original BIOS has some limition: RAM freq, hardware whitelist, missing 'Advanced' BIOS options, etc.
I downloaded latest BIOS with modification from here, if you want upgrade your X220 with faster RAM and 5G wifi(7620AC), you need upgrade your bios first.
If you have a running Windows, you can save some time of creating WINPE USB stick, you should follow BIOS upgrade README.txt, if not, you need create a WINPE USB stick, you can run BIOS updater program on WINPE.
After upgraded BIOS, I can't boot my Ubuntu system, I found a solution about boot loader missing after upgrade bios, here, what should be noticed is, you must use UEFI mode, not legacy mode, so check your BIOS boot mode, select
UEFI only, and run in LIVE terminal:
sudo efibootmgr -c -L Grub -l /EFI/ubuntu/grubx64.efi