Modification Of The Interface Between Na₃Zr₂Si₂PO₁₂ Solid-State Electrolyte And Na Metal Anode For The Improved Performance Of Batteries

Na₃Zr₂Si₂PO₁₂（NZSP）solid-state electrolyte has the characteristics of high ionic conductivity,wide electrochemical window and good mechanical properties,which has great potential in solid-state Na-ion batteries.However,the physical contact and wettability between Na metal and NZSP solid electrolyte are poor,resulting in excessive interfacial resistance,which affect the electrochemical performance of solid-state Na-ion batteries.This limits the development and application of solid-state Na-ion batteries.In this paper,various targeted strategies are proposed to improve the interface between Na metal and NZSP,and improve the electrochemical performance of solid-state Na-ion batteries.The main achievements are shown as follows:The wettability and physical contact of Na/NZSP interface is enhanced by coating TiO₂ film on the surface of NZSP,which increases the transport rate of Na⁺and reduces the interfacial resistance.Na and TiO₂ film forms Na_xTiO₂ passivating layer during the cycling,which promotes the uniform deposition and release of Na⁺at the interface,and maintains a good stability of the interface.However,the modification of Na/NZSP interface by TiO₂ film cannot make the cell work at a higher current density,and further optimization and improvement of film materials are required.By coating the surface of NZSP with SnO_x/Sn film,the Na⁺transport capacity at the interface is enhanced.The Na₁₅Sn₄ layer is formed at the interface during the cycling,which maintains the stability of the interface,and inhibits the side reactions and the growth of Na dendrites at the Na/NZSP interface.Benefited from the improvement of SnO_x/Sn film,the interfacial resistance of Na/NZSP interface is reduced to 3Ωcm²,and the Na symmetric cell can cycle stably at the current density of 0.3 mAcm^-2 and0.5 mAcm^-2,while maintaining a low overpotential.The second-phase of TiO₂ is introduced into the grain boundary of NZSP by co-firing process to improve the stability of Na/NZSP interface and simplifies the modification process.Compared with the film materials to improve the interface,the second phase of TiO₂ also enhances the bonding between NZSP grains,which increases the mechanical properties of NZSP.In addition,the uniform current density in the cell effectively inhibits the growth of Na dendrites,which improves the cycling performance of solid-state batteries and the critical current density of quasi-solid-state batteries.The anode side interface of the solid-state battery is modified by removing side reaction products and forming Na defects on the surface of NZSP after heating treatment.The Na defect results in the presence of active O bond on the surface of NZSP,which enhances the adhesion between Na metal and NZSP,and reduces the interface resistance of Na/NZSP interface.During the cycling,the Na₂O passivating layer formed at the interface maintains the interface stability.Compared with the modification of second-phase,the surface Na defect modification can make the Na symmetric cell cycle stably at higher current densities(0.2 mAcm^-2 and 0.3 mAcm^-2).The performance of solid-state full-battery is also improved by this simple modification process.In this paper,the wettability and physical contact between Na metal and NZSP solid electrolyte are improved by optimizing the film materials and simplifying the interface modification process,and thus the transport capacity of Na⁺at the Na/NZSP interface is improved.Meanwhile,these interface modifications also maintain the stability of Na/NZSP interface during the cycling,and improve the cycling performance of solid-state batteries.