Flywheel

A flywheel comprising

• a plurality of discs arranged in a stack on a common axis, including at least first and second end discs at either end of the stack, in which each disc has substantially the same thickness across its full diameter, and in which each disc includes a disc surface within the stack, the disc surface including a central region on the common axis and a peripheral region disposed around the central region, the peripheral region being adjacent to a peripheral edge of the disc,
• first and second plate members disposed at opposing ends of the stack, and
• bonding means comprising bonding material or bonded interfaces between adjacent discs, in which the bonding means bonds only part of each disc surface within the stack to each neighbouring disc in the stack, including bonding together adjacent peripheral regions of neighbouring discs, and which bonds each of the first and second plate members respectively to the first and second end discs of the stack.