Chaowei Li

An all-solid-state, lightweight, and flexible asymmetric supercapacitor based on cabbage-like ZnCo2O4 and porous VN nanowires electrode materials

A series of high-performance all-solid-state, lightweight, and flexible asymmetric supercapacitors (ASC) were prepared using cabbage-like ZnCo2O4 as the positive electrode material, porous VN nanowires as the negative electrode material, and flexible carbon nanotube film (CNTF) as the collector. Excellent electrochemical performance was achieved with an areal capacitance of 789.11 mF cm−2 for the positive electrode and 400 mF cm−2 for the negative electrode. The assembled all-solid-state flexible ASC device possessed a specific capacitance of 196.43 mF cm−2, large voltage window of 1.6 V, and a volume energy density of 64.76 mW h cm−3. Moreover, the assembled device exhibited good cycling stability with 87.9% initial capacitance retention after 4000 cycles with the coulombic efficiency remaining close to 100%. In addition, the capacitance retention reached 95.7% after 2000 bending cycles, indicating its good flexible and mechanical stability.

Electrical property enhancement of electrically conductive adhesives through Ag-coated-Cu surface treatment by terephthalaldehyde and iodine

One of the largest obstacles for Ag based electrically conductive adhesives (ECAs), as an alternative for Pb-containing solders in electronic packaging, is that the conductivity of ECAs is lower than that of solders due to the limited physical contact area between/among conductive fillers and the insulated organic lubricant and metal oxide layers on the surface of the conductive fillers. What’s more, the high cost of Ag fillers is also restricting the wide use of Ag based ECAs. In this study, Ag-coated-Cu flakes were chosen as a substitute for Ag flakes to reduce the cost. At the same time, the coating of Cu with an Ag layer could protect the Cu-based fillers from oxidation and corrosion. A mixture of weak reducing agents and substituting agents was selected to treat the Ag-coated-Cu flakes to increase the conductivity of the Ag-coated-Cu based ECAs. During the treatment process, the weak reducing agents can reduce the metal oxides on the filler surfaces, enabling more metallic contacts. Meanwhile, the substituting agents can partially remove or replace the long chain fatty acid lubricants on the metal flakes, improving the electron tunneling between/among neighboring flakes. As such, the multiple effects of the reducing agents and substituting agents can improve the conductivity of the ECAs. By using an appropriate amount of terephthalaldehyde and iodine treated Ag-coated-Cu flakes, the resistivity was reduced to as low as 1.28 × 10−4 Ω cm for the ECA with 75 wt% content of treated fillers, which is comparable to that of commercially available Ag-filled ECAs (×10−4 Ω cm). This work suggests that a surface chemical method can enhance the electrical conductivity of metal filler based ECAs.

Controlled growth of MoS2 nanopetals and their hydrogen evolution performance

Edge-oriented MoS2 nanopetals complexed with basal-oriented MoS2 thin films have been mildly grown through a simple atmospheric pressure chemical vapor deposition (APCVD) process with the reaction of MoO3 and S. Dense nanopetals with hexagonal structures exposed numerous chemically reactive edge sites. The roles of growth temperature, time and S/MoO3 mass ratio have been carefully investigated to tune the morphology and density of the as-grown products. Importantly, the carbon nanotube (CNT) films were used as substrates for growing MoS2 nanopetals. The MoS2/CNT composites, used directly as working electrodes, showed remarkable and stable electrocatalytic activity in the hydrogen evolution reaction (HER), as manifested with a low onset overpotential of ∼100 mV and a small Tafel slope of 49.5 mV per decade. The development of the MoS2/CNT electrode provides a promising way to fabricate other multifunctional electrodes.

Chemical vapor deposition growth of few-layer graphene for transparent conductive films

The layer numbers of graphene for graphene based transparent conductive films are crucial. An appropriate number of graphene layers would provide excellent electrical conductivity along with high transparency. Herein, we demonstrated a facile and scalable technique to grow graphene with controllable layers on copper foil substrates using the etching effect of H2 in atmospheric pressure chemical vapor deposition (APCVD), and studied the influence of H2 etching on the properties of graphene transparent conductive films. The etching of formed multi-layer graphene (MLG, 12–14 layers) for Cu substrates assists the formation of few-layer graphene (FLG, 2–3 layers). These as-obtained graphene can be used as high performance transparent conductors, which show improved tradeoff between conductivity and transparency: the transmittance of 96.4% at 550 nm with sheet resistance of ∼360 Ω sq−1, and the transmittance of 86.7% at 550 nm with sheet resistance of ∼142 Ω sq−1. They could be used as high performance transparent conductors in the future.

Hierarchical ferric-cobalt-nickel ternary oxide nanowire arrays supported on graphene fibers as high-performance electrodes for flexible asymmetric supercapacitors

Fiber-based supercapacitors (FSCs) are new members of the energy storage family. They present excellent flexibility and have promising applications in lightweight, flexible, and wearable devices. One of the existing challenges of FSCs is enhancing their energy density while retaining the flexibility. We developed a facile and cost-effective method to fabricate a highly capacitive positive electrode based on hierarchical ferric-cobalt-nickel ternary oxide nanowire arrays/graphene fibers and a negative electrode based on polyaniline-derived carbon nanorods/graphene fibers. The elegant microstructures and excellent electrochemical performances of both electrodes enabled us to construct a highperformance flexible asymmetric graphene fiber-based supercapacitor device with an operating voltage of 1.4 V, a specific capacitance up to 61.58 mF·cm–2, and an energy density reaching 16.76 μW·h·cm–2. Moreover, the optimal device presents an outstanding cycling stability with 87.5% initial capacitance retention after 8,000 cycles, and an excellent flexibility with a capacitance retention of 90.9% after 4,000 cycles of repetitive bending.

In Situ Generation of Photosensitive Silver Halide for Improving the Conductivity of Electrically Conductive Adhesives

Electrically conductive adhesives (ECAs) can be regarded as one of the most promising materials to replace tin/lead solder. However, relatively low conductivity seriously restricts their applications. In the present study, we develop an effective method to decrease the bulk electrical resistivity of ECAs. KI or KBr is added to replace the lubricant and silver oxide layers on silver flakes and to form photosensitive silver halide. After exposure to sunlight, silver halide can photodecompose into silver nanoparticles that will sinter and form metallic bonding between/among flakes during the curing process of ECAs, which would remarkably reduce the resistivity. The modified micro silver flakes play a crucial role in decreasing the electrical resistivity of the corresponding ECAs, exhibiting the lowest resistivity of 7.6 × 10-5 Ω·cm for 70 wt % loaded ECAs. The obtained ECAs can have wide applications in the electronics industry, where high conductance is required.

High-performance flexible all-solid-state aqueous rechargeable Zn–MnO2 microbatteries integrated with wearable pressure sensors

The ever-increasing demand for smart personal electronics has promoted the rapid development of wearable multiple functionalities integrated configurations. However, it is still a great challenge to realize both high-performance energy storage devices and functional sensors in a single device to obtain a stable, self-powering, multifunctional, miniaturized integrated system. Herein, we report an ultrathin microbattery-pressure sensor integrated system to simultaneously achieve energy storage and pressure detection in a single device. Energy storage is achieved by an in-plane, interdigitated, flexible, all-solid-state, aqueous rechargeable Ni@MnO2//Zn microbattery in a thin polydimethylsiloxane film, using MnO2 nanosheets directly deposited on highly conductive 3D Ni skeletons (Ni@MnO2) as an advanced binder-free cathode. Benefiting from synergy between the high electrochemical performance of MnO2 and the outstanding conductivity of 3D highly conductive Ni skeletons, the assembled Ni@MnO2//Zn microbattery displays a high capacity of 0.718 mA h cm−2 and a correspondingly impressive energy density of 0.98 mW h cm−2. More importantly, the wearable pressure sensor, which is powered by the integrated Ni@MnO2//Zn microbattery, can achieve real-time health monitoring both statically and dynamically. Thus, this work paves the way to develop high-performance, multifunctional, miniaturized integrated configurations for portable and wearable electronics.

3D Printing Fiber Electrodes for an All‐Fiber Integrated Electronic Device via Hybridization of an Asymmetric Supercapacitor and a Temperature Sensor

Abstract Wearable fiber‐shaped electronic devices have drawn abundant attention in scientific research fields, and tremendous efforts are dedicated to the development of various fiber‐shaped devices that possess sufficient flexibility. However, most studies suffer from persistent limitations in fabrication cost, efficiency, the preparation procedure, and scalability that impede their practical application in flexible and wearable fields. In this study, a simple, low‐cost 3D printing method capable of high manufacturing efficiency, scalability, and complexity capability to fabricate a fiber‐shaped integrated device that combines printed fiber‐shaped temperature sensors (FTSs) with printed fiber‐shaped asymmetric supercapacitors (FASCs) is developed. The FASCs device can provide stable output power to FTSs. Moreover, the temperature responsivity of the integrated device is 1.95% °C−1.

Metal–Organic Framework Derived Spindle-like Carbon Incorporated α-Fe2O3 Grown on Carbon Nanotube Fiber as Anodes for High-Performance Wearable Asymmetric Supercapacitors

Iron oxide (Fe2O3) has drawn much attention because of its high theoretical capacitance, wide operating potential window, low cost, natural abundance, and environmental friendliness. However, the inferior conductivity and insufficient ionic diffusion rate of a simple Fe2O3 electrode leading to the low specific capacitance and poor rate performance of supercapacitors have impeded its applications. In this work, we report a facile and cost-effective method to directly grow MIL-88-Fe metal-organic framework (MOF) derived spindle-like α-Fe2O3@C on oxidized carbon nanotube fiber (S-α-Fe2O3@C/OCNTF). The S-α-Fe2O3@C/OCNTF electrode is demonstrated with a high areal capacitance of 1232.4 mF/cm2 at a current density of 2 mA/cm2 and considerable rate capability with capacitance retention of 63% at a current density of 20 mA/cm2 and is well matched with the cathode of the Na-doped MnO2 nanosheets on CNTF (Na-MnO2 NSs/CNTF). The electrochemical test results show that the S-α-Fe2O3@C/OCNTF//Na-MnO2 NSs/CNTF asymmetric supercapacitors possess a high specific capacitance of 201.3 mF/cm2 and an exceptional energy density of 135.3 μWh/cm2. Thus, MIL-88-Fe MOF derived S-α-Fe2O3@C will be a promising anode for applications in next-generation wearable asymmetric supercapacitors.

Rational Design of Hierarchical Titanium Nitride@Vanadium Pentoxide Core–Shell Heterostructure Fibrous Electrodes for High-Performance 1.6 V Nonpolarity Wearable Supercapacitors

Extensive progress has been made in fiber-shaped asymmetric supercapacitors (FASCs) for portable and wearable electronics. However, positive and negative electrodes must be distinguished and low energy densities are a crucial challenge and thus limit their practical applications. This paper reports an efficient method to directly grow TiN nanowire arrays@V2O5 nanosheets core-shell heterostructures on carbon nanotube fibers as nonpolarity electrodes. Benefiting from their unique heterostructure, single electrodes possess high specific capacitances of 195.1 and 230.7 F cm-3 as positive and negative electrodes, respectively. Furthermore, all-solid-state nonpolarity FASC devices with a maximum voltage of 1.6 V were successfully fabricated. Our devices achieve an outstanding specific capacitance of 74.25 F cm-3 and a remarkable energy density of 26.42 mW h cm-3. More importantly, their electrochemical performance changed negligibly regardless of whether the charge-discharge process is in positive or negative direction, indicating excellent nonpolarity. Therefore, these high-performance nonpolarity FASCs pave the way for next-generation wearable energy storage devices.