Comment by chrismorgan
4 years ago
So that’s 7kg extra for your 2150Wh, over the original 500Wh battery? So around 250Wh/kg?
I’ve been planning a velomobile that I can live out of, and I’ve been interested to observe that by the time you get to one kilowatt hour, I can’t find any Li-ion batteries at all: they’re all LiFePO₄. https://au.renogy.com/renogy-smart-lithium-iron-phosphate-ba... is then about 1280Wh (12.8V/100Ah) for 11.8kg, 110Wh/kg, around half the specific energy (though I haven’t excluded the weight of the controller electronics or any differences in casing). But I understand LiFePO₄ will live longer, and is generally safer (less prone to thermal runaway and whatnot).
I’m guessing you were going with Li-ion because you were working in the Bosch ecosystem (and potentially for weight as well), but do you happen to have any wisdom to offer about the differences between Li-ion and LiFePO₄?
Yes, LiFEPO4 would have been preferred but the Bosch BMS doesn't know how to deal with that chemistry. There are some interesting developments, have you looked at these?
https://www.youtube.com/watch?v=kYx097cVR48
If I had free pick of chemistry I probably would have gone with those. 250 Wh/kg sounds about right, I'm running the cells in a very conservative regime though, topping them up to about 80 SOC and discharging to about 20, so my effective range is smaller but the battery life-span will be very long, many thousands of cycles. The balancer also helps with that.
LTO definitely sounds very interesting, and I’ve noted it down for further investigation, but on brief examination it’s not sounding particularly compelling for my particular use case over LiFePO₄: I probably wouldn’t actually benefit from any of the places where it’s superior. Life span, for example: sixty years of daily discharge is nice and all, but LiFePO₄ should already easily last me a decade or two (time will kill it, not cycles), and I don’t think it’s useful to forecast beyond there. And I don’t need its more rapid charge or discharge. And so the main thing that’s left is its lower specific energy, and I’m not fond of the idea of lugging around an extra dozen kilograms per kilowatt-hour. (Its lower energy density wouldn’t be a problem; I can readily allow a few extra litres in the design, which you couldn’t do on an e-bike.) Stack all that on the more restricted range of options unless you’re willing to deal with unknown Chinese entities and AliExpress, and I expect I’ll end up staying with LiFePO₄.
For typical off-grid house power needs, on the other hand, LTO sounds extremely compelling.