An Overview of Fiber‐Shaped Batteries with a Focus on Multifunctionality, Scalability, and Technical Difficulties

Abstract

active materials, [13,14] have been made. However, 1D fiber-shaped batteries offer many intriguing features and promising advantages over the conventional bulky or planar structure batteries: 1) fiber-shaped batteries exhibit high compatibility with the current textile industry. Yarn is an essential element of current fabrics, and fiber-shaped batteries can be considered as functional yarn and woven/knitted into an energy textile. 2) The fabric woven/ knitted from fiber-shaped batteries can be air permeable, which solves the problem that most planar structure batteries possess a leather-like feature impermeable to air. 3) Fiber-shaped batteries can be used to fabricate various flexible power sources with unbeatable flexibility, compatibility, and miniaturization potential, providing diverse possibilities.However, the fiber shape adversely results in a few persistent disadvantages: 1) high internal resistance. The long and thin structure of fiber-shaped batteries results in a very high internal resistance, especially considering that a piece of energy storage fabric may be woven from hundreds of meters of fiber-shaped batteries. 2) Difficult fabrication. Short circuiting must be very carefully avoided during fabrication with the long and thin electrode adopted. 3) Difficult set up of the separator. Most of the current reports used a gel electrolyte as the separator. However, considering practical applications, a specific separator cannot be avoided. Setting up a separator film between two long and thin electrodes is much more difficult than setting up a separator film between two planar structured electrodes. 4) Difficult encapsulation. While most of the current reports did not encapsulate the fiber-shaped battery, encapsulating a long and thin device is clearly difficult. 5) Difficult minimization of the thickness. A battery is an electrochemical device with an electrolyte, a separator and two electrodes. With this complicated structure, the current fiber-shaped batteries are usually much thicker than normal yarns. 6) Unsatisfactory mechanical performance of fiber-shaped batteries for weaving with a machine. The tensile strength and surface friction of fiber-shaped batteries are very different from those of traditional yarns. 7) Difficult achievement of yarn texture. With or without encapsulation, fibershaped batteries possess the texture of plastic wire instead of soft and multistrand yarn. These major problems, together with other minor issues, will be further discussed in detail in Section 7.Flexible and wearable energy storage devices are receiving increasing attention with the ever-growing market of wearable electronics. Fiber-shaped batteries display a unique 1D architecture with the merits of superior flexibility, miniaturization potential, adaptability to deformation, and compatibility with the traditional textile industry, which are especially advantageous for wearable applications. In the recent research frontier in the field of fiber-shaped batteries, in addition to higher performance, advances in mult...

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