Recent advancement in metal oxides based fiber-shaped supercapacitors: Materials, fabrication, device assembly, and challenges

With the rapid development of portable, foldable, and wearable intelligent electronic systems, there is an increasing demand for energy storage devices with enhanced flexibility, reduced weight, and high performance. Therefore, the configurations of modern electronics have developed from three-dimensional bulks or two-dimensional thin films to superflexible one-dimensional fibers. Fiber-shaped supercapacitors (FSCs) are widely favored by scholars because of their advantages including quick charge/discharge, high power density, excellent cycle stability, portability, light weight, outstanding flexibility, weavability and favourable compatibility with human body. The energy storage performance of FSCs heavily relies on the fiber electrode materials. Among various electrode materials, metal oxides are widely researched by virtue of earth abundance, low cost, ease of preparation, environmental benignity, tunable nanostructures, and more importantly, ultrahigh theoretical specific capacitance. This article firstly comprehensively reviews the main research progress in the current development and application of high-performance metal oxides based FSCs from the design of active materials, configuration of devices, and the investigation of energy storage properties investigation. Meanwhile, the main issues severely restricting the performance improvement of metal oxides based FSCs are discussed, and the corresponding ideas and the specific methods to address these issues are discussed. Secondly, the influences of different types of fiber-shaped substrates, electrolytes as well as assembly methods on the performance of metal oxides based FSCs are also discussed. Ultimately, a brief conclusion is made, accompanied by comments on the future technological development directions in the field of metal oxides based FSCs.