Here's the mechanism, stripped of the marketing. Every lithium-ion battery moves lithium ions between two electrodes through a medium called the electrolyte. In the cells in your phone and most EVs today, that electrolyte is a liquid — and it's flammable. A solid-state battery does one thing differently: it replaces that liquid with a solid material that ions can still travel through. Everything else about the why-it-matters follows from that single substitution.
The substitution is harder than it sounds, which is why it's patentable. One leading family of solid electrolytes is sulfide-based, and Toyota's grant US11532837B2, "Sulfide solid electrolyte particles and all-solid-state battery," describes the material and how to make it into a working cell. Toyota's earlier grant US10396394B2 covers a method for actually producing such a battery — and the existence of a separate process patent is itself a tell that the manufacturing is the hard part.
Here's what the patents actually fence off, and it's worth being precise: a claim covers a specific material composition or process step, not the entire idea of "solid-state." LG Chem's grant US10854912B2, "Sulfide-based solid electrolyte and all-solid-state battery applied therewith," stakes out a different composition in the same chemistry family. Multiple major players holding adjacent sulfide-electrolyte patents tells you this is a contested space where the winner is decided at the materials level, not the press release.
The hard part the announcements skip is contact. In a liquid cell, the electrolyte flows into every pore and crevice, so ions always have a path. A solid can't do that — press two solids together and you get gaps at the microscopic scale, and gaps are resistance. Much of the engineering in these grants is about maintaining intimate solid-solid contact through manufacturing and through the swelling and shrinking that happens every charge cycle. That's why a solid-state cell that works in a lab coupon is not the same as one you can build a million times on a line.
Why does this matter beyond chemistry trivia? Because solid-state is the technology most often invoked to promise longer EV range and faster charging, and the gap between the demo and the gigafactory is exactly the gap between a materials patent and a process patent. The document, not the press release: when a company says it has "solid-state breakthrough" IP, the useful question is whether it owns the process to make the cell at scale, not just the material that works once.
So the next time solid-state comes up as the thing that will change everything, hold two facts together. The mechanism is real and the safety and density upside is real — that's what the electrolyte patents claim. And the manufacturing is unsolved enough that the same companies are patenting how to build the cell, not just what's in it. Both are in the record.