| Li-S battery delivers the possibility beyond the state-of-the-art lithium-ion battery due to its high specific energy density.However,the uncontrollable ionic dynamicses at S and Li metal electrode interface hinder the actual application.For instance,the shuttling of polysulfide anions and the slow migration of Li ions inside the S electrode result Li-S battery with poor cycling stability and rate performance,respectively.While low concentration and strong solvation of Li ions nearby Li metal electrode interface cause Li metal electrode with many challenges such as Li dendrite growth,interface polarization and SEI reconstruction during cycles,aggravating the degradation of Li-S electrochemical performance,thus hindering the actual applications.Herein,in this dissertation,investegations via slowing down the shullte of polysulfide anions in elelctrolyte,promoting the diffusion of lithium ions within sulfur electrolde,increasing the ion concentration at the lithium metal surface and regulating the solvation of lithium ions nearby lithium metal electrode are preformed,aiming to improve the interface stability of S and Li electrolde for promoting commercialized Li-S battery with higher electrochmical performance.The researches are as follows:1.For the shullte of polysulfide anions in elelctrolyte,the polysulfide anions are suppressed via two amino functionalized polar binders which are prepared by crosslinking polyethylenimine(PEI)with hexamethylene diisocyanate(HDI)or poly(ethylene glycol)diglycidyl ether(PEGDGE),denoted as AFG and PPA binders,respectively.The regulation effects of two binders on polysulfide anions at the reaction interface of S electrode by adopting polar chemical bonds such as S-N,Li-O,Li-N and S-O are investigated.Results show that introducing polar chemical bonds at the reaction interface of S electrode can slow down the shuttle of polysulfide anions in electrolyte and improve the cycling stability of S electrode.For instance,S electrode cycles stability with capacity retention rate of 91.3%over 600 cycles as using AFG binder.Moreover,PPA binder allows the adhesive strength between S electrode material and current collector reachs up to 0.4 Mpa,indicating that hydrophilic groups such as-OH group embed into binder framework can improve the adhesion of binder,ensuring the structural integrity of S electrode.In addition,in-situ techniques such as in situ UV-Vis and Raman are provided to confirm the advantages of proposed binders.2.For the diffusion issues of Li ions,atomic interlamellar ion path lithium-montmorillonite(Li-MMT)via forming interlayer ion channel within S electrode to decrase the migration barrier,facilitating Li ion diffusion within the entire S electrode,is employed.It is found that Li-MMT enhances the Li ion transport and redox kinetic processes at reaction interface,decreasing the concentration polarization under high S loading and high current density.When conbined with 80%sulfur content,the prepared Li-MMT/S composites enable Li-S battery with a discharge capacity of 345 m Ah g-1 with4 mg cm-2 S loading even at a current density of 15 m A cm-2 after constructing Li-MMT as fast ion transfer paths.In addition,the Lewis acid/base site of Li-MMT provides lewis acid-base effect on polysulfides,ensuring stable cycles of S electrode more than 350cycles with a capacity decay rate of 0.049%per cycle when sulfur loading is 5.2 mg cm-2and current density is 8 m A cm-2.3.For the barren region of Li ions at the Li metal surface,lithiophilic MMT coupled with polyethylene oxide(PEO)as additive in the ether-based electrolyte,denoted as MIP-based electrolyte,is reasonably designed to concentrate the Li ions near the surface of MMT and improve the Li ion concentration on the anode surface(e.g.,Li metal anode),thus promoting the homogeneous nucleation of Li ions as well as suppressing Li dendrite growth.The experimental results show that MIP based electrolyte allows Li||Cu half cell with stable Li plating/stripping more than 300 cycles at a current density of 0.5 m A cm-2with a capacity of 1 m Ah cm-2.Moreover,the Li||Li symmetric battery enables stable cycles more than 1200 h as repalcing the ether based electrolyte with MIP based electrolyte,allowing Li-S battery with 99.62%average coulomb efficiency among 100cycles.In addition,the variation of ionic concentration at the electrode interface during plating process is visualized via in-situ Raman technology,confirmed the effectiveness of MIP-based electrolyte on regulating ionic concentration nearby the Li electrode interface.4.For the solvation of Li ions at the Li metal electrode interface,oxidized tri(2,4-di-tert-butylphenyl)phosphite(O-TBP)coupled with tetrabutylammonium fluoride(TBAF),denoted as RMH layer,customized on the interface of Li metal electrode is investigated on the effect of constructing SEI components.Using theoretical simulation,Raman detection,cryo-electron microscopy,X-ray photoelectron spectroscopy deep profiling and other characterization techniques,it is clear that weakening the solvation intensity of Li ions with solvent molecules and introducing fluoride anion(F-)nearby the electrode interface can reduce the participation of solvent molecules and increase lithium fluoride(Li F)component in SEI,forcing the lateral growth of Li nuclei,and avoiding the formation of lithium dendrites.The experimental results show that RMH modified Li metal(RMH@Li)stably cycles more than 800 h at a current density of 3 m A cm-2 with a capacity of 3 m Ah cm-2.Moreover,RMH@Li enables Li-S pouch cells contributing600 m Ah/pouch over 50 cycles with a capacity decay rate of 0.26%per cycle.In addition,the O-TBP component in RMH layer reduces the molecular hydrogen bonding cooperation between Li and water molecules,thus effectively prevents the moisture-sensitive Li from water corruption.In the experiment,RMH@Li still miantians nature features and negligible influences on its electrochemical properties even RMH@Li is exposed to RH=50?60%humid air for 1h. |
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