Yes, if you have FileVault 2, you will essentially securely erase your drive as soon as you format it. Boot from another volume (external clone, Recovery or Internet Recovery, etc.) and choose to format the drive as APFS unencrypted. No password will be set. The drive will still contain the bits that were set there before, but since they had been encrypted with FileVault 2, you’d need that FileVault key to encrypt them. Without that key, anything left on that drive is gibberish.
A problem would be if you did not have FileVault 2 enabled, or possibly, if you only enabled it after you had already stored and later deleted data before turning on FileVault encryption. That is where secure erase via writing zeros or random data (DOE or DOD schemes) come into play. But with FV2 encryption, none of hat is necessary. “Cryptographic erase” is really an awesome feature: it’s quick, it’s thorough, and it’ incredibly easy to carry out. It’s the way we these days with SSDs should be dealing with privacy concerns when selling our Macs or getting rid of an SSD.