Preparation And Properties Of Lithium Cyanide Single Ion Conductor Polymer Electrolyte

Lithium-ion batteries have the advantages of high energy density,long cycle life and low self-discharge rate,and are widely used in the fields of power and energy storage.At present,commercial lithium-ion batteries mainly use liquid electrolyte to transport lithium ions between cathode and anode,but the defects of liquid electrolyte,such as easy leakage and flammability,have become inherent safety hazards of lithium-ion batteries.Therefore,the development of solid electrolyte systems with higher safety and higher energy density has become a research hotspot.Lithium single ion conductor polymer electrolyte（SLIC-SPEs）has fundamentally overcome the phenomenon of concentration polarization and has been widely concerned by researchers.However,the conductivity of SLIC-SPEs is low at room temperature,which can not meet the requirements of lithium-ion batteries.Therefore,in order to improve the lithium-ion conductivity of SLIC-SPEs,two kinds of polymer electrolytes containing cyano-groups were designed and synthesized in this paper.The details are as follows.（1）Poly[（p-styrene sulfonyl）（cyano）imine lithium]（LiPCSI）,a single-ion conductor,was prepared from sodium p-styrene sulfonate by acylation,ammonolysis,ion exchange and polymerization,and was mixed with polyethylene oxide（PEO）to prepare polymer electrolyte membrane PEO_n/LiPCSI（n=5,10,15,20）.Infrared spectroscopy（FT-IR）and nuclear magnetic resonance spectroscopy(¹H NMR,¹³C NMR)was determined the structure of LiPCSI,and scanning electron microscope（SEM）,thermogravimetry（TG）,universal stretcher and electrochemical workstation were used to characterize the performance of electrolyte membrane.The results show that electrolyte membranes with different ratios of oxygen to lithium（EO/Li⁺）have good thermal stability,among which the tensile strength of EO/Li⁺=10 reaches the highest 3Mpa.Moreover,the electrolyte membrane has the best electrochemical performance,its ionic conductivity is 2.99×10^-5 S·cm^-1,the lithium-ion migration number is close to 1(t_Li+=0.94),and the electrochemical stability window reaches 4.77 V,which also shows good cycle stability.（2）LiPSDM lithium salt with anion structure of-SO₂-C^（-）-（C≡N）₂was synthesized by the same method,and PEO_n/LiPSDM（n=5,10,15,20）membranes were prepared by solution casting method.The test results show that PEO_n/LiPSDM has high thermal stability and low crystallinity.The conductivity of PEO₁₅/LiPSDM reached 8.23×10^-5S·cm^-1 at 90℃,the electrochemical window was 4.8 V,and t_Li+=0.98.Compared with PEO-LiPCSI system,PEO-LiPSDM system obviously has higher ionic conductivity and smaller crystallinity,which indicates that the lithium anion structural unit of LiPSDM has better flexibility,which is more conducive to disrupting the ordered structure of PEO,thus reducing the crystallinity and facilitating the transmission of lithium-ions.