Printable magnesium ion quasi-solid-state asymmetric supercapacitors for flexible solar-charging integrated units

Abstract

Wearable and portable self-powered units have stimulated considerable attention in both the scientific and technological realms. However, their innovative development is still limited by inefficient bulky connections between functional modules, incompatible energy storage systems with poor cycling stability, and real safety concerns. Herein, we demonstrate a flexible solar-charging integrated unit based on the design of printed magnesium ion aqueous asymmetric supercapacitors. This power unit exhibits excellent mechanical robustness, high photo-charging cycling stability (98.7% capacitance retention after 100 cycles), excellent overall energy conversion and storage efficiency (ηoverall = 17.57%), and outstanding input current tolerance. In addition, the Mg ion quasi-solid-state asymmetric supercapacitors show high energy density up to 13.1 mWh cm−3 via pseudocapacitive ion storage as investigated by an operando X-ray diffraction technique. The findings pave a practical route toward the design of future self-powered systems affording favorable safety, long life, and high energy.

An Efficient Ultra‐Flexible Photo‐Charging System Integrating Organic Photovoltaics and Supercapacitors

“…Compared with the most recent reported results, we enhanced the performance by 15% while reducing the device thickness to 1/8, through integrating flexible OPVs with a CNT/polymer‐based supercapacitor on a 1‐µm‐thick ultrathin substrate ( Table 1 ; Figure S13, Supporting Information). [ 21 ]…”

“…Additionally, the calculation could explain some results in the literature, such as the poor performance of systems that have a low total efficiency despite utilizing high‐efficiency solar cells, and systems that show a huge deviation (over 100%) of the highest total efficiencies under different light illuminations, as the highest point varies with time even for the same device. [ 21 ] To address the concerns of the slight difference in calculation, we have calculated the total efficiency from one of the discharge curves after photo‐charging for 600 s at 50% light illumination (with a highest total efficiency of 5.91% at 533 s in the profile) (Figure S15, Supporting Information). The total efficiency of the calculated value based on the real‐time voltage (charge energy) is 5.61% on the profile at 0.734 V in Figure 4d.…”

“…The power output is improved while device thickness is reduced, which ensures sufficient lightweight and flexibility. [ 12–21 ] Fiber‐shaped wearable devices were able to deliver a high power conversion efficiency (PCE) of 9.5% in the solar cell part and a total efficiency of 1.8% with a diameter of 5 mm. [ 15 ] A most recent work reported a flexible planar device integrating a commercialized Si solar cell and a magnesium ion based supercapacitor with high total efficiency of 5.2% and a device thickness of over 400 µm, retaining 80% efficiency after 100 bending cycles.…”

“…[ 15 ] A most recent work reported a flexible planar device integrating a commercialized Si solar cell and a magnesium ion based supercapacitor with high total efficiency of 5.2% and a device thickness of over 400 µm, retaining 80% efficiency after 100 bending cycles. [ 21 ]…”

“…Compared with the most recent reported results, we reduced the device thickness to 1/8 while improving the total efficiency by 15%. [ 21 ] Integrating flexible OPVs with a carbon nanotube (CNT)/polymer‐based supercapacitor on a 1‐µm‐thick ultrathin substrate enabled such high performance and thinness simultaneously. The ultrathin device also delivered superior 94.66% efficiency retention after 5000 times bending at a radius ( R ) of around 2 mm, surpassing the performance of other flexible photo‐charging devices.…”