Synthesis And Electrochemical Properties Of Laminated Two-Dimensional Material Composites

In recent years, with the wide popularity of portable power products and the development of electric vehicles, developing high energy density and power density energy, as well as reusable storage devices have attracted wide attention. Among them, lithium ion battery and supercapacitor have high reversible capacity, good cycling stability and high energy density, are the most promising energy storage instruments. In 2011, Queen’s University in Canada reported a concept product called "paperphone" equipment, then, in 2013, Samsung and LG companies introduced flexible smart phones. As a result, flexible electronic communications equipment will be the future trend, which also needs matchable flexible battery. Two-dimensional layered electrode materials with unique lamellar structures, have great application potential in flexible electronic devices. In this study, we developed a facile vacuum filtration method to prepare two-dimensional lamellar composite electrodes and overcome the agglomeration between two-dimensional layered materials. The composites showed improved electrochemical energy storage performance and provide some guidance to flexible energy storage devices.The main research contents are as follows:1. CuO/rGO hybrid lamellar films were fabricated through electrostatic self-assembly and vacuum filtration processes. It is clearly seen that the rGO layers formed a three-dimentional continuous networks, both sides of the rGO are capped with CuO. The hybrid paper was directly used as a free-standing electrode, without adding other conducting additive, or polymer binders. When used as anodes in Li-ion batteries (LIBs), CuO expanded the interlayer spacing between the rGO layers and prevented their agglomeration, which can offer more opportunities for the electrolyte ions to access to the electrochemical active CuO and rGO sheets. Moreover, the combination of rGO and CuO remarkably increased the electrical conductivity and ensure rapid charge transfer and conduction. All the composites exhibit higher Li-ion batteries and supercapacitors performance than the corresponding pure components, as well as good cycling stability.2. This research demonstrates novel flexible Mn3O4/rGO hybrid papers with unique three-dimensional nanoporous networks were fabricated by filtration and a hydrothermal reduction process. The three-dimensional nanoporous networks were generated by the homogeneous intercalation of Mn3O4 nanorods into the lamellar rGO layers, which exhibited excellent mechanical stability and provided electrically conducting channels to promote electrolyte penetration when used as electrodes for Li-ion batteries and supercapacitors. In order to obtain the optimal electrochemical performance, different samples with mass ratios of precursors were fabricated, and the best proportion is 1:1. The prepared MnsO4/rGO hybrid lamellar papers demonstrated excellent cyclic retention with the specific capacity of 669.6 mA h g-1 after 100 cycles in LIBs at the current density of 100 mA/g. Additionally, At the scan rate of 2 mV/s, the three-dimensional porous hybrid Mn3O4/rGO papers also exhibit superior specific capacitance of 204.2 F g-1.3. We developed a general method to directly assemble lamellar composite paper composed of WS2 and graphene oxide nanosheets from their aqueous dispersion through filtration process. After hydrothermal reduction, the flexible lamellar WS2/rGO paper was evaluated as binder-free anodes for Li-ion batteries, which presented a reversible capacity of 697.7 mA h g-1 after 100 cycles at the current density of 100 mA/g. In the uniformly alternated lamellar structures, rGO nanosheets efficiently prevent the restacking of WS2 sheets, increase the conductivity of the electrode, and sustain the volume expansion during Li+ insertion/extraction, which significantly improved the electrochemical performances.4. Hybrid lamellar porous electrodes were successfully fabricated by homogeneously intercalating SWCNT into the lamellar assembled WS2 nanosheets through vacuum filtration. The unique lamellar WS2/SWCNT hybrids were evaluated as electrodes for supercapacitors and Li-ion batteries. As a supercapacitor, the specific capacitance was significantly improved from 67.8 F g’1 of WS2 nanosheets to 240.0 F g-1 of the WS2/SWCNT hybrid films. Furthermore, as an anode for LIBs, this hybrid electrode presented high reversible capacity of 861.6 mA h g-1 after 50 cycles, more than 3 times of pure WS2. Notably, uniformly intercalated SWCNT networks provided electrically conducting channels to promote electrolyte penetration, avoid restacking between the WS2 nanosheets, as well as sustain for the volume variation during the lithiunation and delithulation, resulting significantly improve the electrochemical performances.5. In order to further enhance the capacity of WS2/SWCNT hybrids, a novel ternary WS2/CuO/SWCNT porous laminated hybrids are fabricated with the aid of electrostatic interaction and vacuum filtration. When used as a lithium ion batteries anode, it demonstrates high reversible specific capacity of 962.4 mA h g-1. The thickness of CuO nanosheet is ca.10 nm, which can expand bigger interlayer space between the WS2 sheets than SWCNT, and offer more opportunities for the electrolyte ions to access to the electrochemical active CuO and WS2 nanosheets. Besides, the unique assembled WS2/CuO/SWCNT porous hybrids not only show the improved electrical conductivity, but also provide efficient charge transport channels for electrolyte penetration and sustain for the volume variation during the lithiation and delithiation. CuO has higher theoretical capacity than WS2 and SWCNT, which is beneficial to enhance the specific capacity.6. In order to explore the universal of the filtration method, a two-dimensional layered Ti3C2/carbon nanotubes (CNTs) hybrid thin film is prepared. Ti3C2, a rapidly emerging transition metal carbides recently, but the obtained Ti3C2 layers are usually terminated with F or/and OH groups, which lead to higher diffusion barrier and decreased conductivity. Owing to the excellent conductivity of the CNTs, this unique layered structure provides rapid charge transfer path during the electrochemical reaction, as a LIBs anode, which exhibits higher capacitance and better cycling stability, a reversible capacity of 428.1 mA h g-1 at 0.5 C after 300 cycles, compared with 96.2 mA h g-1 of pure Ti3C2 nanosheets, as well as superior rate capability.