In certain areas it has practical know-how we don’t. CATL is a good example. Not just their sodium-ion batteries, but their production processes in general. We might be able to readily reproduce their battery chemistries in a lab but that’s not the same as having an industrial production process and the experience from ironing out all the kinks that feed back into basic research. With a joint venture, you can tap into that stuff.
If we had invested as heavily in the tech as they did we probably would be ahead right now but we didn’t so we aren’t. If they had invested as much into fusion as we did – oh wait they did. They’re behind, Max Planck is currently looking into the details of building a commercially viable reactor in the early 2030s, they’re confident to have the plasma physics down now it’s about stuff like “do we use a cheap material for the diverters and replace them often or do we develop/use something fancy”, that is, about actual operational costs.