Self‐Healing and Shape‐Editable Wearable Supercapacitors Based on Highly Stretchable Hydrogel Electrolytes

Abstract Shape editability combined with a self‐healing capability and long‐term cycling durability are highly desirable properties for wearable supercapacitors. Most wearable supercapacitors have rigid architecture and lack the capacity for editability into desirable shapes. Through sandwiching hydrogel electrolytes between two electrodes, a suite of wearable supercapacitors that integrate desirable properties namely: repeated shape editability, excellent self‐healing capability, and long‐term cycling durability is demonstrated. A strategy is proposed to enhance the long‐term cycling durability by utilizing hydrogel electrolytes with unique cross‐linking structures. The dynamic crosslinking sites are formed by quadruple H bonds and hydrophobic association, stabilizing the supercapacitors from inorganic ion disruption during charge–discharge processes. The fabricated supercapacitors result in the capacitance retention rates of 99.6% and 95.8% after 5000 and 10 000 charge–discharge cycles, respectively, which are much higher than others reported in the literature. Furthermore, the supercapacitor sheets can be repeatedly processed into various shapes without any capacitance loss. The supercapacitors exhibit a 95% capacitance retention rate after five cutting/self‐healing cycles, indicative of their excellent self‐healing performance. To demonstrate real‐life applicability, the wearable supercapacitors are successfully used to power a light‐emitting diode and an electronic watch.


Characterization of hydrogels
[1-10] Figure S5. The stress-strain curves of hydrogel-5-8 during a self-healing process. The insets show the optical photographs of the self-healing process including fracture, contact, and self-healing.

Preparation of polyurethane-polycaprolactone (PU-PCL) substrate
The polycaprolactone diol (5 g, 1.25 mmol) was heated under vacuum at 120 o C to remove water until no bubbles were observed. The temperature was cooled to 60 o C, and HDI (0.5628 g, 3.35 mmol), DBTDL (10 mg), and THF (40 mL) were added. The reaction lasted for 24 h under an N 2 atmosphere. BDO (0.18 g, 2 mmol) was then added, and the reaction continued for another 24 h. Next, TEA (0.015 g, 0.1 mmol) was added to the system, and the reaction 5 continued for 12 h to obtain a PU-PCL solution. Under vigorous stirring, the PU-PCL solution was poured into a glass mold, and the solvent was evaporated at room temperature for 12 h to obtain a PU-PCL sheet. The PU-PCL sheets were further dried under vacuum at 60 °C and used as supercapacitor substrates. Figure S6. The synthesis of PU.  The R f and R r of the PU-PCL sheets were calculated according to the following formulas:

Characterization of PU-PCL substrate
, S1 , S2 where ε d,load , ε d , and ε r represent the maximum strain under load, the shape-fixed strain, and the recovered strain, respectively.

Preparation of graphene oxide (GO)
First, 1.0 g graphite and 0.50 g sodium nitrate were inserted into a flask at 0 °C, and 23 mL

Preparation of Supercapacitor
An all-solid supercapacitor was fabricated by sandwiching the hydrogel-5-8 electrolyte 10 The values of the specific capacitance (C sp , F·g −1 ), energy density (E, Wh·kg −1 ), and power density (P, W·kg −1 ) of the supercapacitors were calculated according to the following formulas: , S3 , S4 , S5 ， S6 where I is the response current (A), v is the scan rate (mV/s), V = ΔU is the potential window, and Δt is the discharging time (s). 11 Figure S16. The Ragone plot of energy density and power density of a supercapacitor. Figure S17. (a) The CV curves of supercapacitors during 20 "U" shape-editing cycles. (b) The CV curves of supercapacitors during 10 cutting/self-healing cycles. Figure S18. (a) The Nyquist plot of the original supercapacitor, the supercapacitor after 20 "U" shapeediting and 10 cutting/self-healing cycles. (b) The impedance of the original supercapacitor, the supercapacitor after 20 "U" shape-editing and 10 cutting/self-healing cycles as a function of frequency.
12 Figure S19. (a) Capacitance retention of a supercapacitor after 20 "U" shape-editing during 10,000 charging and discharging cycles. (b) Capacitance retention of a supercapacitor after 10 cutting/self-healing during 10,000 charging and discharging cycles. Figure S20. (a) The GCD measurements for different potential windows at a current density of 5 A·g −1 .