Recently, fiber/yarn-based energy-storage systems have attracted enormous attention due to their remarkable promises in smart textiles and high-tech sportswear etc., mainly as more pliable energy-storage units being truly “wearable”. Scalable, inexpensive manufacturing processes that produce yarns capable of storing energy are required for new breakthroughs within the wearable electronics sector. For example, US Army is looking for the manufacturing processes capable of producing kilometers of energy-storage yarns that retain desirable mechanical attributes and can be knitted or woven into wearable fabrics. However, so far such processes are still missing. Current technologies include modified textile yarns, composite yarns containing metal wires, polymers, carbon nanotubes (CNTs), metal oxides, and conductive carbon yarns etc. However, several issues exist in current systems, including the biosafety of CNTs, the weight and corrosion of metal wires, and long-term stability of conductive polymers. These issues need to be addressed before they can be employed for practical use.

Here we introduce a unique process of making graphitic yarns (yarns made of graphitic carbon flakes) that has attracted enormous attention internationally. Yarns made of graphite flakes are lighter and more corrosion-resistive than metal wires, and more stable in electrical conductivity than polymers. More importantly, graphite flakes are generally considered to be biofriendly, since they have been used as the major component in pencils for decades. Furthermore, the process of making graphite fibers has several advantages: 1) large-scale availability of the wet-spinning dope, which is graphite oxide dispersions in water; 2) fiber/yarn precursors labile for various chemical/physical modifications; 3) graphite used as the major precursor, which is low cost and abundant in nature; 4) several prototypes have been demonstrated. This talk will introduce our recent research on process engineering and chemical modification of the detailed yarn structures for high energy density and mechanical flexibility.