Study On Preparation And Modification Of NASICON Electrolyte For Solid State Lithium Batteries

NASICON-type LATP(Li_1.3Al_0.3Ti_1.7（PO₄）₃)material has become a solid electrolyte of great concern due to its good electrochemical stability and high ionic conductivity.In the field of solid-state batteries,it is mainly used in two aspects,as a ceramic electrolyte sheet and as an inorganic frame in the organic solid electrolyte.Because of the side reaction of lithium metal,the use value of the former is greatly limited.Also,the latter has a limited range of applications due to the low conductivity of inorganic-organic composite electrolyte.In order to solve these problems,this article has carried out research from the following three aspects.The specific content is as follows:（1）The LATP nanopowder with a D50 value of 3.8μm is prepared by an improved sol method.The phase formation process of the precursor is analyzed by Tg-DSC and XRD methods.The precursor is hydrothermally coated with boric acid（H₃BO₃）and combined with yttrium oxide（Y₂O₃）,which builds a BY-LATP material with a double coating layer of the matrix LATP.XRD analysis and Rietveld results show that the introduction of boron and yttrium oxide does not destroy the phase structure.The unit cell parameters become smaller.The Tg-DSC analysis explores the thermodynamic process of cold pressing sintering.SEM results show that the porosity and grain boundaries of the ceramic decrease.The large unit cell changes from a curved shape to a brick shape,which the density increases to 95.1%.EDS mapping and TEM results confirmed the existence of the double cladding layer.Under the same conditions,the room temperature ionic conductivity of BY-LATP is about twice that of LATP,which is 2.04×10^-4 S·cm^-1,and the activation energy is also reduced to 0.24e V.At room temperature,the Li Fe PO₄ solid-state battery can still maintain 125 m Ah·g^-1 after 100 cycles of 0.5C rate cycle.Under the long cycle of lithium symmetrical battery,there is no sudden change in polarization voltage.The constructed coating layer effectively solves the problem of side reactions at the Li metal interface while improving ion conductivity.（2）Succinonitrile is introduced to modify the LATP-PEO composite electrolyte.The thermal results show that the glass transition temperature and melting temperature of the system decreased.The enthalpy value decreases.And the decomposition of the organic phase is completed above 440℃.XRD results show that LATP can reduce the crystallinity of PEO,and the SN can amplify this effect.SEM and EDS mapping analysis shows that the introduction of the SN small molecules can reduce the porosity of the membrane and improve the connection between LATP and PEO.The constructed positive electrode and the electrolyte coating interface is in good contact.The infrared results show that the introduction of the SN promoted the decomposition of the long chain of PEO.When SN=0.1,the ion conductivity can reach to 3.0×10^-5 S·cm^-1 at 55℃.The activation energy is 0.44e V.The migration number of Li⁺is 0.41.The introduction of SN increases the electrochemical window of the LATP-PEO composite electrolyte.The assembled Li Fe PO₄ solid-state battery shows a good cycle performance of 134 m Ah·g^-1at a charge and discharge rate of 0.5C at 60℃,and the single crystal NCM811 positive electrode shows a capacity retention rate of 93.5%at high temperatures.The lithium symmetrical battery shows that the long-cycle electrolyte membrane has no puncture and obvious interface side reactions,and the polarization voltage is stable.（3）In this paper,NH₄I/DMSO solution is used to treat Li metal surface to construct an artificial protective layer Li₃N/Li I in situ.In-situ optical observations show that the constructed protective layer can reduce the continuous growth of lithium dendrites without hindering the transmission of lithium ions.XRD analysis detects the presence of two phases.SEM and EDS mapping indicat that the protective layer is in good contact with the lithium metal.Lithium symmetrical battery exhibits good Li⁺shuttle capability and stable polarization voltage.The cycle performance of Li Fe PO₄/LATP/treat-Li solid-state battery shows gradual activation and stability,and the capacity is stable at 121m Ah·g^-1 at a rate of 1C.The charge-discharge curve shows that the platform polarization difference is large,but the platform is stable.XPS results show that Ti⁴⁺still occupies the main valence state after the cycle,and the in-situ treatment of NH₄I/DMSO solution effectively inhibited the side reaction of LATP and lithium metal.