Preparation Of Doped SnO₂ Micro-nano Materials And Their Application In Electrode Materials Of Alkali Metal Ion Batteries

With the increasing problem of environmental pollution and oil consumption,the development and popularization of renewable energy has become an urgent need for vigorous economic development.The development of electrochemical energy storage technology is particularly important,among which the development and application of alkali metal ion batteries promote the storage and utilization of clean energy.Lithium-ion batteries（LIBs）are by far the most widely used because of their small mass and excellent energy storage capacity,reversibility and environmental friendliness.In order to meet the growing demand for power from various electronic devices and energy vehicles,battery performance indicators are also increasing,especially for anode materials.At present,the material widely used in lithium-ion anodes is graphite electrode,but its storage capacity（372mAh/g）is limited,the rate capacity is average,and it is difficult to reuse it in the next generation of metal-ion batteries.Metal oxide SnO₂ nanomaterials are considered to be one of the very promising alternative anode materials.Tin dioxide theoretical specific capacity is high（780mAh/g）,low working voltage（about 3.6eV）,but in the application of lithium-ion batteries have obvious defects,tin dioxide is prone to volume expansion resulting in its high theoretical capacity in the application can not be maintained,according to the literature,element doping,nanotechnology,alloying,multi-compound and other methods can improve the defects of tin dioxide to a certain extent.In this paper,the influence of element doping on the electronic structure and lithiation process of tin dioxide is first explored,the favorable doping elements are screened,and then the tin dioxide doped by the element is prepared experimentally,and on this basis,materials with different advantages are selected for multi-compound to give play to the synergy between materials and overcome the defects of tin dioxide in the application process.The main research contents include:（1）Using density functional theory,the tetragonal SnO₂ unit cell with space group P42/MNM,as well as In-SnO₂,Bi-SnO₂ and Sb-SnO₂ were constructed in CASTEP,and the band structure and state density,electron orbital distribution,charge distribution and differential charge distribution,atomic and bonding residence calculations and transition state search were calculated in the SnO₂ unit cell.In the DMOL3 module,the two-dimensional sheet structures of In_0.3Sn_0.7O₂,Bi _0.3Sn_0.7O₂ and Sb_0.3Sn_0.7O₂ were constructed,and the adsorption of lithium ions during unilateral physicochemical of the layered structure was calculated,and the theoretical capacity was estimated.The results showed that the volume expansion ratios of metal elements M（M=In,Bi,Sb）were 11.37%,10.04%and 6.64%,respectively,and the band gaps of SnO₂,In-SnO₂,Bi-SnO₂ and Sb-SnO₂were 1.23 eV,1.72 eV,1.47 eV and 0.23 eV,respectively,and the bond levels were 0.3,0.22,0.03,respectively.the lithium concentrations of Li_0.47SnO₂,Li0.47In0.3Sn0.7O2,Li0.47Bi0.3Sn0.7O2,Li0.59Sb0.3Sn0.7O2 and Li0.59Sb0.3Sn0.7O2,and the maximum energy required for the diffusion of Li⁺in SnO₂,In-SnO₂,Bi-SnO₂ and Sb-SnO₂ was 1.1 eV,0.75 eV,and 1.03 eV,respectively、0.56 eV;In summary,it can be seen that Sb doping has the least effect on the lattice structure of tin dioxide,increases metallicity,and has the highest theoretical capacity.The metal element Sb doped with SnO₂ can effectively enhance its lithiation ability,and the presence of Sb atoms can promote the diffusion of Li⁺to a certain extent.（2）Sb-SnO₂ and binary materials with different forms of carbon and Sb-SnO₂composite were successfully prepared by simple hydrothermal method using SnCl₄·5H₂O as tin source and Sb Cl₄ as antimony source;Firstly,the charge-discharge performance curves obtained by Sb-SnO₂ and SnO₂ at the same current density were compared,and it was confirmed that antimony doping could improve the electrochemical performance of tin dioxide,which was consistent with the first-principles conclusions.Then,Sb-SnO₂was used as the main body to explore the improvement of the electrochemical performance of different carbon morphologies（graphite,graphene,carbon nanotubes,graphene and carbon nanotubes mixed 1:1）,among which Sb-SnO₂/rGO,Sb-SnO₂/CNT and Sb-SnO₂/rGO/CNT binary composites showed more uniform morphology under scanning electron microscopy,and the morphology of Sb-SnO₂ and Sb-SnO₂/graphite showed certain agglomeration phenomenon.After 100 cycles of charge-discharge cycles,the reversible capacities of Sb-SnO₂,Sb-SnO₂/graphite,Sb-SnO₂/rGO,Sb-SnO₂/CNT and Sb-SnO₂/rGO/CNT micro-nanocomposite structures were 3.2 mAh/g,58.7 mAh/g,158.7mAh/g,267.6 mAh/g and 650mAh/g,respectively.Under different current densities from100mA/g to 1000mA/g,the discharge capacities of Sb-SnO₂,Sb-SnO₂/graphite,Sb-SnO₂/rGO,Sb-SnO₂/CNT and Sb-SnO₂/rGO/CNT micro-nanocomposites after 50cycles were 178.2mAh/g,192.2 mAh/g,326.2 mAh/g,462.4 mAh/g,387 mAh/g,rGO,CNT can have a synergistic effect with antimony-doped tin dioxide,so that the material maintains the high capacity of tin dioxide and exerts the cycle stability of carbon materials,and the overall electrochemical performance of Sb-SnO₂/rGO/CNT and Sb-SnO₂/rGO/CNT micro-nanocomposite structures is better than that of single antimony-doped tin dioxide.（3）Through one-step hydrothermal method,we successfully assembled Sb-SnO₂/Mn_0.6Zn_0.4Fe₂O₄/graphite,Sb-SnO₂/Mn_0.6Zn_0.4Fe₂O₄/rGO,Sb-SnO₂/Mn_0.6Zn_0.4Fe₂O₄/CNT and Sb-SnO₂/Mn_0.6Zn_0.4Fe₂O₄/rGO/CNT micro-nano composites into a perfect micro-nanostructure,and,When the Mn_0.6Zn_0.4Fe₂O₄ material is added,the appearance and properties of this micro-nanostructure have been significantly improved,making it have good plasticity and operability.This substance has a flat appearance and has many tiny holes.After 100 charge-discharge tests,its reversible capacities reached 247.2 mAh/g,496 mAh/g,597.8 mAh/g and 747.3 mAh/g.Ten charge-discharge cycles were carried out sequentially under current densities of 100mA/g,300 mA/g,500 mA/g,1000 mA/g and 100 mA/g,and the discharge capacities were 428.2mAh/g,565.4mAh/g,791.5mAh/g,and 1183.8 mAh/g,respectively.The rate performance and cycle performance are better than the binary composites without composite Mn_0.6Zn_0.4Fe₂O₄,while the different forms of carbon neutral rGO composite are more obvious in terms of capacity improvement,and CNT is more significant in cycle performance,and the simultaneous composite of rGO/CNT can effectively combine the advantages of the two,so that the ternary materials can play a better synergy,The Sb-SnO₂/Mn_0.6Zn_0.4Fe₂O₄/rGO/CNT micro-nano composite material with excellent contrast is applied to sodium ion batteries.After 45 cycles of discharge and discharge cycles,it still retains a high capacity of 351.7 mA/g,and also shows good rate performance.It is further proved that the material has high capacity and good cycle performance.It is expected to become a potential anode material for high-performance alkali metal ion batteries.