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.



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