Modified Preparation And Properties Of PEO-based Polymer Electrolyte

All-solid-state composite polymer electrolyte is a multiphase material that adopted an organic polymer as the main matrix. Performance improvement of electrolyte materials can be achieved by complexation between functional groups from the polymer molecular chain and the ions and, by adjusting the component and proportion of polymer and modified filler. A series of composite polymer electrolytes based on poly(ethylene oxide) (PEO), such as (PEO)i6LiC104-NaA1OSiO(-EC), PEO-LiC104-CeO2 and PEO-LiC1OO4-CeO2-Ti(OH)4 were prepared. The ionic conductivity mechanism, preparation process, structure and performance of (PEO)16LiC104-NaA1OSiO(-EC) composite polymer electrolyte materials were mainly investigated in this work.Nanoscale NaAlOSiO molecular sieves powders as the modified filler were introduced into the system of (PEO)16LiC104. The half transparent polymer electrolytes material (PEO)16LiC104-NaA1OSiO with high ionic conductivity were prepared. The study indicates that the pure PEO and (PEO)16LiC104 system show a obviously crystal morphology and the amounts of NaAlOSiO powders have great influence on the growth stage of PEO spherulites. NaAlOSiO powders can be dispersed homogeneously in the (PEO)16LiC104 electrolyte matrix, which results in breaking PEO molecular chain rule structure, with the growth stage of PEO spherulites being hindered.With the increase of NaAlOSiO contents, the morphologies of electrolyte matrix gradually transform from branch shape to crosslinked network. This structure can provide more Lewis acid sites to interact with the ether 0 atoms of PEO chains. The flexibility of the polymer chain is increased. Molecular chain tends to disorder and the crystallization of PEO tends to become difficult. So the continuous amorphous region is expanded. With increased NaAlOSiO content, the glass transition temperature, melting temperature and melting enthalpy all decrease. The crystallinity of electrolyte system decreased significantly. The lower glass transition temperature and the higher flexibility of the polymer chain are beneficial to the transport of lithium-ion.NaAlOSiO can not only provide more new conductive ion Na+, but also undermine the complexation between ether oxygen groups of PEO polymer and Li+. A large number of Na+ act on ether oxygen groups instead of Li+ and promote complexation and dissociation process of Li+, which is helpful to the transfer of Li+ in the electrolyte system. Thus, the ionic conductivity of the composite polymer electrolyte can be improved significantly. A minimum value of the bulk resistance Rb and the maximum ionic conductivity appears for composite polymer electrolyte with 12 wt.% NaAlOSiO. NaAlOSiO molecular sieve present in ionic form with Na+ and (AlOSiO)-. Na+ ions interact with the functional groups of the PEO, which break the balance of the mass center of the partial molecular and the restore the conditions for nuclei growth. The crystallization behavior of the system can thus be suppressed. So the ionic conductivity can be maintained at high level for a long time.The composite polymer electrolyte based on PEO, LiClO4 and NaAlOSiO powders with 5 wt.% ethylene carbonate (EC) plasticizer is prepared. After adding EC, the electrostatic force between the lithium ion and anion becomes smaller. EC can not only greatly facilitate the dissolution of the lithium salt in the polymer matrix, but also help the dissolution of NaY in electrolyte system. Partial agglomeration effects of NaAlOSiO powders can be avoided too. The average pore size of cross-linked network pore is significantly smaller under the influence of EC. But the maximum conductivity is still the case with 12 wt.% NaAlOSiO. NaAlOSiO, which can introduce a large number of Na+, while too high ion concentration will produce ion pairs cancelling out the positive effect of increased ion concentrations. The introduction of EC can promote the uniform dispersion of Li+ and Na+ in the polymer matrix, and lead to enhanced ionic conductivity of electrolyte maintaining for a long time.A translucent composite polymer electrolyte PEO-LiClO4-CeO2 with larger ionic radius nanosized CeO2 as the modified filler was prepared by solution-casting technique. With the increasing temperatures, the imaginary part maximum of impedance spectra and bulk resistance gradually decreased. The capacitor-like charge and discharge performance gradually increased. Too much amounts of CeO2 nanoparticles are no good for Lithium-ion transmission. Those particles take up space and hinder the migration of lithium ion on the one hand, and on the other hand, CeO2 particles may reform the core of crystal nucleon growth. The ionic conductivity reaches its maximum 1.71 × 10-5 S·cm-1 with the CeO2 content of 9 wt.% at 25 ℃.CeO2 nanoparticles can be dispersed and blended well with PEO matrix. When electrolyte system is subjected to external forces, CeO2 nanoparticle can be well dispersed and thus can transmit stress and absorb plastic deformation energy, which play an important role in enhancing toughness of (PEO)10LiC104 system. The tensile strength can also be greatly improved. The tensile strength reaches 2.07 MPa with the CeO2 content of 15 wt.%, 4.45 times that of the (PEO)10LiClO4.Translucent composite polymer electrolyte PEO-LiClO4-CeO2-Ti(OH)4 can be prepared by solution-casting technique by introducing Ti(OH)4 particles produced by hydrolysis condensation reaction of tetrabutyl titanate or directly introducing CeO2 particles or introducing both Ti(OH)4 particles produced by hydrolysis condensation reaction of tetrabutyl titanate and CeO2 particles. The results show that the effects of inorganic filler on the PEO matrix are related to the size of particles. By two different methods of filler addition, the crystallization behavior of the polymer matrix can be suppressed effectively, with the degree of crystallinity maintained at a low level in the longer time. So the ionic conductivity of the composite polymer electrolyte can be improved noticeably.