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Название: Flexible Supercapacitors
Автор: Группа авторов
Издательство: John Wiley & Sons Limited
Жанр: Физика
isbn: 9781119506157
isbn:
Design of the wave shaped electrode is also an efficient way to obtain a stretchable MSC arrays. Our group proposed a 3D print assisted technology to assembled MWCNT/PANI electrode based stretchable MSC array, as illustrated in Figure 2.10 [72]. Figure 2.10a displayed the fabrication procedures. In details, we used 3D printer to prepare a photosensitive resin‐based mold with a convex wavy electrode. Next, this convex wavy channel was transferred to PDMS film. Then 50 nm of Au film PDMS was sputtered on the surface of PDMS as the current collector. MWCNT/PANI electrode and polyvinylidene fluoride (PVDF) was mixed together to form an adhesive slurry, which was then injected to the concave wavy electrode. After coating the PMMA‐PC‐LiClO4 gel electrolytes, the MSC array was prepared. The initial specific area capacitance calculated from CV curves was 44.13 mF cm−2 for the single MSC without applied strain, which showed negligible difference under various strain ranging from 0% to 40%. The maximum energy density was 0.004 mWh cm−2 at power density of 0.07 mW cm−2. Moreover, the fabricated MSC device showed an excellent cycling stability with capacitance retention of 87% even after 20 000 charge‐discharge cycles. Figure 2.10b showed the optical images of the stretchable MSC array and rolled up devices. The MSC arrays were connected as 4S (series) + 2P (parallel), so it can be charged to 3.2 V. During the test, we found after charging, the MSC arrays can maintain at 1.8 V for more than 20 000 seconds, which could provide a stable power to light a LED (Figure 2.10c). Even after 20 minutes, the LED could work normally. Significantly, the brightness of the LED didn't change after three days under air ambient conditions because of the air‐stable gel electrolyte and encapsulation of the PDMS. Figure 2.10d depicted the normalized capacitance (C/C0) of the device under different deformation, respectively. The retention of the capacitance was kept nearly 100% under stretching, twisting, crimping as well as winding, confirming the electrochemical stability of the MSC arrays, which is a promising candidate for powering other stretchable electronics.
Figure 2.8 (a) Schematics of the fabrication procedures for a MWNT/Mn3O4 based planar stretchable MSC. (b) The encapsulation of the MSC. (c) The stretchable MSCs array with embedded liquid metal interconnections. (d) CV curves of the MSC array measured under different types of deformations.
Source: Reproduced with permission [2]. © 2015, The Royal Society of Chemistry.
Figure 2.9 (a) Schematics of fabricating a stretchable MSC array on a PDMS substrate with serpentine interconnects. (b) Photographs of the μ‐LEDs lighting test under bent and 30% stretched state.
Source: Reproduced with permission [39]. © 2013, American Chemical Society.
Figure 2.10 (a) Schematics of the fabrication procedures of the stretchable MSC arrays. (b) Optical images of the stretchable MSC array under different types of deformations. (c) Real‐time optical images of LED powered by MSC array. (d) normalized capacitance (C/C0) measured before and after deformation, respectively.
Source: Reproduced with permission [72]. © 2017, Wiley‐VCH.
2.2.3 3D Stretchable SCs
The stretchability of 3D stretchable SCs are typically achieved by the configuration design, such as 3D cellular and pyramid structure that omits the utilization of elastic substrate, which is quite different with the strategy toward 1D fiber SCs and 2D planar SCs. Kirigami or patterning‐based editable technique is always employed to assemble the 3D stretchable SCs. Recently, many efforts have been devoted to design the 3D stretchable SCs, which can be divided into two types: cellular structure and editable SCs. The first one is to realize stretchability through cellular electrodes or embedding MSC arrays into a cellular structured elastic substrate. The later one represents the SCs devices arbitrary shape, which can be adjusted according to the demand of wearable electronics.
2.2.3.1 Cellular Structure
In nature, many animals like the North American elk or bird have a cellular bone that provides large deformations under attacking or during flying. Inspired by the biological materials, cellular structure is introduced to stretchable SCs because it can resist a broad spectrum of deformations including bending and stretching. A typical work has been reported by Peng's group, as shown in Figure 2.11a–c [40]. Figure 2.11a displayed the optical images of the stretchable cellular CNT film under increasing strain. The cellular CNT film was synthesized as follows: first, a paper mask with exposed cellular pattern was employed to coat a cellular catalyst in the silica wafer, then the CNT film was prepared by CVD on patterned catalyst covered silica wafer, after pressing and peeling off, the cellular CNT film was finally obtained, which could be stretched by 150%. Afterwards, a sandwiched stretchable SCs with two cellular CNT films separated by PVA/H3PO4 gel electrolyte was assembled. The electrochemical performance was also carried out in Figure 2.11b. The fabricated stretchable SCs showed a specific capacitance of 42.4 F g−1 with the electrode thickness of 38.3 μm. The identical CV curves for 0–140% strain demonstrated the excellent stability of the cellular stretchable SCs. The high specific capacitances can be reserved 98.3% after stretching by 140% for 3000 cycles. Figure 2.11c depicted a watch strap powered by the stretchable SCs that accommodate the deformation of the arm size, suggesting a novel class of possible designs for 3D stretchable SCs.