Construction Of Cathode Catalyst And Optimization Of Redox Mediator For Li-O₂ Batteries

As a new-type energy storage system,Li-O2 battery has attracted extensive attention due to its high theoretical energy density.However,the low energy efficiency and poor cycling stability of Li-O2 battery have been the bottlenecks hindering its further development.In our work,the development of new high-efficiency solid-phase catalysts and the modifications of Redox Mediator system have been carried out to obtain high energy efficiency,high specific capacity and high stability Li-O2 battery.The main results are as follows:1 Preparation and electrochemical properties research of sulfur-based catalysts.Low-cost CuS/PCF with good catalytic properties was prepared through in-situ hydrothermal growth,which effectively reduced the overpotential during charge process.Discharging and charging platform of first cycle and cyclic stability test showed that CuS/PCF had a lower charging voltage and better cyclic stability than PCF,CuO/PCF and CuS powder.Compared with PCF,CuS/PCF could improve the energy efficiency of Li-O2 battery from 68.7%to 78.1%.Studies showed that CuS/PCF could induce the formation of small particles Li2O2 on its surface,thus,the Li2O2 can be decomposed more easily and thoroughly during charging process,showing lower charging overpotential and better cyclic performance.2.Development and research of dual functional Redox Mediator KIBy combining with the solution-phase promotion of K+ and the reduction of I-/I3-couple to the charging potential,KI was proposed to obtain high energy efficiency,high specific capacity and high stability Li-O2 battery.The galvanostatic charge-discharge tests of Li-O2 batteries based on LiTFSI,KTFSI with LiTFSI,LiI with LiTFSI and KI with LiTFSI indicated that the specific capacity increase from 9005 mAh g-1 to 27268 mAh g-1 and the energy efficiency rise from 65.8%to 80.3%,thus,the cycle number increase from 43 to 362 by introducting KI.The comparsion of the Li2O2 sizes between LiTFSI and KI system confirmed that K+ can promote the solution-phase formation of Li2O2 in electrolyte,alleviating the cathode passivation,thus,increasing the discharge capacity.Further,XRD and DEMS patterns showed that I-/I3-couple can completely decompose Li2O2,thereby improving the cycling stability.3.A functional NPG membrane to suppress the shuttle effect of I-/I3-coupleTo counter the shuttle effect of small size RM(I3-),a NPG membrane with steric hindrance and electrostatic repulsion was prepared and successfully inhibited the shuttle of I3-ions and protected the lithium metal anode.As a result,the cycle number of Li-O2 batteries increased from 123 to 472,and the discharge capacity increased from 9458 mAh g-1 to 26917 mAh g-1.The XPS characterization of Lithium metal anode and the analysis of abnormal discharge platform proved that NPG membrane successfully inhibited the shuttle of I3-ions.The Raman and XPS tests of NPG membrane confirmed that the nafion and PEO can couple with each other forming a large network structure,which can confine the shuttle of I3-species.Further,electrochemical measurement of different membranes illustrated that each component of NPG has its own unique function to the improvement of electrochemical performance,and the increasement of discharge capacity was attributed to the facilitation of H+ to the solution-phase process.