hi all:
long long ago, i find Dell E6220 can not use uefi mode boot clover.
now i have a way.
1. install osx as before.
2. inject Ubuntu USB device,boot, try ubuntu
3. mkfs.fat /dev/sda1
4. reboot system,enter osx with USB Clover boot
5. copy EFI folder to disk0s1
6. not nessary, change EFI partion name from none to EFI use diskutil.
now,E6220 can only use UEFI boot option boot clover, clover driver need use UEFIDriver folder