The report notes that Apple may not be ready to ship the device to consumers in 2014 as battery cell suppliers have not been able to meet its demands.
In general, smartphone batteries have a thickness of roughly 2.8 / 2.9 millimeters, but in Apple’s vision, the 5.5-inch iPhone 6 must have a slick profile which can only be achieved by fitting a battery that measures only 2 mm or less. As such, reports claim that the 5.5-inch iPhone 6′s release date will be delayed to 2015, or, in other words: until Apple’s suppliers will be able to meet these technical requirements and output a decent yield.
Due to its thinness, the device is being referred to as the iPhone Air by suppliers; however, that doesn't mean that Apple will use the name at launch.
Previously, it was believed that Apple would ship a 4.7-inch iPhone 6 in the third quarter and follow that with a larger 5.5-inch iPhone 6 in the fourth quarter.