Single Cell Battery

A battery made of a single cell. For something like a car it would be physically impossible, but for a moderately powered ebike or escooter it actually does seem possible according to physics. No doubt it's not the most practical, and the cells/motors/controllers/chargers aren't currently being produced to make this. Never the less it seems like it would have many advantages.

You would have extreme simplicity, just a single cell with 2 wires attached. There would be no issues with cells becoming out of balance. No BMS needed. Very simple charging. No pack needing to be assembled with it's various connections. Extremely safe to touch voltage. You could also potentially get some benefit in energy density due to the lack of packaging and spacing.

For a 1kw motor, would need around 275 amps (with lithium ion) which would be quite thick wire but could be done. Obviously the motor would have to be designed a little differently with this in mind. The cell would have to be huge and nobody is currently making cells like this. I'm assuming a controller could be designed for this voltage, but I'm really not sure. You would need specially designed chargers etc.

So while i understand it's not practical or convenient at this time, does it sound like a good idea in theory? It would require a totally clean sheet vertically integrated approach (Apple or Tesla like approach, and probably price tag). So I doubt it will happen any time soon if ever, but just an idea I've thought about.

like this?

Yeah that would do it! I was thinking about normal l-ions when i said there's none that size, but i actually have seen those type of big lifepo4 before.

Big NMC / LCO etc exist too!

But why 1S? stupid low voltage

you still need big kWh, might as well reduce the amps and Ah needed

I think this has been discussed before, in detail, but I can't find it in a minute's search. Was at least several years ago.

The main problems are:

--you must have a HUGE and expensive (custom) DC-DC to convert the 1S voltage into something a controller can use,
*or*
-- you must design a completely custom controller to do that job as well as that of the controller itself,
*or*
-- you must design a completely custom controller *and* custom motor to operate at that 1S voltage. This probably includes developing custom electronic chips, gate drivers, FETs, etc to all work at that low a voltage.

--*and* you need expensive, very thick heavy cabling, fusing, and switches for the entire run between battery and controller (and motor if not upconverting the battery voltage).

There's other stuff I don't recall at the moment, but it works out that the "advantages" of a 1S setup (no balancing needed in the BMS (or no separate BMS and doing this in the custom controller), no battery connections other than main B+ and B-, are not nearly enough to make up for all the other costs of such a low-voltage system.

If such hardware to run at 1S already existed, the costs would be less, and might make it more worth trying.

There are other compromises though - so things like 24 V or 36 V for an e-bike, or 72 V to 96 V for an e-moto are perfectly reasonable.

There's no good reason to exceed 400 V for a sub-megawatt system nowadays. I ran the race bike on 700 V fully charged as that was the best compromise of power and voltage, but with what's available today 350 V would be fine.

What got me thinking about this was reading Elon Musk's tweet below, responding to a rumored "monocell" for a rumored Apple car. Elon stated the voltage would be 100x too low if using a single cell. Tesla cars are around 100kwh, so in theory a 1kwh ebike with just 1 cell would be in the realm of possibility.

https://twitter.com/elonmusk/status/1341484482302533635

@amberwolf You summed it up pretty well. I'm aware there's no off the shelf parts, needing everything custom designed to work. But I think ultimately it would be the best design if you had the time, money, and expertise to make it a reality. Specifically option 3 where you design a motor to run at that voltage. Whether it could be financially viable as a product is another matter.