Study On Preparation,Compositing And Interfacial Modification Of Li_1.3Al_0.3Ti_1.7（PO₄）₃ Solid Electrolyte

Lithium-ion batteries,with high energy density and long cycle life,have been widely used in consumer electronics,new energy vehicles,energy storage power stations and other fields.However,the organic electrolytes used in lithium-ion batteries have some safety problems,such as volatilization,leakage and combustion.The use of solid electrolytes instead of liquid electrolytes and diaphragm can effectively solve these problems.Besides the energy density of solid-state batteries can be further enhanced by use lithium metal,which has extremely high theoretical capacity(3860 m A h g^-1)and the lowest redox potential（-3.04 V vs.SHE）,as negative electrode.Among all kinds of solid electrolytes,NASICON solid electrolytes(Li_1+xAl_xM_2-x（PO₄）₃,M=Ti or Ge)have the advantages of high ionic conductivity,good air stability,low synthesis cost and low density,becoming one of the most promising solid electrolyte materials.However,there are two important disadvantages when it matched with lithium metal.First,it can be easily reduced by lithium metal along with the valence change from M⁴⁺to M³⁺,resulting in increased interfacial impedance.Second,solid-solid contact between rigid solid electrolyte and lithium metal obstructs Li⁺transmission and promotes lithium dendrite growth.Therefore,in this paper,Li_1.3Al_0.3Ti_1.7（PO₄）₃（LATP）was taken as the typical representative of NASICON solid electrolytes.Polymer in Salt strategy was introduced to prepare composite solid electrolyte and construct interface protective layer to solve the problems of interface reaction and high interface impedance.The specific research contents are as follows:（1）LATP powder with high crystallinity was prepared by high temperature solid-state method combined with ball milling.The effects of sintering temperature and ball milling process on the crystal structure and size morphology of LATP were investigated.By cold pressing and press-free sintering of LATP powder,LATP ceramic with high density was obtained.LATP delivered high ionic conductivity of 3×10^-4S cm^-1 at room temperature,and the activation energy was0.28 e V.It laid a foundation for the preparation of composite solid electrolyte and interface modification.（2）Polymer in Salt（Pi S）solid electrolyte with high ionic conductivity was prepared by adjusting the ratio of Polymer and lithium salt.The introduction of LATP further reduced the crystallinity of polymer matrix,which was conducive to the movement of polymer segments and the migration of lithium ions.The ionic conductivity of the composite solid electrolyte（CSE）was 7×10^-4 S cm^-1.Assembly of Li Fe PO₄||CSE||Li battery had 154 m A h g^-1 discharge specific capacity at 0.2 C,120 m A h g^-1at 2 C.After 200 cycles at 1 C rate,the specific discharge capacity was 63 m A h g^-1 and the capacity retention rate was 46%.（3）Pi S interfacial protective layer was constructed on the LATP surface.The flexible Pi S protective layer with high ionic conductivity could effectively reduce interfacial impedance,avoid the interfacial reaction between LATP and lithium metal.The assembled lithium-symmetric battery could cycle stably for 400 hours at a current density of 0.16 m A cm^-1.The all-solid-state battery with Li Fe PO₄ as cathode and lithium metal as anode had excellent cycling and rate performance.A high discharge specific capacity of 124.0 m A h g^-1 was achieved at a current rate of 2 C.After 300 cycles,a discharge specific capacity of as high as 140.6 m A h g^-1was achieved,corresponding to a capacity retention of 97.2%.No lithium dendrite was formed.