Linden D., Reddy T.B. (eds.) Handbook of batteries

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34.1

CHAPTER 34

RECHARGEABLE LITHIUM

BATTERIES (AMBIENT

TEMPERATURE)

Thomas B. Reddy and Sohrab Hossain

34.1 GENERAL CHARACTERISTICS

Rechargeable lithium batteries operating at room temperature offer several advantages com-

pared to conventional aqueous technologies, including

1. Higher energy density (up to 150 Wh/kg, 400 Wh/L)

2. Higher cell voltage (up to about 4 V per cell)

3. Longer charge retention or shelf life (up to 5 to 10 years)

These advantageous characteristics result in part from the high standard potential and low

electrochemical equivalent weight of lithium metal.

Ambient-temperature lithium rechargeable batteries, on the other hand, do not have the

high-rate capability (because of the lower conductivity of the aprotic organic or inorganic

electrolytes that must be used because of the reactivity of lithium in aqueous electrolytes)

nor, in some instances, the cycle life of conventional rechargeable batteries. In addition,

rechargeable lithium batteries that use lithium metal as the negative electrode present poten-

tial safety problems which are more challenging than those with primary lithium batteries.

This is due to a three- to ﬁvefold excess of lithium, which is required for these types of

cells in order to obtain a reasonable cycle life, and to the reactivity of the high-surface-area

lithium that is formed during cycling.

There is another type of rechargeable ‘‘lithium’’ battery, however, which uses a lithiated

carbon or other intercalation material for the negative electrode in place of lithium. The

absence of metallic lithium in these lithium-ion batteries minimizes these safety concerns.

This type of battery is covered in Chap. 35.

The advantages and disadvantages of rechargeable lithium batteries operating at ambient

temperature are summarized in Table 34.1. (These may not be applicable in all cases because

of the different characteristics of the various rechargeable lithium systems.)

34.2 CHAPTER THIRTY-FOUR

TABLE 34.1 Advantages and Disadvantages of Ambient-Temperature Lithium Rechargeable Batteries

Advantages

High energy density and speciﬁc energy

High voltage

Good charge retention, low self-discharge rate

Disadvantages

Low cycle life with metallic lithium systems

Relatively poor high-rate performance (compared to conventional aqueous rechargeable batteries)

Relatively poor low-temperature performance (compared to conventional aqueous rechargeable batteries)

Capacity fading (with some systems)

Potential safety problems with metallic lithium systems

As with primary lithium batteries, a number of different approaches have been taken in

the chemistry and design of rechargeable lithium batteries to obtain the desired performance

characteristics. These are summarized in Fig. 34.1a for batteries with lithium metal negative

electrodes (the anode during discharge) and in Fig. 34.1b for batteries with other materials,

such as lithium alloys and lithiated carbon.*

A variety of materials have been investigated for the positive electrode (the cathode during

discharge), such as intercalation solid compounds, soluble inorganic cathodes, and polymeric

materials. Liquid aprotic organic and inorganic electrolytes are used in many cells. Solid

polymer electrolytes are also popular as they may provide a safer design because of their

lower reactivity with lithium. These materials are identiﬁed in Fig. 34.1.

Rechargeable lithium batteries have been introduced into the market on a limited scale.

Coin cells, using lithium-aluminum anodes, are available for special applications mainly for

low-power portable applications where they can be conveniently recharged, in some instances

by solar cells. A small cylindrical cell, using a lithium anode, was brieﬂy, and perhaps

prematurely, introduced in the 1980s for consumer electronics applications, but was with-

drawn when safety problems arose. More recently, the lithium-ion cell, which has a safety

advantage over other lithium secondary cells as it does not contain lithium in a metallic

form, has been marketed as a power source for consumer electronics such as cellular phones

and camcorders. This technology has become dominant in the market.

The shipment, use, and disposal of rechargeable lithium batteries are regulated, as for the

primary lithium batteries, by international organizations, government agencies, and quasi-

government institutions because of the concern for potential safety problems with lithium

batteries, particularly if they are physically or electrically abused.

*As discussed in Chap. 1, the electrodes in a rechargeable battery are referred to as

negative and positive. Sometimes they are referred to as anode and cathode, respectively, the

appropriate terminology for the cell during discharge.

RECHARGEABLE LITHIUM BATTERIES (AMBIENT TEMPERATURE) 34.3

FIGURE 34.1 Lithium rechargeable batteries (a) with metallic lithium as negative electrode, (b) with

lithium alloys or lithiated carbon negative electrode.

34.4 CHAPTER THIRTY-FOUR

TABLE 34.2 Negative Electrode Material

Material

Voltage range

vs. lithium,

Theoretical

speciﬁc capacity,

Ah/ g Comments

Li metal 0.0 3.86 Lithium foils readily available

LiAl 0.3 0.8 Generally brittle foils,

difﬁcult to handle

0.5

(coke)

LiC

(MCMB (b), or graphite)

0.0–1.3

0.0–0.1

0.185

冎

0.372 (a)

Used for lithium-ion cells

LiWO

LiMoO

LiTiS

0.3–1.4

0.8–1.4

1.5–2.7

0.12

0.199

冧

0.266

Possible use for lithium-ion

cells

(a) Based on weight of carbon only.

(b) Mesocarbon microbeads.

34.2 CHEMISTRY

The objective of the rechargeable lithium battery development is to produce batteries that

have high energy density, high power density, good cycle life and charge retention, and to

provide this performance reliably and safely. The selection of cell components and designs

is necessarily a compromise to achieve the optimum balance. Many of the characteristics

and criteria for selection are similar to those for primary lithium cells covered in Chap. 14.

The process, however, is even more complex for rechargeable batteries since the reactions

that occur during recharge affect all of the characteristics and the performance on subsequent

cycling.

The different types of lithium rechargeable batteries identiﬁed in Fig. 34.1 can be clas-

siﬁed conveniently into ﬁve categories:

1. Solid-cathode cells using intercalation compounds for the positive electrode, a liquid

organic electrolyte, and a metallic lithium negative electrode.

2. Solid-cathode cells using intercalation compounds for the positive electrode, a polymer

electrolyte, and a metallic lithium negative electrode.

3. Cells using intercalation compounds for both the positive and the negative electrodes and

a liquid or polymer electrolyte (lithium-ion cells) (see Chap. 35).

4. Inorganic electrolyte cells, which use the electrolyte solvent or a solid redox couple for

the positive and lithium metal for the negative active material.

5. Cells with lithium-alloy anodes, liquid organic or polymer electrolytes, and a variety of

cathode materials, including polymers. This technology has been used mainly in small

ﬂat or coin cells.

The components and reactions of typical examples of these types of rechargeable lithium

batteries are summarized in Sec. 34.3.

34.2.1 Negative Electrodes

Typical negative electrode materials for rechargeable lithium batteries are listed in Table

34.2. Of these, lithium is the lightest and most electropositive, and it has a high speciﬁc

capacity, 3.86 Ah/ g. It is also more easily handled than the other alkali metals.

RECHARGEABLE LITHIUM BATTERIES (AMBIENT TEMPERATURE) 34.5

While metallic lithium has the highest speciﬁc capacity, it is more reactive than lithium-

aluminum and other alloys. These have been used mainly in small ﬂat or coin cells, as it is

difﬁcult to scale up to larger and spirally wound designs because most lithium alloys are

brittle and cannot be extruded into thin foils. Another approach is the lithium ion battery

which uses a carbon material for the negative electrode. These are attractive from a safety

viewpoint as reactive metallic lithium is not present in the cell. A suitable intercalation

compound is selected for the positive electrode for these cells so that a high cell voltage is

obtained. The cell operates by the lithium ions shuttling back and forth between the elec-

trodes during the discharge-charge cycle. No metallic lithium is plated during the charge and

no metallic lithium is present in the cell.

Lithium Metal. The search for high-energy-density batteries has inevitably led to the use

of lithium, as the electrochemical characteristics of this metal are unique. A number of

batteries, both primary and rechargeable, using a lithium anode in conjunction with inter-

calation cathodes, were developed which had attractive energy densities, excellent storage

characteristics, and, for rechargeable cells, a reasonable cycle life. Commercial success has

eluded all but the primary batteries due to persistent safety problems.

The difﬁculties associated with the use of metallic lithium stem from its reactivity with

the electrolyte and the changes that occur after repetitive charge-discharge cycling. When

lithium is electroplated, during recharge, onto a metallic lithium electrode, it forms a mossy

and in some cases a dendritic deposit with a larger surface area than the original metal.

While the thermal stability of lithium metal foil in many organic electrolytes is good, with

minimal exothermic reaction occurring up to temperatures near the melting point of lithium

(181

⬚C), after cycling the surface area of the lithium increases signiﬁcantly with a corre-

sponding increase in the reactivity. This lowers the thermal stability of the system, with the

result that cells become increasingly sensitive to abuse as they are cycled.

Another contributing effect is the inability of attaining 100% lithium cycling efﬁciency.

This happens because lithium is not thermodynamically stable in the organic electrolytes and

the surface of the lithium is covered with a ﬁlm of the reaction products between the lithium

and the electrolyte. Every time the lithium is stripped and replated during discharge and

charge, a new lithium surface is exposed and then passivated with a new ﬁlm, consuming

lithium. Because of the mossy deposit, some lithium becomes electrochemically unreactive

on repeated cycling. In order to obtain a reasonable cycle life, a three- to ﬁvefold excess of

lithium is required.

The failure to control the surface area of the lithium anode remains a problem, limiting

the commercialization of lithium anode cells with liquid organic electrolytes. Given this

problem, an alternate solution is to use an electrolyte, such as a solid polymer electrolyte,

which is less reactive with lithium. This is covered in Sec. 34.2.3.

Carbon Materials. In the lithium-ion cell, carbon materials, which can reversibly accept

and donate signiﬁcant amounts of lithium (Li:C

⫽ 1:6) without affecting their mechanical

and electrical properties, can be used for the anode instead of metallic lithium. Carbon

material is used as an anode in lithium-ion cells since the chemical potential of lithiated

carbon material is close to that of metallic lithium, as shown in Fig. 34.2. Thus an electro-

chemical cell made with a lithiated carbon material will have almost the same open-circuit

voltage as one made with metallic lithium. In practice, the lithium-ion cell is manufactured

in a fully discharged state. Instead of using lithiated carbon material, which is air-sensitive,

the anode is made with carbon and lithiation is carried out by subsequent formation of the

cell.

The speciﬁc energy or capacity of the lithium-ion system depends largely on the type of

carbon materials used, the lithium intercalation efﬁciency, and the irreversible capacity loss

associated with the ﬁrst charge process. Table 34.3 lists the properties of some of these

carbon materials. Coke-type carbon, having physical properties such as ash content

⬍0.1%,

surface area

⬍10 m

/g, true density ⬍2.15 g/cm

, and interlayer spacing ⬎3.45 A

, were

used in ﬁrst-generation lithium-ion system. These types of carbon materials can provide about

34.6 CHAPTER THIRTY-FOUR

FIGURE 34.2 Electrochemical potential of some Li-

intercalation compounds vs. Li metal. PPY ⫽ polypyrrole.

PVF ⫽ polyvinyl furan.

TABLE 34.3 Physical Properties of Coke and Graphite Anodes for Lithium-Ion Cells

Item Coke Graphite

Type Petroleum

coke

Synthetic,

KS-15

Synthetic,

KS-44

Isotopic,

EC-110

Natural

Structure Disordered Ordered layer structure

Physical parameters:

Interlayer spacing d002, A

3.46 3.35 3.35 3.34 3.34

Crystalline size L

46 900 ⬎1000 ⬎1000 ⬎2000

Surface area, m

/g 6 14 10 10 —

Density, g /cm

2.14 2.255 2.248 — —

Ash content, % 0.08 0.05

⬍0.1 — —

185 mAh /g capacity (corresponding to LiC

). By controlling the temperature of the heat

treatment, carbon material having speciﬁc properties such as density and interlayer spacing

can be prepared. Doping with nitrogen, boron, or phosphorus can increase the capacity of

coke type materials to 350 mAh/ g. Graphitic carbons having an interlayer spacing of 3.36

can also deliver 350 mAh /g capacity. The capacity delivered by different types of carbon

materials, including natural and synthetic graphite, in ethylene carbonate-based electrolytes

on the ﬁrst discharge is shown in Fig. 34.3.

This ﬁgure shows the advantage of the graphite

materials, which have a ﬂatter discharge and a higher capacity than the coke materials.

Mesocarbon Microbeads (MCMB), which are also graphitized, have also been employed in

lithium ion batteries.

During the ﬁrst electrochemical intercalation of lithium into the carbon, some lithium is

irreversibly consumed forming a solid electrolyte interface (SEI) and cannot be recovered in

the following discharge, resulting in a loss of capacity. (See Chap. 35.) Figure 34.4 shows

the voltage proﬁle of the ﬁrst charge and discharge of petroleum coke and graphite electrodes

versus a lithium electrode, respectively.

This irreversible capacity, which depends on the

electrolyte solution and the type of carbon material, is explained on the basis of the reduction

RECHARGEABLE LITHIUM BATTERIES (AMBIENT TEMPERATURE) 34.7

FIGURE 34.3 First discharge curves of carbon materi-

als.

FIGURE 34.4 Representation of irreversible capacity asso-

ciaed with the ﬁrst charge /discharge process. (a) Coke. (b)

Artiﬁcial graphite.

34.8 CHAPTER THIRTY-FOUR

of the electrolyte solution and the formation of a SEI layer on the Li

C interface.

When the

ﬁlm is sufﬁciently thick to prevent electron tunneling, the electrolyte reduction is suppressed

and the electrode can then be cycled reversibly. The ﬁrst step is, therefore, critical in order

to obtain a uniform passivating ﬁlm. Very little loss usually occurs after the ﬁrst intercalation.

The capacity on the second and subsequent cycles is about the same, and the lithium inter-

calation during charge and discharge is nearly 100% reversible.

The theoretical capacity of metallic lithium is much higher than that of lithiated carbon

material having a composition of LiC

. The advantage of the higher capacity of metallic

lithium is reduced because a three- to ﬁvefold excess of lithium is required in rechargeable

batteries having metallic lithium anodes to achieve a reasonable cycle life. The comparison

is shown in Table 34.4.

TABLE 34.4 Comparison of Usable Speciﬁc Capacity (Ah/ kg)

and Capacity Density (Ah /L) for Lithiated Carbon vs. Lithium

Metal Anodes

Characteristics Li metal LiC

Theoretical speciﬁc capacity, Ah/ kg 3862 372

Theoretical capacity density, Ah/ L 2061* 837

Practical speciﬁc capacity, Ah/ kg

Fourfold excess of lithium 965 372

95% active material in carbon electrode 965 353

Practical capacity density, Ah / L

Fourfold excess of lithium 515 837

Porosity of carbon electrode (50%) 515 418

* Density of lithium ⫽ 0.534 g / cm

Transition Metal Compounds. Transition metal compounds having layered structures into

which lithium ions can be intercalated and deintercalated during charge and discharge and

with electrochemical potentials close to those of lithiated carbon materials have also been

used as the negative electrode in lithium-ion cells. Figure 34.2 shows the electrochemical

potentials of some lithiated transition metal compounds. The electrochemical potentials of

,Li

MoO

, and Li

TiS

are close to that of lithiated carbon and distinctly different

from the values for Li

,Li

CoO

, and Li

NiO

.WO

, MoO

,orTiS

can then be used

as anodes and LiMn

, LiCoO

, or LiNiO

as cathodes. Cells of these types have been

developed using TiS

anodes and LiCoO

cathodes in an organic electrolyte.

34.2.2 Positive Electrodes

There is a wide choice of materials that can be selected for the positive electrodes of lithium

batteries. However, many of these involve reactions which cannot be readily reversed and

are limited to primary nonrechargeable batteries. The best cathodes for rechargeable batteries

are those where there is little bonding and structural modiﬁcation of the active materials

during the discharge-charge reaction.

Intercalation Compounds. The insertion or intercalation compounds are among the most

useful cathode materials. In these compounds, a guest species such as lithium can be inserted

interstitially into the host lattice (during discharge) and subsequently extracted during re-

charge with little or no structural modiﬁcation of the host.

RECHARGEABLE LITHIUM BATTERIES (AMBIENT TEMPERATURE) 34.9

TABLE 34.5 Key Requirements for Positive-Electrode

Intercalation Material (Li

) Used in Rechargeable Lithium

Cells

High free energy of reaction with lithium

Wide range of x (amount of intercalation)

Little structural change on reaction

Highly reversible reaction

Rapid diffusion of lithium ion in solid

Good electronic conductivity

No solubility in electrolyte

Readily available or easily synthesized from low-cost reactants

The intercalation process involves three principal steps:

1. Diffusion or migration of solvated Li

⫹

ions

2. Desolvation and injection of Li

⫹

ions into the vacancy structure

3. Diffusion of Li

⫹

ions into the host structure

The electrode reactions which occur in a Li/ Li

(HOST) cell, where (HOST) is an inter-

calation cathode, are

⫹

yLi ↔ yLi ⫹ ye at the Li metal anode

⫹

yLi ⫹ ye ⫹ Li (HOST) ↔ Li (HOST) at the cathode

⫹

leading to an overall cell reaction of

yLi

⫹ Li (HOST) ↔ Li (HOST)

⫹

A number of factors have to be considered in the choice of the intercalation compound,

such as reversibility of the intercalation reaction, cell voltage, variation of the voltage with

the state of charge, and availability and cost of the compound. Table 34.5 lists the key

requirements for the intercalation materials and Table 34.6 presents some of the character-

istics of the intercalation and other compounds that have been used in lithium rechargeable

batteries. The electrochemical potentials of several lithium intercalation compounds versus

those of lithium, metal and the variation of voltage with the amount of intercalation are

shown in Fig. 34.2.

Transition metal oxides (MnO

, LiCoO

, LiNiO

,VO

), sulﬁdes (MoS

,TiS

), and selen-

ides (NbSe

) have been used in rechargeable lithium batteries. The lithiated transition metal

oxides (such as LiCoO

, LiNiO

, and LiMn

) are attractive materials used as the cathode

in the lithium-ion rechargeable cell. LiCoO

, LiNiO

and LiNi

⫺

have a layered struc-

ture, where lithium and transition metal cations occupy alternate layers of octahedral sites

in a distorted cubic close-packed oxygen-ion lattice. The layered metal oxide framework

provides a two-dimensional interstitial space, which allows for each removal of the lithium

ions. The layered structure can be prepared by high-temperature treatment of a mixture of

lithium hydroxide or other salts and the metal oxide in air,

700

⬚

—

Co O ⫹ 2LiOH → 2LiCoO ⫹ HO

23 2 2

700

⬚

– —

2NiO ⫹ 2LiOH ⫹ O → 2LiNiO ⫹ HO

22 2 2

34.10 CHAPTER THIRTY-FOUR

TABLE 34.6 Positive-Electrode Materials and Some of Their Characteristics

Material

Average

voltage

vs. lithium,*

Lithium/

mole

Practical

speciﬁc

energy, †

Wh/ kg Comments

MoS

1.7 0.8 230 Naturally occurring

MnO

3.0 0.7 650 Inexpensive

TiS

2.1 1 550 Costly

NbSe

1.9 3 450 Costly

LiCoO

3.7 0.5 500 Good for lithium-ion system

LiNiO

3.5 0.5 480 Good for lithium-ion system

LiMn

3.8 0.8 450 Good for lithium-ion system, safe

2.3 2.5 300 Good for SPE system

2.8 1.2 490 Good for SPE system

3.1 0.33 220 Good for pulse power applications,

safety issues

CuCl

3.3 1 660 Good for pulse power applications,

safety issues

Polyacetylene 3.2 1 340 For polymer electrodes

Polypyrrole 3.2 1 280 For polymer electrodes

* At low rates.

† Based on cathode material only and average voltage and lithium / mole as shown.

Spinel LiMn

may be obtained by heating a mixture of appropriate amounts of Li

and MnO

at 800⬚C in air.

5,10

The LiMn

spinel framework possesses a three-dimensional

space via face sharing octahedral and tetrahedral structures, which provide conducting path-

ways for the insertion and extraction of lithium ions.

The removal and insertion of the lithium ion for lithiated transition metal oxides (M) are:

⫹



LiMO Li MO ⫹ xLi ⫹ xe



2(1

⫺

x)2

The reversible value of x for LiCoO

and LiNiO

is approximately 0.5, and the value is

greater than or equal to 0.85 for lithiated manganese oxide. Thus although the theoretical

capacity of LiCoO

and LiNiO

(274 mAh/ g) is almost twice as high as that of LiMn

the reversible capacity of the three cathode materials are in the same range. Figure 34.5

compares the reversible discharge capacity of the three cathode materials. It is to be noted

that lithium-ion cells made with LiMn

require a higher charge voltage to achieve full

capacity. These batteries are typically charged to 4.2 V vs. 4.1 V for Co and 4.0 V for Ni.

The diffusion coefﬁcients of lithium ion (D

⫹

) in the three lithiated metal oxides are

shown in Table 34.7. The diffusion steps play a signiﬁcant role in the mechanistic aspects

of the intercalation process.

Polymers. Electronically conductive polymers may also be used as cathode materials in

rechargeable lithium batteries. The most popular polymers are polyacetylene, polypyrrole,

polyaniline, and polythiophene, which are made conductive by doping with suitable anions.

The discharge-charge process is a redox reaction in the polymer. The low speciﬁc energy,

high cost, and their instability, however, make these polymers less attractive. They have been

used in small coin-type batteries with a lithium-aluminum alloy as the anode.

Another potential approach is an all-polymer cell using a cation-doped polymer for the

anode, a solid polymer electrolyte, and a polymer for the cathode. These cells can be fab-

ricated in thin sections and in a variety of shapes but, again, most of the development has

been in small coin sizes. No progress on these systems has been reported recently.