Uniform heat (perhaps from a solar concentrator) causes an endothermic chemical reaction. Later, when temperatures are colder, you run the same reaction in reverse to generate electricity. Resolves YES if there is a commercialized battery powered this way by 2050. Molten salt energy storage doesn't count because 1. there's no chemical reaction, just a phase change, and 2. It's not a self contained mass produced unit like a battery.

This would not violate thermodynamics because just like a regular heat engine it is moving heat from a hotter source to a colder sink. There's just some additional time-delay between the two. To the best of my knowledge there is no battery based on this principle yet but it is totally possible. This is the only valid way I can think of to extract work from uniform heat - even though the heat is uniform in space in the system at one point in time, it is not uniform across time and that enables work to be done by the heat.

This tech if it got cheap enough would be extremely useful for the base load of a power grid that is heavily dependent on solar.