative to the
conventional pseudocapacitance or EDLCs by combining a battery-like electrode
(energy source) with a capacitor-like electrode (power source) in the same cell
(Simon and Gogotsi 2008). The high specific capacitances, cell voltage, and
charge/discharge rates offered by such hybrid structures make them promising
candidates as the electrodes in supercapacitors. MnO2graphene composite elec-
trodes have been developed for the high-voltage hybrid electrochemical capacitorbased on graphene as the negative electrode and MnO2graphene composite
as the positive electrode in the neutral aqueous Na2SO4 solution as electrolyte
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
22/25
1170 M.K. Devaraju et al.
Nucleation
Growth
a b
Growth further
Aniline
Aniline anion
GO sheet
Fig. 59.14 Schematic illustration of nucleation and growth mechanism of PANI nanowires:(a) heterogeneous nucleation on GO nanosheets; (b) homogeneous nucleation in bulk solution
(Reproduced with permission from Xu (2010))
0.0 0.5 1.0
Voltage (V)
a b c
Potential (V vs. SCE)
CurrentDensity(Ag
1)
CurrentDensity(Ag
1)
0.5
0.4
0.3
0.2
0.1
0.0
0.1
0.2
0.3
0.4
0.5
1.5 2.0 1.0
3
2
1
0
1
2
3
0.80.60.4 0.2 0.0 0.2 0.4 0.6 0.8 1.0
Fig. 59.15 Schematic representation of polyaniline formation on graphene surface via oxidative
polymerization of aniline by MnO2 (Reproduced with permission from Wu et al. (2010))
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
23/25
59 Advanced Energy Devices: Lithium Ion Battery and High Energy Capacitor 1171
Fig. 59.16 Schematic illustration of two key steps for preparing hybrid graphene/MnO2-nanostructured textiles as high-performance EC electrodes. (i) Conformal coating of solution-
exfoliated graphene nanosheets (gray color) onto textile fibers. (ii) Controlled electrodeposition
of MnO2 nanoparticles (yellow dots) on graphene-wrapped textile fibers (Reproduced with
permission from Yu et al.2011)
(Wu et al.2010). These ECs can be cycled reversibly in the high voltage region of
02.0V (Fig. 59.15a). The resulting energy density of 30.4 Wh/kg is much higherthan those of the symmetric ECs based on graphene//graphene (2.8 Wh/kg)
(Fig. 59.15b) and MnO2graphene//MnO2graphene (5.2 Wh/kg) (Fig. 59.15c) and
higher than those of other MnO2-based asymmetric ECs. These findings open
up the possibility of the graphene-based composites for applications in safe
aqueous electrolyte-based high-voltage hybrids systems with high energy and power
densities.
Yu et al. (2011) demonstrated the solution-processed graphene/MnO2 nanos-
tructured textiles for the high-performance electrochemical capacitors applications.
In their study, solution-exfoliated graphene nanosheets (5 nm thickness) were
conformably coated on the three-dimensional, porous textiles support structures,and pseudocapacitive MnO2 nanomaterials was deposited by the controlled elec-
trodeposition (Fig. 59.16). This technique offers high loading of active electrode
materials and facilitates the easy access of electrolytes to those materials. The hybrid
graphene/MnO2-based textile yields high-capacitance performance with specific
capacitance up to 315 F/g. Also, they have fabricated asymmetric electrochemical
capacitors with the graphene/MnO2-textile as the positive electrode and single-
walled carbon nanotubes (SWNTs)-textile as the negative electrode in an aqueous
Na2SO4 electrolyte solution. These devices exhibit promising characteristics with
a maximum power density of 110 kW/kg, an energy density of 12.5 Wh/kg, andexcellent cycling performance of95 % capacitance retention over 5,000 cycles.
These kinds of low-cost, high-performance energy textiles-based nanostructures
offer great promise to realize the future large-scale energy storage devices.
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
24/25
1172 M.K. Devaraju et al.
5 Conclusions
In conclusion, this chapter began with the brief introduction of the advanced energy
devices such as lithium-ion batteries and high energy capacitors. The importance ofthe positive electrode materials and their synthesis by the solution process including
the hydrothermal and solvothermal method were discussed. These methods are
popularly used for the preparation of various inorganic materials owing to their
advantages such as size-controlled synthesis, morphology-controlled synthesis,
safety, easy synthesis, environmentally benign, and cost-effectiveness.
Among the lithium-ion batteries, cathodes are essential parts of the batteries.
The olivine-structured lithium metal phosphates are very much attractive due to
their cheap, environmentally friendly, and high theoretical capacity. The carbon
coating of lithium metal phosphates using different carbon sources via in situ or
ex-situ coating techniques has been discussed. The electrochemical property de-
pended on the morphology of LiFePO4and LiMnPO4cathodes has been discussed.
Most of the LiFePO4 nanomaterials less than 100250 nm in diameter exhibited
the discharge capacity close to the theoretical capacity (170 mAhg1). Thin plate
and rod morphology provides short diffusion length for the LiC-ion insertion and
exertion process. The discharge capacity of LiMnPO4 is not very impressive due
to its low intrinsic conductivity. New strategy development could improve the
electrochemical property of LiMnPO4for commercial purpose.
In the electrochemical capacitors, graphene-based compounds such as metal
oxide-doped graphene and PANI/graphene showed excellent capacitance whencompared to the other capacitors. In addition, asymmetric hybrid capacitors are
promising with higher capacitance for various powder density electric and electronic
devices. Further, continuous study of graphene could enable to understand its
physicochemical property for the electrochemical applications. New breakthrough
in these fields can change the performance of the energy devices and thus can make
human life more comfortable.
References
A.S. Aric-o, P.G. Bruce et al., Nat. Mater. 4, 366 (2005)
G.M. Ehrlich, in Lithium Ion Batteries in Handbook of Batteries, ed. by D. Linden, T.B. Reddy
(McGraw-Hill Handbooks, New York, 2001)
G. Park, Thesis Saga University, Japan, 2010
J.M. Tarascon, J.-M. Armand, Nature 414, 359 (2001)
Encyclopedia Britannica,COLE to DAMA, vol. 6, 14th edn. (New York Press, 1926), p. 216
R. Kotz, M. Carlen, Electrochim. Acta 45, 2483 (2000)
C. Liu, F. Li et al., Adv. Mater. 22, E28 (2010)
A. Yoshino, Electrochemistry 72, 716 (2004)
A.K. Padhi, K.S. Nanjundaswamy et al., Electrochem. Soc. 144, 1188 (1997)
R. Dominko, Proc. SPIE 7683, 76830J (2010)
B. Jin, Q. Jiang, inLithium Batteries: Research, Technology, ed. by R. Greger Dahlin et al. (Nova
Science Publishers Inc., 2009)
D. Choi, P.N. Kumta, J. Power Sources 163, 1064 (2007)
7/25/2019 Advance energy devices Lion and Supercap Ch 2.pdf
25/25
59 Advanced Energy Devices: Lithium Ion Battery and High Energy Capacitor 1173
G. Arnold, J. Garche et al., J. Power Sources 119, 247 (2003)
J.K. Kim, G. Cheruvally et al., J. Power Sources 166, 211 (2007)
M. Konarova, I. Taniguchi, J. Power Sources 194, 1029 (2009)
M.S. Whittingham, G.-A. Nazri, G. Pistoia,Lithium Batteries(Kluwer, Boston, 2004), p. 85
T.G. Chirayil, P.Y. Zavalij et al., Chem. Commun. 33 (1997)K. Byrappa, M.K. Devaraju et al., J. Mater. Sci. 43, 2229 (2008)
S. Yang, P.Y. Zavalij et al., Electrochem. Commun. 3, 505 (2001)
S. Tajimi, Y. Ikeda et al., Solid State Ion. 175, 287 (2004)
X. Huang, S. Yan et al., Mater. Charact. 61, 720 (2010)
C. Xu, J. Lee et al., J. Supercrit Fluids 44, 92 (2008)
D. Rangappa, M. Ichihara et al., J. Power Sources 194, 1036 (2009)
D. Rangappa, K. Sone et al., J. Power Sources 195, 6167 (2010a)
D. Rangappa, K. Sone et al., Chem. Commun. 46, 7548 (2010b)
C. Zhang et al., Ceram. Int. 35, 2979 (2009)
H. Ji, G. Yang et al., Electrochem. Acta 56, 3093 (2011)
A.V. Murugan, T. Muraliganth et al., Electrochem. Commun.10
, 903 (2008)J. Lim, D. Kim et al., J. Alloys Compd. 509, 8130 (2011)
C. Nan, J. Lu et al., J. Mater. Chem. 21, 9994 (2011)
Y.S. Jeon, E.M. Jin et al., Trans. Electr. Electron. Mater. 8, 41 (2007)
K. Saravanan, M.V. Reddy et al., J. Mater. Chem. 19, 605 (2009)
W. Dreyer, J. Jamnik et al., Nat. Mater. 9(5), 448 (2010)
B.E. Conway, Electrochemical Supercapacitors: Scientific Fundamentals and Technological
Applications(Kluwer/Plenum, New York, 1999)
P. Simon, Y. Gogotsi, Nat. Mater. 7, 845 (2008)
L.L. Zhang, X.S. Zhao, Chem. Soc. Rev. 38, 2520 (2009)
A.G. Pandolfo, A.F. Hollenkamp, J. Power Sources 157, 11 (2006)
D.W. Wang, F. Li et al., Electrochem. Commun. 11, 1729 (2009)
J.J. Yoo, K. Balakrishnan et al., Nano Lett. 11, 1423 (2011)D. Hulicova, M. Kodama et al., Chem. Mater. 18, 2318 (2006)
T. Kwon, H. Nishihara et al., Langmuir 25, 11961 (2009)
X. Lang, A. Hirata et al., Nat. Nanotechnol. 6, 232 (2011)
M. Toupin, T. Brousse et al., Chem. Mater. 16, 3184 (2004)
Z. Gao, J. Wang et al., Chem. Mater. 23, 3509 (2011)
L.L. Zhang, R. Zhou et al., J. Mater. Chem. 20, 5983 (2010)
X. Huang, F. Qi et al., Chem. Soc. Rev. 41, 666 (2012)
C. Meng, C. Liu et al., Nano Lett. 10, 4025 (2010)
M. Sathish, S. Mitani et al., J. Mater. Chem. 21, 16216 (2011)
J. Xu, K. Wang et al., ACS Nano 9, 5019 (2010)
Z.S. Wu, W. Ren et al., ACS Nano 4, 5835 (2010)G. Yu, L. Hu et al., Nano Lett. 11, 2905 (2011)
Recommended