[lawrenceyan]

The grammar is perfectly correct though I think?

Perhaps this portion is what confuses you: stores electricity as heat in "the form of a combination of a" high temperature molten salt and cold in a low temperature liquid. This would be an explicit wording which might help to clarify things, but is not used due to redundancy.

[deanCommie]

The 2 consecutive sentence both contain the identical LONG fragment "as heat in high temperature molten salt and cold in a low temperature liquid for days, or even weeks, until it’s needed"