Lithium became drastically cheaper, but has yet to achieve relevance in term of grid scale storage. The US uses 12 TWh of electricity per day. The world used 60 TWh. Global lithium ion battery production is around 600 GWh. Most lithium storage systems are on the order of megawatt hours or single digit gigawatt hours.
It can be very useful for grid stabilization at the scale of seconds to minutes (both with charge and discharge).You don't need that much capacity to do that.
