Study On The Preparation,Modification And Electrochemical Performance Of PEO/LLZGO Composite Solid Electrolyte

Solid-state lithium batteries have attracted more and more attention due to their extremely high safety and reliability.Among them,the cubic garnet electrolyte has the advantages of high ionic conductivity,wide electrochemical window,and good interfacial stability,which is preferred choice of solid electrolyte materials.In this paper,the garnet electrolyte powder Li_6.4La₃Zr₂Ga_0.2O₁₂ is used as the core.First,electrolyte powder particles with different particle sizes are prepared,then LLZGO particles with different particle sizes are added to the polyethylene oxide（PEO）composite solid electrolyte,and matched with Li Fe PO₄.Then,the content ratio of LLZGO and PEO in the composite electrolyte is explored.Finally,the modification of the plasticizer is carried out on the composite electrolyte with the best electrochemical performance to improve the battery performance.The details are as follows:The composite solid electrolyte was prepared by solution casting method.By adding LLZGO electrolyte powders with different particle sizes into PEO-based polymers,the effects of different particle sizes of electrolyte powders on the electrochemical properties,ion mobility,electrochemical impedance and mechanical properties of the composite electrolyte were explored.It was found that isopropanol has better grinding aid effect than acetonitrile and ethanol.This paper systematically explored the influence of ball milling speed,grinding aids,ball milling time,ball milling medium size,material-to-ball ratio,and ball milling medium mixed on the particle size of electrolyte powder in the ball milling process.It was found that isopropanol as a grinding aid,the mass ratio of the material to the ball was 1:15.The 0.5 and0.3 mm yttrium zirconium oxide ball milling media（mass ratio 3:7）were weighed and ball-milled for 12 h to obtain an electrolyte powder with a particle size of about 500 nm.The PEO composite electrolyte prepared by using the electrolyte powder had good mechanical properties,the lithium ion mobility was 0.281,and which was beneficial to inhibit the growth of lithium dendrites.At 60℃and 0.05 C rate,after 74 cycles the discharge specific capacity reached 114.6 m Ah/g,and the capacity retention rate was 81.3%.Optimized and modified composite electrolyte.By optimizing the added mass ratio of inorganic solid electrolyte LLZGO powder（0,10,20,30 wt.%）,the ion migration number,interfacial impedance,interfacial stability to Li metal and thermal stability of the composite electrolyte were explored.It was found that the composite electrolyte had better performance when the addition amount of LLZGO was 20 wt.%.To go further,by adding plasticizers polyethylene glycol（PEG）and lithium nitrate（Li NO₃）to modify the composite electrolyte,the ion migration number reached 0.33.At 60℃and a rate of 0.05 C,after 150 cycles the battery capacity decreased from 155.1 m Ah/g to 87.3 mAh/g.