Rechargeable Batteries

In the last decades, the technology of rechargeable batteries has observed a phenomenal expansion. To date, the century-old lead-acid rechargeable battery has been constantly improved and is still in widespread use. New types of batteries, especially lithium ion rechargeable batteries, are experiencing an explosive growth, and will soon become the dominating distributed storage device for electricity.

Table 12.4 gives the specifications of several types of rechargeable batteries. One of the basic parameters is nominal voltage. Cells with higher nominal voltage are certainly advantageous, because fewer cells are needed to construct the desired system. Energy density and specific energy are also significant parameters. For static applications such as street lights, a smaller specific energy is not a serious problem. For automobile applications, energy density and specific energy are critical parameters. Lifetime is also a critical parameter for automobile applications. Not shown here is the unit cost. Currently, lead-acid batteries are still the least expensive and thus widely used.

Table 12.4: Comparison of Rechargeable Batteries

Type

Voltage

(V)

Energy Density (Wh/liter)

Specific Energy (Wh/kg)

Lifetime

(cycles)

Lead-acid

2.1

70

30

300

NiMH

1.4

240

75

800

LiCoO2

3.7

400

150

1000

LiMn2 O4

4.0

265

120

1000

LiFePO4

3.3

220

100

3000

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Figure 12.7 Electrochemistry of rechargeable batteries. (a) Discharging process. By con­necting the cell to an external load, electrons flow from NE, the anode, to PE. The electric circuit is completed in the electrolyte by the flow of anions and cations to the anode and cathode, respectively. (b) Charging process. An external DC power supply forces electrons to flow into NE, then the circuit is completed in the electrolyte by the flow of anions and cations.

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