Although I agree that this is nothing really new, based on what the Department of Energy considers a Water battery, this would qualify as a sand battery.

Storage of energy to be used at a later time.

Regenerative Braking on a car in motion.
Pumping water to a higher location during cheaper power times.
Larger flywheels.
Space elevators.

Even a capacitor could be considered a short term battery.

Notice that each item has to be charged before it stores energy. Kinetic to Electric.

https://www.energy.gov/eere/articles...ater-batteries

The hard part would capturing enough energy to make the sand cost effective.