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7 Solid Oxide Fuel Cells

7 Solid Oxide Fuel Cells

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high-temperature exhaust from an SOFC can be coupled to another power generation source (e.g., a turbine), boosting the efficiency of a CHP system as described

previously. While scientists work to develop more durable polymer electrolyte membranes that can operate at higher temperatures (for improved kinetics and therefore

efficiency in a PEMFC), scientists working on SOFCs strive to find materials that

will allow the operation of the SOFC at lower temperatures (ca. 500–700°C) for

enhanced safety, durability, and lower operating costs. However, the higher operating temperature of the SOFC allows for more flexibility in fuel use: as long as the

fuel can be reformed in situ to generate syngas (the typical fuel for SOFC), it is

acceptable for use in the SOFC. Another significant feature that distinguishes the

SOFC from PEMFCs is that the higher operating temperature range allows for the

use of less expensive (non-PGM) electrocatalysts, a particularly important consideration with respect to the sustainability of resources.

SOFC stacks that are linked to coal gasification are known as IGFC systems

(integrated gasification fuel cell). These systems fall in the realm of “clean coal”

technology, in which coal is gasified in the presence of steam to generate the syngas

feedstock for an SOFC. In the SOFC, the CO2 generated from the electrochemical

oxidation of CO from the syngas (see Equation 6.26) would, in theory, be sequestered to make this a carbon-neutral process.

There are two general types of SOFCs—those with an oxide-conducting electrolyte and those that are proton-conducting. Proton-conducting SOFCs (naturally

abbreviated PC-SOFC) consist of an oxide electrolyte that is hydrated to allow

for the proton to hop from one stationary oxide to the next. An advantage of these

PC-SOFCs is that the fuel is not diluted with H2O and there is therefore no need for

water management or fuel recirculation. In addition, PC-SOFCs can operate at somewhat lower temperatures (≈400–800°C) because of the lower Eact of proton mobility.

Mixed proton-oxide-conducting solid ion fuel cells are currently under development

as the next generation of SOFCs, but we will focus exclusively on the oxide-conducting fuel cell as the dominant SOFC in current use.

6.7.2 Reactions

The reactions that take place in an SOFC are shown below (Equations 6.25

and 6.26).

2 H 2 + 2 O 2 − → 2 H 2 O + 4e −


2CO + 2O2 − → 2CO2 + 4e −


A detailed theoretical study using density functional theory revealed the plausible

steps whereby CO is oxidized on the metal oxide surface as shown in Figure 6.27.

While this study was focused on an ultrathin film of FeO/Pt(111), the binding of the CO,

release of CO2, and capture of O2 on the metal oxide surface are all likely germane to

the operation of an SOFC electrolyte (Sun et al. 2010). The ion conductor is the O2– ion

that migrates through vacancies in the solid electrolyte. This oxide pathway is a result

of interstitial oxide ion defects formed from doping the electrolyte material with other


Fuel Cells


Surface layer of




FIGURE 6.27  (See color insert.) Proposed steps in the oxidation of CO on a FeO/Pt(111)

surface. (Reprinted with permission from Giordano, L. and G. Pacchioni. 2011. Oxide films

at the nanoscale: New structures, new functions, and new materials. Acc. Chem. Res. 44 (11):​

1244–1252. Copyright 2011, American Chemical Society.)

cations (vide infra). Because these cells operate at such a high temperature, the water

is formed at the anode as steam with the concomitant decrease in the thermodynamic

free energy of formation and 100 mV loss in cell potential relative to other types of fuel

cells (Bartholomew and Farrauto 2006). However, as noted above, the waste heat generated in an SOFC makes for improved efficiency in a combined heating and power system. Given the configuration of a typical stationary SOFC stack installation, the waste

streams—water and CO2—can be separated with the pure water recycled (or used, for

example, for drinking) and the CO2 for sequestration (Adams et al. 2012).

6.7.3 Electrode and Electrolyte Materials

SOFCs are no different from other electrochemical cells in that an electrolyte is

sandwiched between the two electrodes (Figure 6.28). However, given that all of

these materials are solids, the distinction between the electrode, electrocatalyst, and

the electrolyte is not always clear. Electrodes are porous mixed composites consisting of a conducting oxide and an oxide electrolyte. Thus, the electrolyte is often the

medium for the electrode/electrocatalyst, and the specific electrolyte can dramatically impact the performance of the electrode. Furthermore, the “barrier” between

the electrode and the electrolyte must be highly conductive, but the electrolyte must

not react with the electrode. In any case, the compatibility of the electrode materials

with the electrolyte is a big issue, especially given the high operating temperatures at

which unwanted reactions can take place or materials can delaminate.

Many of the considerations we have already examined apply to SOFCs as well:

improving the efficiency and lowering the cost of SOFCs is primarily empirical and

relies upon optimizing the performance of every component in terms of both chemical and mechanical stability. Fabrication of the materials in an SOFC, however, is

wildly different than that seen in PEMFCs since we are now working with inorganic materials, not more easily processed organic materials. Instead of chemical


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CO, H2

CH4, and/

or others

To load




H2 + O= → H2O + 2e–

+ CO → CO2 + 2e–

Solid-State O= conductor



H2O, CO2, and





O2 + 4e– → O= + O=


From load

FIGURE 6.28  Schematic of a solid oxide fuel cell. (From Adams, T.A. et al. 2013. Energy

conversion with solid oxide fuel cell systems: A review of concepts and outlooks for the shortand long-term. Ind. Eng. Chem. Res. 52 (9):3089–3111. Copyright 2012, American Chemical


substances that dissolve in solvents that can be layered as catalyst inks, for example,

instead we are dealing with crystalline materials that must be able to be sintered

(heated to a point at which the particles stick together without fusion or melting) at

elevated temperatures in the fabrication process. Incorporation of nanotechnology to

the improvement of SOFC materials has further led to remarkably creative fabrication methods with simultaneous improvement in the efficiencies of ion conduction

and/or catalytic activity, as we will see. Electrolytes

Oxide-conducting electrolytes in SOFCs, like other electrolytes, must optimize ionic

conductivity. Increasing the conductivity of solid oxide materials can be accomplished by increasing the temperature or by minimizing the thickness of the electrolyte layer. However, extremely high temperatures are unfavorable (as mentioned

above) and if the electrolyte layer is too thin it will not be impermeable to gas and

will lead to crossover problems. As a result, development of improved electrolyte

performance for SOFC electrolytes is, as usual, a balancing act.

The solid materials typically used as SOFC electrolytes are of the AO2 (fluoritetype) or ABO3 (perovskite-type) structure. An example of a fluorite structure can be

seen in Figure 6.29, where the larger spheres are the oxide anions with the smaller

spheres representing the tetravalent metal cation. In the realm of SOFC, the prototypical fluorite electrolyte is zirconia (ZrO2) that has been doped with yttrium oxide

to give (ZrO2)0.92(Y2O3)0.08 (yttrium-stabilized zirconia or YSZ). An yttrium(III) ion

displaces a zirconium(IV) ion in the zirconia lattice to create the oxygen vacancies necessary for conduction by the oxide ion, O2–. YSZ shows good mechanical

and chemical stability as well as measurable oxide ion conductivity at temperatures

above 700°C (at 1000°C the conductance is 0.1 S/cm). (Bartholomew and Farrauto

2006). Zirconia may also be stabilized with scandium oxide to yield the “SSZ” electrolyte that has a higher conductivity but is considerably more expensive.


Fuel Cells

FIGURE 6.29  The fluorite crystal structure; the dark gray interior spheres represent the tetravalent metal ions and the light gray spheres the oxygen anions. (Reprinted with permission

from Orera, A. and P.R. Slater. 2010. New chemical systems for solid oxide fuel cells. Chem.

Mater. 22:675–690. Copyright 2010, American Chemical Society.)

Another popular fluorite electrolyte for the SOFC is ceria (CeO2), which when

doped with gadolinium oxide (Gd2O3) or samarium oxide (Sm2O3) results in higher

oxide conductivities at lower (≈500–700°C) temperatures (Malavasi et al. 2010). The

ceria-gadolinia combination is referred to as CGO. However, complications with

competing redox processes suggest that the best approach for the electrolyte may be

to blend doped ceria materials (with better conductivity) with doped zirconia materials (with better mechanical and chemical properties).

Perovskite materials (ABO3, Figure 6.30) consist of a six-coordinate “B” cation

plus a 12-coordinate “A” cation. These materials have also shown good performance

as SOFC electrolytes. The classic example of a perovskite material used in SOFC




FIGURE 6.30  The perovskite unit cell.


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X = 0.2

Log (σ/Scm–1)



X = 0.15


X = 0.10

X = 0.085

X = 0.05










FIGURE 6.31  Arrhenius plots showing the electrical conductivity of La0.8Sr0.2Ga0.8Mg0.2−

x Cox O3 with varying amounts of cobalt. (Reprinted with permission from Ishihara, T. et al.

1999. Improved oxide ion conductivity in La0.8Sr0.2Ga0.8Mg0.2O3 by doping Co. Chem. Mater.

11 (8):2081–2088. Copyright 1999, American Chemical Society.)

is LaGaO3 that has been doped with strontium or magnesium to give systems of the

general formula La1− x Srx Ga y Mg1− y O3− δ (LSGM). Small amounts of other dopants

(Co, Fe or Ni) can dramatically improve the conductivity, as illustrated in Figure 6.31

for a series of La 0.8 Sr0.2 Ga 0.8 Mg2 − x Co x O3 materials (Ishihara et al. 1999). Electrodes  Cathode Materials

As is the case for cathodes in other fuel cells, the cathode for the SOFC is tasked with

the challenge of reducing oxygen, but the elevated temperatures mean that this sluggish reaction is more facile in the SOFC. Perovskite materials are most widely used,

with lanthanum strontium manganite composites (LSM; La1− x Sr x MnO3− δ ) performing well at high operating temperatures (ca. 1000°C) both in terms of conductivity

and in having a thermal expansion coefficient that matches well with the electrolyte

YSZ, a crucial consideration in fabricating SOFCs. It is the presence of the mixed

valence manganese ions—Mn(III) and Mn(IV)—that results in high electronic conductivity, enhanced even more by doping with strontium. The performance of LSM

declines precipitously, however, at lower temperatures as polarization resistance

increases almost 2000-fold over 500 degrees leading to increased efforts to find a

useful electrode material for lower temperatures (Jacobson 2009). Cobaltites such

as PrBaCo2O5+x (PBC) and GaBaCo2O5+x (GBC) have been studied because they are

Fuel Cells


believed to provide enhanced reactivity for the oxidation reduction reaction. A lanthanum/strontium material doped with cobalt and iron (La 0.6 Sr0.4 CO0.2 Fe 0.8 O3−δ ) has

been shown to work at a lower temperature (<750°C) (Liu et al. 2011). Newer materials being investigated for use at the cathode include Ln 2 NiO 4+ x (where Ln = La,

Pr, Nd) (Jacobson 2009; Orera and Slater 2010) and strontium-cerium mixtures. A

nickel/samarium-doped ceria cell fabricated with a Sr0.95Ce0.05CoO3-δ cathode gave

a peak power density of 0.625 W/cm2 at 700°C—the low end of the SOFC operating

temperature spectrum. These are very encouraging results for the continued investigation of cathode materials that provide reasonable kinetics and conductivity in an

SOFC (Yang et al. 2013).  Anode Materials

The most common SOFC anode material is a composite between nickel and the

ceramic electrolyte known as a nickel cermet. Thus, an anode made for a fuel cell

using the YSZ electrolyte would be a Ni-YSZ cermet. These Ni cermets—usually

about 30–35% nickel—show excellent catalytic activity and electronic conductivity,

while the YSZ of the composite provides the oxide conductivity that allows the O2– to

diffuse into the anode. However, the Ni cermets work best with hydrogen fuel—sulfur contaminants in hydrocarbon fuels can lead to poisoning by formation of nickel

sulfides and deactivation by coking. Thus, the major research push in anode development for SOFCs is to develop an electrocatalyst that is less prone to poisoning and

carbon formation. Much like the pathway seen in the development of electrocatalysts

for the PEMFC, several researchers have taken the approach of using more than one

metal. To this end, strontium titanate (SrTiO3) doped with niobium or lanthanum has

been examined. Another approach has been to add copper, which does not catalyze

carbon formation. It does not catalyze the oxidation reaction either, but it is a good

electronic conductor. The results have been mixed: electronic conductivity, stability,

polarization resistance, and ion conductivity all must be balanced in the continuing

search for the optimal material for the anode (McIntosh and Gorte 2004).

6.7.4  Fabrication and Characterization

Characterization of the components and materials for SOFCs may include FT-IR,

Raman spectroscopy, and powder x-ray diffraction to identify functionality and

chemical structure, and for the analysis of elemental composition. The particle

sizes and morphology of the materials can be examined using transmission electron

microscopy or scanning electron microscopy, and, ultimately, the performance of the

components is tested.

Fabrication of SOFC components, as noted before, is not trivial and the challenges

are many. Cost is, as always, an issue, as is the availability of the elements used in

the electrolytes. Lanthanum is considered a near-critical risk in the short term and

nickel and strontium a future risk to supply (Bauer et al. 2011; Knowledge Transfer

Network 2010). The elevated operating temperature is especially demanding in

terms of long-term stability. Many methods involve sintering; however, these hightemperature (≈1400°C) processes can lead to coarse materials that are less effective,

so low-temperature alternatives are being sought. An “ion impregnation” method


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consists of preparing a metal ion solution, dropping the solution onto a porous framework, then firing the sample at 800°C in air. The resultant layered nanostructured

electrocatalyst was shown to have low polarization resistance and a good peak power

density at 600°C (Wang et al. 2012). A plethora of other techniques have been tried

to yield a good, dense electrolyte sandwiched between porous electrodes, including

the use of advanced deposition techniques such as sputtering, pulsed laser deposition, spark plasma sintering, and spray pyrolysis. Even “sintering aids” have been

added to reduce the sintering temperature (Liu et al. 2010). Improved methods in the

fabrication of SOFCs that will be amenable to mass production at low cost and high

efficiency are ongoing area of study. Overall, future growth in the area of SOFC is

likely, especially in the realm of stationary combined heat and power applications.


6.8.1 Introduction

Biofuel cells take advantage of bio-electrical systems to generate electricity. There

are two subsets of biofuel cells: microbial fuel cells and enzymatic fuel cells

(Cracknell et  al. 2008). Like the microbial electrolysis cell discussed in Section

5.2.4, in MFCs the electrocatalyst(s) are actually living cells in the form of a biofilm

of bacteria or algae affixed to an electrode. In contrast, in enzymatic fuel cells, the

catalysts are inert, isolated enzymes attached to either or both electrodes. There

are several advantages and disadvantages to each type of biofuel cell. The substrate

specificity of enzymes means that an enzymatic fuel cell can be constructed more

simply, since a fuel/oxidant separating membrane is not necessary. Enzymes can

provide higher current density provided enough enzyme can be layered onto the

electrode. At the same time, MFCs—being catalyzed by whole, living cells—can

carry out redox reactions on a wider variety of nutrients, making them more energy

efficient. Enzymes are fragile and difficult to make adhere to an electrode surface,

whereas microbial electrodes, being composed of living matter, last longer and are

self-adhering (enzymatic electrodes last only a few days under operating conditions;

Erable et al. 2012). Because of the particularly attractive application of MFC to electrical generation from municipal solid waste (Rulkens 2008), we will focus on MFCs

in this chapter.

Nature possesses an impressive array of enzymatic electrocatalysts. Micro­

organisms use a wide variety of fuels, oxidants, and chemical intermediates (formates and nitrates, carbon monoxide, hydrogen and oxygen, quinone/hydroquinone

redox mediators, among many others) in in vivo energy-transforming electron transport chains. The birth of the MFC is considered to be 1911, when the electrochemical activity of microorganisms was first reported (Schröder 2012). In recent years,

the pace of research activity on MFCs has increased exponentially, but they present some unique challenges. Obviously, a successful MFC electrode must not only

conduct electrons, but it must also support life in the form of a biofilm of bacteria

or algae. Successful MFCs require a neutral pH, whereas the ORR is more favorable under acidic conditions: the E° for the four-electron reduction of oxygen under

acidic conditions is 1.23 V while in alkaline solution, it is 0.40 V; at 25°C and neutral


Fuel Cells

pH, the O2/H2O reduction potential is 0.82 V (Wiberg 2001). Changes in pH at the

electrode surface can also lead to biofouling and loss in efficiency of the MFC. The

solubility of the oxidant, O2, is low in aqueous solution, so the challenge of mass

transport at the catalyst/substrate boundary is amplified. Furthermore, while the

detailed mechanism is not well understood, generation of reactive oxygen species

such as the superoxide radical anion O•−

2 or the hydroxyl radical HO can mean cell

damage and death to the microbial catalyst.

6.8.2  Components

The schematic of an MFC is not unlike that of other fuel cells: anode, cathode, electrolyte, separator (membrane), circuit, and load (Figure 6.32). Oxygen- and nutrientrich fuel from, for example, municipal wastewater is oxidized by microorganisms

at the anode, releasing protons and carbon dioxide. The freed electrons travel the

circuit to generate the electrical current while at the cathode the oxygen reduction

reaction takes place, capturing the protons and electrons to produce water. The cation-exchange separator membrane plays the same role in an MFC as the polymer





aqueous influent

Air/O2 in

Cation-exchange membrane





air/O2 out





FIGURE 6.32  Schematic of a microbial fuel cell.



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electrolyte membrane in a PEMFC, and is often the same material: Nafion®. Note that

it is the anode in the MFC that qualifies it as an MFC; the cathode may contain a typical transition-metal electrocatalyst, although research is being carried out to develop

microbial catalysts that will efficiently reduce oxygen in an MFC (Erable et al. 2012).  Anode Fabrication

Electron transfer is not quite trivial in an MFC. Some bacteria have the ability to

transfer electrons directly to the anode material, typically some form of carbon,

while others require a shuttle or mediator. This adds another layer of complexity

to the electrode design for the MFC. As the anode is the electrode upon which the

biological community exists, preparation of anodes for MFC is radically different

from that for other fuel cells. The anode material is inoculated with a source of

bacteria, often a colony from an already active MFC. All manner of different forms

of carbon (brush, felt, fiber, mesh, granular graphite, and more) have been used as

the scaffold for the anode. As expected, materials that provide a larger surface area

have demonstrated better performance, with respect to both electron transfer and

bacterial growth. Because of the variety of inoculation sources and reactor types,

it is otherwise difficult to draw conclusions about the performance of these various

types of carbon materials.

Metals such as stainless steel, titanium, and gold have also been used for MFC

anode fabrication, with the requirement being that the metal must not corrode under

the operating conditions of the cell. Because bacteria do not adhere well to a smooth

metal surface, metal-based anodes have generally shown lower power densities than

comparable graphite anodes (Wei et  al. 2011). It is interesting to note that some

sort of surface treatment is helpful even for carbonaceous materials, and several

approaches (primarily chemical modifications such as coatings or surface changes)

have been tried with positive results. In addition, composite materials (e.g., a metal–

graphite pair) have been investigated. However, all of these alterations must take into

account the impact on the growth and health of the bacterial electrocatalysts.  Cathode Materials

It is no surprise that the oxygen reduction reaction is the barrier to improved efficiency for the MFC. Not only is the oxygen reduction reaction the problem reaction

in terms of kinetics, the limited solubility of oxygen in the aqueous media further

hinders the cell efficiency. There are three general types of cathodes for MFCs: air

cathodes, aqueous-air cathodes, and biocathodes, with the materials for their fabrication generally the same as for the anodes (primarily carbon). As noted above,

much research has focused on the development of a functional biocathode for the

ORR (Erable et al. 2012), although much work remains to be done.

A recent approach to the development of larger-scale MFCs has taken advantage

of a poly(vinyl alcohol) (PVA) membrane separator placed against a carbon cloth/

Pt cathode in order to mitigate oxygen diffusion to the carbon-brush anode. While

various other separator materials have been tried their use has often led to increased

ionic resistance in the cell among other drawbacks. By incorporating a neutral,

porous PVA membrane in the cell, both ion transport and pH gradients are avoided.

Comparison of this PVA-separated MFC to one with no separator showed that both

Fuel Cells


oxygen diffusion to the anode and bacterial growth on the cathode were decreased

in the presence of the separator. In addition, although the presence of the separator

did increase the internal resistance in the cell (a result of slowed mass transfer to the

cathodes), the maximum power (Pmax) of the PVA-separated cell (1220 mW/m2) was

about 10% higher than the standard comparison with no separator. Similarly, the

coulombic efficiency (a measure of the efficiency of electron collection at the anode)

was significantly higher than the standard. Thus, this PVA approach resulted in both

greater power production and higher coulombic efficiency, a very promising finding

for the development of high-performing MFCs (Chen et al. 2012).


The development of fuel cells captures well the research process: empirical results

contribute to a better understanding of the molecular basis of macromolecular phenomena. Creation of a better, more efficient fuel cell that can be used for transportation using a sustainably provided fuel is dependent upon the rational discovery of new

electrolytes and electrocatalysts, green syntheses of robust but renewable polymers,

cost-effective and sustainable pathways to hydrogen and methanol, wise choices with

respect to scarce resources, and smart design of the fabricated whole so that, when the

fuel cell life cycle is complete, waste is minimal. Progress must be based on a thorough understanding of the mechanisms of the redox processes involved and breakthroughs in computational research have contributed to this basic understanding. Fuel

cell efficiencies are improving at an impressive rate such that their increasing use in a

sustainable energy scenario for stationary or portable applications is a given.


As noted in Chapter 1, the need for electrical energy storage (EES) is strongly yoked

to cleaner energy producers such as wind and solar because of supply variability:

electricity generated during peak production times is stored and delivered “off peak”

to level the load on the grid. In addition, EES—in the form of rechargeable batteries—is key to reducing our reliance on fossil-fueled transportation via the development of electric vehicles (EV). Therefore, EES, whether stationary or mobile, is

germane to the study of sustainable energy. While supercapacitors are broadly used

for EES and large-scale physical modes of EES exist in the form of compressed

air, flywheel, or pumped hydrodynamic storage, our emphasis on chemistry takes

us directly to electrochemical EES, a huge and expanding area of research that has

progressed more slowly than other areas of energy research.

Rechargeable batteries are the prototypical examples of EES. They must meet

stringent requirements including high energy density, safety and reliability, and the

ability to undergo hundreds of charge–discharge cycles. It is the goal of the U.S.

Department of Energy to achieve a battery performance of 300 Wh/L and 250 Wh/

kg—primarily for transportation purposes—but currently, the cost of electricity provided by these systems is far too high (> $700/kWh) (Liu et al. 2013). As our needs

for storage of electrical energy continue to grow, we need both smaller (for EV and

electronic devices) and larger EES with greater energy density and storage capacity.


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Our focus in this section will be on a few of the more important and recent developments in the field.

6.10.1 Lithium Ion Batteries

A lithium ion battery is likely one of the most familiar high-density EES devices in

that it is found as the rechargeable battery in a multitude of electronic devices such

as smart phones and laptops. It may also be familiar from the negative exposure

received after a fire and explosion in the electronics bay of a Japan Airlines 787

caused the entire fleet of Boeing 787 Dreamliners to be grounded in early 2013,

the result of a failed Li-ion battery (Clark 2013). Because the electrode is made up

of graphite (or some carbonaceous material) intercalated with lithium metal, and

because it operates at a potential nearly matching that of metallic lithium, dendrites

(long fingers) of lithium metal tend to grow in the battery and, potentially, cause a

short circuit and overheat (a thermal runaway). This poses a risk of fire given the

organic solvents used in the cell (vide infra). Thus, the chemistry behind the early

Li-ion batteries is “inherently unsafe” (Yang et al. 2011), but the advantages of Li-ion

batteries make them widely used. The target for improvements is not only to improve

their safety and reliability but also to increase the voltage and specific capacity so

that an improved energy density results. This is particularly important for transportation applications and Li-ion batteries are just beginning to make inroads in

the transportation sector, displacing the nickel–metal hydride batteries in use today

(Girishkumar et al. 2010).

The Li-ion battery works by shuttling the Li+ ion back and forth between host

materials at the anode and cathode during discharge and recharge. Thus, as the battery is delivering electricity to its load, Li+ ions migrate through an electrolyte from

the anode to the cathode (Figure 6.33). The various materials making up the cell are

summarized in Table 6.5. Both electrodes contain lithium and the electrolyte is typically a lithium salt dissolved in an alkyl carbonate solvent (e.g., ethylene carbonate,

dimethyl carbonate, diethyl carbonate, or ethyl methyl carbonate) (Yang et al. 2011).

The “rocking horse” redox chemistry of the Li+ ion in a Li-ion battery is given in

Equations 6.27 through 6.29, below, where C6 indicates some form of graphite.

Reaction at anode: Li x C6 discharge


→ xLi + xe − + C6


Li1− x CoO2 + xLi + + xe − discharge


→ LiCoO2



→ C6 + LiCoO2 ( Ecell = 3.7 V at 25°C) (6.29)

  Cell reaction: LiC6 + CoO2 

These cells can deliver power greater than 200 Wh/kg with a capacity of 150 Ah/kg

(Tarascon and Armand 2001).

Anode materials. Research focused on anode materials has addressed both capacity and safety issues. An anode made solely of lithium metal provides very highspecific capacity but is rarely used. Instead, graphite is interpenetrated with lithium

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