Hi Everyone,
Shortly: I am in the conceptual design stage of my electric scooter project. The most issues to date emerged mainly around the battery design. I already outlined a hub motor with around 5kW cont. power for reasonable hill climbing capability, and around 4kWh battery capacity.
In the end, I would like to have a cube shaped Al box (~5-8 mm walls), with around 300-350 mm edge length, stuffed with the controller, charger, bms, water pump ... and the highest amount of Wh-s possible (~4). I decided to build the battery myself, since this seems to be the most effective both financially and space wise.
In the current stage of my market research, I found pouch cells the best suited for this goal (18650s would be a good purchase too, but I don't want to deal with 500 cells, really). However, there is still one open question and possible show stopper I couldn't research deeply enough which is concerning the expected swelling of the cells.
My top candidate for battery chemistry is LiFePO4, but I wouldn't sort out Li-ion neither. The only paper on this subject I found were claiming that Li-ion pouches are likely to expand by around 10% of their original size through their lifespan in any case, which is normal. I was wondering whether anyone could back this statement with real life experiences? Also, I would really appreciate if someone could tell me about the swelling behaviour of LiFePO4 pouch batteries. I am aware that this may strongly depend on how well the batter is actually treated... So that I am hoping for a """normal""" users experiences, whose batteries are treated well in general, but sometimes suffer some suboptimal dis/charging parameters when unavoidable...
(It is my understanding, that cylindrical cells cannot swell because they are vented in most of the cases?)
Of course I tried to answer this question myself - the first thing coming into my mind are the many tightly packed and shrinkwrapped batteries around. But if I think about it, these wrapped batteries can expand almost unnoticeable (sure, it would be strange, but I did not notice any warning at all to leave some space around the batteries when enclosing them). At the same time, if I stuff my Al box with pouch cells, and they would grow by 10%, my box would be ripped apart... How much space should be left empty that is the question...
Any input would be much appreciated.
Thanks,
Shortly: I am in the conceptual design stage of my electric scooter project. The most issues to date emerged mainly around the battery design. I already outlined a hub motor with around 5kW cont. power for reasonable hill climbing capability, and around 4kWh battery capacity.
In the end, I would like to have a cube shaped Al box (~5-8 mm walls), with around 300-350 mm edge length, stuffed with the controller, charger, bms, water pump ... and the highest amount of Wh-s possible (~4). I decided to build the battery myself, since this seems to be the most effective both financially and space wise.
In the current stage of my market research, I found pouch cells the best suited for this goal (18650s would be a good purchase too, but I don't want to deal with 500 cells, really). However, there is still one open question and possible show stopper I couldn't research deeply enough which is concerning the expected swelling of the cells.
My top candidate for battery chemistry is LiFePO4, but I wouldn't sort out Li-ion neither. The only paper on this subject I found were claiming that Li-ion pouches are likely to expand by around 10% of their original size through their lifespan in any case, which is normal. I was wondering whether anyone could back this statement with real life experiences? Also, I would really appreciate if someone could tell me about the swelling behaviour of LiFePO4 pouch batteries. I am aware that this may strongly depend on how well the batter is actually treated... So that I am hoping for a """normal""" users experiences, whose batteries are treated well in general, but sometimes suffer some suboptimal dis/charging parameters when unavoidable...
(It is my understanding, that cylindrical cells cannot swell because they are vented in most of the cases?)
Of course I tried to answer this question myself - the first thing coming into my mind are the many tightly packed and shrinkwrapped batteries around. But if I think about it, these wrapped batteries can expand almost unnoticeable (sure, it would be strange, but I did not notice any warning at all to leave some space around the batteries when enclosing them). At the same time, if I stuff my Al box with pouch cells, and they would grow by 10%, my box would be ripped apart... How much space should be left empty that is the question...
Any input would be much appreciated.
Thanks,