Application Research Of The Modified Separator With Nano Yttria-Ketjenblack Composite In Lithium Sulfur Batteries

In the early 1990s,lithium ion batteries were widely used as power sources of electronic products.In recent years,with the increasingly prominent environmental problems and the strong demand for battery endurance,many experts began to explore the battery system with high energy density.The theoretical energy density of energy storage system is up to 2600 Wh kg^-1 with sulfur as the positive electrode and the lithium as the negative electrode of the battery,which makes the lithium sulfur battery become the hot spot of the energy storage device.However,there are many defects in lithium sulfur batteries that need to be solved,such as:electron/ion conductivity of sulfur cathode and discharging end-product is poor,the volume change of active substance in the reaction is serious,and soluble lithium polysulfides in organic electrolyte which migrate to the negative bring shuttle effect,above-mentioned defects hider commercialization process.In this paper,in view of the low utilization of the active material,poor cycling stability and serious polarization of the battery caused by the shuttle effect of LiPS in the lithium sulfur battery system,the solution of using the composite of conducting carbon and Y₂O₃ as the modified coating of the sepatator in the lithium sulfur battery is proposed.The carbon materials of high specific surface area in the modified coating of conductive carbon and Y₂O₃ complex have strong physical adsorbability for LiPS.At the same time,Y₂O₃ particles inlaid in the conductive carbon have chemical adsorption and catalytic effect on the LiPS.The physical adsorption of conducting carbon and the synergistic effect of chemical adsorption and catalysis of Y₂O₃ can not only inhibit the shuttle effect of lithium sulfur batteries,but also improve the utilization of active substances,and greatly improve the electrochemical performance of lithium sulfur batteries.The main contents and results of the thesis are as follows:In the first part of the experiment,the commercial nano Y₂O₃ was used as the main separator modification material,and the modified material was coated on the commercial separator surface by mechanical mixing to study the role of Y₂O₃ in the battery with modified separator.The battery of the nano Y₂O₃ modifying separator was compared with the battery without separator modification.The initial discharge capacity?0.1 C?of the battery with modified separator was 1339.1 mAh g^-1,and the discharge capacity of the battery was reduced from 942.6 mAh g^-1 to 659.8 mAh g^-1under 1 C test,and the capacity retention rate was 70%,which was higher than that?51.4%?of the battery without separator modification.The rate performance of the battery with modified separator is also better than that without separator modification.The improvement of these electrochemical properties is attributed to the nano Y₂O₃coating on the modified diaphragm.The rich pore structure in the coating facilitates the infiltration of the electrolyte,which provides a way for the rapid transmission of ions,and the coating can also be used as a physical barrier to inhibit the shuttle of lithium polysulfide and improves the utilization of active substances.Further analysis from the test results,nano Y₂O₃ particles can also play a catalytic and chemical adsorption role in the electrochemical reaction process.Due to the uneven size of commercial Y₂O₃ particles and the poor conductivity of metal oxides,the performance of modified batteries will be affected.Therefore,we carried out second parts of experiments:Y₂O₃ particles were embedded in high specific surface area of conductive carbon.The second part is Y₂O₃ composite Ketjen Black?KB?prepared by wet soaking and freeze-drying.The results of composite detection showed that the size of Y₂O₃nanoparticles was 5¹0 nm and distributed evenly in the channel of carbon material.In order to study the effect of nano Y₂O₃ particles in the modified coating of the separator,we compared the battery of the modified separator with Y₂O₃/KB composite with the battery of pure KB modifying separator.The test results show that the initial discharge capacity of the battery of the modified separator with Y₂O₃/KB composite is up to 1362.1 mAh g^-1 under 0.1 C,and the capacity retention rate is 76.5%after 200 cycles.Under the same test conditions,the battery of the separator with Y₂O₃/KB modification has better performance than the battery of KB modifying separator.It is possible to attribute to the high specific surface and high conductivity carbon materials in Y₂O₃/KB provides a porous conductive skeleton,facilitates the rapid shuttle of ions,inhibits the shuttle of lithium sulfide and plays the role of physical adsorption,and the nano Y₂O₃ particles uniformly distributed in the channel of carbon material are used as active sites at the same time,which plays a role of chemisorption and catalysis,further improving the utilization rate of active substances and the reaction kinetics of batteries.