Study On Fabrication And Properties Of Li_6.4La₃Zr_1.4Ta_0.6O₁₂ Composite Solid Electrolyte By Cold Sintering Process

Li_6.4La₃Zr_1.4Ta_0.6O₁₂（LLZTO）has high ionic conductivity,good chemical stability and wide electrochemical window.The PEO-Li TFSI coordination complex has relatively high ionic conductivity and good thermal stability.The combination of LLZTO and PEO-Li TFSI composite solid electrolyte takes complementary merits of organic and inorganic solid electrolytes.Therefore,it not only has significant advantages in material safety and stability,but also simplifies the design and assembly of the rechargeable lithium batteries.Nowadays,organic-inorganic hybrid solid electrolytes membranes are typically prepared by tape casting or solution casting.Co-sintering of multimaterial systems is difficult due to the differences in thermal stability.The processing temperature windows of sintering ceramics（>1000℃）are much than the temperature of compaction,extrusion,or sintering of polymers（<300℃）.The Cold Sintering Process is a low-temperature sintering technology recently developed for ceramics and ceramic-based composites which can realize the co-sintering of the composite solid electrolyte below300℃.We are looking forward to realize the co-sintering of organic-inorganic hybrid solid electrolytes by Cold Sintering Process.In this paper,based on the Cold Sintering Process,a composite solid electrolyte with excellent performance was prepared through optimization of proportions and sintering conditions.Meanwhile,the correlation between its microstructure and macroscopic electrical properties was obtained.Firstly,based on the Cold Sintering Process,this paper investigated the effects of the addition amount of transport liquid phase Li OH·H₂O,sintering time,and sintering pressure on the microstructure and electrical properties of the LLZTO crystal solid electrolyte.The results show that the ionic conductivity of the LLZTO cold sintered sample is proportional to the relative density of the sample.When more transport liquid phase Li OH·H₂O is added into the raw material powder,the relative density and lithium ionic conductivity of the cold sintered samples both increase at first and then decrease.The LLZTO prepared with 5 wt%of Li OH·H₂O transport liquid phase and cold sintered at 300℃,300 MPa for 3 hours has the best performance,with a relative density of 85.51%and a room temperature ionic conductivity of 1.16×10^-8 S/cm.Secondly,this paper studied the effect of heat treatment on the performance of LLZTO crystal solid electrolyte.The results show that heat treatment can significantly improve the relative density and ionic conductivity of LLZTO cold sintered samples.As the heat treatment temperature increases,the porosity of the sample decreases and the grain size increases.The LLZTO sample heat-treated at 950℃for 2 hours has the best performance.Compared to untreated LLZTO,the relative density increases from 84.32%to 93.14%and the ionic conductivity increases from 1.16×10^-8 S/cm to 7.58×10^-7S/cm.Finally,this paper studied the effects of EO/Li molar ratio n and sintering temperature on the performance of PEO-Li TFSI-LLZTO composite solid electrolyte.As the EO/Li molar ratio n decreases,the relative density of the sample increases,while the ionic conductivity（at room temperature）first increases and then decreases.The relative density of all samples with EO/Li molar ratio n=1 are higher than 85%,and the relative density of the sample with EO/Li molar ratio n=1 and sinter temperature of 270℃reaches 90.34%.When the EO/Li molar ratio n=2,the ionic conductivity is in the order of 10^-4 S/cm.As the sintering temperature gradually increases from 120℃to 300℃,the ionic conductivity of samples with different EO/Li molar ratios all show a downward trend.Under the condition of n=2 and sintering temperature of 150℃,the ionic conductivity（at room temperature）of the cold sintered sample is as high as2.84×10^-4 S/cm.Moreover,the ionic conductivity of the sample maintains at a high level in a wide temperature range.