Duck-Jae You

Novel Synthesis, Coating, and Networking of Curved Copper Nanowires for Flexible Transparent Conductive Electrodes

In this work, a whole manufacturing process of the curved copper nanowires (CCNs) based flexible transparent conductive electrode (FTCE) is reported with all solution processes, including synthesis, coating, and networking. The CCNs with high purity and good quality are designed and synthesized by a binary polyol coreduction method. In this reaction, volume ratio and reaction time are the significant factors for the successful synthesis. These nanowires have an average 50 nm in width and 25-40 μm range in length with curved structure and high softness. Furthermore, a meniscus-dragging deposition (MDD) method is used to uniformly coat the well-dispersed CCNs on the glass or polyethylene terephthalate substrate with a simple process. The optoelectrical property of the CCNs thin films is precisely controlled by applying the MDD method. The FTCE is fabricated by networking of CCNs using solvent-dipped annealing method with vacuum-free, transfer-free, and low-temperature conditions. To remove the natural oxide layer, the CCNs thin films are reduced by glycerol or NaBH4 solution at low temperature. As a highly robust FTCE, the CCNs thin film exhibits excellent optoelectrical performance (T = 86.62%, R(s) = 99.14 Ω ◻(-1)), flexibility, and durability (R/R(0) < 1.05 at 2000 bending, 5 mm of bending radius).

Curved copper nanowires-based robust flexible transparent electrodes via all-solution approach

Curved Cu nanowire (CCN)-based high-performance flexible transparent conductive electrodes (FTCEs) were fabricated via a fully solution-processed approach, involving synthesis, coating, patterning, welding, and transfer. Each step involved an innovative technique for completing the all-solution processes. The high-quality and well-dispersed CCNs were synthesized using a multi-polyol method through the synergistic effect of specific polyol reduction. To precisely control the optoelectrical properties of the FTCEs, the CCNs were uniformly coated on a polyimide (PI) substrate via a simple meniscus-dragging deposition method by tuning several coating parameters. We also employed a polyurethane (PU)-stamped patterning method to effectively produce 20 μm patterns on CCN thin films. The CCN thin films exhibited high electrical performance, which is attributed to the deeply percolated CCN network formed via a solvent-dipped welding method. Finally, the CCN thin films on the PI substrate were partially embedded and transferred to the PU matrix to reduce their surface roughness. Through consecutive processes involving the proposed methods, a highly percolated CCN thin film on the PU matrix exhibited high optoelectrical performance (Rs = 53.48 Ω/□ at T = 85.71%), excellent mechanical properties (R/R0 < 1.10 after the 10th repetition of tape peeling or 1,000 bending cycles), and a low root-mean-square surface roughness (Rrms = 14.36 nm).

Copper nanowire/multi-walled carbon nanotube composites as all-nanowire flexible electrode for fast-charging/discharging lithium-ion battery

A novel lightweight three-dimensional (3D) composite anode for a fast-charging/discharging Li-ion battery (LIB) was fabricated entirely using one-dimensional (1D) nanomaterials, i.e., Cu nanowires (CuNWs) and multi-walled C nanotubes (MWCNTs). Because of the excellent electrical conductivity, high-aspect ratio structures, and large surface areas of these nanomaterials, the CuNW-MWCNT composite (CNMC) with 3D structure provides significant advantages regarding the transport pathways for both electrons and ions. As an advanced binder-free anode, a CuNW-MWCNT composite film with a controllable thickness (∼600 μm) exhibited a considerably low sheet resistance, and internal cell resistance. Furthermore, the random CuNW network with 3D structure acting as a rigid framework not only prevented MWCNT shrinkage and expansion due to aggregation and swelling but also minimized the effect of the volume change during the charge/discharge process. Both a half cell and a full cell of LIBs with the CNMC anode exhibited high specific capacities and Coulombic efficiencies, even at a high current. More importantly, we for the first time overcame the limitation of MWCNTs as anode materials for fast-charging/discharging LIBs (both half cells and full cells) by employing CuNWs, and the resulting anode can be applied to flexible LIBs. This innovative anode structure can lead to the development of ultrafast chargeable LIBs for electric vehicles.

Synthesis of Copper Oxide/Graphite Composite for High‐Performance Rechargeable Battery Anode

A novel copper oxide/graphite composite (GCuO) anode with high capacity and long cycle stability is proposed. A simple, one-step synthesis method is used to prepare the GCuO, through heat treatment of the Cu ion complex and pristine graphite. The gases generated during thermal decomposition of the Cu ion complex (H2 and CO2 ) induce interlayer expansion of the graphite planes, which assists effective ion intercalation. Copper oxide is formed simultaneously as a high-capacity anode material through thermal reduction of the Cu ion complex. Material analyses reveal the formation of Cu oxide nanoparticles and the expansion of the gaps between the graphite layers from 0.34 to 0.40 nm, which is enough to alleviate layer stress for reversible ion intercalation for Li or Na batteries. The GCuO cell exhibits excellent Li-ion battery half-cell performance, with a capacity of 532 mAh g-1 at 0.2 C (C-rate) and capacity retention of 83 % after 250 cycles. Moreover, the LiFePO4 /GCuO full cell is fabricated to verify the high performance of GCuO in practical applications. This cell has a capacity of 70 mAh g-1 and a coulombic efficiency of 99 %. The GCuO composite is therefore a promising candidate for use as an anode material in advanced Li- or Na-ion batteries.

Redox-active ionic liquid electrolyte with multi energy storage mechanism for high energy density supercapacitor

A bimodal redox-active ionic liquid electrolyte for supercapacitors with high energy density was demonstrated. The suggested bimodal electrolyte, which consists of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI) and 1-ethyl-3-methylimidazolium halide (EMI-X, X = Br, I) as a redox active couple, shows the three types of energy storage mechanism: a classical EDL capacitance; a pseudo-capacitance from the redox reaction of halide species, such as bromide and iodide; and an EDL capacitance strongly enhanced by ion size effects. When EMITFSI is mixed with small ions, the thickness of the ionic layer becomes thinner and even more ions are packed into the electrode due to the decrement of excluded-volume effects and the increment of electrostatic interactions. The supercapacitor containing a mixture of EMITFSI and EMI-I showed a considerably high performance with 175.6 W h kg−1 and 4994.5 W kg−1 at 1 A g−1 and excellent cycling stability up to 5000 cycles.