Freestanding ultralight metallic micromesh for high-energy density flexible transparent supercapacitors

Abstract

Flexible transparent energy storage systems are urgently desirable to power flexible intelligent electronics, but their development is hampered by the inevitable trade-off between optical transparence and areal capacity. Here, we report a freestanding ultralight (0.54 mg cm⁻²) nickel micromesh (NM) with exceptional optoelectronic characteristics (R_s = 0.7 Ω sq⁻¹, T = 92.1%) and outstanding mechanical flexibility for flexible transparent supercapacitors. Based on the developed transparent NM, the positive electrode is further constructed by integrating the highly conductive NM with the high-capacity NiCoP (NM@NiCoP), which achieves a specific capacity as high as 11.1 μAh cm⁻² with a transmittance of 80.2%. Additionally, a flexible transparent negative electrode is also developed by loading ZIF-8 derived nitrogen-doped porous carbon onto NM (NM@NPC). The assembled solid-state flexible transparent asymmetric supercapacitor with an optical transmittance of 67.5% yields a high areal energy density of 8.0 μW h cm⁻² and an extremely stable capacity retention of 97.6% with 50 000 cycles at 10 mA cm⁻² as well as mechanical stability even under harsh bending modes. A controllable and universal approach to conquer the trade-off between the specific energy density and optical transparence of the flexible transparent energy supply units is proposed in this work.