Author: admin
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Charging of Batteries
We now shift our discussion from battery design and construction to battery performance. In this section, we begin our look at performance with a description of battery charging. Charging is the process by which electrical energy is put back into the battery. A variety of different procedures or protocols are used for charging. These protocols…
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Cell Construction
To this point in the chapter, we have examined several aspects of cell and battery design. This section takes a brief look at ways in which cells and modules are constructed. The mechanical designs can be complex, and often manufacturers differentiate their products on these attributes. Almost invariably, it is desirable to have cells and…
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Electrode and Cell Design to Achieve Rate Capability
In the previous section, we examined ways to increase cell capacity in order to decrease the number of cells required in a battery pack. In this section, we examine the impact of cell design on the rate capability or power of a cell. For a given cell capacity, the current and current density are inversely…
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Scaling of Cells to Adjust Capacity
We’ve seen that the cells are connected in series to achieve the desired voltage of the battery. The capacity is increased by adding cell strings in parallel. However, each cell requires its own casing, safety reliefs, terminals, and connections, to which we will collectively refer to as ancillary. Clearly, we would like to reduce the…
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Battery Layout Using a Specific Cell Design
A battery consists of a collection of cells that are electrically connected with series and parallel combinations. The general nomenclature is (mS-nP), which means that m cells are connected in series and n of these series strings are connected in parallel. The total number of cells, Nc, is m × n. All of the cells together make up the battery (also referred to…
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Introduction to Battery Design
Given the critical role that the battery plays in many applications, the specifications or requirements that a battery must meet can be numerous and detailed. For example, an engineering specification for an automotive battery may be 30 pages or more in length. In contrast, we will only consider design of the main features of a…
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Capacity Fade in Secondary Cells
As is well known by any user of rechargeable batteries, performance degrades over time. Although a new battery might last for 3 or 4 hours, with extended use, the working time before recharging may now be just 1 or 2 hours. This reduction in operating time, also known as aging, represents a loss in the…
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Charge Retention and Self-Discharge
Charge retention refers to the amount of charge, usually expressed as a percentage of capacity, remaining after a cell is stored for a period of time and not connected to an external circuit. Self-discharge describes the mechanism by which the capacity of the cell is reduced. Rates of self-discharge can vary dramatically—a 10% loss in…
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Efficiency of Secondary Cells
The most basic efficiency of a rechargeable cell is the coulombic efficiency. Note that in contrast to the faradaic and current efficiencies that were defined in Chapters 1 and 3, this coulombic efficiency refers to a battery that undergoes a complete charge–discharge cycle. (7.21) Why would the number of coulombs be different for charge and discharge? The principal…
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Heat Generation
For a commercial secondary cell, the polarization losses discussed in Section 7.4 are usually quite low when the cell is used as designed. Hence, most of the available chemical energy is converted into electrical work rather than heat. Nonetheless, heat generation plays an important role in cell performance, system design, battery safety, and useable cell life.…