Design,Preparation Of Tin Based Composite Electrode Materials Based On Defect Engineering And Its Lithium/Sodium Ion Batteries Performances

In order to achieve the strategic goal of "carbon peaking and carbon neutralization",it is particularly important to develop clean and renewable energy.Although wind and solar power have been deployed on a large scale,the challenge of storing these renewable energy sources safely remains formidable.The emergence of secondary rechargeable batteries has successfully solved this problem,and different energy storage systems can be selected according to different application scenarios.However,both lithium-ion batteries,which are widely used in commercial applications,and sodium-ion batteries with abundant reserves and lower prices,need to develop high-performance anode materials.As an important component of secondary battery,anode electrode materials still face many problems that need to be solved urgently.At present,the commercial used graphite anode has limited its application in equipment with high energy density requirements due to its low lithium storage capacity,and it is also difficult to store sodium ions.Therefore,it is urgent to develop anode materials with high capacity and suitable for both lithium and sodium ions storage.Among the many candidate materials,Snbased materials have attracted much attention due to their advantages of high theoretical capacities,good conductivity,abundant resources,and easy preparation.However,Sn-based materials also face the problems of large volume expansion and rapid capacity decay in the energy storage process.How to improve the electrode capacity while ensuring excellent high rate and long cycle performance is the current research focus.The key to solve this problem is to increase the reactive sites of Sn-based electrodes during the energy storage process,and to alleviate the volume expansion of Sn nanoparticles.In this thesis,based on the theory of defect engineering,a variety of Sn-based composite electrode materials were designed and prepared by combining various strategies such as structure optimization,heteroatom doping,heterostructure construction and vacancy regulation,and their lithium/sodium storage properties were studied.The research contents are as follows:(1)P-Sn/NG(phosphorus-modified Sn nanoclusters encapsulated by nitrogen-doped graphene)composites were prepared through phosphorization process from Sn6O4(OH)4/NG(Sn6O4(OH)4 nanoparticles encapsulated by nitrogen-doped graphene)precursor,and the effect of phosphorous modification on the structure and electrochemical properties of electrode material was studied.The structure and morphology characterization proved that the phosphorous modification treatment optimized the nanostructure of P-Sn/NG composite into nano/micron primary particles,and modified the surface of the material into amorphous state.The electrochemical results showed that the stability of SEI film was improved,the initial Coulombic efficiency was enhanced(ICE,82.2%on average),and the ion transport efficiency was accelerated,owing to the phosphorous modification treatment.The experimental results show that the P-Sn/NG electrode has excellent cycling stability and rate capability for LIBs(620.0 mA h g-1 after 3200 cycles at 5.0 A g-1).The sodium ion storage performance of PSn/NG composite is worse than that of LIBs due to the larger sodium ion radius and more serious volume expansion during energy storage.This study shows that phosphorous modification can optimize the structure of tin metal electrode,modify the surface of electrode,improve the energy storage performance,and provide guidance for our subsequent experimental design.(2)SnxPy/RGO(tin phosphide nanoplate with the multiphase encapsulated by reduced graphene oxide)composites were prepared by phosphating treatment with Sn/RGO(Sn nanoparticles encapsulated by reduced graphene oxide)composites as precursor,and the effect of multiphase complex on its energy storage performance and mechanism was investigated.The morphology and structure characterization proved that SnP0.94/RGO(SnP0.94 nanoparticles encapsulated by reduced graphene oxide)with single phase and SnxPy/RGO composites with multiphases can be synthesized by controlling the heating rate and the amount of phosphorus source in the phosphating process.The electrochemical test results show that the capacity of SnxPy/RGO composite as the anode material for LIBs can be kept at 713.0 mA h g-1 after 1400 cycles at a current density of 2.0 A g-1,and it delivered a capacity of 421.0 mA h g-1 after 100 cycles at 0.5 A g-1 as the anode for SIBs.Compared with SnP0.94/RGO,SnxPy/RGO has excellent rate capability and cycling properties.The experimental results showed that the electronic conductivity and structural stability of SnxPy/RGO were significantly strengthened due to the synergistic effect of graphene encapsulation structure and multiphase complex structure,and the ion transfer rate was also significantly improved.At the same time,the existence of multiphase complex structure can improve the kinetic reaction in the process of electrochemical energy storage,greatly promote the reversible formation of Sn4P3 and enhance the electrochemical performance.This design strategy provides a new concept for the design,preparation,and energy storage application of tin-based phosphide anode materials.(3)SnxPy/NG(yolk-shell tin phosphide composites with yolk-shell nanostructure encapsulated by nitrogen-doped graphene)composites are designed and synthesized by onestep carbonization and phosphorization from the precursor of Sn6O4(OH)4/NG,and the effects of different preparation processes on the nanostructure and phase of the materials and their relationship with energy storage performance were studied.SEM and TEM tests proved that nanocomposites with nanoclusters,nanoparticles and yolk-shell structures could be obtained by adjusting the preparation process,and the electrochemical test results showed that SnxPy/NG composites with yolk-shell structure possessed better energy storage performance than those composites with nanoclusters and nanoparticles.The experimental results show that the SnxPy/NG composite with yolk-shell nanostructure has stable high-rate long term cycling performance for LIBs/SIBs.As the anode of LIBs,its capacity can be maintained at 521.0 mA h g-1 after 3000 cycles at a current density of 5.0 A g-1.As the anode of SIBs,it has a capacity of 203.0 mA h g-1 after 300 cycles at 1.0 A g-1.The void space in the yolk-shell nanostructure can alleviate the volume expansion,the phase hybridization of Sn4P3 and SnP0.94 can promote the reaction kinetics,and the synergistic effect of phase hybridization and yolk-shell structure can effectively improve the energy storage performance of electrode materials.This design strategy points out the direction for the design and preparation of tin-based phosphide with unique nanostructure,and provides guidance for other metal-based phosphide electrode materials.(4)SnS2-xPx/RGO(tin-based sulfide composites with heterojunctions and sulfur vacancies encapsulated by reduced graphene oxide)composites with three-dimensional porous structure were designed and prepared by hydrothermal assisted phosphating method.The influence and mechanism of synergistic effect between three-dimensional network structure,phosphorus doping,sulfur vacancy and SniS-SnS2 heterostructure on the energy storage performance of electrode materials were investigated.SEM and TEM results showed that the self-assembly of graphene induced by Sn6O4(OH)4 nanoparticles in hydrothermal process formed a threedimensional network structure,EPR confirmed the existence of sulfur vacancies,XRD,Raman and TEM tests confirmed the construction of SnS-SnS2 heterostructure.The electrochemical test results show that SnS2-xPx/RGO possesses excellent high-rate long-term lithium/sodium storage performance.As the anode of lithium-ion battery,its capacity can be kept at 337.0 mA h g-1 after 3000 cycles at a current density of 10.0 A g-1.As the anode material of sodium-ion battery,it has a capacity of 199.0 mA h g-1 after 4000 cycles at 2.0 A g-1.The synergistic effect of sulfur vacancy,heterostructure and phosphorus doping increases the reactive sites,improves the conductivity,accelerates the ion transport dynamics,and enhances the structural stability of the electrodes.This design strategy is of great significance for improving the energy storage performance of Sn-based sulfide,and can be extended to the design and preparation of other metal-based sulfide electrode materials.