Electrochemical Study Of Molybdenum Boride As The Separator Modification Material For Lithium-sulfur Batteries

The new energy industry is developing with each passing day,and the lithium-ion battery system has already dominated the market for small portable electronic products.However,with the development of technology and the limitation of the theoretical energy density of lithium-ion batteries,the lithium-ion battery system has been unable to support the development of next-generation portable electronic products and electric vehicles which require higher energy density.Therefore,the need to develop a secondary battery system with higher energy density is imminent.Lithium-sulfur battery system has become the most potential new generation of secondary battery system due to its high theoretical specific capacity and theoretical energy density.Besides,the abundance,low cost,and environmental friendliness of the sulfur cathode can be another reason.Even so,there are still some problems in the lithium-sulfur battery system that need to be resolved.The most important problem is the shuttle effect,that is,the liquid-phase polysulfides produced by the electrochemical cycle of the lithium-sulfur battery will dissolve in the electrolyte and pass through the separator,then an irreversible side reaction would occur between polysulfides and lithium anode,the capacity of the battery would be attenuated and the cycle life be reduced.In order to solve this problem,in this paper,through a series of characterization and electrochemical methods,it can be proved that molybdenum boride as a separator modification material of lithium-sulfur batteries can adsorb polysulfides effectively and inhibit the shuttle effect of lithium-sulfur batteries significantly.Thus,the reaction kinetics of the battery can be promoted,then the electrochemical performance can be further improved.The main research results and conclusions can be shown as follows:Firstly,we used MoB₂ as the separator modification material for lithium-sulfur batteries,coated it on the PP separator uniformly by the doctor blade coating method,and S@CNT composite material can be used as the positive electrode.Electrochemical test results show that at a current density of 0.5 C,the initial discharge specific capacity of the battery is as high as 1115 m Ah g^-1.At a current density of 2 C,the battery still retains a specific capacity of 431.3 m Ah g^-1 after 500cycles.Such excellent electrochemical performance benefits from the strong chemical binding ability of polar MoB₂to polar polysulfides,which effectively anchor the liquid-phase polysulfides produced during the reaction,thus inhibiting the shuttle effect and improving the electrochemical performance of the battery significantly.Subsequently,in order to further catalyze the multi-step reaction process of the lithium-sulfur battery,we prepared a Mo-MoB heterostructure material by the molten salt method and used it to modify the separator of lithium-sulfur battery.The initial discharge specific capacity at 0.5 C is 1130 m Ah g^-1,and after 300 cycles,the capacity retention rate of the battery is as high as 78.9%.Besides,at a current density of 2 C,the specific capacity of 471.4 m Ah g^-1 can be still retained after 500 cycles.Experimental data shows that the heterogeneous structure material of Mo and MoB perfectly combines the advantages of catalysis ability of Mo and chemical adsorption ability of MoB.Both of them can collaborative promote the reaction kinetics,suppress the the shuttle effect,and the electrochemical performance of the battery can be further improved.