Study Finds a Way to Prevent Fires in Next-Generation Lithium Batteries

Oh absolutely, we had what it nominally referred to as a 'motor-generator' set in the basement of the building where I worked to provide backup power for the machine room. It worked by using regular AC power to spin a flywheel which was then spinning a generator through a continuously variable transmission (CVT). If the power failed, and you did your math right [1], the flywheel's momentum would continue to keep the generator going for another couple of seconds before power actually shut off. During those two seconds though the computers would know that power was "off" and to do the appropriate things to be ready for that (like park the heads on the drives, unload vacuum column tape drives, shutdown the drum, etc etc.) All stuff you could do in 100 - 250mS which saved a lot of work later on.

The engineering challenges though were size (it ended up being this horizontal thing that filled the room). Keeping it sealed with a vacuum (if there was air in the flywheel chamber it adds drag to the wheel which robs you of energy), and dealing with its very strong desire to precess if the ground moved in any way. The engineer responsible for its installation suggested that if there was 6" of ground movement in an earth quake the gyroscope effect would wrench the flywheel off its mount and it would rapidly climb out of the basement on its own momentum. (something I was secretly desiring to see in action)

[1] The first one they installed they did the calculations incorrectly and when they tested it the flywheel stopped in just under 10mS with a very loud bang. Fortunately you can boost energy storage by increasing mass and/or increasing RPM which they did (both off) and got it to a sustain duration of 1800mS (not quite 2 seconds worst case)