I have seen the GM Batteries on the spark EV , they are long and flat and I don't think they are as efficient as tesla battery technology.
The Spark EV uses pouch cells, which are also long and flat, and don't have cases. As always with pouch cells, they are stacked into boxes to form modules, with almost no wasted space. The original (2014) Spark EV uses modules from A123. The
later Spark EV uses the same cells as the Chevrolet Volt, because A123 went broke and GM started making their own batteries from cells made by LG Chem.
Tesla uses cylindrical cells, which are the same thing as a pouch cell but rolled up and stuffed in a can. The cylinders don't pack together well, leaving spaces between them - just look at beverage cans in a case. Tesla has no battery technology - the cells are designed and manufactured by Panasonic. Also, Tesla has moved on from the 18650 size (18 mm diameter by 65.0 mm long) to the 2170 size (21 mm diameter by 70 mm long).
While any battery company can build cylindrical cells, and several make lithium cells in the 18650 size, Tesla is the only EV manufacturer which uses cylindrical cells.
That's all about the shape and physical format. Electrode materials and chemistry are a different subject, and there's not much difference between brands, although the early Spark EV's cells are different from the later Spark Ev's. If you buy 18650 cells, unless they actually came from a Tesla they're not the same as the Panasonic cells which Tesla uses.