Preparation And Performance Characterization Of Siloxy-terminated Polyether Electrolyte For Lithium Ion Batteries

As an important part of the lithium ion batteries, the polymer electrolyte plays a significant role in insulating the cathode and anode to avoide the cell short circuit, and providing the function of transporting the lithium ions. In this dissertation, gel, composite gel, composite solid polymer electrolytes were prepared with Bis[3-(methyldimethoxysilyl)]-terminated polypropylene oxide(abbreviated as “BSPPO”) as matrice by adding liquid plasticizer, inorganic nano-materials, plastic crystals. The structure, physical properties, electrochemical properties and battery performance of polymer electrolyte was characterized by FTIR, DSC, TGA, AC impedance, linear sweep voltammeter and polarization current-time curve methods. The as-prepared polymer electrolyte exhibited high mechanical strength and excellent thermal stability. Meanwhile, it possessed excellent electrochemical stability, favorable ionic conductivity and high lithium ion transference number. The main contents are listed as follows:(1) Gel polymer electrolyte(BSPPO-Li BOB-PC) based BSPPO was prepared by chemical cross-lingking reaction, and the relationship between structure and properties was investigated. The results showed that the as-prepared gel polymer electrolyte possessed high ion conductivity of 7.55×10-3 S cm-1 at room temperature, wide electrochemical window of 4.6 V(vs. Li+/Li), high ion transference number of 0.56, meanwhile, it exhibited high mechanical strength(1.12 MPa) and excellent thermal stability, when the-O/Li molar ratio was 8:1 and the mass fraction of PC was 15%. The Li-Li Fe PO4 cell was assembled, it exhibited good cyclic stability and rate capability. The capacity retention was 80% after 1000 cycles(rate: 0.5 C), and discharge capacity was 80 m Ah g-1 at 2 C.(2) Composite gel polymer electrolyte(Al2O3-BSPPO-Li BOB-PC) based BSPPO was prepared by adding Al2O3 nanoparticles. The results showed that the asprepared composite gel polymer electrolyte exhibited high tensile strength(1.53 MPa) and good thermal stability. Furthermore, it possessed high ion conductivity of 1.1×10-3 S cm-1 at room temperature, wide electrochemical window of 4.8 V(vs. Li+/Li) as well as high ion transference number of 0.61, when the mass fraction of nano-Al2O3 was 15%. The Li-Li Fe PO4 cell was assembled, it exhibited good cyclic stability and rate capability. The capacity retention was 95% after 100 cycles(rate: 0.5 C), and discharge capacity was 95 m Ah g-1 at 2 C. Thus nano-Al2O3 could improve both the mechanical properties and ionic conductivity, the interface stability between electrolyte and lithium metal.(3) Composite solid polymer electrolyte(BSPPO-SN-Li BOB) based BSPPO was prepared by adding succinonitrile by chemical cross-lingking reaction, and succinonitrile could effectively improve the ion conductivity of polymer electrolyte. The results showed that the as-prepared composite solid polymer electrolyte possessed high ion conductivity of 5.3×10-4 S cm-1 at room temperature, wide electrochemical window at room and high temperature(>5 V vs. Li+/Li), high ion transference number(25 ℃: tLi+ = 0.24, 50 ℃: tLi+ =0.32, 80 ℃: tLi+ =0.42) and good thermal stability, when the mass fraction of succinonitrile was 30 wt%. The Li-Li Fe PO4 cell was assembled, it exhibited good cyclic stability under 0.1 C at 25 ℃. The capacity retention was 96.5% after 50 cycles; Meanwhile, the cell exhibited good cyclic stability and rate capability under 0.5 C at 50 ℃ and 80 ℃, The capacity retention was 92.5% and 90% after 100 cycles, the discharge capacity was 103.5 m Ah g-1 and 112.8 m Ah g-1 at 1 C, respectively. In addition, the Li-Li Fe0.2Mn0.8PO4 cell was assembled, it exhibited good cyclic stability and excellent rate capability under 0.5 C at 50 ℃. The capacity retention was 81% after 200 cycles, and discharge capacity was 91.6 m Ah g-1 at 3 C.