If they did that, the cells would be larger and heavier, and you'd be complaining about their poor energy density. Having relatively soft cell walls and requiring the battery designer to add stiff plates at the ends of a battery block allows for the best energy density, as you, the battery designer, are in the best position to determine where to put those plates. Two stiff plate for, say, 10 cells, results in a lighter and smaller battery block than stiff casing on each cell.I would say Chinese LFP cells are of decent quality, but not great - one thing that definitely needs improvement is the rigidity of the cell casings.
Compare the energy density of cylindrical cells (which do include a stiff casing) with that of otherwise equivalent prismatic cells (which have a relatively soft casing) and with pouch cells (which do not include any casing at all). If you want a stiff casing, buy cylindrical cells. If you want high energy density, buy pouch cells. If you want ease of installation with a bit of hassle with the end plates, buy prismatic cells.
I am sorry, but I believe there is a big misunderstanding. The swelling is NOT heat related! And it is independent of cell resistance. The swelling is SOC level related.The cells tend to swell during heavy use
- 0 ~ 90 % SOC = not swollen, regardless of usage.
- ~100 % SOC = swollen, whether sitting on a shelf, charging, or discharging (at any current, and for any cell resistance)
Cooling cells has practically NO effect on swelling. On a first order, swelling will occur at high SOC levels regardless of cell temperature.Because of cell casing swell,you invent LPF cooler, or the same function as BMS.
Cooling is done when cells are used continuously at high discharge rates, higher than their C rating. It allows you to use cells that would otherwise be too small for an application. A pack that is properly designed to handle the power requirements of an application (high quality cells, large enough cells or a sufficient number of cells in parallel) does not need any cooling.
Prius stock battery pack: needs cooling
Prus PHEV conversion battery pack (LiFePO4 cells, > 5 kWh, A123 or Thundersky cells) requires no cooling.
And, while some BMSs include some form of thermal management, I would certainly not say that cooling and BMS are the same thing.
Reference: http://www.artechhouse.com/Detail.aspx?strBookId=2099 chapter 1.2 and 220.127.116.11.2
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