Karthikeyan Gopalsamy

Coaxial wet-spun yarn supercapacitors for high-energy density and safe wearable electronics

Yarn supercapacitors have great potential in future portable and wearable electronics because of their tiny volume, flexibility and weavability. However, low-energy density limits their development in the area of wearable high-energy density devices. How to enhance their energy densities while retaining their high-power densities is a critical challenge for yarn supercapacitor development. Here we propose a coaxial wet-spinning assembly approach to continuously spin polyelectrolyte-wrapped graphene/carbon nanotube core-sheath fibres, which are used directly as safe electrodes to assembly two-ply yarn supercapacitors. The yarn supercapacitors using liquid and solid electrolytes show ultra-high capacitances of 269 and 177 mF cm−2 and energy densities of 5.91 and 3.84 μWh cm−2, respectively. A cloth supercapacitor superior to commercial capacitor is further interwoven from two individual 40-cm-long coaxial fibres. The combination of scalable coaxial wet-spinning technology and excellent performance of yarn supercapacitors paves the way to wearable and safe electronics.

Graphene fiber-based asymmetric micro-supercapacitors

Fiber-based micro-supercapacitors (F-mSCs) are new members of the energy storage family, which facilitate SCs with flexibility and expand their application to fields such as tiny, flexible and wearable devices. One of the biggest challenges for F-SCs is to enhance the energy density (E) and keep the flexibility at the same time. Here, for the first time we assembled a type of fiber-based asymmetric micro-supercapacitors (F-asym-mSCs) with two different graphene fiber-based electrodes. The excellent electrochemical performances (59.2 mF cm−2 and 32.6 mF cm−2) of both electrodes offered a chance to achieve high performance two-ply F-asym-mSCs. The potential window of F-asym-mSCs was expanded to 1.6 V, and both the area energy density (EA: 11.9 μW h cm−2) and the volume energy density (EV: 11.9 mW h cm−3) are the highest E ever reported in F-SCs. The F-asym-mSCs exhibit good cycling stability with a 92.7% initial capacitance retention after 8000 cycles and can be integrated into a fiber-like device to realize the flexibility of fibers.

Flexible high performance wet-spun graphene fiber supercapacitors

We have explored a new method to produce flexible and all-solid-state graphene fiber supercapacitors (GFSs) from wet-spun graphene fibers. The GFSs exhibited high capacitance (3.3 mF cm−2) and good stability (almost no changes occur after 5000 charge cycles and bending cycles). Moreover, we decorated GFSs with polyaniline nanoparticles and the resulting pseudocapacitors exhibited a capacitance of 66.6 mF cm−2.

A novel wet-spinning method of manufacturing continuous bio-inspired composites based on graphene oxide and sodium alginate

Nacre is a lightweight, strong, stiff, and tough material, which makes it a mimicking object for material design. Many attempts to mimic nacre by various methods resulted in the synthesis of artificial nacre with excellent properties. However, the fabrication procedure was very laborious and time-consuming due to the sequential steps, and only limited-sized materials could be obtained. Hence, a novel design enabling scalable production of high-performance artificial nacre with uniform layered structures is urgently needed. We developed a novel wet-spinning assembly technique to rapidly manufacture continuous nacremimic graphene oxide (GO, brick)-sodium alginate (SA, mortar) films and fibers with excellent mechanical properties. At high concentrations, the GO-SA mixtures spontaneously produced liquid crystals (LCs) due to the template effect of GO, and continuous, 6 m long nacre-like GO-SA films were wet-spun from the obtained GO-SA liquid crystalline (LC) dope with a speed of up to 1.5 m/min. The assembled macroscopic GO-SA composites inherited the alignment of the GO sheets from the LC phase, and their mechanical properties were investigated by a joint experimental-computational study. The tensile tests revealed that the maximum strength (σ) and Young’s modulus (E) of the obtained films reached 239.6 MPa and 22.4 GPa, while the maximum values of σ and E for the fibers were 784.9 MPa and 58 GPa, respectively. The described wet-spinning assembly method is applicable for a large-scale and fast production of high-performance continuous artificial nacre.

MXene/graphene hybrid fibers for high performance flexible supercapacitors

Two dimensional MXene materials have demonstrated attractive electrical and electrochemical properties for various applications, particularly in energy storage, benefiting from their intrinsic 2D atomic thick topological structures. However, assembling MXene into macroscopic fibers with regular alignment still remains a huge challenge, inherently due to the insufficient interlaminar interaction between MXene sheets and the lack of well-developed assembling techniques. Herein, we report a wet-spinning assembly strategy for the continuous fabrication of MXene-based fibers through a synergistic effect between graphene oxides liquid crystals and MXene sheets. MXene sheets are orderly aligned between graphene oxides liquid crystalline templates and assembled into hybrid fibers with the highest MXene mass ratio achieving 95 w/w%. An excellent overall fiber electrical conductivity (2.9 × 104 S m−1) and superior volumetric capacitance (586.4 F cm−3) of the integrated fiber-constructed supercapacitor exceeding those of neat reduced graphene fibers were achieved.

Wet-spinning of ternary synergistic coaxial fibers for high performance yarn supercapacitors

Graphene/CNTs/35% PEDOT:PSS@CMC (GCP-35@CMC) ternary coaxial fibers were continuously prepared through coaxial wet-spinning technology. The GCP-35@CMC-assembled flexible fiber-shaped supercapacitors (FSCs) exhibited an advanced area specific capacitance (396.7 mF cm−2 at 0.1 mA cm−2) and energy density (13.8 μW h cm−2). This performance was ascribed to the synergistic effect of the well-designed ternary system and its special microstructures.