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

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RECHARGEABLE LITHIUM BATTERIES (AMBIENT TEMPERATURE) 34.41

FIGURE 34.23 Typical discharge curve of the Argo-Tech’s battery NPS-4V80.

(Reprinted by permission of 3M Company, St. Paul, Minnesota.)

FIGURE 34.24 Schematic of a SPE battery design conﬁguration. (From Va-

lence Technology, Inc.)

Polymer Electrolyte Battery Using V

. The design of another conﬁguration of an SPE

cell which was being developed for portable applications and for scaling up to larger batteries

is illustrated in Fig. 34.24. A folded ‘‘bicell,’’ which is formed by folding the cathode lam-

inate and inserting the lithium foil anode, is the basic assembly unit. The bicells are stacked,

the terminal leads are attached, and the unit is hermetically sealed into the ﬁnal package.

The size and number of stacks used in each cell assembly depend on the desired capacity

and cell and battery dimensions.

The heart of the process was the fabrication of the polymer laminate for the cathode. The

cathode formulation, including polymer precursor, vanadium oxide, and carbon, was mixed

and coated onto the carbon current collector. A second layer, the electrolyte, was coated on

the cathode to provide the ionic conductivity and separate the cathode from the lithium

anode. The coated laminate was then passed through an electron beam generator to cross-

link the polymer precursors and produce the solid polymer material.

Figure 34.25 shows the discharge-charge curve for this lithium polymer battery, using a

lithium foil anode and a vanadium oxide cathode (V

). The capacity of the battery is

about 50 mAh. The discharge curves at different rates at 20

⬚C are shown in Fig. 34.26. The

sloping discharge proﬁle is characteristic of the intercalation cathode. The voltage plateaus

relate to the intercalation of the lithium ions into the vanadium oxide. The midpoint voltage

decreases with increasing current, but there is relatively little change in Ampere-hour capacity

if the cell is discharged to 1.8 V at rates slower than the 1-h rate. The self-discharge rate of

these cells was very low, on the order of 0.5% per month at 20

⬚C. The battery was expected

to deliver about 200 cycles, with the capacity dropping slightly with cycling until near the

end of life. During cycling, the impedance of the cell increases gradually, accounting for

this loss of capacity. Work on this system has been discontinued in favor of lithium-ion

technology using PVDF-based electrolytes (see Table 34.16).

34.42 CHAPTER THIRTY-FOUR

FIGURE 34.25 Laboratory prototype SPE cell (50-mAh size).

Typical discharge/ charge curve. (From Valence Technology, Inc.)

FIGURE 34.26 Laboratory prototype SPE cell, typical discharge curves at 20⬚C.

(From Valence Technology, Inc.)

34.4.4 Lithium Batteries Using Sulfur-based Polymeric Positive Electrode

Materials

Polymeric sulfur-based positive electrodes are under development for use in rechargeable

batteries with lithium metal negatives.

55,56

Both liquid dioxolane-based and proprietary pol-

ymer electrolytes have been employed with this system.

Examples of the positive electrode

polymers used in this system are shown in Fig. 34.27. These positive electrode materials are

claimed to have speciﬁc capacities of 700 to 1200 mAh /g. Initial work was carried out with

AA-size batteries using liquid electrolytes which operated at 2.1 V, provided 1 Ah capacity,

a speciﬁc energy of 215 Wh/ kg and an energy density of 260 Wh/ L. This system is claimed

to provide an intrinsic overcharge and over-discharge mechanism involving soluble sulfur

species which shuttle between the electrodes under these conditions. See Fig. 34.28. The

AA-size battery demonstrated its ability to operate on the standardized GSM cell-phone test

as shown in Fig. 34.29 Approximately 200 cycles were obtained under C/3 charge-discharge

cycling conditions with the AA-size battery. The cylindrical design has been superceded by

a tin-foil laminate structure, which has evolved from 66 micron to 47 micron thickness for

use in ﬂattened wound cell designs. See Fig. 34.30. A 1 Ah unit is projected to have an

electrode surface area of over 1000 cm

, allowing operation at low current density. Prismatic

designs (34

⫻ 48 ⫻ 3.5 mm) were stated to give 950 mAh at 2.1 V, providing 310 Wh /kg

and 350 Wh /L. Self-discharge is high, at 10 to 15% per month, probably due to the presence

of soluble sulfur species. This design concept provides high power capability for this system,

as shown in the Ragone plot of Fig. 34.31, which demonstrates that this system is capable

of discharge rates of up to 8C, delivering 800 W/kg at 100 Wh/ kg, which makes it poten-

tially useful in hybrid electric vehicle applications. This technology continues under devel-

opment by several companies.

RECHARGEABLE LITHIUM BATTERIES (AMBIENT TEMPERATURE) 34.43

FIGURE 34.27 Sulfur-based electrode materials consist of congurated

carbon backbones connected to contiguous sulfur rings or chains. Cath-

ode discharge process is a redox reaction in which the sulfur rings open,

providing 700 to 1200 mAh /g. The sulfur rings reform on recharge.

(From Ref. 55.)

FIGURE 34.28 Redox shuttle protection mecha-

nism provided by sulfur-based polymeric materials.

(From Ref. 56.)

FIGURE 34.29 GSM cell-phone test of AA lithium/ sulfur-based cathode AA-size battery. Test consists of

1.5 A pulse for 0.6 millisec followed by 0.1 A for 4.4 millisec. (From Ref. 55.)

34.44 CHAPTER THIRTY-FOUR

FIGURE 34.30 Schematic illustration of thin, ﬂat rechargeable lithium

battery with sulfur-based polymer cathode material. (From Ref. 56.)

0 100 200 300 400 500 600 700 800

Specific Power (W/kg)

100

120

140

160

180

Specific Energy (Wh/kg)

FIGURE 34.31 Ragone plot for 0.8 Ah thin-ﬁlm lithium battery with sulfur-based cath-

ode material. (From Ref. 56.)

RECHARGEABLE LITHIUM BATTERIES (AMBIENT TEMPERATURE) 34.45

The solid polymer electrolyte technology provides ﬂexibility in battery design as the cell

can be fabricated in a variety of shapes, conﬁgurations, and sizes. The estimated speciﬁc

energy and the energy density are very attractive. Major interest is in using this battery

system for applications requiring high voltages and capacity such as electric and hybrid

electric vehicles and for stand-by power applications such as large uninterruptible power

supplies.

34.4.5 Inorganic Electrolyte Batteries

Since the introduction of lithium/SO

primary batteries, signiﬁcant research efforts have been

directed to the development of rechargeable lithium /SO

batteries. Among the different elec-

trolyte salts investigated, LiAlCl

, LiGaCl

, and Li

are noteworthy because of their

good ionic conductivity and lithium cycling efﬁciency. High-surface-area carbon such as

Ketjen black

11,19,57–61

or CuCl

26,60,62,63

are used as cathode materials. Microporous Tefzel

separator was found to be compatible in these electrolytes. This material is no longer avail-

able commercially, however.

Inorganic electrolyte batteries offer several advantages, including high-rate capability, ex-

cellent shelf life, and the ability to accept limited overcharge through a shuttle mechanism.

The major disadvantages of these batteries are safety issues, capacity fade on cycling,

signiﬁcantly low capacity at low temperature, and high toxicity of electrolytes.

Lithium/ Carbon Batteries. These batteries are made in an hermetically sealed stainless-

steel container with a metallic lithium anode, a Ketjen black carbon cathode, and a

LiAlCl

䡠 6SO

electrolyte. The cathode composition is 96% Ketjen black and 4% Teﬂon.

Teﬂon-rich carbon-coated nickel exmet is used as the cathode substrate. These batteries are

made cathode-limited with the anode capacity at least twice the cathode capacity. Batteries

are vacuum ﬁlled with the electrolyte. The open-circuit voltage of the system is about 3.3

V. The average discharge voltage is 3.1 V at 1 mA/ cm

. It is believed that high-surface-area

carbon forms a complex with the electrolyte, and this complex takes part in the cell reaction.

Typical discharge-charge curves of lithium/carbon batteries of 3 Ah capacity using a

LiAlCl

䡠 6SO

electrolyte are shown in Fig. 34.32a for selected cycles. The change in voltage

with time for the cell and the cathode versus the lithium reference are almost identical,

indicating little anode polarization at the 1 mA/ cm

discharge and charge rate. The gradual

loss of capacity and the increased charge plateau on cycling are related to cathode polari-

zation. Scanning electron microscopy and X-ray diffraction analyses of discharged cathodes

conﬁrm that the polarization is caused by irreversible deposition of a nonconductive dis-

charge product (LiCl).

The lithium /carbon system in SO

-based LiAlCl

electrolyte has excellent shelf life (⬍1%

capacity loss per month) and insigniﬁcant voltage delay, even after 3 years of storage at

room temperature.

The cell delivers signiﬁcantly lower capacity at low temperature. Figure

34.32c shows the discharge characteristics of a lithium/carbon cell at

⫺20⬚C. The system is

particularly suitable for high-rate pulse power applications. Figure 34.32b shows the pulse

discharge behavior of a lithium/carbon battery in LiAlCl

䡠 6SO

at 20 mA/ cm

Lithium/ Copper Chloride Battery. In this system, the copper chloride cathode is directly

reduced and oxidized and no lithium intercalation-deintercalation occurs during the dis-

charge-charge process. The use of CuCl

as the active cathode material provides a higher

discharge voltage (3.3 V) for the reduction of Cu

⫹

to Cu

⫹

. Figure 34.33 shows the discharge-

charge behavior of a prismatic D-size Li /CuCl

battery at 1 mA /cm

. If the discharge is

limited to a single-electron process, high cycle life (

⬎200) with good capacity (0.9e /CuCl

)

can be achieved. This system shows excellent coulombic efﬁciency (see Fig. 34.33b).

34.46 CHAPTER THIRTY-FOUR

FIGURE 34.32 (a) Discharge / charge behavior of a

Li / LiAlCl

䡠 6SO

C-size battery at 1 mA / cm

. Voltage

limits; 2.8–4.0 V. Line—battery, symbols (䉭)—cathode

vs. ref. (b) High-rate pulse discharge of a Li / LiAlCl

䡠

6SO

C-size battery. Pulse rate at 20 mA/ cm

for 20 s.

Rest period for 180 s. (c) Discharge characteristics and

voltage recovery (without load) of a Li / LiAlCl

䡠 6SO

C-size battery at ⫺20⬚C. Discharge at 3.2 mA/ cm

(From Yardney Technical Products, Inc.)

RECHARGEABLE LITHIUM BATTERIES (AMBIENT TEMPERATURE) 34.47

FIGURE 34.33 (a) Discharge/ charge behavior of a Li / CuCl

prismatic D-size battery in LiAlCl

䡠 6SO

electrolyte at 1 mA / cm

(b) Coulombic efﬁciency of a Li/ CuCl

battery at 1 mA/ cm

(From Yardney Technical Products, Inc.)

34.48 CHAPTER THIRTY-FOUR

FIGURE 34.33 (c) Discharge behavior of a Li / CuCl

rechargeable

battery in LiAlCl

䡠 6SO

electrolyte at 1 mA / cm

.(d ) Cycling behav-

ior of a Li / CuCl

prismatic D-size battery at 1 mA/ cm

.(From Yard-

ney Technical Products, Inc.)(Continued ).

When an optimal combination of Ketjen black carbon and CuCl

is used as the cathode,

limited overdischarge-overcharge protection can be achieved. These batteries can also deliver

extra capacity when needed. The discharge-charge as well as the overdischarge-overcharge

characteristics of such a battery are shown in Fig. 34.33c. Possible cell reactions are as

follows:

Discharge:

⫹⫹

Cathode: Cu ⫹ e → Cu

⫹

Anode: Li → Li ⫹ e

RECHARGEABLE LITHIUM BATTERIES (AMBIENT TEMPERATURE) 34.49

FIGURE 34.34 Discharge behavior of a Li / CuCl

prismatic D-

size battery after 100 cycles at 100% DOD and 500 cycles at 10%

DOD. Discharge rate at 1 mA / cm

.(From Yardney Technical

Products, Inc.)

Overdischarge:

Cathode

Anode

Charge:

⫹

Cathode Cu → Cu ⫹ e

⫹

Anode Li ⫹ e → Li

Overcharge:

Cathode

Anode

The composition of the cathode is typically 67% CuCl

, 25% Ketjen black, and 8% Teﬂon.

The cycling behavior of a Li /CuCl

Ketjen black prismatic D-size cell in LiAlCl

䡠 6SO

electrolyte is shown in Fig. 34.33d for the ﬁrst 100 cycles at 100% depth of discharge (the

cell was cycled with time limits rather than voltage limits), then 500 cycles at 10% depth

of discharge, and ﬁnally the total discharge and overdischarge capacity of the cell (see Fig.

34.34). The extra capacity is due to the reduction of the complex formed by the SO

-based

LiAlCl

with the high-surface-area carbon.

The Li /CuCl

Ketjen black system in LiAlCl

䡠 3SO

electrolyte has been investigated in

a bipolar conﬁguration for high-rate pulse power applications. Figure 34.35 shows a portion

of the cycling behavior of a four-cell-stack bipolar battery. The battery delivered more than

1000 pulse cycles.

34.50 CHAPTER THIRTY-FOUR

FIGURE 34.35 Discharge/ charge behavior of a bipolar Li/

CuCl

battery (four-cell stack) at 50-mA / cm

(total 24 A) dis-

charge for 20 s and 5.56-mA / cm

charge for 180 s. Voltage limits:

11.0–16.0 V. (From Yardney Technical Products, Inc.)

Laboratory-scale work has continued to improve the safety and cycle-life of the Li /CuCl

system.

Design modiﬁcations and electrolyte additives are claimed to reduce the tendency

of this battery to form dendrites on overcharge, leading to internal shorts and ventings. Three

hundred charge-discharge deep-discharge cycles are claimed with these changes. The elec-

trolyte modiﬁcation apparently involves the addition of chlorine, which leads to corrosion

of 300-series stainless steel case-positive cells during charging, and this ultimately limits

cycle life. Proprietary shut-down separators are also stated to be under development to im-

prove the safety of this battery system.

Although the SO

-based inorganic electrolyte systems have been investigated for some

time and may be of interest for special application because of their advantageous performance

characteristics, the toxicity and corrosivity of the electrolyte present a potential safety hazard

limiting commercial applications. Safety problems have also been persistent with these sys-

tems and have limited their development beyond the laboratory level.

A lithium-metal LiAlCl

-SO

/LiCoO

battery is currently under development.

12,65,66

This

system is built in the discharged state and is charged by plating lithium metal on a nickel

metal substitute. In this way, no excess lithium is present. The lithium electrode has been

found to have a SEI layer on lithium of lithium dithionite (Li

) through which the

electrochemical reactions occur.

Early versions of this battery used a microporous Tefzel威

separator, but this material is no longer commercially available. This system also possesses

an overcharge mechanism in which chlorine is evolved at the positive electrode above 4.5

V and reacts with excess lithium on the negative electrode. Lithium is plated in ﬁlamentary

form during charge using this electrolyte, which contains a SO

/LiAlCl

ratio of 1.5 to 1.8.

Cycling efﬁciencies of 98 to 99% for the lithium plating and stripping reactions have been

found in this electrolyte.

Prototype 7 Ah batteries are stated to provide a speciﬁc energy

of about 200 Wh/kg and reach speciﬁc power levels of 1300 W/ kg.

Development of this

system continues.