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Comparing LiFePO4 with Lithium-Ion LiCoO2 Batteries, notes to self


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This is a short summary of information I collected comparing Lithium Iron Phosphate (LiFePO4, LFP) batteries as used in the Uniwheel with the wide spread Lithium-Ion (LiCoO2) batteries used AFAIK in all other brands, no-names, mobile phones...
 
LiFePO4 are roughly about twice as heavy and twice as large as LiCoO2, and they have a higher self-discharge rate. Otherwise, they seem to have only advantages. They are safer, more environment friendly, about 10 times more powerful(!), have a very low voltage drop under discharge (i.e. considerably less power drop on low charge), are more tolerant to abuse, live about twice as long, and are cheaper per cycle.
 
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13 minutes ago, Smoother said:

So why aren't we using them in our EUCS?

Double the weight and volume is unfortunately a non-trivial disadvantage. LiFePO4 weigh about 10kg for 1000Wh. Another reason I didn't list above could be that they are less widespread, so it may be more difficult to get components which work with them out-of-the-box.

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If you have a grasp of electron shells (S, P, D), the valence electrons of the elements in the periodic table (O, P, Li, and transition metals[Mn,Fe,Co,Ni] ) used in Lithium ion based batteries, and a grasp of what 'valence electrons' are you might find the work of Janina Molenda - faculty of Energy and fuels, Department of Hydrogen Energy, AGH University of Science and Technology, Krakow , Poland

http://home.agh.edu.pl/~molenda/

to be of interest if you allow yourself to be slightly challenged by additional scientific observations.

A recent publication in '2017, Vietnam Academy of Science & Technology'  (Hanoi, VietNam ) discusses 'engineering' aspects of batteries by doping with other elements. This paper was way over my understanding but introduced new concepts used in solid state electronics such as 'Fermi level'.

http://iopscience.iop.org/article/10.1088/2043-6254/aa5955

 

My school knowledge of batteries includes concepts like:

Transition metal elements 4S shell electron energies and transition elements 3D shell energies are similar.

Valence electron configurations , relative energy levels and notations should be understood.

Example for valence electrons notation

Li =   2S-1

(an unpaired 2S orbital)

 

Mn = 4S-2, 3D-5

(5 unpaired 3D orbitals)+ 1 paired 4S orbital

 

Fe = 4S-2, 3D-6

(1 paired 3D orbitals)+(4 unpaired 3D orbitals)+ 1 paired 4S orbital

 

Co = 4S-2, 3D-7

(2 paired 3D orbitals)+(3 unpaired 3D orbitals)+1 paired 4S orbital

 

Ni = 4S-2, 3D-8

(3 paired 3D orbitals)+ (2 unpaired 3D orbitals)+1 paired 4S orbital

 

Note#1

the transition metal 4S orbitals (2 spin opposite electrons) are oxidized (loss of electrons) before the available 3D electrons when forming salts with materials like phosphate...so lithium-iron-phosphate(PO4) results from doubly oxidized iron (+2 charge) forming an ionic salt with single oxidized lithium (+1 charge, no electrons in the 2S shell) and phosphate (-3 charge)

Net overall charge (+2+1-3)=0

Note#2

Fe(2+) is without the two 4S electrons

Fe(3+) is without the two 4S orbital electrons and without one of the 3D electrons from the 'paired' orbital

Note#3

Quantum theory calculations describe the shape of electron orbitals which gives the compounds formed by 'bonding electrons' a geometry.

S electron orbitals(2 total max possible electrons per full S shell in spin opposite shell level filling)

S orbitals are spherical about the nucleus where the protons are located. Protons attract the oppositely charged electrons.

P electron orbitals (6 total max possible electrons per full P shell of 3 paired levels containing two electrons each with opposite spins) For carbon (C) the P and the S orbitals can hybridize to form SP hybrid orbitals with a unique covalent bonding geometry.

P orbitals are 'dumbbell' shaped and exist as three pairs , one pair for each axis (x,y,z)

D electron orbitals (10 total max possible electrons per full D shell of 5 paired levels containing two electrons each with opposite spins) with a set of 'D electrons only' shapes seen at the urls

https://www.google.com/search?q=d+electron+orbital+shapes&oq=d+electron+orbital+shapes&aqs=chrome..69i57j0l2.11150j0j7&client=ms-android-sprint-mvno-us&sourceid=chrome-mobile&ie=UTF-8

or

https://ch301.cm.utexas.edu/section2.php?target=atomic/H-atom/orbital-shape.html

75116.png

 

 

75118.jpg

 

Iron (neutral) electron orbital energies diagram with 8 valence electrons (4S2, 3D-6)

75119.jpg

75120.png

 

I hope this becomes a constructive learning endeavor into the subject and concepts of Lithium ion batteries. 

 

Burp....drinking beer...☺

 

 

 

 

 

 

Edited by Bob Eisenman
Drinking beer
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  • 1 year later...

To bad there is not more info on these,  I mean simplified knowledge in regards to how they could work with EUC's that is is, not braking down chemical and physical attributes part cause I would not understand it anyway. :lol:

Jokes aside though it's sad no one knowledgeable did laborate with them, I am at 9p now inside the 84v MSX and I still cannot accept the v drop, for example the HTCFR26650-3000mAh may not be a 18650 cell and hence less can fit inside the wheel, but they seem to be at a decent point between capacity and discharge characteristics, claim 3000mAh but discharge is rated at 30A continues, 45A for 5s pulse.

Sure they are bigger, 85 gram/piece and I do suspect that for those who appreciate clam and collected, long cruising and staying out half day at a time on the wheel would surely want to stay on maximum capacity train and continue with li ion, but I think about those of us who cannot stop ourselves from maximum attack and every acceleration is at full angle where even the hardest MSX mode feels swampy and sad, too weak!

Could this not be something for us, seems as if some 80% discharge can happen between 3.6 and 3.4 volts, nominal at 3.2v, 3.5v should be over 90% yet quite not full and 24x3.5=84v, perhaps even charge to some 83-83.5v for a 24s pack? Should last for a long time and at that rating backed up by a few p whatever can fit inside the MSX, could it not be a better way if can find the right 24s BMS?

Did the 1600-2400Wh mod to have more for the aggressive style, not necessarily to ride these long cruising trips, different yes but not enough imho so feels like just dragging around lots of extra cell that never will be utilized fully anyway, or else super capacitors? But those could be good for 3-5 sec hard acceleration, not hard acceleration and then stay at speed for a while, ahh anyway just say the thread and if anyone have got more input around this battery chemistry and what is possible with it?

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