There are probably a good dozen very promising and radically different approaches I've read about in recent years, from compressed air storage, to liquid metal,

There are probably a good dozen very promising and radically different approaches I've read about in recent years, from compressed air storage, to liquid metal, to MXene clay, to salt water, to 'carbon enhanced anodes' in a tweaked lead acid battery, and many more... In late 2013, it looked like we were on the cusp of finally breaking through the cost per kWh barrier in a matter of months, and I got so excited I started a business built around the anticipation of just one of these things panning out. Then? Crickets. One company I invested in is now a penny stock, and just announced a product which costs twice as much as the Powerwall for the same storage (oh, and it's probably worse in about every other way, too). I might cry if I had any tears left to shed over this. To be honest, I've started to wonder if any breakthroughs that may have happened in this field are being suppressed for some kind of political reason(s). You would think that couldn't go on indefinitely, though.