Design,Preparation Of Three-Dimensional Micro-Nanostructure Composites Based On Electrostatic,Coordination And Molecular Self-Assembly And Their Lithium Storage Properties

With the rapid development of industry and economy,energy and environmental issues have become more serious.The increasing demand for energy urgently requires the development of more efficient and more eco-friendly energy conversion and storage systems.Electrochemical energy storage devices characterized by lithium-ion batteries play a major role in both economic and social development,on the other hand it also faces some challenges.As the key component of the lithium-ion battery system,the electrode materials would significant effect on the overall performance of the battery.Based on the structure-rctivity relationship?morphology,structure and performance?of materials,according to the different lithium storage mechanisms of lithium-ion batteries,the design and preparation of micro-nano-structured lithium-ion battery anode materials with high specific capacity and long cycle life have attracted wide attention.According to the theories of electrostatic interaction,coordination and molecular self-assembly,a series of micro-nanostructure composites?such as titanium tin oxide solid solution,nickel/cobalt bicarbonate or basic nickel/cobalt carbonate?with various morphological structures were successfully fabricated.This paper intends to systematically study the design,controllable synthesis and electrochemical performance of the 3D micro-nano structure functional composite materials.The research is focus on unraveling the structure,morphology,composition relationships and developing some novel structure electrode materials with high performance,easy preparation and low cost.The synthesis mechanism and construction strategy of the as-prepared anode materials were explored.The lithium storage mechanism of electrode materials were closely studied by HR-TEM,in-situ XRD and ex-situ XPS.The specific research work is as follows:?1?Controllable synthesis and lithium storage properties and mechanism of 3D nanostructured Ti-Sn-O solid solution/reduced graphene oxide composites(Ti_xSn_1-xO₂/rGO).Nanostructure Ti_xSn_1-xO₂ solid solution composite materials efficiently combine with the mechanical stability of TiO₂ and the high specific capacity of SnO₂on the atom level mixing of Sn and Ti in their oxide states,At the meanwhile avoiding the low capacity and poor cycle life of TiO₂@SnO₂ composite material due to TiO₂phase and SnO₂ phase separation on cycling.However,their metal oxides also have the dark side on Low conductivity and low ion mobility.Based on electrostatic interaction,coordination principle and self-assembly process,a series of Ti_xSn_1-xO₂?0?x?1?solid solution with different sharps wrapped by reduced graphene oxide hybrid nanostructure were successfully fabricated by one-step hydrothermal process and adjusting the total concentration and proportion of titanium-tin metal ions(C_Ti+C_Sn)for lithium ion batteries.In this strategy,K₂TiO?C₂O₄?₂ is used as titanium source,tin tetrachloride(Sn⁴⁺)is used as tin source.Because of the same negative-charged surface,when graphene oxide?GO?and K₂TiO?C₂O₄?₂?PTO?were mixed in aqueous ambience,the TiO?C₂O₄?₂^2-ions were not absorbed onto GO surface by the strong electrostatic repulsion force.In contrast,Sn⁴⁺ions subsequently added that they were easily absorbed onto the GO surface.At the same time,Sn⁴⁺ions were also easily coordinated with the carboxyl groups of PTO species.Interestingly,in this Ti_xSn_1-xO₂/rGO series,the Ti_0.74Sn_0.26O₂/rGO sample exhibited the highest specific capacity of 514 mA h g^-1at 0.1 A g^-1 even after 1000^th cycle?nearly 100%efficiency?.Additionally,the lithium storage mechanism of the as-prepared Ti_xSn_1-xO₂/rGO has been studied via in-situ X-ray diffraction?XRD?measurement for the first time.?2?The morphology-controllable synthesis and lithium storage performance of Ti_0.8Sn_0.2O₂/C micro/nano structure composites via surfactant-assisted.In view of the fact that the electrochemical performance of the Ti_xSn_1-xO₂?0?x?1?solid solution material is best when the ratio of titanium to tin is 4:1.Using PTO as titanium source and stannous chloride(Sn²⁺)as tin source,when the total concentration of metal ions(C_Ti+C_Sn)is 0.4 M,based on the coordination principle and molecular self-assembly theory,the starfish-like,petal-like and core-shell spherical Ti_0.8Sn_0.2O₂ materials have been successfully prepared via a one-step hydrothermal method with the surfactant assisted to further study the effect of the structural morphology of the Ti_0.8Sn_0.2O₂material.The effects of the different surfactants and concentrations on the morphology of the precursors are discussed.The novel carbon-wrapped Ti_0.8Sn_0.2O₂ solid solution material(Ti_0.8Sn_0.2O₂/C)composites are obtained by glucose hydrothermal and sintering process.In comparison,the lithium storage properties of Ti_0.8Sn_0.2O₂precursors and Ti_0.8Sn_0.2O₂/C composite are studied.The morphologies,structures and properties of those materials are discussed.The performances of Ti_0.8Sn_0.2O₂/C composites are better in comparison with their precursor each other,especially the starfish-like Ti_0.8Sn_0.2O₂/C composites synthesized by the surfactant assisted of PVP(1g L^-1),which shows the best rate performances and cycle stabilities.?3?A novel 3D layered nano-archiecture network of Ni?HCO₃?₂/rGO composite with highly uniform Ni?HCO₃?₂ nano-cubes?average diameter of 100±20 nm?wrapped by rGO films is facilely fabricated by an one-step hydrothermal self-assembly process based on the electrostatic interaction and coordination principle.Benefiting from the synergistic effects,the Ni?HCO₃?₂/rGO electrode delivers an ultrahigh capacity(2450 mA h g^-1 at 0.1 A g^-1),ultrafast rate capability and ultra-long cycling stability(1535 mA h g^-1 for the 1000^th cycle at 5 A g^-1,803 mA h g^-1 for the 2000^th cycle at 10 A g^-1).The detailed electrochemical reaction mechanism in-situ investigation further indicates that the 3D architecture of Ni?HCO₃?₂/rGO not only provides good conductivity network and takes confinement effect of rGO films,but also benefits the reversible transfer from LiHCO₃ to Li_xC₂?x=0²?,further oxidation of nickel,and the stable/durable solid electrolyte interface?SEI?film?LiF and LiOH?formation,which are responsible for the excellent Li-ions storage performance.?4?The open porous 3D architectures with Co₂?OH?₂CO₃ nanowires wrapped by high conductive reduced graphene oxide films were designed and exploited for the first time as anode for lithium ion batteries,which fabricated via an one-step hydrothermal synthesis and self-assembly based on the electrostatic interaction and coordination principle,delivering a superior rate performance and long cycle stability(1380 mA h g^-1 for the 150^th cycle at 0.2 A g^-1,and 5000^th reversible capacity of 550 mA h g^-1 at current of 10 A g^-1).This extremely encouraging result is attributed to the open porous3D networks and ultrafine diameter of nanowires?d=20²5 nm?by achieving better electrical contact between the active materials to shorten ion/electron transport paths,which highlights the synergistic effect from combining the Co₂?OH?₂CO₃ nanowires and rGO films.Additionally,the lithium storage mechanism of the as-prepared Co₂?OH?₂CO₃/rGO electrode has elaborately been studied by in-situ XRD,ex-situ XPS techniques and kinetic analysis.This work not only provides a new type of open porous3D architecture hybrid transition-metal hydroxyl carbonate anode with great potential prospective application for high energy lithium storage,but also endows one more strategy to designing the graphene based composite materials via the coordination principle and molecular self-assembly theory to achieve other functional materials.