Fig. 1 is a block diagram of circuitry in a typical Li-ion battery pack. It shows an example of a safety protection circuit for the Li-ion cells and a gas gauge (capacity measuring device). The safety circuitry includes a Li-ion protector that controls back-to-back FET switches. These switches can be
The packs’ primary components are the modules, often connected electrically in series and constructed by a set of cells. These cells can either be cylindrical, prismatic or pouch as illustrated in Figure 6. (4) The electrolyte used in the battery packs varies depending on what kind of cell that is employed.
It is composed of 16 modules with 432 cells of the type 18650 and a NCA chemistry, resulting in a total of 6912 cells in each pack. (42) Furthermore, the cells inside the modules are packed in groups which are wired in series to each other, creating a battery inside the battery. The same goes for the modules which also are connected in series.
When designing a battery pack, it is important to weigh different parameters against each other to acheive a suitable design. It is therefore significant for these tradeoffs to have a valid foundation to stand on. One tradeoff that needs to be accounted for is comparing safety of the battery against its weight.
The important battery pack interface properties, from an assembly and disassembly perspective, on the housing are that the same material (steel) and joining method (mechanical fastening) is used on all available sizes. The box has a modularised length that is doubled or tripled if more capacity is desired.
There must be a connection between the cell and the BMS in order to interface with each other. Nickel strips are the preferred method of connecting a battery cell to the control system. A thin strip of nickel is capable of carrying high amounts of current, is flexible, durable, and can be attached to the cell without the use of excessive heat.