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Combat Hybrid Power System Component Technologies: Technical Challenges and Research Priorities (2002)

Chapter: 3 Battery Technologies for Military Hybrid Vehicle Applications

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Suggested Citation:"3 Battery Technologies for Military Hybrid Vehicle Applications." National Research Council. 2002. Combat Hybrid Power System Component Technologies: Technical Challenges and Research Priorities. Washington, DC: The National Academies Press. doi: 10.17226/10595.
×

3
Battery Technologies for Military Hybrid Vehicle Applications

INTRODUCTION

Chemical batteries have been used as electric energy storage devices for many years. With the revival of interest in electric transportation, great effort and investment have been put into the research and development of high-performance chemical batteries. Until recently, however, the battery performance has been far from meeting the requirements of the vehicle application. One of the major problems is the very limited amount of energy stored per unit weight (specific energy). Compared with conventional petroleum and internal-combustion-engine-based systems, far less energy is stored in a practical onboard battery, resulting in limited operation time. This chapter examines the current state-of-the-art of batteries for vehicle propulsion, and promising research areas that could lead to improved performance.

ENERGY DENSITY OF CHEMICAL BATTERIES

The theoretical specific energy density of selected existing batteries is shown in Table 3-1.

TABLE 3-1 Theoretical Specific Energy of Typical Existing Batteries

Reaction

Voltage (V)

Specific Energy (Wh/kg)

Lead acid cell:

 

PbO2 +2H2SO4 +Pb ↔ 2PbSO4 + 2H2O

2.04

170

Edison (Ni-Fe) cell:

 

Fe + 2NiOOH +2H2O ↔ Fe(OH)2 +2Ni(OH)2

1.25

260

Ni-Zn cell:

 

Zn + 2NiOOH +2H2O ↔ Zn(OH)2 +2Ni(OH)2

1.9

360

Zn-chlorine cell:

 

Zn + (Cl2+8H2O) ↔ ZnCl +8H2O

2.1

410

Al-S cell:

 

2Al +3S +3OH- ↔ 2AL(OH)3 +3 HS-

1.3

910

Organic lithium:

 

Li(y+x)C6 + Li(1-(y+x))CoC ↔ LiyC6 + Li(1-y)CoO2

 

320*

*For maximum value of x = 0.5 and y = 0.

Suggested Citation:"3 Battery Technologies for Military Hybrid Vehicle Applications." National Research Council. 2002. Combat Hybrid Power System Component Technologies: Technical Challenges and Research Priorities. Washington, DC: The National Academies Press. doi: 10.17226/10595.
×

However, practical batteries have specific energies that are much lower than their theoretical values. This is due to the need for a container, electrode support, connectors, diluted electrolyte, unreacted materials and so on. Table 3-2 shows the data for some existing batteries, and compares them with the mid-term and long-term goals of the U.S. Advanced Battery Consortium (USABC). Lithium-ion batteries have the highest current values of specific energy. These may be designed in a high-power (HP) or high-energy (HE) configuration, depending on the requirements of the load.

TABLE 3-2 Expected Practical Energy Density

 

Specific Energy (Wh/kg)

 

Battery

Theoretical

Current

Ratio

Projected

Ratio

Existing

Lead acid

170

40

4.25

50

3.40

 

Adision Ni-Fe

260

50

5.20

60

4.33

 

Ni-Zn

260

50

5.20

60

4.33

 

Zn-Cl

260

50

5.20

60

4.33

 

Li-ion high power

 

85-95

 

 

Li-ion high energy

 

135-150

 

USABC

Mid-term

 

80

 

Goal

Long-term

 

200

 

Al-based

Al-Fe-O

2,278

 

455

5.0

 

Al-Cu-O

2,198

 

440

5.0

 

Al-Fe-OH

1,903

 

380

5.0

SPECIFIC POWER CHARACTERISTICS OF CHEMICAL BATTERIES

Specific power is the maximum power per unit battery weight that the battery can deliver in a short period. Theoretically, there is no top limit for specific power. It depends mostly on the manufacturing and material processing technologies. Specific power is also important in the reduction of battery weight, especially for the high power demand applications, such as hybrid electric vehicles. The maximum power that the battery can deliver to the load is limited by the conductor resistance and the internal resistance caused by the chemical reaction. Accurate determination of battery resistance by analysis is difficult. Specific power is usually obtained by measurement.

Table 3-3 shows the status of battery systems potentially available for hybrid vehicles. Although it can be seen that specific energies are higher in advanced batteries, until recently the specific powers showed no such improvement over mature lead acid technology. Li-ion high-power and high-energy batteries with about 4000 W/kg and 600 W/kg, respectively, have been reported.1 If these results are proven in vehicle tests, they would represent a significant step forward. Work continues on the development of batteries with very high power capabilities of at

1  

T. Matty. 2002. “Battery Systems for DoD Applications.” Briefing presented to the Committee on Assessment of Combat Hybrid Power Systems, National Research Council, San Jose, Calif., August 26.

Suggested Citation:"3 Battery Technologies for Military Hybrid Vehicle Applications." National Research Council. 2002. Combat Hybrid Power System Component Technologies: Technical Challenges and Research Priorities. Washington, DC: The National Academies Press. doi: 10.17226/10595.
×

least 10 to 15 kW/kg, and tests indicate that power levels in excess of 15 kW/kg are possible. New processing techniques are expected to deliver in excess of 30 kW/kg. This will require significant advancement in processing capabilities.2 The Department of Defense (DoD) has supported and continues to support the development of higher power systems required for future needs—for example, for directed energy systems such as lasers and high-power microwaves. At the same time, the DoD requires lower power density and higher energy density batteries to satisfy the silent watch requirements and stealth operation capabilities.

TABLE 3-3 Status of Battery Systems for Hybrid Vehicles

System

Specific energy (Wh/kg)

Specific power (W/kg)

Energy efficiency (%)

Cycle life

Cost (US$/kWh)

Lead acid

35-50

150-400

>80

500-1000

120-150

Nickel/cadmium

40-60

80-150

75

800

250-350

Nickel iron

50-60

80-150

65

1500-2000

200-400

Nickel zinc

55-75

170-260

70

300

100-300

Nickel/metal/hydride

70-95

200-300

70

750-1200+

200-350

Sodium/sulfur

150-240

230

85

800+

250-450

Lithium/ion/sulfur

100-130

159-250

80

1000+

110

Lithium-ion

80-130

200-300

>95

5000+

200

Li-ion high power

85-95

~4000

>95

Li-ion high energy

167

~600

>98

TYPICAL MOBILITY REQUIREMENTS OF MILITARY VEHICLES FOR BATTERIES

Figure 3-1 shows the typical tractive effort and speed of military vehicles under various operational conditions. In order to evaluate the requirements to batteries, these three typical operations are selected: (1) high-speed highway operation, (2) hill-climbing operation, and (3) hard acceleration. The first operation represents the energy demand for continuous operation, and the last operation represents the power demand for intermittent operation. It is assumed that the maximum acceptable ratio of battery weight to total vehicle weight is 0.25. Table 3-4 shows the data of these three operations.

2  

T. Matty. 2002. “Battery Systems for DoD Applications.” Briefing presented to the Committee on Assessment of Combat Hybrid Power Systems, National Research Council, San Jose, Calif., August 26.

Suggested Citation:"3 Battery Technologies for Military Hybrid Vehicle Applications." National Research Council. 2002. Combat Hybrid Power System Component Technologies: Technical Challenges and Research Priorities. Washington, DC: The National Academies Press. doi: 10.17226/10595.
×

FIGURE 3-1 Power requirement of typical mobility of military vehicles.

Table 3-4. Typical Operations of Military Vehicles

Operation

Speed (mph)

Power (kW/ton)

Traction

Battery

Time

High-speed highway

70

12

16

Continous

Hill-climbing

6

16

21

Continous

Hard acceleration

25

54

72

Seconds

When the vehicle demands hard acceleration, sufficient battery power must be supplied. Referring to Table 3-4 and Figures 3-2 and 3-3, this power demand is about 72 kW per ton of vehicle weight. In Figures 3-2 and 3-3, the total weight is defined as the total vehicle weight minus the battery weight. The calculated ratios of battery weight to total vehicle weight for typical batteries are listed in Table 3-5. It is clear that SAFT Li-ion high power and high energy batteries can meet the power demand. Even lead acid batteries may be able to supply sufficient power for hard acceleration.

The driving range performance of the Li-ion batteries is somewhat less satisfactory, however. The maximum driving range on the highway at 70 mph is about 105 miles for the SAFT HE battery and 63 miles for the SAFT HP battery, while the maximum hill-climbing range for the SAFT HE and HP batteries is 6.4 and 4.1 miles, respectively.

Suggested Citation:"3 Battery Technologies for Military Hybrid Vehicle Applications." National Research Council. 2002. Combat Hybrid Power System Component Technologies: Technical Challenges and Research Priorities. Washington, DC: The National Academies Press. doi: 10.17226/10595.
×

FIGURE 3-2 Battery weight/total weight ratio versus driving range on highway at the speed of 70 mph.

FIGURE 3-3 Battery weight/total weight ratio versus driving range while climbing hill.

Suggested Citation:"3 Battery Technologies for Military Hybrid Vehicle Applications." National Research Council. 2002. Combat Hybrid Power System Component Technologies: Technical Challenges and Research Priorities. Washington, DC: The National Academies Press. doi: 10.17226/10595.
×

TABLE 3-5 Ratio of Battery Weight to Total Vehicle Weight

Battery

Specific Power (W/kg)

Battery Weight/ Vehicle Weight

Lead acid

300

0.24

SAFT Li-high power

3,000

0.024

SAFT Li-high energy

500

0.144

Proposed Al-Fe-OH

Another battery requirement for military applications is that the fully sealed and water-cooled battery packs can be submerged in 10 feet of water. These batteries should also be intelligently managed with module management and data collection systems. These systems are now being researched by companies in the United States and elsewhere.

BATTERY PERFORMANCE IMPROVEMENT TECHNIQUES

The intrinsic properties of the active electrode materials and electrolyte used determine the cell potential, capacity, and energy density, each of which has a theoretical top limitation. However, battery power capability has no theoretical top limitation. It heavily depends on manufacturing technology to reduce the battery internal resistance, which causes voltage drop on the battery terminals and consequently limits the battery power. The battery voltage drop is generally caused by reaction activity and electrolyte concentration.

The voltage drop caused by the reaction activity may be reduced by two approaches. One is to develop advanced electrode materials and electrolyte that have high chemical reaction activity on the reaction surface. The other approach is to employ electrodes with large surface areas. This will decrease the current density for a given load current and consequently reduce the voltage drop. In addition to simply increasing the geometric size, the electrode area can be dramatically increased by using active materials with high intrinsic surface area, for example, porous matrices.

The voltage drop caused by the electrolyte concentration (sometimes called a mass-transfer overpotential) can be reduced by using high concentrations of reactant species and technologies to reduce the ion transfer resistance. In addition to the voltage drop caused by the chemical reaction, there is also a voltage drop due to the electric ohmic resistance in the connectors and terminals. This can be addressed through the application of low-resistance materials.

The new technologies for improving battery power capability may also include use of nanomaterials, engineered interfaces and surfaces in materials, advanced energy storage and conversion materials, and advanced materials processing and systems manufacturing techniques.

Suggested Citation:"3 Battery Technologies for Military Hybrid Vehicle Applications." National Research Council. 2002. Combat Hybrid Power System Component Technologies: Technical Challenges and Research Priorities. Washington, DC: The National Academies Press. doi: 10.17226/10595.
×

SUMMARY

SAFT high power and high energy Li-ion batteries may be able to meet the power demands of military hybrid vehicles, though their ability to satisfy requirements for vehicle driving range on the highway or up grades appears less certain. Theoretical analysis indicates that hypothetical aluminum-based batteries potentially have high energy density, which is over two times that of the long-term goal of USABC. However, their specific powers are uncertain. Technical challenges and opportunities for improvement in battery performance are summarized in Table 3-6.

TABLE 3-6 Technical Challenges, Performance Metrics, and Research Priorities Associated with the Application of Batteries to Combat Hybrid Power Systems

System/Component

Technical Challenge

Performance Metric

R&D Priorities

Advanced battery concepts

Validation of batteries in vehicle applications

Specific power

Specific energy

Triple the power and energy with nanomaterials technology and new chemistries

 

Safety

 

Increased safety (eliminate flammable materials; better packing for isolation, containment, venting; thermally stable materials; diagnostics/ prognostics integrated in pack; eliminate ground fault and arcing; improved materials that reduce gassing)

 

Battery management (state of health, state of charge, power availability, life prediction, temperature management, diagnostics, and prognostics)

 

Electrode/electrolyte interface

Voltage drop caused by limited chemical reactivity at the interface

 

Advanced electrode/electrolyte materials with high surface reactivity

 

Increased electrode surface area by increased matrix porosity or perhaps application of nanomaterials

Electrolyte

Voltage drop caused by mass transfer overpotential

 

Electrolytes with high concentrations of reactant species and low ion transfer resistance

Connectors and terminals

Ohmic resistance of materials

Minimized resistance

Low-resistance materials

Suggested Citation:"3 Battery Technologies for Military Hybrid Vehicle Applications." National Research Council. 2002. Combat Hybrid Power System Component Technologies: Technical Challenges and Research Priorities. Washington, DC: The National Academies Press. doi: 10.17226/10595.
×

BIBLIOGRAPHY

Crompton, T.R. 1996. Battery Reference Book, 2nd ed. Warrenton, PA: SAE International.


Kajs, John. 2001. "Combat Vehicle Mobility Requirements," seminar at Texas A&M University, Dec


Messerle, Hugo K. 1969. Energy Conversion Statics. New York: Academic Press.


Rand, D.A.J., R. Woods, and R.M. Dell. 1998. Batteries for Electric Vehicles. Somerset, England: Research Studies Press.


Severinsky, Alex J. 1994. Theoretical Limits to Application of Batteries for Automobile Propulsion (System Study). National Challenges for the Commercialization of Clean Fuel Vehicles: Conference Proceedings. Online. Available at http://www.adlabs.com/library/battery.html. Accessed December 2002.

Suggested Citation:"3 Battery Technologies for Military Hybrid Vehicle Applications." National Research Council. 2002. Combat Hybrid Power System Component Technologies: Technical Challenges and Research Priorities. Washington, DC: The National Academies Press. doi: 10.17226/10595.
×
Page 23
Suggested Citation:"3 Battery Technologies for Military Hybrid Vehicle Applications." National Research Council. 2002. Combat Hybrid Power System Component Technologies: Technical Challenges and Research Priorities. Washington, DC: The National Academies Press. doi: 10.17226/10595.
×
Page 24
Suggested Citation:"3 Battery Technologies for Military Hybrid Vehicle Applications." National Research Council. 2002. Combat Hybrid Power System Component Technologies: Technical Challenges and Research Priorities. Washington, DC: The National Academies Press. doi: 10.17226/10595.
×
Page 25
Suggested Citation:"3 Battery Technologies for Military Hybrid Vehicle Applications." National Research Council. 2002. Combat Hybrid Power System Component Technologies: Technical Challenges and Research Priorities. Washington, DC: The National Academies Press. doi: 10.17226/10595.
×
Page 26
Suggested Citation:"3 Battery Technologies for Military Hybrid Vehicle Applications." National Research Council. 2002. Combat Hybrid Power System Component Technologies: Technical Challenges and Research Priorities. Washington, DC: The National Academies Press. doi: 10.17226/10595.
×
Page 27
Suggested Citation:"3 Battery Technologies for Military Hybrid Vehicle Applications." National Research Council. 2002. Combat Hybrid Power System Component Technologies: Technical Challenges and Research Priorities. Washington, DC: The National Academies Press. doi: 10.17226/10595.
×
Page 28
Suggested Citation:"3 Battery Technologies for Military Hybrid Vehicle Applications." National Research Council. 2002. Combat Hybrid Power System Component Technologies: Technical Challenges and Research Priorities. Washington, DC: The National Academies Press. doi: 10.17226/10595.
×
Page 29
Suggested Citation:"3 Battery Technologies for Military Hybrid Vehicle Applications." National Research Council. 2002. Combat Hybrid Power System Component Technologies: Technical Challenges and Research Priorities. Washington, DC: The National Academies Press. doi: 10.17226/10595.
×
Page 30
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This book provides the detail from the NRC Committee on Assessment of Combat Hybrid Power Systems. This committee targeted three emerging technology areas: advanced electric motor drives and power electronics, battery technologies for military electric and hybrid vehicle applications, and high temperature wideband gap materials for high-power electrical systems. This committee also addressed three additional emerging technologies: high power switching technologies, capacitor technologies and computer simulation for storage system design and integration.

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