MIT is working to develop large scale solar energy storage. This tech is similar to molten salt but with some important differences. They are looking to store the heat in molten sodium which can get hotter and is less corrosive. In order to do this they first had to develop a pump that could handle the extremely high temps (>4000ºF!). They have succeeded now and are proceeding to develop storage tank systems.
https://techxplore.com/news/2018-12-sun-renewable-energy-grid.html
https://techxplore.com/news/2018-12-sun-renewable-energy-grid.html