Flexible Interface Design for Stress Regulation of a Silicon Anode toward Highly Stable Dual‐Ion Batteries

Abstract Dual‐ion batteries (DIBs) have attracted increasing attention due to their high working voltage, low cost, and environmental friendliness, yet their development is hindered by their limited energy density. Pairing silicon—a most promising anode due to its highest theoretical capacity (4200 mAh g −1 )—with a graphite cathode is a feasible strategy to address the challenge. Nevertheless, the cycling stability of silicon is unsatisfactory due to the loss of electrical contact resulting from the high interface stress when using rigid current collectors. In this work, a flexible interface design to regulate the stress distribution is proposed, via the construction of a silicon anode on a soft nylon fabric modified with a conductive Cu–Ni transition layer, which endows the silicon electrode with remarkable flexibility and stability over 50 000 bends. Assembly of the flexible silicon anode with an expanded graphite cathode yields a silicon–graphite DIB (SGDIB), which possesses record‐breaking rate performance (up to 150 C) and cycling stability over 2000 cycles at 10 C with a capacity retention of 97%. Moreover, the SGDIB shows a high capacity retention of ≈84% after 1500 bends and a low self‐discharging voltage loss of 0.0015% per bend after 10 000 bends, suggesting high potential for high‐performance flexible energy‐storage applications.