Study On Preparation And Performance Of Solid Polymer Electrolytes Based On Chelated B-Type Lithium Salts

New energy vehicles are now developing rapidly because people's concept of environmental protection is continuously strengthened,and their awareness of energy conservation is getting stronger and stronger.However,the hidden safety hazards they face will frequently appear with the increase in sales.Among the many hazards,the most serious is the electrolyte leakage or even explosion of the liquid organic electrolyte,which leads to the spontaneous combustion of the car.Solid-state lithium-ion batteries are thought highly and that are inseparable from their superior safety performance.The solid polymer electrolyte directly incorporates lithium salt into the polymer,and there is no need to add electrolyte during the assembly process to avoid the hidden danger of electrolyte leakage.As a new type of organic lithium salt,the chelated B lithium salt has a strong lithium ion dissociation ability,which makes the solid polymer electrolyte exert excellent performance.First,a two-step method was used to synthesize three lithium salts of LiBBB,LiBMB and LiBDMB.The first step,in order to improve the solubility of boric acid in the solvent,we synthesize intermediate products in distilled water.Because the lithium salt is unstable in water,the second step is to react in acetonitrile to synthesize lithium salt.This not only improves the efficiency of the reaction,but also makes the synthesized lithium salt higher in purity.Mainly through:infrared analysis,nuclear magnetic analysis as well as XRD analysis to confirm the structure of the synthesized lithium salt.The result of characterization showed that the three synthesized lithium salts had corresponding characteristics.To figure out whether the synthesized lithium salt could be used in a normal battery or not,both the thermal stability test and the electrochemical performance test were conducted.While results show that the three synthesized lithium salts will not have heat loss below 100?,and the conductivity ranges from 5.2 m S/cm to 12.07 m S/cm at 25?to 70?.Then the three synthesized lithium salts were doped into a system of PEO and TPU containing BaTiO₃ filler to synthesize solid polymer electrolytes.For the comparability of the experiment,a set of solid polymer electrolytes containing commercial lithium salt LiBF₄were introduced.Analyze whether the three synthesized lithium salts can be used in batteries,and discuss the performance of the solid polymer electrolytes of the four lithium salt systems.Through a range of characterization results,it can be concluded that the morphology of the LiBF₄ solid polymer electrolyte without a large anion radius shows the accumulation of crystalline polymers,while the morphology of the synthesized three lithium salts is relatively flat.The LiBF₄ solid polymer electrolyte In the mechanical performance test,the tensile strength is the lowest and the elastic potential energy is the worst.The solid polymer electrolyte of LiBDMB with a larger anion radius and different coordination ions on both sides has the best mechanical properties,electrochemical properties and battery performance.Finally,the LiBDMB lithium salt with better performance in the second set of experiments was selected for comparative analysis in the solid polymer electrolyte containing LLZO and PEO to study the optimal content of LiBDMB lithium salt in it.Setting the mass fractions of LiBDMB lithium salt in the solid polymer electrolyte 0%,5%,10%,15%,20%,and 25%,respectively during the experiment.A series of characterizations show that the XRD characteristic peaks of 20 wt%and 25 wt%solid polymer electrolytes are the lowest,the melting peak of DSC is the smallest,and the mechanical properties are also the most outstanding.However,from the perspective of the morphology and structure of solid polyelectrolytes with different contents,the distribution of 20 wt%solid polymer electrolytes is relatively standardized,with a large pore size and a three-dimensional structure;in addition,its lithium ion conductivity also performs best,and by The solid polymer electrolyte of this system was assembled into a battery for testing and found that at a rate of 0.2 C,the battery's specific charge capacity reached 181 m Ah/g,the specific discharge capacity is 169 m Ah/g,and the coulombic efficiency is as high as 93%.After 300 cycles,the specific discharge capacity remains over 155 m Ah/g.In addition,after 500 cycles,the battery capacity declines slowly.