Cells develop more internal resistance as they age, and this resistance creates heat which must be dissipated.
In general terms I also believe this to be true. Obviously we are speculating about something that is seen by some as 'my range has dropped', others as 'my car could burst into flames any minute, or my battery doesn't charge to the same voltage as it used to or it takes all day to charge etc..... Behind all these is a technical reason / reasons that may be unavoidable or not. Inter-related or coincidental.
By Tesla they are seen as something they need to find a way to explain and own up to without screwing themselves too badly...
Then there is every single twist, nuance, quirk, design element, component that makes up the manuci of the battery.
So we need to be detailed, accurate and specific about something we don't (and to some extent can't / aren't allowed) to understand.
So, is it true to say that all lithium cells degrade with age, use patterns and net energy throughput?
Is it true that lithium cells have multiple aging 'modes'?
If so, what are these modes?
Maybe:
Towards lower internal resistance -
Plating
Dendrites
? Thermal related behavior?
Towards higher resistance -
(I don't know what these effects are called or even if the effects exist)
Electrolyte aging.
Electrode decay / chemical change.
Age related increase in internal resistance.
Temperature accelerated degradation.
Are there any other modes?
Eg: mechanical? Is Dendrites electrical or mechanical?
Functional? 'operating stress' required in battery to maintain acceptable performance. Like a redundant system is only redundant until the redundancy is not available. So the battery is able to remain functional (safely) while it has not experienced degradation.
Is it possible / likely that cells (used by Tesla) exhibit a mix of 'aging' effects towards both ends of the spectrum?
Have bricks (blocks of parallel cells) ideally from a battery showing signs of stress) been inspected with public results showing any data like:
Number of blown cell fuses.
Condition of cells remaining connected and (presumably) sharing same charge / discharge current as a good cell but between (far?) fewer cells?
Is this the kind of situation (bad bricks) that the 'diagnostic' software Tesla rolled out was looking for?
If not, then what other battery behavior could Tesla usefully have looked for to tell them something they didn't already know about battery condition?