| Lithium-ion battery is the most potential chemical energy storage device,but the current commercial lithium battery mainly uses organic electrolyte,energy density has been developed to close to the limit,and there are serious security risks and other problems.It is of great significance to develop all-solid-state lithium batteries with inorganic solid ceramic electrolytes,which is expected to break through the energy density bottleneck of traditional lithium batteries,and is expected to completely solve the burning,explosion and other safety problems.In order to completely replace liquid organic electrolytes,solid electrolytes developed should have the basic properties of high lithium-ion conductivity,wide electrochemical window and good chemical stability to electrode materials.The Li7La3Zr2O12-based garnet type lithium-ion conductor meets the above three requirements and is considered to be one of the candidates for the next generation of high safety all-solid lithium battery electrolyte materials.This thesis focuses on the ionic conductivity at room temperature,interfacial resistance and cyclic stability,carries out related work around the garnet LLZO electrolyte material performance optimization and interface modification.Specific research contents include the preparation and electrochemical performance of Nb/Ta co-doped LLZO electrolyte material,the integrated design and performance of double-layer composite electrolyte membrane with cathode,and the performance of double-layer integrated structure in high-nickel NCM ternary cathode cells,etc.The main achievements obtained are summarized as follows:（1）LLZO solid electrolyte with high ionic conductivity was prepared by high-temperature solid-state reaction.The cubic-LLZO with stable structure at room temperature was obtained by using the strategy of Nb and Ta co-doping Zr sites.It was found that 900℃was the best temperature for phase synthesis.The Nb0.4Ta0.2 co-doping garnet Li6.4La3Zr1.4Nb0.4Ta0.2O12 powder has the optimal sintering activity,using conventional non-pressure sintering technology can obtain the high density of 98.44%.The density of ceramic sintering in O2 is 3%higher than that of sintering in air The LLZNTO ceramics sintered at1100℃for 6 h can be densified,with the ionic conductivity is 7.9×10-4 S cm-1 at 25℃,and the assembled Li-Li symmetric battery can stably cycle for more than 1 200 h at the current density of 0.5 m A cm-2,indicating that it has a high ability to inhibit lithium dendrites.（2）The flexible composite solid electrolyte membrane was prepared by the hybrid strategy of garnet LLZNTO and polymer PEO,and the in situ integrated of double-layer functional electrolyte and cathode structure（ID-FCC）was designed,which significantly improved the interface contact problem.In order to solve the problem of high pressure oxidation decomposition of PEO components,an extra layer of PVDFLi FSI-10 wt%LLZNTO composite membrane transition layer with high pressure resistance was constructed at the cathode surface.The double-layer design avoided the oxidation decomposition of the original PEOLi TFSI-10 wt%LLZNTO.At the same time,the transition layer plays a role in strengthening the interface contact.The test results show that the electrochemical window of the membrane is 4.64 V,and the ionic conductivity at room temperature reaches a high level of 4.60×10-4 S cm-1.The symmetrical cell test showed that it could cycle for more than 2400h at a current density of 0.05 m A cm-2 without short circuit.The EIS test of the full cell showed that the interface contact improved significantly with cycling,and the resistance decreased from the initial 600Ωto 480Ωafter 180 cycles.These results indicate that ID-FCC structure design has excellent dendrite inhibition and interfacial wetting ability.（3）The LFP-ID-FCC/Li solid-state battery with this design showed an initial discharge capacity of 161.5m Ah g-1 at 0.1 C and a stable 1000 cycles with a capacity decay rate of0.044%.The initial discharge capacity of 130.2 m Ah g-1 and the remaining capacity of 106m Ah g-1 after 400 cycles were achieved at a high rate of 0.5 C,showing excellent cyclic stability.The applicability of the design of ID-FCC was tested in four kinds of cathode materials with different nickel content.The results showed that the performance of ID-FCC was relatively best in the Ni83-ID-FCC/Li.The initial discharge capacity of 0.1 C is close to200 m Ah g-1,and the capacity fading is 0.33%per cycle.But in the other three kinds of ternary cathode system performance is not good.（4）The multilayer composite electrolyte and cathode were synthesized by the method of casting and scraping coating.In situ construction technology simplifies the complex process of preparing and assembling cathode and multilayer electrolyte film respectively,saves a lot of time,reduces the material loss,and is expected to achieve large-scale production. |
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