I'm all for new technology and approaches, and it looks like this is just at the beginning for this approach so I would assume it could grow in efficiency in the future.

However, as it stands today its pretty far away from a good replacement for existing solutions or approaches.

The new material, called a pyrimidone, can store more than 1.6 megajoules per kilogram. That is almost double the energy density of a conventional lithium-ion battery, which is about 0.9 MJ/kg.

1.6 MJ/kg..that's....not very dense for a thermal solution for this new material. This is especially true with the likely increase complexity of adding a plumbing system and heat exchanger to extract the energy. With the lithium battery its a pair of wires going in and the same wires coming out to move the stored energy. Further, the lithium battery energy is electrical which certainly can be converted to thermal energy at 100% efficiency with a simple coil of wire (resistor), but it can also be used electrically for all the fun things we use electrical energy for. The new technology solution looks to only be a thermal storage medium.

For reference 1 kg of gasoline has 45 MJ/kg. Keep in mind I'm not saying gasoline is a replacement, I just wanted to offer a scale for reference. Another approach suggested for storing sun energy in chemical form is ammonia which has about 19 MJ/kg. Yet another approach for storing solar thermal energy is sand batteries. A sand battery has a density of .4 to .8 MJ/kg ( 500 °C to 1000 °C respectively). Sand batteries would come with the same burden of a plumbing system and heat exchanger though but without any exotic materials.

None of this is to discourage the basic reseach these folks are doing. They could be onto the "next big thing", but I just wanted to put it in perspective as to where it is today.