Preparation Of Transition Metal Compounds And The Application In Lithium Sulfur Batteries

Energy is one of the lifelines of modern economy.The country attaches great importance to the development of the new energy industry,which also provides an opportunity for the rapid development of the battery industry.Lithium sulfur batteries have become one of the hot research directions for future high-performance batteries due to their high theoretical capacity,low production costs,and low toxicity.However,the shortcomings of slow charge and discharge kinetics and low utilization rate of active substances hinder the development and large-scale application of lithium-sulfur batteries.As a key part of lithium-sulfur battery,the diaphragm plays an important role in solving the above deficiencies.At present,the commercial diaphragm is mostly olefin diaphragm,which has problems such as low wettability and inability to block the shuttle of polysulfide,so it is urgent to conduct modification research to obtain the diaphragm with excellent performance.Transition metal compounds have the advantages of abundant resources and good catalytic performance.This kind of materials has been widely used in the field of electrocatalysis,and has shown its good catalytic performance.This paper applies transition metal compounds as modifying materials for lithium-sulfur battery separators.By modifying and studying the conductivity of transition metal materials,it is expected to effectively suppress the shuttle effect of polysulfides.The specific research work and conclusions are as follows:（1）The preparation and catalytic performance research of Co₃O₄@rGO composite materials.Transition metal oxides have a large number of polar bonds to effectively absorb polysulfides.However,the poor conductivity limits their catalytic performance.In this paper,Co₃O₄ was taken as the research object,and high conductivity reduced graphene oxide was added to it,so as to successfully prepare Co₃O₄@rGO composite material with strong adsorption and catalytic properties of polysulfide,and it was used for membrane modification of lithium sulfur batteries.The results of CV test and Li₂S deposition test show that the addition of rGO can significantly improve the catalytic performance of the composite on polysulfide.In terms of electrochemical performance,the battery using Co₃O₄@rGO modified diaphragm,at 0.1 C(167.2m Ah g^-1)current density,the battery has 1304.8 m Ah g^-1 initial discharge capacity;At a current density of 0.2 C,the battery capacity retention rate after 150 charge-discharge cycles was 21.0%(initial specific capacity 1043.5m Ah g^-1).（2）The preparation and catalytic performance research of CoP@rGO composite materials.CoP can form P-S bonds with polysulfides,effectively adsorbing polysulfides;Meanwhile,CoP has good electrical conductivity,which can effectively prevent the appearance of"dead sulfur"in the membrane modification layer and catalyze the conversion of polysulfide.In this work,Co₃O₄@rGO composite material was further phosphating,and CoP@rGO composite material was prepared and applied in lithium sulfur battery membrane modification.The lithium-sulfur battery is assembled using a diaphragm modified by CoP@rGO composite material.The initial specific capacity of the battery is 1238.3 m Ah g^-1 at 0.2 C current density,and the capacity retention rate can reach 41.1%after 150 times of charging and discharging.（3）The preparation and catalytic performance research of Mo based catalysts derived from MOF.Compared to the preparation of composite materials,the preparation of transition metal compounds derived from MOFs is more controllable and has a broader commercial application prospect.This part of the work prepares Micron flower-like Mo₂C and Mo S₂ based on MOF and apply them to the membrane modification layer.Density functional theory calculation and test results show that Mo₂C has better performance.This is attributed to the large number of exposed Mo atoms on the surface of Mo2C,which provide adsorption and catalytic active site for catalytic reactions;At the same time,band structure calculations show that Mo2C has better electronic conductivity,resulting in higher catalytic activity of Mo₂C.In addition,the battery demonstrated excellent electrochemical performance with the Mo₂C modified polypropylene diaphragm,the initial specific capacity was 1003.7 m Ah g^-1 at 0.2 C,and the battery was able to achieve a capacity retention rate of 67.3%after 150charges and discharges.