Performance Of Blending Solid Polymer Electrolyte And Its Application In Lithium-ion Batteries

Recent reports about the lithium-ion battery lead to accidents such as the burning of a fire or explosion has been uncommon, the safety issues of lithium-ion battery caused widespread concern by researchers. Polymer electrolyte material is the key to solve the safety performance of lithium-ion batteries, while the lithium salt and the polymer electrolyte as a new class of materials that can effectively solve the problem of low electrolyte conductivity and poor mechanical properties of lithium-ion batteries. In order to improve the ionic conductivity, electrochemical stability, mechanical performance and safety of lithium-ion batteries, we started the research by preparing a new type of polymer electrolyte membrane, and the electrolyte film was prepared by solution casting method in this thesis. By analysis the electrochemical properties and mechanical properties of the polymer electrolyte and study the relationship between structure and properties of the polymer lithium salt at the same time, we committed to improving the performance of lithium-ion batteries.In the first chapter, the author reviewed the development history of the polymer electrolyte and the structure, composition and working principle of lithium-ion battery was also briefly introduced. Then, the article focuses on the homopolymer, copolymer and ionic liquid of three kinds of new polymer lithium salts, revealing the present situation of the lithium salt application and optimization progress from three aspects of the polymer structure, composition and performance. And future research directions and priorities were also discussed.Experimental drugs and instruments used in the experiment is introduced in the second chapter and the basic steps of the molding process and the battery assembly of polymer electrolyte membrane was also illustrated. A detailed description of a series of tests such as scanning electron microscopy, infrared spectroscopy, AC impedance and polymer films in electrochemical, mechanical properties and high temperature stability tests have been launched.For the third chapter, the lithium salt LiClO₄/LiTFSI and PEO-PMMA polymer matrix composites were prepared using a solution casting method and different kinds of all-solid polymer electrolyte?solid polymer electrolyte, SPE? film were obtained. PEO-PMMA composite polymer matrix can improve both the ionic conductivity of PEO at room temperature and optimize mechanical strength of PMMA to obtain a balance for the compatibility of ionic conductivity and mechanical properties. The ionic conductivity measured at room temperature for PEO-PMMA-LiTFSI?EO/Li+=10? and PEO-PMMA-LiTFSI-Al₂O₃?EO/Li+=10? system were 6.67×10-7 S/cm and 9.37×10-7 S/cm, respectively. Thermal stability analysis has found that the decomposition temperature of PEO-PMMA-LiClO₄?Al₂O₃,? and PEO-PMMA-LiTFSI?Al₂O₃,? the four different solid electrolyte films were above 300 ?. Analysis showed that the mechanical properties of tensile strength of the PEO-PMMA-LiTFSI and PEO-PMMA-LiTFSI-Al₂O₃?EO/Li+=10? were 1.02 MPa and 1.76 MPa, respectively. The thermal shrinkage of PEO-PMMA-LiTFSI polymer film was 8.7%, while the PEO-PMMA-LiTFSI-Al₂O₃ polymer film was 6.6%..In the fourth chapter, we introduced the basic steps and key preparation of the molding progress and battery assembly. An improved solution casting method was applied in the preparing of polymer electrolyte membrane, which could effectively solve the problem of excessive evaporation rate of the solvent, a better appearance and smoother uniform of the polymer films were prepared. In order to study the influence factors of the ionic conductivity of the polymer films, some methods such as adding inorganic nano-particles, the selection of different solvents and temperature control were discussed. Finally, the polymer film was assembled into a battery and electrochemical stability window, the first charge-discharge performance and cycle performance were tested. The study found that the Li/PEO-PMMA-LiTFSI/LiCoO₂ half-cell at the discharge rate of 0.1C obtained a 100 mAh/g capacity in the first charge and discharge progress, and the coulombic efficiency was 91.8%, which achieved 71.4% of the actual LiCoO₂ capacity?140mAh/g?.In summary, these new lithium salt-containing polymer solid electrolytes showed good overall performance. Preparation of the blending polymer electrolyte can optimize the compatibility between the ionic conductivity and mechanical properties, and the blending solid polymer electrolyte has excellent performance in terms of thermal stability and heat-shrinkable.