Batteries specific peak power

Specific peak power (W kg ) of the battery determines the EV acceleration capability. Not only the energy storage but also the power/weight ratio comparisons with ICEs are not favorable for... 

In general, the specific peak power decreases with the depth of discharge (DOD) (cf. Fig. 3). Therefore, EV battery specification with respect to range and allowable depth of discharge limit should pertain to (whichever comes first) DOD values at which EV becomes incapable of the demanded acceleration, or to which the system... 

Figure 3. Specific peak-power, averaged over the last 10 s of a 20-s pulse, as a function of the depth of discharge for Lucas-Chloride, 535 kg, 192-V ISDA tubular Pb-A batteries. EV power-train constraints imposed. (Courtesy of Lucas Chloride EV Systems, 1984.)...

The EV power requirements depend on the car s end use and assumed acceleration demands. For example, the specifications for safe driving in a mixed ICEV and EV urban traffic of a small compact-type EV have been defined as acceleration from 0 to 50 mph in <20 s. The specific peak-power corresponding to these demands has been calculated as 80-90 wkg for conditions of optimum use of the AC power train (i.e., for constant-power acceleration following the initial period in which the peak-power is attained at the maximum tractive effort ). The majority of near-term and advanced batteries could, at least potentially, meet these demands. 

The specific peak power of the battery strongly depends on the depth of discharge nevertheless, acceptable acceleration seems to be achievable even at 80% DOD (cf. Fig. 3). 

The Electricity Council Research Centre has developed a 960-cell (40 modules of 24 tubular electrolyte cells each), 50 kW-hr, 100-V traction battery. The modules are shown in Figure 4. The battery was rated at 15.5 kW of average power, 29 kW of peak power, and weighed 800 kg. The specific peak power and specific energy are therefore 36 W/kg and 63 W-hr/kg, respectively. 

The theoretical specific energy of the battery is 460 Whkg Several battery prototypes have been tested in specially modified vans and vehicles. For example, effective values of specific energy and peak power are reported as 64 Wh kg and 59 Wh kg respectively, when tested in a passenger car powered by a 636-kg battery (refrigerating system off-board) and driven at a constant speed. ... 

C under the Dynamic Stress Test for EVs in accordance with the United States Advanced Battery Consortium Procedure 5B. This has a variable discharge profile based on specific power requirements, with a maximum of 150 Wkg when related to a full-sized EV battery. For the experimental cells, the peak power was equivalent to a current density of 16.3mAcm . ... 

Self-contained, man-portable Al-air alkaline batteries are widely used in battlefield applications and remote military locations. The battery units initially come with dry alkali contained in the cells, and water can be added when electrical power is desired. The modules can provide temporary electrical power for mobile shelters, command and control communications centers, and field medical facilities. The man-portable Al-air batteries can act as power supplies for unmanned vehicles. Specific details on the components used in the self-contained, man-portable Al-air battery are shown in Figure 6.3. Such a battery was designed and developed about 15 years ago for UAVs and UUWVs and is capable of providing a nominal power of 1.6 kW and a peak power of 4 kW. But, the next generation of such a battery with high-quality alloy is expected to have a peak power exceeding 5 kW. 

FIGURE 24.32 Comparison of characteristics of conventional lead-acid and experimental high-rate design batteries, (a) Specific energy vs. specific power, (h) Peak power vs. depth of discharge. Proceedings of International Seminar on Primary and Secondary Batteries, Boca Raton, Fla., 1994.)... 

Based on these experiments a conceptual design was made for a 55 kW (peak power) electric-vehicle battery. Projected specific energy of the battery was 110 Wh/kg at 97 W/kg under a modified Simplified Federal Urban Driving Schedule (SFUDS). These values were increased to 228 Wh/kg at 100 W/kg when the battery was designed for optimum capacity, and to 100 Wh/kg at 150 W/kg when designed for optimum power output, based on the results of discharge experiments at 45°C. 

Calculations show that battery specific energies of around 100-150Wh/kg and peak power capabilities of 120W/kg" are needed for traffic compatible electric delivery vans with worthwhile ranges, with even more demanding requirements for smaller vehicles such as automobiles. 

T Tigh-performance lithium—sulfur secondary batteries are being devel-- oped for use in electric automobiles and for off-peak energy storage in electric utility systems. These applications impose severe performance requirements that cannot be met by present batteries. For the electric automobile, the battery must have a minimum specific energy of <— 200 W-hr/kg, a specific power of at least 200 W/kg, and a lifetime of 3-5 yrs. The projected performance requirements for a battery for off-peak energy storage are a maximum cost of 12-15/kW-hr, a specific power of /—50 W/kg, and a minimum lifetime of 5-10 yrs. 

The power of supercapacitors is almost in all cases obviously higher than that of batteries. It is notable that it is not quite correct to compare high-performance specific power for supercapacitors with the corresponding impedance specific power of batteries, as it is usually done. Power options of both device types depend primarily on their resistance and knowing their resistance is the key for determining peak useful power. Thus, measurement of resistance of the device in the pulse mode of operation is critical for estimation of its ability to provide high power. 

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