Study On The Interfacial Performance And Mechanical Performance Of Porous Polymer Electrolytes

Polymer lithium ion batteries(PLIBs) have been extensively studied due to their environmentally friendly features and safety. Most research focused on ionic conductivity, electrochemical stability window and mechanical performance, etc. In fact, the electrode / polymer electrolyte(E/P) interfacial compatibility has important effect on the safety performance of PLIBs. Some issues, such as battery explosion and spontaneous combustion, are closely related to E/P performance. Therefore, the E/P interfacial performance of PLIBs is very critical during the battery cycling.As a core component of PLIBs, the polymer electrolyte was one of the important objects of the E/P interfacial compatibility. Among the polymer electrolytes, the porous polymer electrolyte(PPE) attracted great attention with relatively high conductivity and mechanical properties compared with solid polymer electrolyte and gel polymer electrolyte. In this dissertation, we improved the preparation of PPEs, by optimizing the E/P interfacial compatibility to reduce the interfacial resistance. The mechanical properties and conductivity of PLIBs are jointly optimized.In order to optimize the E/P interfacial performance and mechanical properties, two kinds of PPEs were prepared by doping nano-Al2O3 and phytic acid(PA) respectively. The microstructure, mechanical properties, thermal properties and E/P interfacial performance were studied. The main contents were as follows:(1) In chapter 1, the research background of PLIBs and the E/P interfacial formation mechanism were discussed in detail. The E/P interfacial research status mainly focused on the main affecting factors and the research methods. The electrode materials, polymer electrolyte matrix, lithium salt, plasticizer and ionic liquid, inorganic filler and other factors were discussed. The research technique including microscopic method, AC impedance method, spectral method and in-situ method were introduced.(2) In chapter 2, the instruments and reagents, battery assembly technique, the characterization method and technology of polymer electrolyte used in the experiment and the condition of the test were illustrated.(3) In chapter 3, the PPE doped with nano-Al2O3 was prepared and the preparation process, microstructure, thermal properties and interfacial performance, mechanical properties were discussed in detail. Nano-Al2O3 could improve the tensile strength, thermal properties of the PPE and the E/P interfacial performance effectively. However, there was the lack tensil rate. The comprehensive performance of PPE with 10 wt.% Al2O3 was best, of which the tensile strength and elongnation were 3.37 MPa and 22.6 %, respectively. The stable value of its interfacial resistance was about 450 Ω when time was influencing factor.(4) In chapter 4, the mechanical properties and interfacial performance of the PPE were improved by the use of PA as a crosslinking agent and doping agent. And the tensile strength and elongnation of the mechanical properties were improved simultaneously. The comprehensive performance of PPE with 15 wt.% PA was best, of which the tensile strength and elongnation were 2.85 MPa and 45.7 %, respectively. The stable value of its interfacial resistance was about 560 Ω when time was influencing factor. PA helped to form three dimensional elliptic pores which could optimize polymer electrolyte membranes surface and internal pore structure by controlling the proportion between PA and polymer. Moreover, PA has environmentally friendly features, good biocompatibility, low prices, variety of sources. Therefore, the PPE with PA has a good application prospect in electric vehicles.