Preparation Of Hydrogenated TiO₂-S And PbS/S Composite Materials And Their Application In Lithium-sulfur Batteries

Sulfur has the advantages of simple preparation,low cost,abundant resources and environmental protection requirements.At the same time,the theoretical specific capacity of sulfur applied to batteries can reach 1672 mA h g-1,and when applied to lithium-sulfur batteries simultaneously with metallic lithium,the theoretical energy density will be as high as 2600 W h kg-1.Therefore,as a recyclable secondary rechargeable battery,a lithium-sulfur battery is considered to be one of battery systems that meet current environmental conditions and the most promising development.However,there are still many problems with large-scale industrial production of lithium-sulfur batteries.For example,sulfur is usually an insulating element,and polysulfides are easily separated from the dispersion in the electrolyte,and volume expansion of sulfur during charging and discharging is a challenge.These problems are caused by the inefficient use of active materials in the battery,the low efficiency of Coulomb and the severe internal polarization of the battery,which leads to limited development of lithium-sulfur batteries.Based on these shortcomings,this paper looks for a positive carrier material suitable for lithium-sulfur batteries.First,hydrogenated titanium dioxide is added thereto,and then the encapsulated core-shell structure is designed.Metal sulfides are used as sulfur carriers and sulfur is produced.A composite cathode electrode material of a metal oxygen compound or a sulfur/metal sulfide for improving cycle stability performance and rate performance of a lithium sulfur battery.The main research areas are:1.In view of the poor conductivity of sulfur and the severe shuttle effect during charge and discharge,another hydrogenated titanium dioxide was designed and sulfur composite was used as the cathode electrode material.The presence of oxygen vacancies and Ti3+ ions after hydrogenation can significantly increase the conductivity of TiO2.The strong chemical bond between Ti3+ and active material S will significantly adsorb the active material during charging and discharging,effectively limiting the destruction of polysulfide.Continue to add metal oxides to the matrix composite,which can improve the conductivity of the cathode material,thereby increasing the rate performance of the lithium-sulfur battery and increasing the number of battery cycles.2.The electrochemical properties of titanium dioxide and sulfur composites(Ti02/S-n(n=l,2,3))with different degrees of hydrogenation were also investigated.The first discharge capacities of hydrogenated TiO2/S-0 and hydrogenated Ti02/S-1,hydrogenated Tio2/S-2 and hydrogenated Tio2/S-3 at 0.5C rate were 554.2 mA h g-1,663.6 mA h g-1 respectively.,731.4 mA h g-1 and 770.9 mA h g-1,the average retention rates after 50 cycles were 50.3%,85%,87.5%and 90.1%,respectively.As the degree of hydrogenation increases,the increase in Ti3+ and the chemical interaction between the polysulfide and the polysulfide effectively reduce the dissolution of the polysulfide during charge and discharge,and the capacity retention rate of the battery increases.Hydrogenation of Tio2/S-3 exhibited more excellent cycle stability by a 1C rate cycle test.The average capacity retention rate after 50 cycles can reach 99.4%,which makes the battery have a higher capacity retention rate at a larger current density.3.Given the poor conductivity sulfur,soluble polysulfides in the electrolyte,the inevitable polarization,paper examines a hollow shell structure as lead sulfide sulfur support matrix,the cathode to stabilize the sulfur cycle.Reaction and rate performance.The core-shell structure material adopts the SILAR method to maintain the shape of the lead sulfide outer shell by the cooperation of the inorganic chalcogenide metal complex.Applying this composite structure in the battery,the hollow core shell can also eliminate the volume effect during charging and discharging under the premise of ensuring the sulfur loading.Moreover,the core-shell structure can also limit the dissolution of polysulfide in the electrolyte.The shell layer with mesoporous structure increases the specific surface area while providing convenient conditions for ion diffusion and transport.PbS reduction reaction rate improving battery performance and cycle stability by catalytic oxidation of polysulfides.Making such a change increases the cycle stability of the cathode electrode material,increases the retention of the battery capacity,and the rate performance.At a 0.5C rate,after 50 cycles,the battery capacity still has 921 mA h g-1 and the capacity retention rate is as high as 89.6%.At 1C rate,there will still be 79.9%retention rate after 50 cycles.After optimization,the battery rate performance was characterized,and the discharge specific capacity was maintained at 787 mA h g-1 at a magnification of 1.5C.