Preparation LLZO/PEO Composite Solid Electrolyte And The Characteristics Of Interface With Lithium Metal

All-solid-state batteries have attracted much attention because of their higher safety,but inorganic solid electrolytes and polymer solid electrolytes have been extremely limited due to their performance differences in the practical applications of all-solid-state batteries.Therefore,it is crucial for solid electrolyte to have excellent performance to be further developed in the all-solid-state batteries.In this paper,the high-density,high-ionic-conductivity cubic LLZO prepared by field assisted sintering technology（FAST）were used to grind into LLZO powders,and then were used as inorganic fillers in the PEO polymer solid electrolyte matrix,the LLZO/PEO composite solid electrolyte with high ionic conductivity and stable electrochemical performance was prepared at room temperature.The effect of LLZO on the lithium ion conductivity,electrochemical performance,and thermodynamic properties of LLZO/PEO composite solid electrolyte was systematically studied.The copolymer PEDOT-co-PEG was used as the surface modification layer of the metal lithium negative electrode to improve its stability in the all-solid-state battery,At the same time,the LiFePO₄ positive electrode material and the LLZO/PEO composite solid electrolyte material were used to assemble all-solid-state batteries and their performance in all-solid-state batteries was tested.Transparent and uniform thickness LLZO/PEO composite solid electrolytes were prepared by solution casting method.The lithium ion conductivity,electrochemical window,thermal stability and stability with metal lithium were systematically studied.The results showed that LLZO/PEO composite solid electrolyte with 7.5 wt.%LLZO at room temperature had the highest ionic conductivity of 5.5×10^-5S·cm^-1,and the electrochemical window exceeded 5.5 V with good thermal stability,the lithium ion transference numbers has also been improved,and the interface with lithium metal is relatively stable.XRD and DSC tests were used to analyze the phase transition behavior of LLZO added to PEO polymer.The mechanism of LLZO on improving the ionic conductivity of it was discussed by FT-IR,that is,the addition of LLZO weakened the complexation between ether oxgen and Li⁺in PEO.And the LiFePO₄/Li all-solid-state batteries fabricated with LLZO/PEO composite solid electrolyte exhibits fascinating cycle performance and attractive rate capacities of 150.1 mAh·g^-1,138.6 mAh·g^-1,127.5mAh·g^-1,100.2 mAh·g^-1 under current rates of 0.1 C,0.2 C,0.5 C and 1 C at 60^oC,respectively.The interface compatibility between the electrode and electrolyte was studied on the fabricated LiFePO₄//LLZO/PEO//Li all-solid-state battery,the reasons of the battery capacity decay were analyzed and a specific modification method was proposed.The LiFePO4/LLZO/PEO/modified Li all-solid-state battery was assembled,and a good electrode electrolyte interface contact effect was obtained,the specific discharge capacities of LiFePO₄/modified Li all-solid-state batteries rates increased to 158.46mAh·g^-1,142.63 mAh·g^-1,and 125.13 mAh·g^-1 at 0.1C,0.5C and 1C under 60^oC,respectively.