Twisting Carbon Nanotube Fibers for Both Wire‐Shaped Micro‐Supercapacitor and Micro‐Battery

Abstract

Energy storage systems including supercapacitors and lithium ion batteries typically appear in a rigid plate which is unfavorable for many applications, especially in the fi elds of portable and highly integrated equipments which require small size, light weight, and high fl exibility. [1][2][3] As a result, fl exible supercapacitors and batteries mainly in a fi lm format have been widely investigated, while wire-shaped energy storage devices are rare. [ 4 , 5 ] However, compared with the conventional planar structure, a wire device can be easily woven into textiles or other structures to exhibit unique and promising applications. The limitation is originated from the much stricter requirement for the electrode such as a combined high fl exibility and electrochemical property in wire-shaped devices. [ 6 , 7 ] It remains challenging but becomes highly desired to obtain wire-shaped supercapacitors and batteries with high performances.On the other hand, due to the unique structure and remarkable mechanical and electrical properties, carbon nanotubes (CNTs) have been widely studied as electrode materials in conventional planar energy storage devices. [ 8 , 9 ] However, CNTs are generally made in a network format in which the produced charges had to cross a lot of boundaries with low effi ciencies. It is critically important to improve the charge transport in CNT materials. [8][9][10][11][12][13] Herein, we have developed wire-shaped micro-supercapacitors and micro-batteries with high performances by using aligned multi-walled carbon nanotube (MWCNT) fi bers as electrodes. The micro-supercapacitor wire was fabricated by twisting two aligned MWCNT fi bers and showed a mass specifi c capacitance of 13.31 F/g, area specifi c capacitance of 3.01 mF/cm 2 , or length specifi c capacitance of 0.015 mF/cm at 2 × 10 − 3 mA (1.67 A/g). The wire-shaped battery was produced by twisting an aligned MWCNT fi ber and a lithium wire which functioned as positive and negative electrodes, respectively. The specifi c capacity was calculated as 94.37 mAh/cm 3 or 174.40 mAh/g at 2 × 10 − 3 mA. The energy and power densities in both supercapacitors and batteries could be further greatly improved by incorporation of MnO 2 nanoparticles into MWCNT fi bers. For instance, the charge and discharge energy densities achieved 92.84 and 35.74 mWh/cm 3 while the charge and discharge power densities were 3.87 and 2.43 W/cm 3 at 2 × 10 − 3 mA in the wire-shaped micro-battery.Spinnable MWCNT arrays were fi rst synthesized by chemical vapor deposition, and aligned MWCNT fi bers could then be spun from the array with controlled diameters from 2 to 30 μ m and lengths up to 100 m. Figure S1a shows a typical scanning electron microscopy (SEM) image of MWCNT fi ber with uniform diameter of 20 μ m. Figure 1 a further shows that MWCNTs are highly aligned in the fi ber, which enables high tensile strengths up to 1.3 GPa and high electrical conductivities of 10 3 S/cm. Therefore, the MWCNT fi bers had been further used as electrodes to deposit MnO 2 on the MWCN...

Elastomeric and Dynamic MnO2/CNT Core–Shell Structure Coiled Yarn Supercapacitor

“…Nevertheless, most fiber-based supercapacitors (FBSs) simply possess the flexibility with limited tensile strain and stretchability [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16] because they are mostly based on nonstretchable electrodes such as carbon nanotube (CNT) spun yarn, 2-7 graphene fiber, [8][9][10][11][12] carbon fiber, 13,14 and metal wire. 15 This lack of stretchability of these FBSs leads to limitation for more advanced utilization, e.g., as a power source for artificial muscles 17 or wearable devices that are exposed to high strain, especially in the joint part.…”

Fiber‐Type Solar Cells, Nanogenerators, Batteries, and Supercapacitors for Wearable Applications

“…Since LIB contains liquid electrolytes, it should be completely protected when fabricated in the form of fibers for wearable energy storage applications. The active material for the Li‐ion intercalation should be strongly attached to the conductive fiber electrode by physical or chemical methods 111, 112, 113. In addition, as the wearable devices undergo vigorous mechanical motion, all the components should be supportive to endure the mechanical stresses.…”

“…Planar supercapacitors usually have their rear electrode fabricated from metal sheets, foams, papers, or textile substrates 105, 137, 138, 139. In the case of a planar architecture, presence of large area collector electrodes, active materials, conductive additives, and separator membranes results in devices without adequate flexibility, bendability, and air permeability that are necessary for wearable devices 111, 140. The supercapacitors with linear architecture made from fiber electrodes have an interlaced structure, which allows the constituent filaments to move freely relative to each other providing freedom for body movements and permeability to air and moisture 141.…”

In Situ Solution Process for Fabricating Thermally and Mechanically Stable Highly Conductive ZnO-CNT Fiber Composites

“…The use of fiber-shaped materials in flexible, lightweight and portable electronic devices has been extensively explored [1][2][3][4][5][6]. Fiber-shaped materials such as Kevlar [1], metal fibers [2], metal wires [3], carbon fibers [4], carbon nanotubes (CNTs) [5], or graphene [6] fiber have been explored for their utility. Polymer fibers have enabled significant breakthroughs in the fabrication of flexible devices although they tend to provide poor electrical conductivity or insulation properties [7,8].…”

“…The excellent mechanical and electrical conductivity properties [5,10,11] of CNT fibers have been widely studied. Dry or wet spinning processes [12] have been used to spin CNTs into fibers hundreds of meters in length and * corresponding author; e-mail: jrhahn@jbnu.ac.kr a few micrometers in width CNT fibers tend to exhibit relatively low electrocatalytic activities, which presents a significant barrier to their electronic applications.…”