Coaxial fiber-shaped supercapacitors with short charge carrier diffusion paths are highly desirable as high-performance energy storage devices for wearable electronics. However, the traditional approaches based on the multistep fabrication processes for constructing the fiber-shaped energy device still encounter persistent restrictions in fabrication procedure, scalability, and mechanical durability. To overcome this critical challenge, an all-in-one coaxial fiber-shaped asymmetric supercapacitor (FASC) device is realized by a direct coherent multi-ink writing three-dimensional printing technology via designing the internal structure of the coaxial needles and regulating the rheological property and the feed rates of the multi-ink. Benefitting from the compact coaxial structure, the FASC device delivers a superior areal energy/power density at a high mass loading, and outstanding mechanical stability. As a conceptual exhibition for system integration, the FASC device is integrated with mechanical units and pressure sensor to realize high-performance self-powered mechanical devices and monitoring systems, respectively.

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Miniaturized electrochemical energy storage devices (MEESDs) are widely utilized in microelectronic devices because of their lightweight, controllable size and shape, excellent electrochemical performance and flexibility, and high durability. Current strategies, such as electrodeposition, electrospinning, and chemical-vapor-deposition methods, for fabricating MEESDs still encounter the persistent limitations on low fabrication efficiency, tedious preparation procedure, and non-scalability. To address this challenge, the new emerging three-dimensional (3D) printing technology has been developed for customizable MEESDs because of its scalability, low-cost, high manufacturing efficiency, and complexity capability. Among the 3D printing technologies, a direct-ink-writing (DIW) technique with well-controlled geometry and architecture of the electrode structures, is an ideal tool for building high-efficient MEESDs via designing the ink components and regulating the device configurations. In light of this, our Perspective provides fundamental insights into rational printable inks design principles towards high-performance MEESDs. We start the discussion on the design principle of printable inks, and the selection criteria for electrode materials and electrolytes inks. Then, the recent progress in fabricating the high-performance MEESDs via the DIW technology is summarized. Finally, the existing problems and future perspectives on functional MEESDs fabrication are also discussed. We envision that this review serves as the basic design principles of 3D printing ink for the rational design of high-efficient MEESDs.

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