| Sodium/potassium secondary batteries exhibit promising application prospects in large-scale energy storage systems due to abundant resources of sodium/potassium and low manufacturing cost.However,the large ionic radius of sodium/potassium leads to sluggish diffusion kinetics in the electrode material and broken material structure during the electrochemical process.Two-dimensional materials exhibit fast ion transport kinetics due to the shorter ion diffusion length,and two-dimensional transition metal chalcogenides show promising application potential because of high capacity.To solve the dynamics and stability problems of sodium/potassium batteries,a series of two-dimensional structures of transition metal chalcogenides are accurately constructed,realizing fast energy storage dynamics and high cycle stability.In addition,we revealed the electrochemical mechanism of the constructed two-dimensional materials in the energy storage process via series of in-situ characterization methods.In Chapter 1,we briefly introduced the beyond-lithium batteries,and systematically described the research status of beyond-lithium batteries and research progress of two-dimensional materials in beyond-lithium energy storage systems.In Chapter 2,we introduced the chemicals and materials,equipment and characterizations used in the experiments of this dissertation.In Chapter 3,we constructed an ultra-thin two-dimensional heterostructure reinforced by chemical bonds of molybdenum sulfide(selenide)layer and twodimensional carbon nanosheets via a vapor deposition method for the anode materials of potassium-ion batteries.Potassium ions exhibit rapid diffusion in the ultra-thin twodimensional heterostructures.The abundant chemical bonds between the nanosheets and the carbon substrate stabilized the structure of nanosheets.Thus,excellent potassium storage performance and high cycle stability could be achieved.In addition,the "intercalation-transition" electrochemical mechanism of MoSe2 was revealed.In Chapter 4,we constructed two different structures in aqueous solution with different growth process via different intrinsic properties of crystal and amorphous molybdenum sulfide.By characterize series of the reaction intermediates,we revealed the anisotropic and isotropic growth processes of crystal and amorphous molybdenum sulfide,respectively.The amorphous molybdenum sulfide/graphene two-dimensional heterostructures show excellent energy storage performance and cycle life in potassium and zinc ion batteries.In Chapter 5,the sodium storage process of amorphous molybdenum sulfide/graphene two-dimensional heterostructure(MoS3-on-rGO)is systematically researched.Theoretical calculation and electrochemical kinetics characterization exhibit a fast diffusion process of Na+in amorphous heterostructure,and the heterointerface could improve the electron density of active materials.Thus,excellent electrochemical kinetics could be achieved.In addition,the MoS3-on-rGO exhibited negligible isotropic expansion,which could maintain the amorphous microstructure.Because of these advantages,MoS3-on-rGO exhibit excellent electrochemical performance and stability in sodium ion half-cells,full-cells and solid-state sodium batteries.In Chapter 6,we obtained that tungsten disulfide could be used as potassium ion channel to modify the surface of potassium metal via series of theoretical calculations and COMSOL simulations.Potassium ions exhibit rapid diffusion kinetics in the twodimensional channels,and the potassium intercalation compounds show extremely high structural and chemical stability in the electrochemical processes.Because of these advantages,the modified potassium metal anodes exhibit smaller polarization voltage,larger cumulative capacity and longer cycle life in the symmetric cells,and potassium full-batteries with high specific energy/power density are also constructed.In Chapter 7,we summarized the innovations and shortcomings of this dissertation,and look forward to the future works. |
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