Novel Synthesis of Copper Nanowires and Hybrid Nanocomposites with Carbon for Functional Electrodes

Abstract

As a new type of promising conductive nanomaterials, copper nanowire (Cu NW) and their nanocomposites have been widely investigated for various functional conductive electrodes, due to their solution-process ability, low cost, high conductivity and excellent flexibility. Compared with general nano-shapes, such as sphere, cube and plate, the Cu NWs have many unique properties, because of their unique one dimensional structure with a high aspect ratio. In this work, our research has primarily focused on the Cu NWs and their nanocomposites synthesis with shape control and special electrode applications for next generational electronics. Firstly, a whole manufacturing process of the curved Cu NWs (CCNs) based flexible transparent conductive electrode (FTCE) with all solution process was introduced as an alternative for Indium tin oxide (ITO), due to their excellent opto-electrical property and flexibility. Although a traditional transparent electrode of ITO has an outstanding opto-electrical performance, as a ceramic material, the brittleness is a critical limitation to apply for various flexible devices. Interestingly, the highly purity and good quality CCNs are designed and synthesized by a binary polyol co-reduction method. In addition, a meniscus-dragging deposition method is used to uniformly coat the well-dispersed CCNs on the glass or polyethylene terephthalate (PET) substrate with vacuum-free and transfer-free conditions. Furthermore, networking of the CCNs was achieved by a solvent-dipped annealing method to fabricate the FTCE at the low temperature of 50 °C. The CCNs thin film on PET substrate exhibited high transparency (86.62% at 550 nm), low sheet resistance (99.14 Ω·□–1), and excellent flexibility and durability (R/R0 < 1.05 at 2000 bending, 5 mm of bending radius). Secondly, we introduce an all-solution fabrication of the CCNs-based FTCEs utilizing a combination of self-designed innovative techniques, such as multi-polyol synthetic method, meniscus-dragging deposition method, polyurethane (PU)-stamped patterning method, solvent-dipped welding method and PU-embedded transfer method. These suggested methods effectively solved the technical problems of the high-cost fabrication, the low robustness, the high roughness and the difficulty of patterning. As a result, the CCNs thin film partially embedded into PU matrix exhibited excellent opto-electrical performance (Rs = 53.48 Ω·□–1 at T = 85.71%) and high mechanical stabilities (R/R0 < 1.02 at 1,000th bending and R/R0 < 1.10 at 10th tape peeling) with low surface roughness (Rrms = 14.36 nm). Thirdly, the reduced graphene oxide (RGO) nanosheets bridging oriented copper NWs were introduced for flexible, annealing-free and air-stable electrode. The RGO nanosheets connecting the Cu NWs not only provided conductive pathways for electron transfer but also acted as a protective layer of oxidation on contact points. As a result, the composite film exhibits a low sheet resistance (0.808 Ω·□–1) and high flexibility (1,000th bending) without considerable change over 30 days. Furthermore, the Cu NW-RGO composites can be filtered on polyester cloth as a lightweight wearable conductor with high durability and simple process-ability, which are highly promising in kinds of electronic devices. Finally, the novel 3-D Cu NW-MWCNT composites were introduced as a promising battery anode for fast charge-discharge lithium ion battery (LIB). When composite film formed, both Cu NWs and MWCNT as the highly conductive 1-D nanomaterials present tremendous advantages to be applied to the current collector and active materials for LIBs, because their high aspect ratio and large surface areas induce better transport for electrons and ions. As an advanced anode for LIBs, the Cu NWs-MWCNT composite film exhibited low sheet resistance and excellent stability with high flexibility. The 3-D porous architecture of Cu NWs is strongly contact with the MWCNTs leads to the improvement of the LIB performances. Furthermore, both half cell and full cell showed high specific capacities (466 mAh·g–1 and 113 mAh·g–1 at 0.2 C) with a high columbic efficiency, even operated at a high current (215 mAh·g–1 and 48 mAh·g–1 at 5 C). When applied for flexible LIBs, the specific capacity still remained 92.8% after bending 1,000 cycles.