Preparation Of LATP-based Solid Electrolyte Membrane And Its Application In All-solid-state Lithium Batterie

All-solid-state lithium batteries（ASSLBs）are the effective substitute for future energy storage battery technology due to its high safety and potential excellent energy density.Solid electrolyte is the key to realize the application of high activity cathode and anode electrodes.Designing and developing solid electrolyte with high ionic conductivity and high stability is the core of developing all-solid-state lithium battery.NASICON-type Li_1+xAl_xTi_2-x（PO₄）₃（LATP）solid electrolyte is considered as the ideal electrolyte material for all-solid-state lithium batteries due to its superior ionic conductivity and stable chemical/electrochemical performance.Therefore,it is of great significance to further study the membrane forming process of LATP solid electrolyte and further solve the interface problem between LATP and electrode for promoting the practical development of all-solid-state lithium batteries.In this paper,from two aspects of LATP solid electrolyte membrane forming process and interface problems,the applicability of new forming process to the preparation of LATP solid electrolyte membrane was discussed,and the influence of structure design on improving the interface problems was studied.The main contents are as follows:LATP solid electrolyte powders were prepared by sol-gel method.The characterization results of X-ray diffraction,Raman spectroscopy,and transmission electron microscopy showed that the LATP solid electrolyte powders were pure phase powders with small particle size（1-10μm）and large specific surface area(8.62 m² g^-1).The prepared LATP solid electrolyte powder was used as the casting powder,and the LATP tape was prepared by the aqueous tape casting technique.The surface of the tape was smooth and flat without defects,and then the LATP solid electrolyte membrane was prepared by the lamination/hot-pressing/sintering technique.By optimizing the sintering conditions of LATP solid electrolyte membrane,it was found that the LATP solid electrolyte membrane prepared by sintering at 850℃for 3 h can provide 3.75×10^-4 S/cm ionic conductivity at 25℃,and its density is as high as 95.56%.A sandwich type PPAL-LATP-PPAL solid electrolyte membrane was prepared by coating the self-made PPAL polymer electrolyte on both sides of LATP solid electrolyte membrane.The PPAL-LATP-PPAL solid electrolyte membrane has good electrochemical performance,the ionic conductivity can reach 5.04×10^-4 S/cm at 60℃,and the electrochemical stability window limit is extended to 5.71 V vs Li⁺/Li.Li/PPAL-LATP-PPAL/Li symmetrical battery can cycle stably for more than 500 h at different current densities.The Li Fe PO₄/PPAL-LATP-PPAL/Li all-solid-state lithium battery has a high discharge specific capacity of over 120 m Ah g^-1 at 1 C and a capacity retention rate of 82.5%after 100 stable cycles at 0.2 C.LATP/PPAL composite solid electrolyte was prepared by dispersive LATP solid electrolyte into PPAL polymer electrolyte.According to the mass ratio of LATP to PPAL,it can be divided into PPAL-LATP polymer-rich electrolyte and LATP-PPAL ceramic-rich electrolyte.The addition amounts of LATP solid electrolyte in PPAL-LATP polymer-rich electrolyte and LATP-PPAL ceramic-rich electrolyte were optimized respectively.X-ray diffraction and differential scanning calorimetry showed that the addition of LATP solid electrolyte can reduce the crystallinity of PPAL polymer electrolyte.Impedance results showed that 20%LATP-80%PPAL polymer-rich electrolyte and 70%LATP-30%PPAL ceramic-rich electrolyte could provide 3.21×10^-4 S/cm and 4.02×10^-4 S/cm ionic conductivity at 60℃,respectively.A sandwich structure of CIP-PIC-CIP composite solid electrolyte was prepared by combining 20%LATP-80%PPAL-rich polymer electrolyte and 70%LATP-30%PPAL-rich ceramic electrolyte using multi-layer tape casting technology.The design of multilayer structure not only improves the stability of solid electrolyte against lithium metal(polarization voltage is only 0.07 V at 0.1 m A cm^-2 current density),but also improves the electrochemical window of solid electrolyte（the upper limit of electrochemical window is 6.17 V）.The assembled Li Fe PO₄/CIP-PIC-CIP/Li all-solid state lithium battery can provide 161.97 m Ah g^-1 discharge specific capacity（60℃）at 0.2 C,and can still provide 160.29 m Ah g^-1 discharge specific capacity after the rate cycle back to 0.2 C.And after 100 cycles can still reach 158.58 m Ah g^-1,its capacity retention rate is as high as 98.93%.