Designing hierarchical serpentine interconnects for ultra-stretchable lithium-ion battery modules

Stretchable interconnects are pivotal components for flexible batteries, enabling mechanical compliance and electrical conductivity. However, existing designs suffer from a critical trade-off between stretchability and electrochemical performance. Key aspects like volumetric energy density and mechanical reversibility are rarely considered. Here, we present a novel hierarchical serpentine interconnect design for ultra-stretchable batteries, featuring a dual-level architecture. This highly scalable design consists of horizontally serpentine conductive layers encapsulated within a vertically serpentine, multilayered shell. Numerical models were developed to systematically investigate how the key geometric parameters influence stress distribution, mechanical reversibility, and energy density. The fabricated batteries incorporating hierarchical interconnects demonstrated exceptional performance, maintaining high capacity retention of 95% over 200 charge/discharge cycles, high rate capability, and robust operational reliability even under dynamic tensile strains of up to 300%. This study proposes an integrated design and fabrication strategy for stretchable interconnects with balanced performance, which serves as a critical foundation for deformable batteries.