Deep-seafloor mining is a complex topic that leaves out a crucial starting point: mining the potato-sized rocks on the seafloor called “nodules” only yields four metals of any economic consequence: nickel, cobalt, copper, and manganese. Since copper and manganese are plentiful on land, deep-seafloor mining is really all about nickel and cobalt. And, unlike many have tried to claim, you cannot in fact get meaningful amounts of rare earth elements from the seafloor.
In the early 2020s, deep-seafloor mining was advertised as a source of key metals for electric vehicle (EV) batteries. However, battery technology has moved dramatically forward with new chemistries that require no cobalt or nickel and instead use inexpensive iron, phosphorus, and sodium.