Preparation And Performance Research Of CoSe₂/CoO Heterojunction Catalysts Modified Separator Of Lithium-sulfur Batteries

The current dominant lithium-ion battery typically has difficulty meeting the requirement of a high energy storage density due to the limited theoretical capacity of the electrode materials.As a new lithium secondary battery,lithium sulfur（Li-S）battery not only has the theoretical energy density(2600 Wh kg^-1)higher than lithium-ion battery,but also has the advantages of low cost,non-toxic,environmental friendliness.However,the shuttle effect of soluble lithium polysulfides（Li PSs）and the sluggish redox kinetics of different sulfur species,hinder commercialization.In cobalt-based materials,Cobalt diselenide（Co Se₂）has a unique electronic structure and excellence catalytic activity can play an important role in catalytic and stabilizing sulfur chemistry,especially controlling solid sulfur deposition.cobalt oxide（Co O）has a stronger polarity surface,which can provide more polar activity sites toward Li PSs and slow the shuttle effect.However,the compounds of a single component often cannot meet the needs of catalytic activity,limiting the development of its application of lithium sulfur batteries.In order to solve this problem,this study designed CoSe₂/CoO and CoSe₂/CoO-CNTs composite materials and were used in the separator of lithium sulfur battery to inhibit the shuttle effect and effectively improve the performance of lithium sulfur batteries.The main studies content are as follows:（1）Firstly,Co（OH）₂ precursor particles were synthesized by hydro-thermal method,and then CoSe₂/CoO heterojunction were prepared by partial selenization.CoSe₂/CoO composites were coated onto a commercial polypropylene（PP）separator as a modifier for a Li-S battery.Utilize the curves of the Mott-Schottky test,Co Se₂ and Co O are p-type semiconductors.When Co O and Co Se₂ are in contact,electronic transfer between Co O and Co Se₂ can change the distribution of electronic density.An oriented and strong built-in electric field is spontaneously generated at the CoSe₂/CoO heterogeneous interface,which can accelerate reaction kinetics to suppress the shuttle effect of Li PSs.By using CoSe₂/CoO as a separator modifier,the electrochemical properties of Li-S batteries are significantly improved.An initial discharge capacity of 1342 m Ah g^–1 was obtained at 0.1C,and retention rate of 65.9%was achieved over 450 cycles at 0.5 C.（2）By introducing high-conductive materials carbon nanotubes（CNTs）to improve conductivity,CoSe₂/CoO materials and carbon nanotubes compound to form a three-dimensional stereo network structure to obtain CoSe₂/CoO-CNTs composite materials.Compared with CoSe₂/CoO,the CoSe₂/CoO nanoparticles of the composite were blended with conductive CNT matrix promotes three-dimensional precipitation of Li₂S and thus boosts the performance of Li-S batteries.As a result,the Li-S batteries with CoSe₂/CoO-CNTs modified separator shows excellent percentage performance and cycle stability,an initial high initial discharge capacity of 1573 and 910 m Ah g^–1 at 0.1 and 2 C,respectively.Furthermore,a low decay rate of 0.070%per cycle was acheived over 500 cycles at 2 C.