Conversely, smartphones could have batteries 1/100th the size of their current batteries and still have the same battery life. Nothing says that if we want to use this tech in smartphones we have to have 100x the battery life (although that would be fantastic). Even 2x or 3x would be game-changing for power users, especially if battery performance degraded at only the same rate that current smartphone batteries do.
You wouldn't need a huge array of coin cell batteries; one coin cell might well be enough.
The article says "100 times greater than TDK’s current battery in mass production" but they are not referring to the current LiIon/LiPo batteries, but the current _solid state_ battery. The capacity per liter of the new solid state battery is less than 2x of the current phone batteries (1000Wh/liter vs 5-700Wh/liter for LiPo). So no, you cannot replace one phone battery with a coin cell with the same battery life.
You wouldn't need a huge array of coin cell batteries; one coin cell might well be enough.