For plenty of industries, that kind of thing is true, but there are loads of manufacturers of batteries so forming a cartel and agreeing not to bother with any new technologies is impractical, and buying out new competitors with new technology and stifling it only works if your competitors also stifle everything new that they buy. There are a bunch of nation states backing their domestic battery producers and desperate for any way for them to outcompete those of other countries, and cartels tend not to form between state-backed companies from geopolitical rivals.

The big thing stopping new technology appearing is that we're pretty good at making lithium-based batteries, so you generally end up with a better battery for less R&D effort by making a small improvement to lithium batteries than coming up with something new, even if the theoretical limits for the new thing would blow modern batteries out the water. Sodium batteries have the advantage that lots of the knowledge that applies to lithium batteries is still useful, so the road from theoretical to good is much shorter, and we're already using all the lithium we can extract and that's representing a large fraction of a battery's cost, so there's a market for something cheaper even if it's worse.