Preparation And Properties Of High Performance Flexible Cathode Materials For Lithium Sulfur Batteries

The development trend of electronic products is changing towards flexibility and miniaturization.With the rapid development of flexible electronic devices,the field of energy supply and the storage of flexible electronic devices have also received more attention.If there is no high-performance energy storage system to provide energy for it,then the development of flexible electronics will be meaningless.With its high theoretical energy density(2600 Wh kg^-1),the lithium-sulfur battery is considered to be one of the most promising energy storage system for powering sources,and an ideal choice for miniaturization and lightweight energy supply.Therefore,it is necessary to design a flexible high-performance lithium-sulfur battery as a power source for flexible devices.However,the commercial application of lithium-sulfur batteries is facing many challenges,such as poor conductivity of sulfur and its discharge products,resulting in slow reaction kinetics,low utilization of sulfur,and shuttling effects caused by polysulfides.In view of the above reasons,this paper constructs MXene-based flexible electrodes and carbon cloth fiber flexible electrodes as cathode materials for lithium-sulfur batteries through conventional methods such as solid phase method and liquid phase method.Meanwhile,in order to verify their practical application performance,the electrodes were made into soft-pack batteries and electrochemical tests were carried out.The specific research content,electrochemical performance,results and discussion are demonstrated as the following aspects:1.Ti₃C₂T_x nanosheets were coated on the surface of common fabric by simple compounding and high-speed centrifugation to form MXene fabric(MF)with good conductivity.At the same time,liquid phase method was used to prepare mxene fabric The surface of Ti₃C₂T_x nanosheets was in-situ loaded with nano sulfur(Ti₃C₂T_x/S)as the active material,and then the Ti₃C₂T_x/S nanosheets were coated on the surface of MF to form a layer by layer three-dimensional network structure(MF@Ti₃C₂T_x/S)?In the foremost,this structure encapsulates the active material sulfur between layers,which limits the volume expansion during the charging and discharging processes.What's more,the oxygen-containing groups on the surface of Ti₃C₂T_x can effectively adsorb and catalyze polysulfides.Last but not least,MF@Ti₃C₂T_x/S based Li-S batteries has excellent cycle stability,the initial discharge capacity of the MF@Ti₃C₂T_x/S50 electrode is 916 m Ah g^-1 at1C rate,after 1000 cycles,MF@Ti₃C₂T_x/S50 the capacity retention of the electrode was 73.7%.In the actual wearable electronic devices,it is enormously crucial to bend the soft pack battery repeatedly and release energy normally.The results show that the robust and flexible electrodes work normally under bending and folding conditions.2.Hierarchical porous Co-MOF nanoarrays were in-situ grown on the surface of carbon cloth fibers using cobalt nitrate as cobalt source,and then part of the Co was transformed into CoSe nanoparticles by solid phase method(CF@N-CoSe).At the same time,the Co/C nanoarraies using Co-MOF as the cobalt source has a small amount of nitrogen doping.Co,Se,N and C elements are uniformly distributed on the surface of the nanosheets.HRTEM characterization shows that the surface of the nanosheet has a large number of hollow nanocluster structures,this structure has a significant effect on limiting the volume expansion of sulfur and inhibiting the shuttle effect.Benefit from this structure,CF@N-CoSe/S sulfur cathode exhibits initial specific capacity of 1383 m Ah g^-1 and 911 m Ah g^-1,and capacity decays of 3.2%and 0.3%per cycle at 0.2 and 1 C,respectively.The preparation and synthesis method of the flexible electrode material is simple,and the sulfur loading method is easy to implement,which provides feasibility for commercial application.In addition,this robust and flexible electrode can work safely and normally under bending and folding conditions,which reflects its application potential in the flexible energy storage field.