Synthesis Of Organic-Inorganic Laminar Composite Membranes And Investigation Of Lithium Sulfur Battery Performance

Lithium–sulfur?Li–S?batteries,based on sulfur electrochemistry involving multi-electron conversion and phase transformation,have spawned intensive research owing to its high theoretical specific energy density of 2600 Wh kg^-1.However,liquid Li–S batteries often confront the shuttling of intermediate polysulfides,leading to fast capacity decay and high self-discharge.Meanwhile,the inflammable and explosive nature of organic electrolyte tends to cause thermal runaway of battery.By comparison,solid electrolyte possesses some inherent advantages,including:stable thermal property,high mechanical strength and polysulfides-inhibiting ability.However,the high thickness?>100?m?,low inherent Li-ion conductivity,and high area-specific resistance limit their applation for all-solid-state Li–S batteries.In light of these problems,this study mainly aims at improving polysulfides-inhibiting and Li⁺conduction by properly constructing organic-inorganic laminar composite membrane and synergistically manipulating microenvironments.The microstructure-property relationship could be comprehensively elucidated,and a new strategy for intensifying polysulfides-inhibiting and Li⁺conduction was proposed.Consequently,Li–S cells with high-performance modified separator and solid composite electrolyte were fabricated.The details were summarized as follows:?i?Modification of commercial separator surfure:For solving the problem of polysulfide shuttle effect in porous commercial separator?PP?of liquid lithium–sulfur battery,a modification strategy of organic-inorganic laminar composite membrane was proposed.A highly ordered layer-by-layer laminar modified layer was obtained by mixture-filtration methods,where rigidity and conductivity MXene and Nafion with rich sulfonic acid groups were employed as modified materials.As a result,the2D MXene sheet stacked into defect-free laminar film.This film brought long-range channels to physically inhibit the diffusion of polysulfides,and the electron conduction of MXene helped the film to reutilize the trapped polysulfides.For another,Nafion could work as a surfactant to realize the ordered layer-by-layer deposition of MXene sheets.The intercalated Nafion tuned channel microenvironments,where–SO₃^–groups on Nafion could electrostatically repulse polysulfides.The laminar MXene-Nafion composite realized the synergism of electrostatic repulsion,physical resistance,and polysulfide reutilization.Thus,the cell combined with MX-NF/PP achieved highly enhanced initial capacity(1234 vs.834 m Ah g^-1 for PP cell).Moreover,the resultant Li–S cell showed exceptional cycling stability:ultralow capacity decay of 0.03%per cycle over 1000 cycles at 1C,outperforming PP cell?0.1%??ii?Development of new laminar composite solid electrolyte:According to the requirements of all-solid-state lithium–sulfur batteries,a tactic for preparing high Li⁺conductive organic-inorganic laminar composite electrolytes was proposed.It was prepared by a swelling-filtration method using electronic insulation vermiculite nanosheet with rich Lewis acid and ion-conducting PEO as building blocks.It showed that the thickness of Vr-PEO-CSPE was only 10?m.The orderly stacking of vermiculite could ensure the stability of layered structure and its acidic surface facilitated lithium salt dissociation by Lewis acid-base interaction.Further infusing PEO into interlayer,the nanoconfinement effect reduced PEO crystallization,thus constructing a long-range continuous lithium ion transfer channel with low-energy-barrier interlayer channels.The area-specific-resistance of resultant composite electrolyte was only 66?cm²,which was two orders magnitude lower than that of pure PEO electrolyte.After 150 cycles,the Li–S cell assembled with Vr-PEO-CSP at 0.05 C and 60 ^oC remained a high capacity of 1017 m Ah g^-1,which was even more than 183 m Ah g^-1 higher than the initial capacity of Li/PEO-SPE/S cell.