No EV that I'm aware of has the ability to bypass a single cell in a series string.
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.
I guess you can put a relais/switch in for each cell in a series but then you need to account for voltage differences when taking them out. Either by over provisioning within the series and rotating in different cells. Or by have other strings take up the slack.
Either way you need some form of overbooking / compensating capacity.
A relay would allow you to switch it out and then back in again. Which you don't need. Just a fusible link that can be blown to permanently disconnect the battery from the string might be simpler and more ideal for the application.
There's NCA (drones), NMC (laptops, phones, many electric cars), LFP (stationary/grid), and LFMP (many new electric cars; slightly more expensive but higher current variant of LFP).
If you just close the bypass switch, a large current will flow out of the (dying) cell, making a lot of heat.
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.
Okay, I understand. I was definitely imagining some sort of latching switch, that would connect to the bypass instead of the cell. Makes sense that would be more expensive.
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.