Synthesis Of Ag_0.68V₂O₅and Ferrum-based Micro/Nanocomposites And Their Applications In Lithium Ion Battery

In this paper, we synthesized a series of metal compound nanocrystals, and some composites of carbonaceous materials and metal compound nanocrystals through solvothermal reactions in a low temperature autoclave and solid-phase reactions in a high temperature autoclave. We selected several composite materials as anode materials for lithium ion batteries, and investigated their electrochemical performance for lithium storage. The main points are summarized as follows:1. We report a facile room-temperature approach for GO-and RGO-wrapped Fe2O3nanocrystals. In the assembly processes, Fe2O3nanoparticles could be positively surface charged according to Fajans rule without any other molecular linkers assistant, and the overall assembly process can be accomplished in only several minutes through the Colloidal Coagulation Effect (CCE). This work not only successfully extended the classical CCE to rationally control the assembly of nanocrystals on graphene, but also realized different densities of Fe2O3nanoparticles distributed uniformly on GO/RGO sheets. When as-prepared Fe2O3/RGO is evaluated for its lithium storage properties, this composite manifests improved capacity retention compared to that of bare Fe2O3nanoparticle. Interestingly, a simple extension of this method yields GO-and RGO-wrapped CO3O4, SnO2, Ni(OH)2, Y(OH)CO3composite materials, and even Fe2O3-SnO2/GO multiphase nanostructures. Furthermore, the pre-select nanoscale structure of these crystals remains unchanged after the assembly process, which is the key to materials whose properties are closely related to their morphologies in both fundamental studies and technological applications. Our graphene-wrapped method should pave an alternative way for the design and synthesis of graphene-based composites aiming at special applications.2. Graphene-encapsulated α-Fe2O3nanorice (GE-FN) has been facilely fabricated via a solution-mixing method at room temperature. The Fe2O3nanorice with an average of～350nm was uniformly wrapped in the graphene sheets. As an anode material for rechargeable lithium batteries, this GE-FN composite exhibits enhanced cyclability and rate performance compared with free α-Fe2O3nanorice. Even after500cycles, it still delivers a capacity over1000mA h g-1. The morphology of the active materials after the cycling process was firstly investigated by transmission electron microscopy (TEM), and found that the bare α-Fe2O3nanorice agglomerated severely, while the α-Fe2O3nanorice encapsulated by the graphene sheets could keep their pristine morphology well and almost isolate from each other after500cycles.3. Carbon-coated a-FeSe nanoparticles in an average size of200nm have been prepared by a facile one-pot reaction. As an anode material for lithium batteries, the core-shell a-FeSe@C composites showed a discharge plateau at1.5V, which could effectively avoid the formation of the lithium dendrites and the solid-electrolyte interface layer. They delivered a sustainable reversible capacity of340mAh g-1after40cycles, which is about twice as much as that of the Li4Ti5O12(175mAh g-1), thereby indicating its promising applications for lithium storage.4. Peony-like Ag/Ago.68V205hybrid assembled from nanosheets with the thickness of40nm was synthesized through a one-pot hydrothermal approach from vanadium pentoxide (V2O5), oxalic acid (H2C2O4), and silver nitrate (AgNO3) at180℃for24h. Study shows that the hybrid exhibits high performance as both anode (firstly studied) and cathode materials for rechargeable lithium batteries. Electrochemical measurements revealed that the as-prepared Ag/Ago.68V20s hybrid displayed excellent cycling stability, especially as an anode material. The resulting anode retains100%of the initial capacity after1000times under the current density of400mA g-1. This phenomenon may be attributed to the electron conductivity improvement by the existence of metallic silver in the hybrid, and the convenient access to lithium ion ingress/egress by the unique structure.