Two-dimensional Amorphous Nanomaterials Produced By Ball-milling And Their Properties

Two-dimensional(2D)nanomaterials have outstanding structural and physicochemical properties,and play an important role in the fields of electrocatalysis,mechanics,energy storage devices and energy conversion.At present,there are a large number of methods to produce two-dimensional nanomaterials,such as micromechanical cleavage,chemical vapor deposition,ion intercalation exfoliationl,etc.However,these preparation methods have some defects,it is necessary to continuously improve and enrich its preparation strategy.Recently,two-dimensional amorphous nanomaterials have shown excellent properties in catalysis,energy storage,energy conversion,mechanics,etc.,because of their special long-range disordered atomic arrangement structure.Based on this,two-dimensional Li₂C₂ alloy nanosheets formation through the ball milling-induced“intercalation and exfoliation”,and amorphous carbon coated Li₂C₂ alloy nanosheets foil was prepared by vertical cold-pressing,which was used as anode material of lithium-ion batteries,showing excellent structural,chemical stability and electrochemical properties;In addition,ultrathin amorphous nanosheets and heterostructure nanosheets were prepared by two-step methods of“ball milling solid-phase insertion”and“pure water liquid-phase exfoliation”.The Celgard separator was modified by ultrathin amorphous nanosheets to improve the thermal conductivity,mechanical strength,cycle performance and magnification performance of the batteries.The main research contents and results are as follows:1.Zirconia ball as ball-milling medium,graphite and Li foil as raw materials.Li₂C₂ alloy nanosheets formation through the ball milling-induced solid-state intercalation and exfoliation.The effect of ball-milling time on the preparation of Li₂C₂ alloy nanosheets from graphite was systematically studied,it was found that ball-milling time plays a key role in the formation of Li₂C₂ alloy nanosheets.Scanning Electron Microscopy(SEM),Transmission Electron Microscopy(TEM)and High Resolution Transmission Electron Microscopy(HRTEM)tests show that the prepared Li₂C₂ alloy nanosheets is a hexagonal structure coated with amorphous carbon,with a thickness of several nanometers and a width of several hundred nanometers.After Li removal by liquid-exfoliation,high-quality ultrathin amorphous carbon nanosheets can be obtained.The SEM,TEM,HRTEM and AFM test results show that the prepared Li₂C₂alloy nanosheets is a hexagonal structure coated with amorphous carbon,with a thickness of several nanometers and a width of several hundred nanometers,and there are a large number of amorphous carbon and graphene quantum dots with high defect density on the surface.2.The above prepared Li₂C₂ alloy nanosheet powders as raw material.A simple method,“vertical cold-pressing”,is proposed to produce Li₂C₂ alloy nanosheets foil(Li/C alloy foil),which can be used in anode,improving its structural stability and electrochemical performance.The symmetric Li/C|Li/C cells exhibit stable cycling performance at 1 m A cm^-2 after 800cycles,no Li dendrite growth was found.After the 1000th charge and discharge cycle at 1 C,the Li Fe PO₄|Li/C liquid full cells show a discharge capacity of 159 m A h g^-1and the capacity retention of 97.5%.At 0.57,1.7,and 2.8 m A cm^-2,the Li/C|Li liquid half cells exhibit excellent first cycle Coulombic efficiency,indicating that the Li/C alloy anode has a highly reversible lithium storage capability.3.Iron ball as ball-milling medium,layered materials(Graphite,V₂O₅,Mo S₂,WS₂ and BN)and Li foil as raw materials.A simple two-step strategy,“ball-milling insertion and pure-water exfoliation”,is proposed to produce ultrathin 2D amorphous nanosheets or heterostructure nanosheets.The preparation process of ultrathin amorphous nanosheets was studied.When dissolved in 100 m L 60°C pure water,1 mg alkali metal compounds can react violently with pure water to generate H₂ gas and alkali metal hydroxide,and the resulting gas-flow and electrostatically repelling force between the charged sheets break the weak van der Waals force between the layers of the layered material,realizing the effective exfoliating of the layered materials to form the ultrathin amorphous nanosheets or heterostructure nanosheets.In addition,the results of SEM,AFM,TEM and HRTEM show that the size of the obtained ultrathin amorphous nanosheets or heterostructure nanosheets is?1?m,their thickness is about 1.11?1.12 nm,and the number of layers?3.Moreover,the peak changes in Raman,XPS and FTIR spectra further indicated that the structure of ultrathin amorphous nanosheets or heterostructure nanosheets.4.A strategy,"solution deposition coating"method,is proposed to modify Celgard separators with ultrathin amorphous nanosheets or heterostructure nanosheets.To enhance the thermal conductivity,mechanical property and electrochemical performance of Li-S cells.To compare with the pure Celgard separator,the modified separator exhibits good mechanical property and high thermal conductivity,and improves the electrochemical performance of Li-S cells.Among them,the cells with BN/Mo_xS_y/C@Celgard separator show the best cycling performances and rate capability,which obtain an initial discharge capacity of 1408 m Ah g^-1at 1 A g^-1,The Li-S cells with pure separator only show an initial discharge capacity of 846m Ah g^-1.After 500 cycles,the Li-S cells with BN/Mo_xS_y/C@Celgard separator show a discharge capacity of 371.7 m Ah g^-1,while that of Li-S cells with pure Celgard separator is only 132 m Ah g^-1.In the rate performance,the Li-S cells with BN/Mo_xS_y/C@Celgard separator show a discharge capacity of 1550 m Ah g^-1 at 0.2 A g^-1,the Li-S cells with pure separator show discharge capacity of 1128 m Ah g^-1.When the current density is increasing to5 A g^-1,the Li-S cells with BN/Mo_xS_y/C@Celgard separator still obtain the discharge capacity of 635 m Ah g^-1,the Li-S cells with pure separator only obtain discharge capacity of 300 m Ah g^-1.