"If Apple so desires?" Because throwing money at the engineering problem will instantly make the technology production ready and scaleable? Apple puts their R&D money into research and development of products they make. They do not, for instance, put R&D money into RAM chips. They buy them basically off the shelf. Batteries are one of the many, many things they source from suppliers.
The solid-state batteries you linked to look promising, sure. But again, they exist only in labs at the moment. Presumably they are being researched by the companies who actually, you know, make batteries. And you cannot prove that it isn't, unless you have some crazy good internal connections at every battery manufacturer on the planet. I'd imagine that solid-state batteries just aren't scaleable yet.
Apple is using the best batteries currently available in the market. It's great that you are so excited about new battery technology that might be ready for mass production within the next five years, but you have to accept that it's not ready right now, and that's why you can't find it anywhere in a consumer product.