Design And Electrochemical Performance Of Separator And Solid Electrolyte For High Performance Li/Al Sulfur Batteries

With the rapid development of 3C electronic products,electric vehicles,solar cells,large power grids,there is an urgent need for energy storage devices with high energy density,high power density and long cycling life.Lithium ion batteries have the advantages of high energy density,high energy efficiency,long cycling life,no memory effect,low self-discharge rate,wide operating temperature and safety.Sulfur,with a high specific capacity(1675 mAh g^-1),has received great attention of energy storage due to its low cost and non-toxic.As an anode material,metal lithium has a high specific capacity of 3860mAh g^-1,however,its high cost and the lithium dendrite limit its further application.As a light,inexpensive and high energy density anode material,metal aluminum has also attracted attention from high power and high energy density energy storage system.It is worth noting that the dissolved polysulfids could migrate to the negative electrode in the charging-discharging process for Li/Al-S batteries,resulting in shuttling effect,resulting in poor cycle stability and low Coulombic efficiency of the batteries.In order to improve the electrochemical performance of the Li/Al-S batteries,it is important to suppress the shuttling effect of polysulfides.This paper aims to solve the shuttling problem of polysulfides by modifying the separators and designing a solid electrolyte with high ionic conductivity.?1?Low-cost,non-toxic,biomass-derived eggshell membrane?ESM?is proposed as a separator material for Li-S batteries.ESM has good mechanical strength,excellent thermal stability and large electrolyte infiltration compared to the commercial PP and PE separators.In addition,the hydroxyl and amino functional groups on the surface of the ESM can adsorb lithium polysulfides to inhibit polysulfides migration.Coating MXene nanosheets on ESM could suppress shuttling effect by physical barriers and chemical Lewis acid-base interactions.At the same time,high electron conductivity of MXene could act as a secondary current collector,increasing the reutilization of the captured lithium polysulfides.The Li-S battery using the KJC/S as positive electrode and the metal Li as negative electrode exhibits excellent cycling stability with an initial discharging specific capacity of 1185 mAh g^-1 at 0.5 C and a capacity retention of 74%after 250cycles.At the same time,the specific capacity of the battery is 1321 mAh g^-1 at 0.1 C,1112 mAh g^-1 at 0.2 C,1003 mAh g^-1 at 0.5 C,and 948 mAh g^-1 at 1 C.When the current density recovers to0.1 C,the specific capacity is 1147 mAh g^-1.The outstanding electrochemical performance indicates that the MXene/ESM functional separator significantly improves the cycling stability and rate performance of the sulfur electrode.?2?TiO₂ quantum dots?TQDs?is prepared by hydrothermal method using MAX as precursor,then TQDs is used as an additive to improve the ionic conductivity of PEO-based polymer electrolyte.The PEO-TQDs composite polymer electrolyte shows a high Li⁺migration number and a wide electrochemically stable window.The all-solid Li-S battery with the PEO-TQDs as polymer electrolyte exhibits excellent cycling stability and stable electrolyte-electrode interface.The composite polymer electrolyte with a TQDs content of 4%has the highest ionic conductivity.The Li-S battery with PEO-TQDs composite polymer electrolyte has a discharging specific capacity of 1108.1 mAh g^-1 at 0.05 C,862.4 mAh g^-1 at 0.1 C,685.7 mAh g^-1 at 0.2 C,and 524.4mAh g^-1 at 0.5 C.When the current density recovers to 0.05 C,the specific capacity is 899.7 mAh g^-1.At the same time,the Li-S battery of PEO-TQDs composite polymer electrolyte has an initial discharging specific capacity of 929 mAh g^-1 at 0.1 C,and still remains 918 mAh g^-1 after 150cycles,showing excellent cycling stability.?3?Polyaniline?PANI?coated glass fiber?GF?is used as a functional separator for Al-S battery,using KJC/S composite as positive electrode and metal Al as negative electrode to construct a new energy storage system with high volumetric energy density and low cost.Polyaniline?PANI?has a chemical interaction with polysulfides,whereby could adsorb polysulfides to prevent the shuttling effect.The Al-S battery with the PANI/GF functional separator shows outstanding electrochemical performance.At the current density of 50 mA g^-1,the first discharge specific capacity is 1392 mAh g^-1,the capacity is still as high as 1003 mAh g^-1 after25 cycles,and the capacity retention rate is 72%.