Bookmarks: Farasis Battery Farfle-ated

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Jackson Edwards (AKA Farfle) just posted some sincerely in-depth info on Farasis batteries on EMF, which you can find here: Battery notes from a Farasis Engineer.  Remember Jackson?  Of course you do.  20130609_200242

Due respect to EMF, but posts come and go in this day-and-age on the interwebs, so along with the link I want to snag a bunch of the information there in case the post gets moved or lost.  Here’s the yummy bits, edited a bit for spelling only:

The 25Ah cells are a solid cell, and are Farasis’ oldest chemistry design. They are a manganese-rich cathode (NMC) 25ah cell with excellent cycle life, and acceptable C-rate. These were used in MY13, MY14 and MY15 FX only.

The 27Ah cell introduced for the model year 15 bikes is an adaptation of the 25ah cell chemistry with thinner foils and more of them, this means that there is more active materiel (more capacity)  but less conductive path to get that capacity in and out. So for the slow discharge S/DS bikes, you get more capacity, but they are lower C rate, and cannot handle being used in the FX platform. (Used in MY15 S/DS only)

The 29Ah cell was introduced for MY16, the 29 is Farasis’ newest generation of NMC cell, and they are awesome. They have both higher discharge rate (peak and continuous) than the 25Ah cell, and more capacity (especially at higher C rates/cooler temperatures) than the 27. This is used in all MY16 bikes.

The cells mainly age in two ways (there are other processes going on, but not dealing with those today):

No.1: The electrolyte reacting with the active components of the cathode and anode in the cells, and releasing gas (calender life),

No.2: The Interaction between the lithium ions and the anode/cathode blend that causes a small amount of damage each time they are cycled. (Cycle life)

These factors affect the cells about equally, but extreme conditions can sway it either way.

Things that speed up degradation, and make your battery sad ( AKA the “Dont’s”):

Hot temperatures: This causes the electrolyte to become more reactive. At Farasis, we have one of the most stable electrolyte blends in the biz, and use a lot of proprietary tech to keep our cathode/anode blend as least reactive as possible, but the effect is unavoidable.

High voltage: Again, The higher the potential between the cathode and anode, the faster the reaction between the electrolyte and the actives occurs.

Super low voltage: Below a certain voltage (2.0-2.2V/cell) the potential between the cathode and anode is such that the battery has used all its high potential  lithium, and so it starts picking on the next easiest thing, which is the copper.

This process is super ugly, as it electroplates the copper off the negative foils (anode) and electrodeposits it onto the positive foils (cathode).

PERMANENT IRREVERSABLE DAMAGE. This is super dangerous too, as the next time it is charged, that copper gets blasted back to the negative foils and lands wherever it feels like, as the anode isn’t designed to deal with copper Ions. So they form big crystal stabby structures called dendrites, which at best can pierce the separator and cause high self discharge and gassing as the electrolyte nucleates (gas builds up, the cell goes to 0V and looks like a balloon) , or at worst, the dendrite is able to get a solid connection between the cathode and anode, and this causes the cell to short internally and results in fire.

Luckily for you, Zero has an amazing BMS and pack topology that sips hardly any power from the cells in a key-off state, but you still can murder the bike by approaching 0% SOC as slowly as possible until it is at its absolute lowest SOC (state of charge) and the BMS shuts the bike off. What happens is that the bike has the smallest amount of reserve battery then, and the BMS sipping away at that small amount will eventually murder the cells over a period of several years.

Basically, the way to kill a zero the fastest is to either ride it to absolutely dead as possible, and then store it in a shed for six years, or to store it at absolutely tip top charge in direct sunlight in a super hot desert in arizona somewhere. Either way, you will still struggle to kill them before the warrantee is up.

So, to prolong your battery life, you can do the exact opposite. Store the bike in a cool place with a stable temperature at low SOC.   ~20% or so is fine for S/DS (one BMS sipping on 3-5 cellboxes) or 30-40% for the FX modules (one BMS per cellbox)

When you get done flogging the crap out of your S/DS on a hot day, let it cool down for 4-6hrs before charging it (takes less time for FX modules)

Fast charging is fine, but know that around the .8C mark is the point where at normal ambient temp, you go from cooling off to heating up. If your pack is already hot from a ride thru the desert at WOT, and you fast charge, you are still going to be on a hot pack when you continue your WOT journey. Not a big deal, but you will get some extra high temp degradation. The BMS will keep you from really buggering your pack, so don’t worry about it.

The one point that I found most interesting is the explanation of what happens at low voltage – that is, the battery starts eating copper.

 

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