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

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LITHIUM-ION BATTERIES 35.39

0123456

2.50

2.75

3.00

3.25

3.50

3.75

4.00

4.25

Voltage (V)

Discharge Energy (Wh)

0.5W (1.44 Ah, 5.61 Wh)

1.0W (1.43 Ah, 5.52 Wh)

2.0W (1.42 Ah, 5.42 Wh)

5.0W (1.31 Ah, 4.79 Wh)

FIGURE 35.39 Constant power discharge of a C /LiMn

18650 battery. The battery was charged in a

CCCV regime at 1.4 A to 4.2 V for 2.5 hours at 21⬚C. (Courtesy of NEC Moli Energy.)

0.2 0.4 0.6 0.8 1 2 4

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

2.25

2.50

Discharge Capacity (Ah)

C Rate

Moli 18650F (2000)

Sanyo 18650P (1999)

Moli 18650F (1999)

A&T LSR18650 (1996)

FIGURE 35.40 Comparison of the rate capability at constant current for C /LiCoO

18650 batteries.

High and Low Temperature Discharge. The voltage and capacity on discharge at the

C/ 5 rate for 18650-type C /LiMn

and C /LiCoO

batteries at high and low temperatures

are illustrated in Fig. 35.41, for a C/ LiMn

battery, and in Fig. 35.42 for a C/LiCoO

product. Comparing the C/ LiMn

and C/LiCoO

batteries, the spinel product provides

nominally 0.25 V higher voltage, although the C/LiCoO

product provides typically 20%

more coulombic capacity at any given temperature than the C/ LiMn

unit. Between ⫺10⬚C

and 60

⬚C, the C/LiMn

18650 battery delivered 1.4 Ah with an average voltage of 3.9 V

above 20

⬚C, and 3.7 V at ⫺10⬚C. At ⫺20⬚C, the C /LiMn

product provided 1.3 Ah at

3.5 V, on average.

35.40 CHAPTER THIRTY-FIVE

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

2.25

2.50

2.75

3.00

3.25

3.50

3.75

4.00

4.25

4.50

60°C (1.4 Ah)

45°C (1.4 Ah)

21°C (1.4 Ah)

0°C (1.4 Ah)

-10°C (1.4 Ah)

-20°C (1.3 Ah)

Voltage (V)

Discharge Capacity (Ah)

FIGURE 35.41 Discharge of an 18650-type C/ LiMn

battery at various temperatures

when charged in a CCCV (constant current-constant voltage) regime at 1.4 A to 4.2 V for 2.5

hours and discharged at 0.28 A (C/ 5). The average voltage at 21⬚C was 3.9 V, at ⫺20⬚C, 3.5

V. ( Courtesy of NEC Moli Energy.)

0.00.51.01.52.0

2.50

2.75

3.00

3.25

3.50

3.75

4.00

4.25

Voltage (V)

Discharge Capacity (Ah)

60°C (1.66 Ah)

45°C (1.66 Ah)

21°C (1.66 Ah)

0° C (1.62 Ah)

-10°C (1.60 Ah)

-20°C (1.50 Ah)

FIGURE 35.42 Discharge at 0.2C (0.33 A) of an 18650-type C/ LiCoO

battery at various tem-

peratures when charged in a CCCV regime at 1.65 A to 4.2 V for 2.5 hours and discharged at 0.33

A (C / 5 rate). The average voltage at 21⬚C was 3.6 V, at ⫺20⬚C,

3.2 V. (Courtesy of NEC Moli Energy.)

As illustrated by Fig. 35.42, C /LiCoO

batteries provided similar capacities over the range

of temperatures evaluated. At or above

⫺10⬚C, the battery provided 1.6 Ah and 1.5 Ah at

⫺20⬚C. The average voltage at 21⬚C was 3.6 V, and at ⫺20⬚C, 3.2 V.

At high rates, self-heating effects are observed upon discharge at low temperature. This

is illustrated in Fig. 35.43 which shows discharge curves at 1.5 A (0.9C rate) for an 18650-

type C /LiCoO

battery at temperatures from 60⬚Cto⫺20⬚C. At 21⬚C or above, the discharge

curves appear similar to those in Fig. 35.42 for the C /5 rate as the battery delivered similar

capacity (1.64 Ah) with similar average voltage (3.6 V). At

⫺10⬚C and ⫺20⬚C, the voltage

recovered in mid-discharge as self-heating ensued. At

⫺10⬚C, 1.2 Ah was delivered at 3.0

V on average. At

⫺20⬚C, 1.0 Ah was delivered at 2.8 V, on average.

LITHIUM-ION BATTERIES 35.41

0.0 0.5 1.0 1.5

2.50

2.75

3.00

3.25

3.50

3.75

4.00

4.25

Voltage (V)

Discharge Capacity (Ah)

60°C (1.65 Ah)

45°C (1.66 Ah)

21°C (1.64 Ah)

-10°C (1.17 Ah)

-20°C (1.00 Ah)

FIGURE 35.43 Approximate C-rate discharge of an 18650-type C / LiCoO

battery at various temperatures

when charged in a CCCV regime at 1.65 A to 4.2 V for 2.5 hours, then discharged at 1.5 A. The average

voltage at 21⬚C was 3.6 V, and at ⫺20⬚C, 2.9 V. (Courtesy of NEC Moli Energy.)

-20 0 20 40 60

1.0

1.5

2.0

LiCoO

LiMn

Energy (Wh)

Capacity (Ah)

Temperature (°C)

-20 0 20 40 60

LiCoO

LiMn

FIGURE 35.44 Discharge capacity and energy of 18650-type C / LiMn

bat-

teries at 0.2 C (0.28 A), and C / LiCoO

batteries at 0.2 C rate (0.33 A), at tem-

peratures from 60⬚Cto⫺20⬚C to 2.5 V. (Courtesy of NEC Moli Energy.)

The capacity and energy of 18650-type C/LiMn

and C /LiCoO

batteries when dis-

charged at 0.2C rate are summarized in Fig. 35.44. Illustrated in the ﬁgure is the higher

capacity and energy available from the C /LiCoO

chemistry, although because of the higher

voltage of the C /LiMn

product, the energy difference is less than the capacity difference

at any given temperature. As shown, the batteries offer consistent capacity and energy be-

tween 0

⬚C and 60⬚C, and 90% of the 21⬚C capacity at ⫺20⬚C. The average cell voltage is

depressed signiﬁcantly at the lower temperatures.

35.42 CHAPTER THIRTY-FIVE

Cycle Life of Commercial Products. A desirable characteristic of Li-ion batteries is their

long cycle life and ability to cycle continuously at ambient, low, or elevated temperature.

This is illustrated in Fig. 35.45 for a C /LiCoO

battery which shows the discharge capacity

when cycled at either 21

⬚Cor45⬚C at either the 1C, 0.5C or 0.2C rate. As shown, the fade

rate in all cases was comparable and relatively linear. At 21

⬚C, the batteries had a fade rate

of 0.024% /cycle, while the battery at 45

⬚C had a fade rate of 0.028% /cycle. Thus after 500

cycles, the battery cycled at the 1C rate at 21

⬚C delivered 1.42 Ah, 91% of the initial value,

and the one cycled at 45

⬚C at the 1C rate delivered 1.35 Ah on the 500

cycle, or 87% of

the initial value.

The capacity of 18650-type C /LiMn

batteries cycled at 21⬚Cor45⬚C at the 1C, 0.5C

or 0.2C rates is illustrated in Fig. 35.46. At 21

⬚C at the 1C rate, after 75 cycles, the fade

rate was linear at 0.42%/ cycle, and at the 0.5C rate, 0.32%/ cycle. After 500 cycles at the

1C rate, the battery delivered 1.01 Ah, or 70% of the initial capacity. For comparison, the

cell cycled at the 0.5C rate at 21

⬚C delivered 1.16 Ah after 500 cycles, or 80% of its initial

capacity. Higher fade rates are observed at 45

⬚C.

As batteries are cycled their impedance increases, resulting in reduced voltage and lower

delivered energy. Illustrated in Fig. 35.47 are discharge curves at various cycles for a

C/ LiCoO

battery cycled at the 1C rate at 21⬚C. As shown, the battery voltage decreased

by typically 0.3 mV/cycle. For comparison, Fig. 35.48 shows discharge curves at various

cycles for an 18650-type C/ LiMn

battery cycled at the 1C rate at 21⬚C. As the cycling

proceeded, the average voltage decreased, by 0.3 mV /cycle, comparable to that observed

with the C/ LiCoO

chemistry.

0250500

1.00

1.25

1.50

1.75

Discharge Capacity (Ah)

Cycle

21°C, 1.65A (1C)

45°C, 1.65A (1C)

21°C, 0.825A (0.5C)

21°C, 0.33A (0.2C)

FIGURE 35.45 Capacity of 18650-type C /LiCoO

batteries when cycled at ei-

ther 21⬚Cor45⬚C at rates from 0.2C (0.33 A) to 1.0C (1.65 A) between 4.2 V

and 2.5 V. (Courtesy of NEC Moli Energy.)

LITHIUM-ION BATTERIES 35.43

0 250 500 750 1000

0.00

0.25

0.50

0.75

1.00

1.25

1.50

Discharge Capacity (Ah)

Cycle Number

21°C, 0.27 A

21°C, 0.68 A

21°C, 1.35 A

45°C, 1.35 A

FIGURE 35.46 Capacity fade of 18650-type C/ LiMn

batteries when cy-

cled at various rates at either 21⬚Cor45⬚C between 4.2 V and 2.5 V. (Courtesy

of NEC Moli Energy.)

0.0 0.5 1.0 1.5

2.0

2.5

3.0

3.5

4.0

200

Cycle Number:

10500

Voltage (V)

Discharge Capacity (Ah)

Cycle 10

Cycle 100

Cycle 200

Cycle 300

Cycle 400

Cycle 500

FIGURE 35.47 Discharge curves for an 18650-type C / LiCoO

battery

when cycled at 1.65 A (1C) charge and discharge illustrating the increase in

resistance upon cycling. (Courtesy of NEC Moli Energy.)

35.44 CHAPTER THIRTY-FIVE

-0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

2.00

2.25

2.50

2.75

3.00

3.25

3.50

3.75

4.00

4.25

600

100

Cycle Number:

300 10500

Voltage (V)

Discharge Capacity (Ah)

FIGURE 35.48 Discharge curves from an 18650-type C / LiMn

battery at various

cycle numbers illustrating the increase in resistance upon cycling. The battery was charged

in a CCCV regime at 1.4 A to 4.2 V for 2.5 hours, and discharged at 1.35 A. (Courtesy

of NEC Moli Energy.)

Storage Performance. Two criteria that can be used to characterize the storage performance

of batteries are their self-discharge rate and capacity recovery after storage. The capacity of

a battery may be determined by discharge before storage. After storage in the charged state,

discharge enables determination of self-discharge, subsequent charge and discharge enables

determination of capacity recovery, also termed reversible capacity. These effects are illus-

trated by the discharge curves in Fig. 35.49. As shown, the voltage is minimally reduced

(0.1 V) by extended storage (6 months) at 20

⬚C and while self-discharge of 10% occurred

over six months, after the battery was charged, 97% of the original capacity was delivered.

For a 17500-type C /LiCoO

Li-ion battery, the self-discharge performance (capacity reten-

tion) is illustrated in Fig. 35.50 and capacity recovery further illustrated in Fig. 35.51. Self-

discharge for 18650-type C /LiCoO

batteries over a range of temperatures is illustrated in

Fig. 35.52. As shown, at low and ambient temperatures, low self-discharge was observed,

11.5% over six months at 25

⬚C, and 25% at 40⬚C. However, over 6 months at 60⬚C, 80%

self-discharge occurred.

FIGURE 35.49 Discharge of a 17500-type cylindrical C /LiCoO

battery before

and after six months storage at 20⬚C in a fully discharged state. Charge conditions:

Constant voltage/ constant current, 4.2 V, 550 mA (max.), 2 hours, 20⬚C. Discharge

conditions: Constant current 156 mA to 3.0 V at 20⬚C. (Courtesy of Panasonic.)

LITHIUM-ION BATTERIES 35.45

FIGURE 35.50 Self-discharge performance of a 17500-type cylindrical C / LiCoO

battery at 20⬚C

when discharged after storage in the charged state for periods of up to six months. Charge conditions:

Constant voltage / constant current, 4.2 V, 550 mA (max.), 2 hours, 20⬚C. Discharge conditions:

Constant current 156 mA to 3.0 V at 20⬚C. (Courtesy of Panasonic.)

FIGURE 35.51 Capacity of a 17500-type cylindrical C/ LiCoO

battery when charged then dis-

charged after storage at 20⬚C in the fully charged state for periods of up to six months. Charge

conditions: Constant voltage/ constant current, 4.2 V, 550 mA (max.), 2 hours, 20⬚C. Discharge

conditions: Constant current 156 mA to 3.0 V at 20⬚C. (Courtesy of Panasonic.)

35.46 CHAPTER THIRTY-FIVE

024681012

100

% Capacity Retained

Time (Months)

0°C

25°C

40°C

60°C

FIGURE 35.52 Self-discharge performance of fully charged 18650 C / LiCoO

Li-ion

batteries over a range of temperatures. (Courtesy of Sanyo.)

35.4.3 Large Cylindrical Batteries

To power space probes, such as those intended for use by NASA to explore Mars, 25 Ah

cylindrical C /LiCoO

Li-ion batteries have been developed. Given the mission’s low tem-

perature requirements, these batteries have been designed to charge and discharge at low

temperature. An electrolyte of 1 M LiPF

in EC:EMC is used. The capacity of a 25 Ah

cylindrical cell when cycled at 23

⬚C at 5 A, on charge and discharge, is shown in Fig. 35.53.

The cell delivered 26.8 Ah initially and 24.1 Ah on the 500

cycle, thus provides a fade

rate of 0.02% /cycle. Figure 35.54 shows the capacity of another 25 Ah cell when cycled at

the C/5 rate (charge and discharge) at 0

⬚C and ⫺20⬚C. This 890 g cell, with a nominal

capacity of 29 Ah at 20

⬚C (121 Wh/kg and 280 Wh/L), delivered comparable capacity at

⬚Candover25Ahat⫺20⬚C.

0 100 200 300 400 500

Discharge Capacity (Ah)

Cycle Number

FIGURE 35.53 Capacity of a 25 Ah cylindrical Li-ion bat-

tery when cycled at the C / 5 rate between 4.1 V with taper

charge to C/ 50 and 3.0 V for 500 cycles at 23⬚C. (Courtesy

of Blue Star Advanced Technologies. Reproduced with per-

mission from SAE paper 01-1390, 1999.)

LITHIUM-ION BATTERIES 35.47

10 20 30 40 50 60

Discharge Capacity (Ah)

Cycle Number

0°C

-20°C

FIGURE 35.54 Capacity of a 25 Ah cylindrical Li-ion cells when cycled at 0⬚C and ⫺20⬚Catthe

C / 5 rate between 4.1 and 3.0 V. (Courtesy of Blue Star Advanced Technologies. Reproduced with

permission from SAE paper 01-1390, 1999.)

40 Ah Cylindrical Batteries for Low Earth Orbit Satellites. A unique battery application

is in Low Earth Orbit (LEO) satellites. This application is more completely described in the

chapter on Nickel Hydrogen batteries (Chap. 32). Satellites in low earth orbit (550 km) orbit

the earth approximately every 100 minutes, or approximately 15 times per day. When in

sunlight, the batteries are charged, while during eclipse they are discharged. Over the course

of the year, depending on the speciﬁc orbit, the eclipse duration varies, typically from 26 to

36 minutes. Given this regime in which the discharge rate is nominally twice the charge

rate, LEO batteries are typically required to provide 30,000 to 50,000 cycles enabling a

5- to 10-year operational life. LEO applications are currently addressed almost entirely using

nickel-hydrogen batteries as they offer high cycle life, despite their low speciﬁc energy (64

Wh/ kg) and low energy density (105 Wh/ L). Li-ion cells are being developed for LEO

applications as their use will enable the development of dramatically lighter, smaller and

less expensive satellite batteries, if the required cycle life can be obtained. Because of the

high energy efﬁciency of Li-ion cells (95 to 98%) on discharge and charge relative to

Ni-H

cells (80 to 85%), further reduction in spacecraft weight and cost is anticipated as

improved energy efﬁciency permits a reduction of other systems, including solar arrays, the

electrical buss and thermal controls.

Described here is the performance of 40 Ah cylindrical Li-ion cells tested over 1.33 years

under LEO requirements. The cells provided over 40 Ah (41 Ah to 43 Ah) or 120 Wh/ kg

when charged to 4.0 V and discharged at the C/3 rate to 2.7 V. The case negative cells

utilized a stainless steel case and glass to metal seals. The cell chemistry was based on a

LiNiO

positive electrode, coated onto Al with a PVDF binder, and graphite negative coated

onto copper. The separator was Celanese 2300, a microporous tri-layer laminated PPE/PE/

PPE ﬁlm.

The C /LiNiO

chemistry is not used in commercial cells due to safety issues.

35.48 CHAPTER THIRTY-FIVE

Three accelerated LEO regimes were used to shorten the typical 100 minute orbit time.

One set utilized a 24 minute orbit and cycled at 20% DOD (8 Ah), a second set utilized a

44 minute orbit and cycled at 20% DOD (8 Ah), the third set cycled within a 47 minute

orbit and cycled at 30% DOD (12 Ah). The test parameters are summarized in Table 35.14.

In this regime, cells cycling at 20% DOD occurred between 60% and 40% state of charge

(SOC), and those at 30% DOD cycled between 60% and 30% SOC. The accelerated regime

was used for 48 of every 50 cycles, the remaining two cycles were performed at normal

LEO rates to determine the residual capacity. In this testing, the cells were operated at 25

⬚C

with an end of charge (EOC) voltage of 3.75 V.

The residual energy of the cells (the discharge energy to 100% DOD at C/3 rate), with

the recommended end of charge voltage of 3.75 V, is shown in Fig. 35.55. The data

presented in this ﬁgure are the average of three cells. As shown, the energy fade rate for the

longest regime (20% DOD, 44 minute) is one-third less than that of the faster regimes. In

the worst case, the cells cycled at 30% DOD had an average fade rate of 0.00092%/cycle.

Using this data, the cycle life of the batteries in a LEO application has been estimated.

Here, the cycle life was deﬁned as that when residual energy upon discharge from 3.75 V

to 2.7 V was 42 Wh for cells cycled at 30% DOD or 28 Wh for cells cycled to 20% DOD.

The results of a calculation based on the energy fade data, considered to be the most con-

servative, are presented in Table 35.15. As shown, cycle lives between 55,000 and 137,000

cycles are predicted, suggesting lithium ion technology is capable of meeting LEO satellite

requirements. These projections are based upon cycling these batteries in the middle of the

useable voltage range.

TABLE 35.14 Parameters for the Accelerated LEO Testing

Discharge rate Discharge time Charge rate Charge time

20% DOD 60 A 8 min. 35 A 16 min.

20% DOD 60 A 8 min. 15 A 36 min.

30% DOD 60 A 12 min. 25 A 35 min.

0 5000 10000 15000 20000

Residual Energy (Wh)

Cycle Number

20% DOD, Medium Acceleration

20% DOD, Fast Acceleration

30% DOD

FIGURE 35.55 The residual energy of a 40 Ah Li-ion cell cycled

in an accelerated LEO regime. (Courtesy of SAFT.)