| In order to meet future energy demands of long lifespan,stability cycling and high energy/power density for a variety of applications including kinds of portable electronics,electric vehicles,and smart grid storages,the design and development of advanced anode materials for batteries are very necessary.Lithium-ion battery（LIB）is an efficient secondary battery.Tin disulfide（Sn S2）is considered as potential anode material for LIB owing to its high theoretical capacity,excellent electrochemical activity and low cost.However,the pure Sn S2 exhibits dramatic capacity fade and poor rate capability as electrode material due to its poor conductivity and severe pulverization from very high volume fluctuations in charge and discharge processes.In this dissertation,in order to tackle the mentioned challenges above,various synthetic methods of coating,confinement growth,layer stacking and self-assembly have been explored to prepare Sn S2 and carbon composite materials from micron,submicron,nano and atomic layer levels,which can effectively improve the conductivity of Sn S2-based composites and alleviate the volume change as a anode in LIB.Main contents are shown as following:1.Preparation and lithium storage properties of Sn S2-based micron flower composites.Sn S2 flowers at the micron level were prepared by simple hydrothermal method and coated with carbon from different sources of glucose and dopamine.The initial and coated Sn S2 micron flowers were heat treated at 400°C,500°C and 600°C for 4 hours in argon atmosphere to prepare Sn S2-based micron flower composites.The effects of different carbon sources and heat treatment temperatures on the structure and properties of the Sn S2-based micron flower composites and their electrochemical properties as cathode materials were studied.The results show that Sn S2 exhibits obvious structural transition to cubic Sn S with the increase of temperature,and the reduction of carbon accelerates the phase transition process.The structural phase transition enhances the proportion of active materials in the samples,leading to higher initial coulomb efficiency of the corresponding electrodes.For the Sn S2 micron flowers coated dopamine with heat treatment for 4 h,the sample still maintains a complete morphology,so that the active material avoids direct excessive contact with the electrolyte in LIBs,leading to reducing continuous consumption in charge/discharge cycling and improving the cycle stability of the battery.2.Preparation and lithium storage properties of Sn S2@CS composites.Thin-walled carbon shells were prepared by template method,and then submicron Sn S2 was synthesized by hydrothermal method in the inner and outer confinement of thin-walled carbon shells.The Sn S2@CS hierarchical structure show that Sn S2 not only grows along the carbon wall,but also grows Sn S2 particles in the inner cavity of the hollow thin-walled carbon shell.The Sn S2@CS hierarchical structure is beneficial to enhance the conductivity and electrochemical activity of anode,which is conducive to the formation of stable solid electrolyte interphase（SEI）and has enough buffer space to alleviate the volume change of the electrode material at the charge-discharge process,resulting in excellent cycling stability in LIBs.The Sn S2@CS hierarchical structure anode delivers a high reversible capacity of 200 m A h g-1 at a current density of 1 A g-1after 1000 cycles.3.Preparation and lithium storage properties of Sn S2/r GO heterostructures.Sheet-like stacked Sn S2/r GO（reduced Graphene Oxide）heterostructures at the nanometer level were developed using a facile solvothermal approach.The composites between the Sn S2 nanoplates with a thickness of 12 nm and a transverse size of about 100nm and reduced graphene oxide nanosheets were closely coupled via van der Waals interactions.The Sn S2/r GO heterostructures improves the conductivity of Sn S2 material,and provides an efficient electron/ion pathway to ensure excellent electronic conductivity and alleviate the volume expansion with considerable buffer space as the anode in LIB,so as to obtain a stable long cycle performance.At a current density of 1 A g-1,the high reversible specific capacity of the electrode is 450 m A h g-1 after 1000 cycles.The structural evolution of Sn S2/r GO heterostructures electrode in the initial two cycle was studied using in-situ XRD.It was revealed that Sn S2/r GO underwent typical initial intercalation,conversion and subsequent alloying in the first discharge process,and most of the reactions in the subsequent cycles pertained to dealloying/alloying.The galvanostatic intermittent titration technique（GITT）showed that more rapid diffusion of lithium ions in the Sn S2/r GO heterostructures occurred in the intercalation and conversion reactions than in the alloying reactions,and the diffusion rate on the surface is higher than that in the interior of particles.4.Preparation and lithium/sodium storage properties of Sn S2/PDDA-GO multilayers.The Sn S2/PDDA-GO multilayers are synthesized through a solution-phase direct assembly method by electrostatic interaction between monolayer Sn S2 and PDDA-GO nanosheets at the atomic level.The Sn S2/PDDA-GO multilayers have a close coupling between the monolayer Sn S2 sheets and the PDDA-GO nanosheets at the atomic scale,which can not only effectively alleviate the volume expansion of electrode materials in charge/discharge process,but also facilitate the charge transfer during cycle process.The Sn S2/PDDA-GO multilayers electrode exhibits excellent rate performance and good cycling stability in lithium and sodium ion batteries.The Sn S2/PDDA-GO multilayers electrode has a large pseudocapacity contribution for enhanced lithium and sodium storages with a stable reversible capacity of～160 m A h g-1 at a current density of 2 A g-1after 2000 cycles for lithium and～142 m A h g-1 at a current density of 1 A g-1 after 1000cycles for sodium,respectively. |
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