Research On The Construction Of Quasi-solid Electrolyte For Lithium-sulfur Battery And Performance With Titanium Dioxide And Ionic Liquid

With the rapid development of technologies around the world,the portable electronic devices are utilized worldwide.Most portable electronics chose lithium-ion battery as a power source.However,the energy density of lithium-ion batteries is low and cannot meet the requirements of large-scale energy storage equipment such as electric vehicles and national power grids,as well as other equipment like drones which require a long-term energy supply.Therefore,how to provide sufficient energy for these electronic devices is an extremely important issue.The research and development of batteries with small size,light weight,high energy density,and long cycle life are very urgent.Among many rechargeable batteries,lithium-sulfur batteries have a high theoretical energy density.From the perspective of theoretical calculations,lithium-sulfur batteries are sufficient to meet the energy supply most of the electronic equipment in the future.But there are two prominent problems with lithium-sulfur batteries:One problem is that the negative electrode will form a lithium dendrite structure,which may puncture the separator and causes the battery to short circuit,resulting the battery to short circuit and reduce the cycle life;Another problem is that the polysulfide is preferentially generated when the positive electrode is discharged,and the polysulfide will dissolve into the electrolyte to generate a shuttle phenomenon,which causes the energy density decrease and the negative electrode passivated.To obtain a better practical application of lithium-sulfur batteries,these two problems must be solved.This thesis is mainly studied from the perspective of electrolytes.By designing titanium dioxide with different structures and ionic liquids to build a quasi-solid electrolyte,solving the two problems,and improving the performance of lithium-sulfur battery.The research content is mainly divided into two parts:The first part had designed and prepared polymer films?TiO₂IO-PILs?with inverse opal structure titanium dioxide and ionic liquids.Inverse opal titanium dioxide?TiO₂IO?has three-dimensional ordered periodic and porous structure,which is conducive to the rapid transfer of Li ions.The reflected spectrum?RS?and scanning electron microscope?SEM?confirmed the periodically ordered structure of TiO₂IO.The inhibition test of TiO₂IO-PILs on lithium polysulfide proved that it has a good inhibitory effect on the lithium polysulfide shuttle.Electrochemical impedance experiments proved that TiO₂IO-PILs has an ionic conductivity of 10^-2 S/m to 10^-3 S/m.In the second part of the work,we designed and prepared polymer films of titanium dioxide nanotubes and ionic liquids?TiO₂NTs-PILs?.In the design,titanium dioxide nanotubes with a high aspect ratio are entangled with each other to form a three-dimensional network structure,which can reduce the intersection of connections and junctions,create longer ion transport channels,and promote rapid Li⁺transfer.The polyionic liquid filled in the titanium dioxide nanotube framework can form a dense structure that blocks the movement of polysulfides at the physical level The electrostatic attraction between TiO₂ and sulfur?S-Ti-O?can further suppress the shuttle effect of polysulfides.The combination of these two substances can effectively inhibit the shuttle of polysulfides and avoid the loss of active substances.The polysulfide inhibition test directly proved that TiO₂NTs-PILs has a good inhibitory effect on polysulfides.The conductivity of TiO₂NTs-PILs as the quasi-solid electrolyte is between 10^-22 S/m to 10^-33 S/m,which suggests that polymer films of TiO₂nanotubes and ionic liquids have higher ionic conductivity.At a rate of 0.1 C,the capacity of the lithium-sulfur battery still maintains 1360 mAh·g^-1 after 40 cycles,which proves that the TiO₂NTs-PILs film has good electrochemical performance as a quasi-solid electrolyte for the lithium-sulfur battery.It is further proved that the inhibition of lithium polysulfide by TiO₂NTs-PILs film avoids the decline of battery capacity.