Synthesis of fully foldable nickel film with inverted pyramids towards Li-ion batteries with high folding endurance

Forthcoming wearable and portable electronics such as Google Glass and smart cloths urgently require the development of foldable Li-ion batteries (LIBs) to fit diverse shapes, operate under repeated folding motions, and facilitate collapsible designs. Here we report for the first time a hydrothermal reduction synthesis of a very thin (5-mu m-thick) Ni film with inverted pyramids (NFIP); the resultant film exhibits an extremely high conductivity of 1.25 x 10(5) S cm(-1). This inverted pyramid design enables the realization of an NFIP whose resistance deviates by 0.19% and 0.72% from its initial value after 22,000 (outward) and 18,000 (inward) folding cycles. The foldable LIB show a capacity retention of 98.4% at 20 C after being subjected to 5000 cycles of full folding (180 degrees) compared to that delivered under the initial flat state. We also demonstrate a foldable LIB integrated with a Google Glass model in which the battery powers an LED lamp during 9000 cycles of folding (90 degrees) motions.