Synthesis And Properties Of Carbonate And Phosphate Based Polymer Solid Electrolytes

At present,global energy and environmental issues have become increasingly serious,and battery cars,automobiles and other transportation vehicles are beginning to use energy storage batteries as the main energy source.Among them,Lithium battery has the advantages of long service life,high specific energy,portability and high voltage.The electrolyte of conventional lithium-ion batteries on the market is a carbonate-based solvent（e.g.,vinyl carbonate）,which has led to a gradual shift in scientific research focus to polymeric solid-state electrolytes in view of the drawbacks such as the poor thermal stability of conventional liquid electrolytes and the resulting leakage phenomenon.However,polymeric solid electrolytes are characterized by low ionic conductivity at room temperature and need to be modified or further developed to improve their comprehensive performance and provide the possibility of future large-scale generation for use.First of all,polycarbonate,with its amorphous structure and flexible molecular chains that can be rotated at will,and its main chain with ultra-high dielectric constant groups（containing strong polar carbonate groups）,will help improve its ionic conductivity and electrochemical window when used as an electrolyte.Secondly,polyphosphate,which contains phosphorus elements,can produce a barrier layer that can be isolated from oxygen during ignition and thus act as a flame retardant.Therefore,on the basis of referring to a large number of relevant literatures and combining with the successful synthesis of imidazole-based ionic liquid electrolytes in the early stage of the research group,this paper proposes a new method for synthesizing polymer solid electrolytes using imidazole derivatives as raw materials,in order to improve the performance of polymer electrolytes.The ionic conductivity of the electrolyte can also have better safety performance.Specifically,using lithium hydroxide and imidazole-4,5-dicarboxylic acid as the main raw materials,carbonate and phosphate were respectively introduced into imidazole ionic liquids through transesterification,and finally carbonate polymers with different degrees of polymerization were obtained（G-NTOC-n）electrolyte and phosphate ester polymer（G-NPPT-n）electrolyte,and the physicochemical and electrochemical properties of these two electrolytes were systematically studied.Conclusion as below:（1）The molecular structures of the target carbonate monomer NTOC,phosphate monomer NPPT,carbonate polymer G-NTOC-n,and phosphate polymer G-NPPT-n were studied by ¹H NMR and IR spectroscopy,indicating that the target Molecules have been successfully prepared.（2）The crystalline properties of polycarbonate and polyphosphate were studied by XRD and POM,and the results showed that they were partially crystalline compounds,and their crystal structures were completely destroyed when the temperature was higher than 120°C.（3）The prepared solid polycarbonate and polyphosphate electrolytes have room temperature ionic conductivity of the order of 10^-4 S?cm^-1,excellent electrochemical stability,and excellent compatibility with electrodes and cycle stability,which are expected to be used in Rechargeable lithium-ion battery.（4）The oxygen index of the obtained polyphosphate is more than 34,and it is a flame-retardant material.The combustion test results show that the prepared polyphosphate solid electrolyte is difficult to burn at normal temperature and pressure.