Last night Robinhood, the American fintech unicorn that provides free securities trading services to consumers via an app, announced that it raised an additional $460 million in its previously-known Series G. That round is now worth $660 million at an $11.7 billion post-money valuation. A little over a month ago Robinhood announced that it had raised a $200 million Series G, bringing its valuation to $11.2 billion at the time. The Exchange explores startups, markets and money. Read it every morning on Extra Crunch, or get The Exchange newsletter every…