Refinement of the raw materials, through cell assembly and finally to battery pack the manufacturing process is complex and requires a broad range of skills.
In order to engineer a battery pack it is important to understand the fundamental building blocks, including the battery cell manufacturing process. This will allow you to understand some of the limitations of the cells and differences between batches of cells. Or at least understand where these may arise.
Cell manufacturing covers a lot of specialist areas and hence there is a range of equipment suppliers.
The cell manufacturing process requires 50 to 180kWh/kWh.
Note: this number does not include the energy required to mine, refine or process the raw materials before they go into the cell manufacturing plant.
When assembling cells into a module, pack or directly into a product there are a number of tests that need to be done to ensure quality control.
What level of cell matching do you do prior to assembling a battery pack? Assuming the battery pack will be balanced the first time it is charged and in use. Also, assuming the cells are assembled in series.
- none, force the cell supplier to deliver cells matched to within +/-0.02V
- none, gross balance the pack during first charge once built
- preselect and group cells prior to build
- pre-charge/discharge all in-coming cells to a set voltage/SOC
- average-balance cells in parallel group prior to building in series
- average top-balance cells in parallel group prior to building in series
There are 7 Steps in the Module Production Process:
- Incoming Cells Inspection
- Stacked Cells Tightening/loading with End Plates
- Connecting the Cells inside the Module
- Mounting of the BMS Cell Sensing Circuit (CSC)
- Cell Stack is Loaded into Module Housing
- End of Line Testing and Quality Control of the Module
End of Line Testing – the module needs to have a number of checks, including: OCV, DCIR, BMS slave tests.
The application of thermal interface materials is also an important consideration in manufacturing as this pattern can result in non-uniform or even voids in the TIM.
End of Line Testing – once the battery pack is assembled it is important that a number of tests are done to check it’s safety, status, mechanical integrity and operation. Some tests will be run on every pack, whereas other more in-depth tests will be just run on a few random packs.