Optimization Of The Beta-Al₂O₃ Solid-state Electrolyte/Sodium Metal Anode Interface And Electrochemical Performance

Large-scale energy storage technologies urgently demand electrochemical energy storage devices with high energy density,high security and low cost.Sodium ion batteries（NIBs）and sodium metal batteries（NMBs）based on abundant sodium elements are considered as two main secondary batteries.The inflammable and explosive safe hazard organic solvent electrolyte in the present NIBs or LIBs promotes the development of various solid-state electrolytes.Beta-Al₂O₃,an oxide solid state electrolyte,has high mechanical strength,high Na⁺conductivity,competitive electrochemical stability and a wide electrochemical operating voltage window.However,the large interfacial impedance between Beta-Al₂O₃ solid electrolyte and sodium metal at room temperature and the growth of sodium dendrites are bottlenecks that hinder the development of Beta-Al₂O₃ solid electrolytes.This thesis focuses on the Beta-Al₂O₃/Na interface issue and proposes the following three modification strategies to achieve interfacial property modulation and electrochemical performance optimization.The specific achievements that have been made are summarized as follows:（1）Gel polymer interlayer modified Beta-Al₂O₃/Na interface.An elastic and porous PVDF-HFP/PMMA polymer film was used as an intermediate layer between the Beta-Al₂O₃ solid electrolyte and the sodium metal electrode,by taking the absorption and coverage capability of the gel polymer film for the electrolyte to optimize sodium ion transport providing an effective pathway to reduce the interfacial impedance and increase the critical current density to 0.85 m A cm^-2,which in turn inhibited sodium dendrite growth.The modified tight-contact Beta-Al₂O₃/Na interface was applied to a room-temperature all-solid-state sodium-metal cell,which could be stably cycled for 500 cycles at room-temperature with a capacity retention rate of88.9%.（2）Constructed a tightly bound Beta-Al₂O₃/Na interface by ultrasonic welding.The introduction of high-frequency ultrasonic vibration energy to Beta-Al₂O₃/Na leads to atomic slip then extension coverage of sodium for plastic deformation on Beta-Al₂O₃even at room temperature.A uniform and continuous Beta-Al₂O₃/Na-UW interface was constructed within one minute,enabling the Beta-Al₂O₃ solid sodium cell to operate stably at room temperature.Benefiting from the physical contact between the Beta-Al₂O₃ solid-state electrolyte and the sodium electrode,the improved Beta-Al₂O₃/Na-UW interface impedance was reduced to 73?cm~2.The Na₃V₂（PO₄）₃??Beta-Al₂O₃??Na-UW solid-state sodium metal battery assembled by room temperature ultrasonic welding were capable of 200 stable cycles with a capacity retention rate of87.7%.（3）In situ derivation of hybrid conductive layers from SnS₂ modified layers to modify the Beta-Al₂O₃/Na interface.The Na₂S and Na-Sn alloy generated by the in situ chemical reaction between Na and SnS₂ were applied to construct a hybrid conductive layer at the Beta-Al₂O₃/Na interface to achieve a high stability of the Beta-Al₂O₃/Na solid electrolyte interface.The interfacial resistance of the modified Na??SnS₂-Beta-Al₂O₃-SnS₂??Na symmetric cell was reduced to 96Ωcm~2;The modified symmetric cell had a critical current density of 1m A cm^-2 and it cycled steadily for 2100 h at a current density of 0.2 m A cm^-2 with an overpotential of less than 60 m V.The ameliorative Beta-Al₂O₃-SnS₂/Na interface was applied to a room-temperature all-solid-state sodium-metal battery,which can be cycle stably for 200 cycles with a capacity retention rate of 95.8%.