This 9v battery contained six cells stacked like a layer cake
Picture of a disassembled Duracell 9v battery. Below the terminal assembly is a clear plastic case where you can see six sets of stacked rectangular terminals and fillings.
Open any lithium battery pack and you’d find those cylindrical lithium cells. Even a Tesla battery has those. Only things that need to be flat like a laptop or a phone use a pouch battery.