Why Trickle Charge a Deeply Depleted Li-Ion Battery?
When Li-Ion batteries become the discharged the ESR rises significantly. Therefore when charging with a high constant current the battery does not charge efficiently with a high constant current and risks over-heating from the high ESR. Therefore you must use a lower CV rate until the battery ESR drops at a certain charge level or voltage level then CC mode can resume. Excess heat can cause excess forces inside from outgassing but also internal excess temp causes premature aging.