| Lithium-sulfur batteries represent one of the next-generation energy candidates for high specific energy storage,due to the high theoretical specific capacity of 1675 mAh g-1,theoretical energy density of 2600 Wh kg-1 and low cost and environmental friendliness of raw material.However,lithium-sulfur batteries are still facing many challenges from commercial application,such as low conductivity of sulfur cathode and its discharge products,low surface loading of sulfur cathode,slow reaction kinetics,and shuttle effect of lithium poly sulfide.Meanwhile,with the improvement of people’s quality of lives,the popularity of wearable flexible electronic devices has become a new trend,so the design of a flexible self-supporting electrode is essential for the development of flexible power supplies.Based on the above discussion,a flexible PTFE nano fiber/acetylene black electrode(FPAB)with good mechanical properties was prepared by low-temperature sintering method,which was used as a sulfur carrier for Lithium sulfur batteries to study its electrochemical properties.Adopting MoS2 as a catalyst,the electrode structure was regulated to improve the reaction kinetics and cycling stability of the cell to achieve high sulfur loading and long cycle life.The major discussions are as follows:(1)The flexible self-supporting architecture is formed by PTFE nanowires bonded with acetylene black particles,which exhibit good bending performance;the cancellation of the fluid collection improves the sulfur utilization and energy density.The FPAB electrodes have a substantial specific surface area and internal pores,achieving a maximum sulfur loading of 20.6 mg cm-2 and a sulfur mass ratio of 69%.The interconnected pore structure inside the FPAB improves the wettability of the electrolyte and facilitates the rapid transport of Li+.At a sulfur loading of 2.9 mg cm-2,the FPAB/S electrode achieved a discharge specific capacity of 811.8 mAh g-1 after 400 cycles at 0.5 C,with a decay rate of only 0.012%per cycle.Even when the sulfur loading was increased to 20.6 mg cm-2,the FPAB/S electrode still had a reversible capacity of 14.50 mAh cm-2 and a capacity retention of 98.5%after 50 cycles.(2)To improve the acceleration of the redox kinetics of lithium polysulfide,a MoS2/acetylene black composite was prepared using the preform method,PTFE nano fibers were used to bond the composite to prepare a flexible electrode(named:FPMAB).It was demonstrated that MoS2 has a good chemisorption effect on lithium polysulfide,which can also improve the reaction kinetics.At an area sulfur loading of 2.9 mg cm-2,FPMAB/S achieved discharge specific capacities of 1439.3,1263.4,1123.6,1027.3 and 854.2 mAh g-1 at 0.1,0.2,0.5,1 and 2 C,respectively,showing a significant improvement in rate performance.When the current density returned to 0.1 C,the capacity was maintained at 1403.9 mAh g-1,showing good reversibility.After 400 cycles at a current density of 2 C,the capacity of FPMAB/S was sustained at 684.7 mAh g-1 with a 0.056%decay rate per cycle.Moreover,with a sulfur loading of 20.6 mg cm-2,the reversible specific capacity was 15.95 mAh cm-2,demonstrating the potential of MoS2 to improve the electrochemical performance of lithium-sulfur batteries.(3)A 3D spherical MoS2,created through a hydrothermal process,was incorporated into the FPAB electrode as an embedded catalyst(FMPAB)to enhance the cycling behavior and stability of the lithium sulfur battery at higher current density and sulfur loading.The design of the spherical MoS2 can drastically decrease the sulfur and its discharge products that accumulate on the catalytically active surface,revealing more marginal active sites,improving cycling performance and stability of the cell at high load and current density.After 400 cycles at 0.5 C,the FMPAB/S flexible electrode maintained a discharge specific capacity of 1099.3 mAh g-1 without deterioration.When the current density rose to 1 C and 2 C,the discharge specific capacities were 957.6 and 917.9 mAh g-1 after 400 cycles,respectively,with a capacity retention of over 97.6%.The FMPAB/S electrode,with a sulfur loading of 20.6 mg cm-2,demonstrated remarkable reversibility,achieving an initial discharge capacity of 17.33 mAh cm2 and a Coulomb efficiency of 98.8%.After 50 cycles,the discharge specific capacity was sustained at 17.78 mAh cm-2,resulting in a marked enhancement of cycling performance and stability. |
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