The shape of the battery doesn't really matter. They're made with the same materials regardless of shape. The only concerns I can think of are stack pressure (making sure all the layers have good contact) and ensuring that no electrical shorts occur from components slipping out of place. Both of those factors are easily engineered for each shape. There might be some slight differences in energy density with different shapes, but there's generally very little wasted space in batteries.
Some shapes might be safer than others in the event of a short/puncture, but I'm not sure. There isn't really a standard way to test battery safety between different designs.