Watchband‐Like Supercapacitors with Body Temperature Inducible Shape Memory Ability

Abstract

shopping, detecting body-health, and so on. Nowadays, many major companies are working on exploring more functions on smart watches. In view of diverse functions of smart watches, there are increasing demands on their corresponding energy storage devices with high energy and/or power supply ability. [9][10][11][12][13] However, the energy storage devices are commonly placed in the watches with very small volume, which seriously limit their current energy storage ability and the future boost space. As we know, watchband is an important part of a watch and it plays the fixation function of the watch with a human wrist. Therefore, it can be imagined that, if the watchband had energy storage function, it might meet energy and/or power demands for the smart watches. Taking this into account, such smart watchband should have the right characteristics of flexible energy storage devices, including outstanding electrochemical performance, excellent flexibility, and good performance reliability while bending. In addition, good biocompatibility is a requirement for its practical application because of its direct touch with human skin.Supercapacitors are important energy storage devices, and they have attracted great attention for wearable electronic equipment due to their high power delivery ability, long cycle life, good safety as well as simple manufacturing. [14][15][16][17][18][19][20][21] Here, we demonstrate a new design and fabrication of flexible asymmetric supercapacitors with a smart "watchband-like" function, using reduced graphene oxide (rGO) coated on TiNi alloy (TNA) flake as the negative electrode, MnO 2 deposited on ultrathin Ni foil as the positive electrode, and aqueous or ion liquid-based gel electrolyte as the separator. TNA is a shape memory alloy (SMA) which can "remember" a presupposed shape at high temperature and it is free to bend and can hold the corresponding bending-shape below its phase transition temperature (PTT), and it can restore to the presupposed shape when the temperature is higher than its PTT. [22][23][24][25] In our study, as-made supercapacitors are able to possess excellent electrochemical capacitive properties, maintain the inherent characteristics of SMA (flexibility and shape recovery ability), and have outstanding electrochemical performance reliability while bending. Interestingly, because the PTT of TNA we used is 15 °C, the human skin temperature can directly actuate the shape recovery of the devices. Specifically, we use such a shape Smart watches have gained worldwide popularity because they can integrate diverse functions all in one. However, their energy storage devices currently being used are placed in the watches, and this design seriously limited the energy support ability and the future boost space. Herein, for the first time, a strategy to integrate energy storage device with watchband is put forward, which is realized by the preparation of watchband-like solid-state supercapacitors using graphene coated on TiNi alloy flake as the negative electrode, ultrathin MnO ...

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“…Reproduced with permission. [109] Copyright 2016, Wiley. c) CV curves of the SMSCs before and after shape restoration.…”

“…Yan et al reported a smart design for a watchband-like supercapacitor based on a TiNi alloy, with a shape memory ability inducible by body temperature (Figure 6a). [109] The shape-memory TiNi alloy is renowned to its outstanding flexibility, stability and biocompatibility, and its shape restoration is driven by the reversible crystalline phase transformation between martensite and austenite triggered by heat. For device assembly, reduced graphene oxide (rGO) coated on TiNi alloy (TNA) flake was used as the negative electrode, while MnO 2 deposited on ultrathin Ni foil served as the positive electrode.…”

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“…e,f) Reproduced with permission. [172] The asymmetric supercapacitor consisted of reduced graphene oxide on a shapememory TiNi foil as negative electrode and MnO 2 onto a Ni film as positive electrode, showing stable performance under static bending at different angles and dynamic shape-memory restoration bending (Figure 19e). g-i) Reproduced with permission.…”

“…In these cases, the shape restoration is not appropriate to repair failures. [172] Copyright 2016, John Wiley and Sons. Thanks to healable materials, a self-healing symmetric supercapacitor has been achieved by using healable materials as substrates to disperse Figure 19.…”