Ti₃C₂T_x-SnS₂ Modified Porous BC Separator And Its Electrochemical Performance For Lithium-sulfur Battery

With the increasing demand for long-term endurance of energy products,people have carried out in-depth research on high-capacity battery energy storage systems.Because the theoretical specific capacity（1675 m Ah/g）of lithium-sulfur batteries is 5 times that of traditional lithium-ion batteries,its commercial applications have attracted much attention.However,commercial polyolefin separators have caused problems such as safety accidents,lithium polysulfide shuttles,serious loss of active materials,and low utilization rates due to their own defects,which severely hindered the commercial development of lithium-sulfur batteries.As an indispensable component of the battery,the separator is of great significance for the development of high-performance battery to develop high quality separator in response to battery problems.Therefore,the subject used porous bacterial cellulose membrane（PBC）with high puncture resistance and high temperature resistance as the basic separator to avoid battery fire,explosion and other safety risks,and the PBC membrane was functionally modified by the preparation of Ti₃C₂T_x and SnS₂ to improve the comprehensive performance of Li-S battery.First of all,in order to obtain a separator with high mechanical properties and heat resistance,and to improve its porosity and lyophilicity,BC membrane was selected as the subject.The subject used foaming pore-making technology to optimize BC and prepared a PBC membrane with a porous network structure to solve the problem of high interweaving and dense mesh of ultrafine fibers.The BET,porosity,and mechanical properties were carried out,the results showed that increase of specific surface area of PBC,porosity as high as 75.1%,and excellent mechanical strength（180.0 MPa）.High polarity Ti₃C₂T_x were obtained by etching MAX phase with strong acid.The Ti₃C₂T_x-PBC modified separator was prepared by vacuum filtration.SEM showed that the modified layer had a smooth and flat surface morphology,and the thickness of the cross section was only 1.5μm.In addition,the strong hydrogen bond between the hydroxyl group of PBC and the-OH and-F of Ti₃C₂T_x reduces the powder removal of the coating.Secondly,the mechanical properties,thermal stability and electrochemical characteristics of Ti₃C₂T_x-PBC separators were explored,in which commercial PP and PBC separators were used as reference samples.The results showed that Ti₃C₂T_x-PBC separator had excellent mechanical tensile（174.0 MPa）and puncture resistance（0.17 N/μm）,which were 27.0% and 35.3% higher than that of PP separator,respectively.The Ti₃C₂T_x-PBC separator still has excellent thermodynamic properties at high temperature（PP separator ruptures at 167.3℃）.High heat resistance make it still maintains dimensional integrity at 200.0℃,and the heat shrinkage rate close to zero,PP up to 83.8%.High porosity（74.3%） and electrolyte affinity make it get good ionic conductivity（3 times PP）and interfacial impedance（69.0Ω）.The initial discharge specific capacity of the battery with Ti₃C₂T_x-PBC separator reached 1294.3m Ah/g,and remained 734.7 m Ah/g after 500 cycles.Finally,in order to further improve the redox kinetics reaction and the utilization of active materials,the Ti₃C₂T_x-SnS₂-PBC composite separator was prepared by adding by adding SnS₂.EDS-Mapping proved that Ti₃C₂T_x and SnS₂ were fully mixed and formed a uniform modified layer.Electrochemical performance of the Li-S battery with Ti₃C₂T_x-SnS₂-PBC separator showed that the redox reaction was fast and the polarization was improved.The charge-discharge platform is the most stable and the longest,and the initial discharge capacity of 1390.9 m Ah/g is much higher than 41.4% of PP（815.0 m Ah/g）,and the long cycle decay rate of 500 weeks is only 0.07%/week.It still maintains a high level（607.9m Ah/g）under high current discharge（5C）,and obtains excellent fast charge and discharge characteristics.Redox studies have proved that SnS₂ can accelerate the catalytic conversion of multi-sulfide lithium,and sulfur substances can be used efficiently.In addition,diffusion experiments,XPS and EDS-Mapping tests of the separators after cycling have systematically proved the inhibitory effect of Ti₃C₂T_x-SnS₂-PBC separator on lithium polysulfide,which is conducive to the long-term and stable use of lithium-sulfur batteries.