This is for charging safety reasons.
Because the battery is composed of a number of cells, charging is actually to charge the cell, if the charging current is larger, the faster the charging speed, so most of the current is the use of DC high-power charging mode.
At the beginning of charging, there is a charging \"warm-up\" process, when the battery is charged in a certain amount of electricity, it will increase the constant current on the charging mode, to reach the fast charging mode, generally 30 minutes later can be charged to 80%.
For safety, even if the fast charging pile when the battery capacity is charged to about 80%, it will limit the charging current, reduce the charging risk, and will continue to reduce with the increase of vehicle power, to further ensure safety issues.