Preparation Of Sulfide Solid Electrolyte And Its Electrochemical Properties

Among inorganic solid electrolytes,sulfide solid electrolytes have many advantages,such as high lithium ionic conductivity at room temperature,wide electrochemical window(>5.0 V vs.Li+/Li),and good stability for lithium metal.Therefore,sulfide solid electrolyte has excellent application prospects in the new generation of lithium batteries.However,there are still some problems to be solved:1)raw material Li2S has high purity requirement,complex preparation process and high price;2)synthesis process of ternary sulfide solid electrolyte needs to be optimized;3)electrochemical stability of ternary sulfide solid electrolyte needs to be further improved.In order to solve the above problems,an optimized synthesis process and element doping method are used to improve the structural stability and electrochemical stability of sulfide solid electrolyte.The main research contents are as follows.(1)Li2S synthesized by high-energy ball milling.In the glove box filled with Ar(H2O<1 ppm,O2<l ppm),lithium and sublimated sulfur powder were mixed and weighed for high-energy ball milling.The experimental results show that the optimum milling time is 180 min and the optimum raw material ratio is Li=0.42 g and S=1.00 g under the condition of 370 rpm rotational speed.The Li2S powder prepared by this method has high purity whose XRD diffraction peak is consistent with the standard peak.(2)Optimized synthesis of ternary sulfide solid electrolyte Li 10GeP2S12(LGPS).The raw materials were weighed and mixed in a glove box filled with Ar(H20<1 ppm,O2<1 ppm)at the molar ratio of Li:Ge:P:S=10:1:2:24,considering sublimation,sulfur needed excessive.Li10GeP2S12 with thio-LISICON structure was synthesized by high energy ball milling and two-stage sintering process.The synthesized LGPS possesses regular morphology and uniform particle distribution without agglomeration.Simultaneously,it presents the room temperature conductivity aL;of 3.27×10-3 S cm-1,a low activation energy Ea of 25.5 kJ mol-1 and a wide electrochemical voltage window of over 6.0 V(vs.Li+/Li).The first discharge capacity and the capacity retention rate after 20 cycles of LiCoO2 in Li/LGPS/LiCoO2 solid-state battery are 119.6 mAh·g-1 and 89.6%.The new method with low cost,high efficiency and simple process can well replace the traditional method.The LGPS synthesized by the above method has broad application prospects in lithium-negative solid-state batteries.(3)The electrochemical stability of ternary sulfide solid electrolyte Li10GeP2Si2 optimized by doping A1 element.Li10AlxGe(1-3x/4)P2S12(x=0.1,0.2,0.3,0.4,0.5,0.6)solid electrolyte with thio-LISICON structure was synthesized from Li,Ge,Al,P and excess S by mechanical ball milling and subsequent heat treatment.The structure,morphology and electrochemical properties of the solid electrolyte were characterized by XRD,SEM,EIS and CV.The results show that the conductivity of the electrolyte at room temperature is the highest(2.96×10-3 S·cm-1)when the doping amount of Al is x=0.3.The cyclic voltammetry results show that the lithium decomposition voltage of Li10Al0.3Ge0.775P2S12 was +0.05 V,which is lower than LGPS(the reduction decomposition voltage of LGPS was+0.1 V).It shows that the doping of Al element effectively reduces the reduction decomposition voltage of LGPS electrolyte and makes the electrolyte with better electrochemical stability.The first discharge capacity and the capacity retention rate after 20 cycles of LiCoO2 in Li/Li10Al0.3Ge0.775P2Si2/LiCoO2 solid-state battery are 106.0 mAh·g-1 and 89.9%.