| Solid electrolytes as ion charge transfer layers play a crucial role in all solid-state lithium batteries.NASION type Li1.5Al0.5Ge1.5?PO4?3?LAGP?has attracted a large amount of attention in the past decade,and is considered as one of the most promising solid electrolytes,primarily because of its high ionic conductivity,wide electrochemical window and high interfacial stability.Therefore,it is of great scientific significance and application value to study the solid electrolyte of LAGP,develop low-cost preparation methods,prepare its thin film materials and explore its ion transport characteristics.Firstly,LAGP is prepared by novel sol-gel method and solid-state sintering at different sintering temperatures of 8001000? using low cost inorganic Germanium?GeO2?as the precursor,respectively.The composition,phase transformation and elemental composition during the heating of the LAGP precursors are analyzed by XRD,EDS and TG-DSC.It is found that the LAGP samples are well crystallized and are determined as pure phase LAGP.The structures,morphologies and ionic conductivity of the LAGP are studied by SEM,TEM and EIS.The results show that the grain size increases with the sintering temperature,and the average particle size of LAGP particles sintered for 8h at 950? by novel sol-gel method and solid-state sintering were 1?m and 0.5?m.In addition,The LAGP particles prepared by sol-gel method contain a large number of nanoscale grains surrounded by amorphous regions.However,the further coalescence of grains during the recrystallization increases the interspace between large grains,and is thus harmful to the transportation of Li ions.The conductivities of the sintered LAGP samples first increase and then decrease with an increase in the sintering temperature.The sample with the highest ionic conductivity were sintered at 900?.But The ionic conductivity of the materials prepared by the gel-gel method(4.18×10-4S/cm,activation energy of 0.30eV)is better than that of the solid-state sintering?3.76×10-44 S/cm,activation energy of 0.35eV?.Then,LAGP films were successfully deposited on silicon substrates by RF magnetron sputtering at different substrate temperatures?50600??under Ar atmosphere.The XRD analysis showed that amorphous LAGP films were obtained by RF magnetron sputtering when the substrate temperatures were lower than 200?.Crystalline films with preferred orientation of?104?crystal plane were deposited when the substrate temperature reaches 500?.The surface morphology of the films evolved from a uniform and smooth amorphous structure to a coarse-grained structure with the increase in the substrate temperature,and the crystallized LAGP films exhibit an irregular morphology with a grain size of approximately 1?m as confirmed from the SEM analyses.The EIS measurements show that LAGP film deposited at 200? presents a high ionic conductivity of 1.29×10-66 S/cm,with an activation energy of0.25 eV,and the conductivities of the deposited LAGP samples first increase and then decrease with increasing deposition temperature.The good ionic conductivity of amorphous LAGP is attributed to its open and disordered structure with large excessive volumes. |
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