Parting out two or three dead battery packs to cull the best of the survivors can improve things quite a bit. And as you say, on a stationary pack you can afford to overdo telemetry, cooling, and safety circuitry because it doesn’t have to move, let alone accelerate.
I don’t know what the half life is like for the reused cells though. Do the cells that lasted twice as long as their neighbors continue to outperform or do they revert to the mean over time? I could see either being true. The days when you accidentally produce cells that are several stddev better than your target quality should make cells that last longer, unless they’re sold to a leadfootted driver.
You can still have a working battery even with some "bad" (i.e., way out of spec) cells, depending on the BMS. All the thresholds are configurable, just that a regular EV setup would lean towards safety.
This is true (and in some cases potentially dangerous) when you have a several cells of varying voltages in parallel but it's fairly trivial (by EE standards at least) to overcome this with something similar to a charge pump.
they’re being unreasonable
No one is being 'unreasonable' you just started talking about something different.
I'd wager the bulk of them are hybrids where the batteries see a pretty aggressive charge/discharge cycle on a relatively small capacity (and therefore being relatively cheap to replace compared to a full electric). Of course then there are also full electrics where the owners get upgraded capacity or replacements due to degradation from use.
And importantly they aren't just recycling EV batteries here. They are using lithium-ion, nickel metal-hydride, and lead-acid batteries. So they are also buying up traditional ICE automotive batteries as well.
Also worth noting this project is a collaboration between Toyota, JERA, and local universities for use at JERA's facilities. JERA is a large battery reprocessing and recycling company so they are already getting second hand batteries into their facilities on a regular basis. This project is primarily about doing the design and engineering work necessary so that JERA can set up an array of these battery containers, get notified when a unit fails, and swap out the battery with one from their stock for recycling.
I have been out of the battery tech game for a while now but decades ago we were balancing individual NiCd and NiMH cells for optimal performance, is this basically the same thing?
https://electronics.stackexchange.com/questions/463591/nicke...
In a parallel bank, a single cell going bad can bring down the rest to the same voltage. Even worse, if the bank is directly connected to other banks it can take out them as well. Also, if there is an internal short in one battery, the rest will pump current through it very effectively lighting it on fire. Individual battery protection circuits, smart switches, and internal short detection can help with this.
With battery packs probably you can do some smart things to make the degradation curve look more linear, but again there is only so much you can do.
Also in RC car world it's generally preferred to have one cell per voltage step, I've had way more dual-cell(per series) packs fail than single ones. Though my experience is only 6s/~22v but it's "the same shit on a bigger scale" as far as I can comprehend.
I have often wondered if it would be worth designing an EV battery that can permanently short out a bad cell in a string, perhaps by deliberately disabling balancing, letting the bad cells voltage fall to zero, and then perhaps having a single use 'bypass' that latches on.
It wouldn't be a seamless user experience, because if you discharge the cell to say 0.5 volts but then the user tries to charge their car, you can't let them, since you cannot safely charge a lithium cell which has fallen below the minimum voltage, but you also cannot bypass it till the voltage falls to zero. Could be done automatically at 3am though like system updates.
Either way you need some form of overbooking / compensating capacity.
My car's high voltage circuitry seems to work down to about half of the nominal voltage.
Search this page for "PTC": https://www.electricbike.com/inside-18650-cell/
The PTC protects the rest of the battery if a single cell internally fails short.
You could have a two-way bypass, disconnecting the original cell, but that would cost more. Remember the bypass switch is duplicated for every series cell group (hundreds) and must carry the whole battery current.
Or you could have some kind of slow drain resistor - but then you're back to the time issue.
You don't, if one cell fail you shut off the whole array of cells that is in series. But a pack has several arrays of cells.
If it happens multiple times in the same module you replace a whole module of cells. The packs can usually be disassembled and parts replaced, but the modules are usually soldered down to prevent/mitigate thermal runaway.
Also you can't mix cells of different chemistry or capacity together in the same module. So really if one fails in a module you replace the whole module. Or, in their case, just keep the module there disconnected until the whole battery fails then you scrap the whole battery pack. I assume it is not worth it for them to do any kind of replacements.
It can be solved by isolating each battery in its own steel box, but that gets fairly expensive fairly fast.
I've personally set RC lipo on fire with the wood-nail-hammer technique and while the fire out of the pack is intense I can't imagine it igniting another pack.
If we could develop some basic standards for packs (which voltage steps per row and some kind of connector interface standard like for charging) I think we have a really good way to maximize the lifetime and use of EV batteries to help the environment.
I paraphrase Bill Gates: There's no one energy source which will save us, many will complement eachother.
Your interpretation seems to be "we don't use caution when building them" which is not what I meant at all, we do but the risk is non-zero.
Yes. Dams in particular. You calculate for various failure modes and you design around mitigating the disaster if failure should occur. That's why dams are designed with emergency spillways. If there is a bunch of rain, gate failures, etc and you suddenly have more water than you know what to do with, you have the emergency spillway as a last resort. They exist to route water in high volume out of the resevoir, often in a sacrificial manner in an attempt to prevent the dam from failing. And if a dam would fail, it's preferably that it do so at the emergency spillway than elsewhere. So there is a certain amount of "in certain conditions failure can/will happen so this is how we design the system to fail as gracefully/least destructively as possible".
Nuclear has this as well. The plans for this are called "Severe Accident Mitigation Guidelines" or SAMGs with the general practice being called SAM (same abbreviation, just drop the G). Each nuclear site has them and they are generally framed as "this shouldn't go wrong but if it does". You can try to avoid those failure modes but they can always still potentially occur and the most you can do is just try to keep the damage from spreading to the best of your ability.
If one battery pack catches fire, you can start moving the others away from it.
If you normally keep 0.5m between them, you have plenty of buffer space to eat into.
Basically it would start as . . . X . . . with X being the pack on fire "." being a battery pack not on fire, and " " being the half metre between them. Then you move them to get:
... X ...
Where the dots now have perhaps only 30cm between them, but the space to the X is increased.
I’m imaging every firefighter I’ve ever known suddenly having the hair stand up on the back of their necks.
Very space inefficient though, but there's more than enough of that in the US.
Well, you could perhaps put photovoltaic cells on top to use that space? Your battery park needs to be connected to the grid anyway.
worn-out batteries can swell and fail spectacularly, with fireworks
Car battery packs are really good; even the oldest Teslas are only now getting to less than 80% capacity. They are designed not to swell/fail if they're worn, else there would be a lot more car fires.
Making your own cells is fun.
For Toyota, this is trivial and the energy storage these “left over” batteries provide, given a tinkering, is sufficient.
If you're building a battery pack in this day and age, use something like LiFePo prismatic cells and bolt-on busbars instead - way less dangerous chemistry, way less spicy process - but realistically speaking just buy the premade packs. For normal sizes, they're not more expensive (but don't buy the "too good to be true" ones) and means not having to deal with entirely unprotected battery terminals eager to give you a Very Bad Time.
The proper tools to do this are not that expensive anymore in the greater scheme of things. It is just a question of whether or not it is worth to do it at the scale you are doing it or pay somebody else to do it.
Of course if you buy cells that are designed to be bolted together then bolt them together.
Of course the bolts, or whatever else provides the threads, on those cells are welded on.
... by automated spot welder programmed to the specified timing and temperature control from the cell spec sheet, in a controlled environment with suitable protection and fire suppression for a battery manufacturing line. Not by a hobbyist's first try with a homemade spot welder and a safety squint.
I have made such spot welder and done such spot welding. Sure it's fun to do stupid things, but it remains stupid and unnecessary. For a homebrew battery bank, this is the wrong tool, wrong cell and wrong chemistry.
Buy premade, or if you must, buy boltable prismatic lifepo cells. They can dump a lot of power if your short them, but you can drill straight through them and they'll remain stable. The random 18650 li-ion cells... Not so much.
Energy autarky has never been so affordable, progress on batteries and solar panels was awesome over the last decade.
One tabs each are placed onto each ends of cells, held down with the sticks, and instantly welded upon push of a button. This is much safer than heating up the whole battery by attempting to solder wires directly onto the battery cells(which are made of unsolderable materials anyway). The tabs limit heat conduction into the battery and it is considered safe to solder onto them.
If you're going to build your own battery pack no matter whatever whoever says or do, this types of cigarettes contain significantly less amounts of nicotine and tar components than others.
If they do it with different types of batteries it is even more complicated, like you need to write some custom software to sync all that up. This is not a trivial project.
This is definitely not worth doing for small scale operations. As far as I know there is no generic solution for doing this kind of thing (I used to work in the area, but not directly on the BMS systems).
Old EV batteries are great for energy storage. A worse weight-to-capacity ratio doesn't matter for batteries sitting on the ground. A battery that holds only 70% of its original capacity is considered worn-out for EVs (and even replaced under warranty), but grid storage isn't driving anywhere, so any capacity left is still useful.