Preparation And Properties Of PVDF-HFP Composite Solid Polymer Electrolyte

Solid-state lithium batteries have been extensively studied due to their advantages such as good safety,high energy density,and strong durability.As the most important part of all solid-state lithium batteries,solid electrolyte directly affects the performance of the battery.Polymer solid electrolytes have attracted the attention of researchers because of their good flexibility and light weight.However,the shortcomings of low ionic conductivity at room temperature and poor interface stability limit their commercial applications.This article focuses on the low room temperature ionic conductivity of polymer solid electrolytes,narrow electrochemical window and metal lithium dendrites as the subject,and the composite modification of Poly(vinylidene fluoride-co-hexafluoropropylene)(PVDF-HFP)-based polymer with inorganic materials.Continuously optimize the traditional polymer solid electrolyte,and at the same time find a new type of composite solid polymer electrolyte with better performance,continue to optimize its room temperature ionic conductivity,thermodynamic properties,interface stability and inhibit lithium dendrites,and finally it can be expected to achieve allsolid lithium metal For batteries,the realization of this goal should be carried out from the following aspects:(1)Graphite phase carbon nitride(g-C3N4),as a new two-dimensional material,can be easily prepared by thermal oxidation etching.Three different N sources were used to prepare g-C3N4.Through Fourier Transform Infrared Spectroscopy(FTIR),X-ray Diffraction Spectroscopy(XRD)and X-ray Photoelectron Spectroscopy(XPS)and other test methods,the structure change and crystallinity and other information were studied respectively;then x-g-C3N4 and PVDF-HFP was mixed with lithium bis(trifluoromethanesulfonyl)imide(LiTFSI)to successfully prepare a composite polymer electrolyte(PVDFHFP/LiTFSI/x-g-C3N4)with excellent comprehensive performance.The effect of x-g-C3N4 prepared from different N sources on the performance of the composite solid polymer electrolyte and the effect on the performance of the prepared allsolid lithium battery were explored.Scanning electron microscopy(SEM)results showed that D-g-C3N4 prepared by dicyandiamide had the largest size.(2)Using the same method,the fluorine-doped dicyandiamine derivative DxF-C3N4 was prepared with different fluorides and different ratios of sodium fluoride,and was supplemented by the surfactant ethyl cellulose(EC)The D-xFC3N4 was peeled off to prepare F-C3N4 nanosheets.Based on PVDF-HFP,PVDFHFP/LiTFSI/D-xNF-C3N4,PVDF-HFP/LiTFSI/D-2.4xF-C3N4 composite solid polymer electrolytes are constructed.The effects of D-xNF-C3N4 nanosheets doped with different sodium fluoride ratios and D-2.4xF-C3N4 doped with different fluorides under the same ratio on the performance of composite solid polymer electrolytes and the all-solid lithium prepared were investigated.The impact of battery performance.The following specific instructions:Using liquid phase stripping method,adding surfactant EC,Nmethylpyrrolidone(NMP)as a solvent to strip D-xNF-C3N4 and D-2.4xF-C3N4,and finally prepare D-xNF-C3N4 and D-2.4 xF-C3N4 nanosheets.XRD spectroscopy was used to characterize the changes of D-xF-C3N4 nanosheet spacing,grain size and crystallinity before and after peeling.The TEM test was used to observe the changes of D-xF-C3N4 morphology before and after peeling.The results showed that D-xNF-C3N4 and D-2.4xF-C3N4 were successfully peeled off to obtain D-xNF-C3N4 and D-2.4xF-C3N4 nanosheets.D-xF-C3N4 and PVDF-HFP have a strong cross-linking effect.The addition of D-xF-C3N4 significantly destroyed the crystallinity of the polymer electrolyte and improved its comprehensive performance.The lithium ion migration number is as high as 0.79.More importantly,this composite solid polymer electrolyte(CSPE)has excellent mechanical strength,which enables it to effectively inhibit the growth of lithium dendrites.In addition,the electrochemical window of CSPE doped with D-2.4BF-C3N4 nanosheets can be extended to 5.2 V vs.Li/Li+compared with that without fillers.In addition,all solid-state lithium batteries have achieved good electrical performance because of the use of CSPE.These advantages indicate that the PVDF-HFP/LiTFSI/D-2.4BF-C3N4 developed is expected to be used as the electrolyte for the next generation of solid-state lithium batteries.