Flexible integrated metallic glass-based sandwich electrodes for high-performance wearable all-solid-state supercapacitors

The design and preparation of nanoporous metal (NPM)/metallic oxides (or hydroxides) electrodes with good flexibility as well as high energy storage performance has become a great challenge for applications in wearable electronic products. Herein, we report a novel strategy to synthesize flexible nickel oxide/hydroxide coated nanoporous nickel (np-NiOxHy@Ni) electrode containing metallic glass (MG) interlayer (np-NiOxHy@Ni/MG/np-NiOxHy@Ni sandwich) by one-step dealloying of Ni40Zr20Ti40 MG ribbons. Benefiting from the ductile MG interlayer, the sandwich-like electrode presents excellent flexibility, which has not been reported for other dealloyed porous ribbons. Electrochemical measurements show that the electrode is essentially a battery-type material while it also exhibits pseudocapacitive behavior. Due to an integrated sandwich structure and np-NiOxHy@Ni shell@core network, the electrode displays an enhanced capacitance of 778 F cm−3 at 1 A cm−3 in KOH solutions (achieves 3536.01 F cm−3 when just considering the volume of the dealloyed layer) and a remarkable rate performance (80.3 % retention when the current density increase by 128-fold), as well as an outstanding cycle stability (100 % capacitance retention after 8000 cycles). Furthermore, the cable-like all-solid-state flexible supercapacitor (CAFS) device assembled by this flexible electrode can bear a bending of 0–180° without significant performance change. The highest volumetric energy density of 28.52 mW h cm−3 with a power density of 0.10 W cm−3 is obtained, which far exceeds commercially available supercapacitors (<1 mW h cm−3) and thin-film lithium batteries (0.3–10 mW h cm−3). Moreover, a wearable system by the integration of the CAFS device with an electronic watch is achieved, which amazingly runs for more than 25 min. The introduction of MG into NPM composites greatly improves the flexibility, which harnesses the promise for applying dealloyed materials in advanced wearable devices.