Quote:
Originally Posted by numus
I might not have made it clear.. We aren't talking about an actual linear discharge here... You take the semi linear curve based around the nominal voltage.. and take the derivative of the curve... THAT will give you a linear discharge... We aren't talking about the actual discharge, we are talking about integrating the curve.. You then create a calibration and model based upon the derivative of the nominal voltage and reconstruction reporting values based upon this data... Assuming nominal voltage is hit at <90~100 (in that range) and >~10 ... Then you create a minimum voltage before total discharge (usually around 1/2 nominal) and set that as 0 point.. Then creating reporting levels at 5 (halfway) and 3 (point at which basic functions should be dumped except basic phone calls).. 0 point is set at the recovery voltage (anything below that and you can have cell damage which will lead to a decreased overall capacity)... I agree with you on the cell design and capacity but the problem is with standard Lithium polymers that are currently avalible you can't reach sufficient density to increase capacity without increasing size (and cost).. When olivine-type lithium iron phosphate becomes cheaper, we will see a capacity increase due to higher achievable densities.. There is also a newer lithium cell structure that i think samsung or someone else is developing that will increase density ~50% over standard (1.5 times standard densities) but the cost of these is to high for mass production in portable electronic terms..
Also look into the research done at Bringhamton University where they can increase olivine lithium ion cells by introducing vanadium into the cathode material..
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You made yourself clear. I completely understood you.
Why would you think olivine LiFePO4 batteries would benfit mobile devices besides energy density? I do not have much knowledge on "olivine" but I do own a high capacity 48V 20AH LiFePO4 battery pack and the cells are very sensitive. They require a BMS to balance each individual cells. Basically, 1 faulty cell could cripple the whole pack. Of course I am working with dozens of cells and a pack used on mobile devices would be much less. Maybe even 1 cell but from my understanding, lithium poly batteries are the main choice for mobile devices because of their shape and not energy density which is a shame.
Just so you understand me, I am not trying to pick an argument. I know what I and and you obviously know what you know.
"samsung or someone else is developing that will increase density ~50% over standard (1.5 times standard densities) but the cost of these is to high for mass production"
I am very much aware of this. A Korean scientist developed a method that made the cathode material porous. This, in effect, increased the surface area of the lithium up to 4x.
LiFePO4 batteries, although good, can only discharge at about 2C safely. This may be sufficient for the mobile platform but for what I am using it for, it's not enough
. I still think this chemistry is not reliable for mass marketing. A BMS takes room and it's a hassle to deal with.
I'll look into the Bringhamton University research but I doubt the increase in capacity would increase the C-rating if the chemistry is still LiFePO4. Check into the Lithium Nano Phosphate cells by A123. They can discharge at 90C!
Let me show you what discharging at 90 plus C looks like via A123 cells.
This is going way off topic. Sorry.