Study Of Ameliorating The Conductivity Of Poly (Ethylene Oxide)-based Solid State Electrolyte At Ambient Temperature

As one of the key component of the secondry batteries,electrolyte plays the vital role in ions transportation.Liquid ester-based electrolyte is suffering leakage,volatility and combustability although it has been applied successfully in Lithium ion batteries.Thus,the batteries featured with the solid state electrolyte are attracting more and more attention in the field.Currently,solid state electrolyte(SSE)can be categorized into oxide-and sulfide-based inorganic and organic polymer.Compared with the first two types of SSE,polymer-based electrolyte outperforms a lot in flexibility,the interfacial impedence and adhesion.One of the extensively investigated solid polymer electrolyte(SPE)is based on Poly(ethylene oxide)(PEO)and its derivatives,which is considerd to be the most promising candidate at present,but its high crystallinity restrains the operation only at higher temperature(>60℃),severely straitening the application of solid state batteries as a result.Aimed at the problem,the attempts were conducted by adding the organic plasticizer,ethylene carbonate,inorganic plasticizer Mg2B2O5,NASICON,respecitively,to reduce,the crystallinity of PEO-based solid electrolyte,enhancing the conductivity at ambient temperature.The investigation consists of the four parts as follow:(1)Preparition of the ultra-thin polypropylene-supported manbrane of poly(ethylene oxide)polymer electrolyte.Due to polypropylene is an extremely non-polar material,the manbrane is barely soaked with the strong polar PEO thoroughly.Therefore,the PP manbrane was mildly treated with KMnO4 to promote the hydrophilism,resulting from carbonyl generated on its surface,which favorably overcame the poor impregnation.The electrolyte manbrane was facilely prepared with 25 μm CR2500 polypropylene acting as supporting backbone impragnated with PEO solid electrolyte.The results revealed more than 350 h cycling was achieved with Li/SPE/Li symmetric cell intergrated with as prepared solid state electrolyte manbane and with less polarization.(2)Ethylene Carbonate(EC)was added into Lithium-based PEO solid electrolyte in molar ratios as plasticizer to reduce the crystallinity of complex of lithium salt and PEO,forming the homogeneous solid solution gradually.X-ray diffraction displayed the SPE crystallinity continuously decreased from 56%to 30%with the EC content from 10 mol%to 50 mol%,and completely disappeared at 60 mol%EC.Meanwhile,the SPE conductivity was remarkably enhanced from 1.36×105 S/cm(0 mol%EC)to 1.53×10-4 S/cm(60 mol%EC)at 60℃,especially,5.49×10-5 S/cm was attained even at 25℃ for the SPE containing 60 mol%EC.Li+and Sodium-based SPE were further evaluated with LiFePO4 and Na3V2(PO4)3 half cell,respectively.The preferable cyclability also implied the excellent compatibility with electrochemical systems.(3)Generally,electrolyte would own the various compatibilities with the negative materials,which is quite important to the cell system.Furthermore,the electrochemical behaviors of the negative materials were primarily investigated in aforementioned SPE.As a result,the commercial hard carbon showed the favorable stability compared with MCMB.(4)In the meantime,as inorganic plasticizer,nano rodlike Mg2B2O5 was synthesized as a Li fast ion conductor,then was added into PEO-based SPE in order to assess the efficacy.The obvious promotion was obtained too,originating from the addition of Li fast ion conductor reduced the crystallinity of PEO solid electrolyte and provided the excessive channel for the ion transportation,giving rise to the intensified performance synergistically.The preferable stability was also verified with Na3 V2(PO4)3/SPE/Na half cell.