Why LTO?
The amount I need comes in under 40Lbs,
That could be halved with LIFEPO4 or better still storage capacity (range) could be approx doubled.
Fits in space unneeded by anything else.
So does lifepo4
As safe as LiFePo4
True. Possibly more so due to low energy density. But higher connections and BMS cell counts decrease reliability and safety long term though.
Can be charged in subzero temperatures
True. But if you had twice the capacity of lifepo4 you probably dont need to till it warms up some anyway.
Very high charge/discharge rate
LiFe can have high or low discharge rates. I have some 25C lifepo4 packs here. But with double the capacity compared to a LTO pack it wouldnt matter. It is effectively halving the required c rate anyway.
Very long cycle life. Over 20,000 cycles.
Cycle life depends on many things. With a small pack that gets worked heavily and discharged more deeply then cycle life drops quite severely compared to a lightly loaded pack. So in real terms a LFP pack wih double the capacity would likely match the cycle life. Even if you only discharged LTO by say 50% daily then the LFP with double the capacity wouldnt need charging as often. So each cycle is then 2 days long. So it would only need half the cycle life to live the same length of time. But that charge every 2 days thing means even a 5000 cycle lifespan and I would expect more, is 27 years. But you wouldnt discharge that deeply with a doubl sized pack in reality. So you would get north of 30 years. How long do you think the chair/van/you will last?
Thats why a bigger pack always wins. Why a slower C rate discharge always wins. Why a limited charge/discharge level allows 3 to 10x the cycle life. Its why a Tesla with lithium ion fireorks and a 500 cycle limit on its 21700 cells doesent last 18 months! They look like they will be good for 2 decades or more.
I have chairs here with too small packs made up from old style cells that are now 15 years old and they have the same capacity today as they did when new.
If you fitted LTO or LIFE (LFP) and did so with a larger capacity pack (same weight/size) they will all outlive your van or chair and possibly you! With the big advantage that you will have double the storage.
I can leave a discharged chair in the freezing van over night and be mostly charged before I reach Memphis. And I'll never need another set.
That applies to both chemistries is treated properly! At least if its not freezing. How often will this occur? If its often then you have no choice.