Atomic Modulation of 3D Conductive Frameworks Boost Performance of MnO₂ for Coaxial Fiber-Shaped Supercapacitors

Coaxial fiber-shaped supercapacitors are a promising class of energy storage devices requiring high performance for flexible and miniature electronic devices. Yet, they are still struggling from inferior energy density, which comes from the limited choices in materials and structure used. Here, Zn-doped CuO nanowires were designed as 3D framework for aligned distributing high mass loading of MnO₂ nanosheets. Zn could be introduced into the CuO crystal lattice to tune the covalency character and thus improve charge transport. The Zn-CuO@MnO₂ as positive electrode obtained superior performance without sacrificing its areal and gravimetric capacitances with the increasing of mass loading of MnO₂ due to 3D Zn-CuO framework enabling efficient electron transport. A novel category of free-standing asymmetric coaxial fiber-shaped supercapacitor based on Zn_0.11CuO@MnO₂ core electrode possesses superior specific capacitance and enhanced cell potential window. This asymmetric coaxial structure provides superior performance including higher capacity and better stability under deformation because of sufficient contact between the electrodes and electrolyte. Based on these advantages, the as-prepared asymmetric coaxial fiber-shaped supercapacitor exhibits a high specific capacitance of 296.6 mF cm^-2 and energy density of 133.47 μWh cm^-2. In addition, its capacitance retention reaches 76.57% after bending 10,000 times, which demonstrates as-prepared device's excellent flexibility and long-term cycling stability.