'06 Prius battery upgrade to LTO 55Ah cells

Charging appears to be limited to -10*C but discharge to -30*C, but that is not verified by lab testing and are from a well known chinese reseller of similar capacity and dimension cells ... but they also have a poor reputation for selling seconds and even factory reject stuff, so I don't have a lot of faith in anything I read on their listings regarding the accuracy of any specs, actually, I don't trust any specs I haven't personally verified .....
As for -35*F, Google says that's around -38*C .... I don't thing our deep freeze goes that low, surely nothing lives in that sort of cold, surely it's kept warm inside or something?

T1 Terry

 

Define "freeze proof"? Water freezes at 0*C or 32*F .... it's a lot warmer than that I deem to be freezing cold, like anything below 10*C :lol: but then hot over here is anything above 45*C or 113*F ... so we live in a heat sensitive climate, not likely to see below b-10*C anywhere in Australia really ....

T1 Terry

 

The data sheets don't all match the tech specs and there is no chart for cell operation at low temp, the lowest appears to be 23*C, but worth a try I guess ... no idea what QRP stands for, but as long as the 2.5Ah capacity with an end voltage of 2vdc will power what you need, then it looks as though they would do the job as far as low temp goes

T1 Terry

 

Odd cell voltages for sodium ion, all that I've look into run at a very similar voltage range as LFP/LYP cells.

The heating during charging and discharging is tied to the voltage at the max charging and discharging the cell will experience ... if the charging is faster than the ion intercalation into the negative graphite coating, the voltage climbs, if the load is greater than the ion release from the graphite, the voltage drops ..... the more abuse the cell suffers, the more extreme the heating/cooling cycle within the cell, the more elements within the electrolyte break down and coat the surface of the negative plate graphite coating, resulting is slower ion movement in and out of the graphite .... the death spiral.

With LFP/LYP cells, keeping the cell terminal voltages above 2.5v and below 3.8v at all times, including charging and discharging, will not cause the electrolyte to heat and retain the C rating for the life of the cell .... yet to see just how long that is, 13 yrs and still retaining 100% of the advertised capacity under a 0.5C load, so far, so the 10 yr myth is certainly dead and buried, yet to fully understand just what a cycle is regarding to the LFP/LYP chemistry goes.

Sodium ion is a whole new minefield, so many electrolyte and negative plate coating combinations ... and none of the true cell manufacturers are saying what combination they are using in what product number cell

CATL are already on their second generation mass production run with hundreds of combinations still at the lab/testing stage, hundreds and hundreds abandoned, who knows what combinations the minor manufacturers are using and how exhaustive their testing is prior to production ......

I see even more pain navigating this newest chemistry, the basic chemistry is the same, so it can't be determined using that criteria ...... hands on testing will be the most reliable method, not simply trusting the reseller to tell the truth ... or even knowing the truth ......

T1 Terry

 

Hmmm.... the Gen 2 Prius can pump out more than 180 amps on regen under heavy braking, you would need three sets of these battery configurations to handle that, so you are going to need to retain the original traction battery as well so it can at least absorb the high current, then some sort of current limiting to the extended range battery you are adding.

With the 15Ah sodium ion cells I'm about to test (too many projects already) they are spec'ed to handle between 1.8v and 4v, 4 cells in series would handle 160v, but the Gen 2 Prius can belt out close to 200v sometimes, so I'll be building 5 cell in series strings to handle the high inrush voltage and hopefully the 10C charge rate is actually possible for 1,000s of cycles, or I'll have to build 2P5S strings to reduce the C rating to a peak of 6C (180 amps)
A series string of 5 of these 15Ah cells is slightly smaller than 2 modules of the original NiMh cells (12 cells), so 14 strings will build a battery with 3 times the capacity, yet fit in the same position as the existing battery .... if the cells can actually handle the charge current ...

T1 Terry

 

Yet another thing to determine during these battery tests, is the charge voltage linear and relates to state of charge in each cell. Lithium ferrous phosphate (LFP and LYP) chemistries don't, so to get the cells fully charged, the max charging voltage must be very close to the fully charged voltage, there is only 1v between 100% SOC and 0% SOC, yet 0.5v above 0% SOC does not equate to 50% SOC, it just equates to not fully discharged or fully charged.

That 180 amps was measured using an independent shunt and recording logger at the battery terminal. The majority of each brake application is in the form of regen until the wheel speed is below 6km/h, Dr Prius only sees an average of what the computer interprets to be the charging current, it allows a Peukert exponent related to the charging efficiency of the NiMh chemistry and the voltage it senses at the battery to alter the current very rapidly to guard against module over voltage causing a cell to go bang, the peaks are blurred over, but they do briefly show up using a Scan Gauge 2

T1 Terry

 

That is why you need to do a lot of research, then buy samples and do your own testing to identify just what the ability of the cells you have chosen ..... If you could get your hands on genuine CATL gen 2 cells you will find they can handle better than 20C in both directions, but you and I are not a big enough enterprise for the likes of these companies to even return an inquiry. Fortunately, I have someone who can get access where many can't, but it is still a trial and error thing to get what you need, these days, factories don't do the lab testing any more, that is up to the purchaser and feed back between the two develops the battery the purchaser needs ..... China is a very strange market to work in, just about any product you can find on the market that sells direct to the public is a secondary reseller who is selling factory rejects, none of them have the $$ to do factory testing, half of them don't even know what they are selling, just look at the number of them that seem to end up with lithium ion somewhere in their product description .....
At the moment, sodium ion is a very new product with very little genuine information available .... LiFeP04 was that way 12yrs ago when I started testing those for various load applications, there is an absolute flood of them on the market now, but only 1 or two brands that are the real thing, the rest are relabelled factory rejects .... the good manufacturers don't sell their rejects, they break them down to find out why they didn't reach the minimum requirements, then they reprocess the materials ..... that is why quality lithium cells are still very expensive ...

T1 Terry