Synthesis And Electrochemical Performance Research Of Metal And Metal Oxides Quantum Dots Based On Graphene Nanosheets

To meet the ever-increasing demand of energy storage devices for high power/energy density, it's urgent to explore high-performance anode materials. Metal oxides?MOs?, such as SnO₂, MnO, Fe₃O₄, have been considered as advanced anode materials, which have a high theoretical capacity(> 900 m Ah g^-1). However, the low diffusion of Li⁺ ions and huge lithiation-induced volume expansion seriously hamper their practical applications. Accordingly, available solutions are exploited to address these issues and mainly focus on two aspects: nanotechnology and composites. 1) Compared to bulks, nanomaterials with ultrasmall size endow a faster Li⁺/electron diffusion and smaller mechanical strain, which could greatly improve the cycle stability. 2) Combining nanomaterials with high conductive materials?such as pyrolytic carbon, graphene? can further increase the electronic conductivity and simultaneously accommodate the unavoidable volume swings during repeated cycling processes. In this work, MOs quantum dots/graphene nanoshheets hybrids?MOs QDs/GNS? were synthesized as anode materials and exhibited excellent lithium storage performance. Various characterizations?such as X-ray diffraction, thermal gravity, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectrometer? and electrochemical measurements?such as cyclic voltammetry, electrochemical impedance spectroscopy and cycling tests? were performed to investigate their components, morphologies, structures and electrochemical performances and reveal the underlying insights for the superior performance of metal oxides QDs/graphene hybrids as anode materials.?1? The well-dispersed SnO₂@C/GNS hybrids were fabricated by one-pot hydrothermal method. Profiting from the unique complex architecture, SnO₂@C/GNS exhibited a high reversible capacity(1100 m Ah g^-1 after 200 cycles) and excellent rate performance(860 m Ah g^-1 at 2.0 A g^-1). Notably,SnO₂ QDs exhibited a high reversibility which contributed a high reversible capacity of 1331 m Ah g^-1. The cooperation of carbon coated SnO₂ QDs with GNS can alleviate the serious volume variation and the agglomeration of SnO₂ as well as enhance the electronic conductivity remarkably. One-pot hydrothermal method with its simplicity and mild condition could make a great contribution to the expanded production of SnO₂-based anode materials.?2? GF-assisted method?Gel-like Film assisted method? was proposed for the first time to synthesis transition metal oxides quantum dots/graphene hybrids. FT-IR, XRD and TEM were performed to illustrate the mechanism of GF-assisted method, which could make great contributions to promote the synthesis and application of metal oxides QDs. Mn O-QDs/GNS and Fe₃O₄-QDs/GNPs were obtained with the help of GF-assisted method and showed superior energy storage performance.In summary, the study of this work is valuable for the research of MOs QDS/GNS hybrids. Firstly, MOs QDs/GNS displayed tremendous application potential in lithium storage. Secondly, the unique structure of quantum dots endow MOs with high reaction activity, which could further illustrated the lithium storage mechanism for metal oxides. Finally, the proposal of one-pot hydrothermal method and GF-assisted method broadens the synthesis system for MOs QDs/GNS.