The Study On Multifunctional Additives And Solid-State Garnet Electrolyte For Lithium-Sulfur Batteries

Lithium-sulfur?Li-S?battery with the advantages of a high theoretical specific capacity(1672 m Ah g^-1),low cost and environmental friendliness consists of lithium metal anode and sulfur cathode,which is expected to be developed and applied in the field of power batteries in the future.However,the scale application of Li-S batteries is restricted by the disadvantages of Li and sulfur.In the sulfur electrode,the insulating property of the sulfides causes a low utilization rate of the active material.More importantly,the“shuttle effect”of polysulfides?Li PSs?leads to continuous loss of the active material,so the cycling capacity of Li-S battery is rapidly decreased.In the Li anode,lithium dendrites grow severely in conventional liquid electrolytes,which can cause short circuits,inflammation and even explosion.Therefore,the key to achieving Li-S battery with a high stability is to suppress the shuttling of Li PSs and the growth of lithium dendrites.This thesis proposes that using multi-component material Li Ni_0.8Co_0.15Al_0.05O₂?NCA?as a multi-functional additive for Li-S battery.NCA can simultaneously promote the conversion of Li PSs and absorb Li PSs,which was verified theoretically and experimentally.In addition,through the structure and interface design of garnet electrolyte,the application of hybrid solid-state electrolyte and all solid electrolyte in Li-S battery is studied,which is of great significance for the development of Li-S battery with high stability and safety.Firstly,based on the layered ternary NCA,a strategy of"kill two birds with one stone"was proposed to enhance the cycling stability of Li-S batteries.The interaction mechanism between NCA and Li PSs was first studied.The formation of Li-O and Co-S bonds is beneficial for NCA to effectively immobilize Li PSs.In addition,NCA can reduce the impedance and improve Li⁺diffusion coefficient of Li-S batteries,thereby enhancing the redox reaction kinetics of Li PSs conversion.The addition of NCA greatly improved the cycling stability of the Li-S battery,and a specific capacity of 755.4 m Ah g^-1 with a high capacity retention rate of 90.0%was achieved after 500 cycles at 1 C.Secondly,three-dimensional,disordered and connected channels were constructed in the LLZO electrolyte by template method,and the morphology and structure of the channels were characterized in detail.The hybrid electrolyte based on porous LLZO electrolyte can inhibit the penetration of lithium dendrites effectively.Li-Li symmetry cell based on hybrid electrolyte with a current density of 0.5 m A cm^-2 and an areal capacity of 0.5 m Ah cm^-2 per half cycle can cycle for 1380 h and the cumulative discharge capacity reached 345 m Ah cm^-2.At last,the Sn N_x-based interfacial layer was modified on the surface of LLZO electrolyte by magnetron sputtering,and the chemical composition of Sn N_x was characterized as Sn₃N₄.The interfacial layer has a good wettability with Li,so the interfacial impedance between the LLZO electrolyte and Li is significantly reduced.Moreover,the interfacial layer can effectively inhibit the growth of lithium dendrites in the solid electrolyte,and Li-Li symmetry cell stably cycled for 500 h at 50?A cm^-2 and100?A cm^-2.