Human joint-inspired structural design for a bendable/foldable/stretchable/twistable battery : achieving multiple deformabilities

Flexible lithium-ion batteries (LIBs) with high energy density and stable electrochemical performance are regarded as the most promising power source for supplying wearable electronics. Simultaneously achieving a small bending angle, multiple deformation modes, superior mechanical durability and high energy density remains a challenge. Here, inspired by a human joint, a novel and rational structural design for flexible LIBs is reported. In the battery, thick and rigid stacks for storing the main energy are equipped with cumbered surfaces and interconnected thin parts, imitating the articular surface-ligament structure of a human joint providing flexibility for the whole battery. The configuration of thick stacks can be changed by different winding technologies, which endows the battery with abundant deformabilities, including bending, twisting, stretching and even winding. A finite element simulation confirmed that our designed battery will not lead to the irreversible plastic deformation of metal current collectors under various harsh and complex deformations. The flexible battery with cubic energy storage units exhibits a high energy density of 371.9 W h L^-1, which is 92.9% of a conventional pouch cell. Furthermore, it can maintain stable cycling performances, even undergoing over 200 000 times dynamic bending and 25 000 times dynamic twisting deformations. The battery with cylindrical energy storage units can withstand more harsh and complex deformations. After undergoing over 100 000 times dynamic stretching, 20 000 times twisting and 100 000 times bending deformations, a high-capacity retention of over 88% can be attained. Accordingly, the novel and unique flexible LIBs provide great promise for its practical applications in wearable electronics.