I am pretty sure it must be a joint account if you are trying to increase your coverage. At the moment, I believe it's $250,000 per individual, til December (next month). It used to be $100,000 per person.
For a joint account, at this moment, you are covered up to $500,000.
You can divide money up into different banks if you want to be completely sure. The limit, was, and may go back to $100,000 per person, per bank.
What is your objective?