Think wider.... think not only "how can we store energy", but also "What would they want to use the energy for?".
Fresh water. Desalination requires energy. Fresh water can be stored indefinitely.
Fertilizers. Making them requires energy. These can be easily stored.
Metals and other base materials. Breaking and refining metals requires lots of energy. Break them now and store them as ingots. Same for other materials that we use in our daily lives.
Hydrogen. Can be used in fuel cells for electricity, for heat, for combustion. Create by electro-hydrolizing sea water, which requires energy.
...and the list goes on. So - again - think wider, not only in terms of storing raw energy only, but also in terms of what we are using the energy for and which of those products are storable.
And a quick note on hydrocarbon storage: bad idea. And anyone that cannot figure out why should be thoroughly ashamed of themselves for missing the entire climate issue. Let us not repeat nature's mistake by — yet again — making hydrocarbon reserves available for humans to use.