I don't have a technically grounded hypothesis based on battery chemistry. My speculation is based on observed supercharging behavior at low ambient temperatures and low SOC. Unfortunately, we don't have access to battery temperature, obviously an important variable, and I did not keep notes of ambient temperature so I am going from memory.
Ambient temperature around freezing (32F). Battery cold soaked after being parked outside overnight. Starting at 18%, initial supercharge was limited to 49 Amps (17kW). After 30 minutes charge was only 40% and current was still limited to 200 Amps (73 kW). During this whole period the charging current was slowly increasing. Much of this can be attributed to battery warming. Charging rates where captured with VisibleTesla.
That evening, with about the same ambient temperature but the battery probably warmer from 20 minutes of city driving, supercharging from 34% started at around 150 Amps (60kW). While not definitive without knowing the battery temperature, it appeared that the battery was willing to accept more current due to higher SOC when cold.
Net at low temperatures, acceptable charging current at low SOC is lower than at intermediate SOC, indicating that battery management factors low SOC into charging current limits at low temperatures. I will try to capture better data as future opportunities present themselves.
