Filling Modification And Properties Of Polymer Electrolytes For Lithium Metal Batteries

In recent years,due to the changes in the international situation and the support of national policies,the new energy industry has developed rapidly,and lithium batteries stand out from a variety of energy storage devices due to their portability,lightness,and high energy density.With organic liquid electrolytes,the safety performance of lithium batteries is worrying.In order to solve the safety problem of lithium batteries,reducing the use of organic liquid electrolytes in lithium batteries is an effective and feasible method.For this reason,gel-state lithium batteries and solid-state lithium batteries emerge as the times require.Although gel-state electrolytes and solid-state lithium batteries have higher safety than liquid lithium batteries,their poor ion transport capacity at room temperature and poor electrochemical stability prevent their further applications.By adding different inorganic fillers and additives,the crystallinity of solid electrolyte electrolytes can be effectively reduced,and the electrochemical stability of solid electrolytes and gel electrolytes can be improved.In view of the poor ion transport capacity and poor electrochemical stability of PVDF-HFP solid electrolyte and PVCA gel electrolyte,different methods were used to modify them to improve their electrochemical and physical properties.1.The g-C₃N₄ nanosheets were prepared by thermal oxidative exfoliation and added to PVDF-HFP solid electrolyte.Through XRD,infrared,thermal analysis and other tests,it can be seen that the addition of g-C₃N₄ nanosheets can effectively change the orderly arrangement of molecular segments in the solid electrolyte and reduce the crystallinity of the solid electrolyte.Through a series of electrochemical performance tests,it can be found that the addition of g-C₃N₄nanosheets effectively reduces the bulk impedance of the solid electrolyte membrane,improves the ion migration number and oxidation potential of the electrolyte membrane,and stabilizes the interface between the lithium metal anode and the electrolyte.After adding 15%PVDF-HFP and Li TFSI total weight of g-C₃N₄ nanosheets,the ionic conductivity of solid electrolyte membrane at room temperature was increased from 0.85×10^-4 S·cm^-1 to 1.67×10^-4 S·cm^-1,the oxidation potential was increased from 4.35 V to 4.7 V,the full battery assembled with NCM622 positive electrode and lithium metal negative electrode was cycled for 100 cycles at a charge-discharge rate of 0.5 C,and the capacity retention rate was 76.6%（higher than 55%without filler）,showing good cycle performance.2.The commercial thickener lithium magnesium silicate was added to the PVDF-HFP solid electrolyte.Through XRD,thermal analysis and other tests,it was known that the addition of magnesium lithium silicate not only effectively improved the melting point and thermal stability of the solid electrolyte membrane,but also The crystallinity of the solid electrolyte membrane is reduced.Through the electrochemical performance test,it can be found that the addition of lithium magnesium silicate can effectively improve the ion migration number,ion transfer ability,oxidation potential,and stability between lithium metal and PVDF-HFP solid electrolyte.After the addition of 5%PVDF-HFP and Li TFSI total weight of lithium magnesium silicate,the electrochemical properties of the solid electrolyte membrane at room temperature were also improved,the ionic conductivity was as high as 2.56×10^-4 S·cm^-1,and the ion migration number increased from 0.25 to 0.41,the oxidation potential was as high as 4.8 V,and the full battery assembled with NCM622 cathode and lithium metal anode could stably cycle for 50 cycles at a charge-discharge rate of 0.5 C（capacity retention rate was 89.6%）.3.The precursor solution containing vinylene carbonate（VC）and Li TFSI was converted into polyvinylene carbonate（PVCA）gel electrolyte by thermally-initiated polymerization,And by increasing the content of Li DFOB in the electrolyte,the oxidative decomposition potential,ion migration number and stability to lithium metal anode of the polyvinylidene carbonate gel electrolyte were improved.Through the electrochemical potential window test,it can be found that the potential for rapid oxidative decomposition of the modified polyvinylene carbonate gel electrolyte increases from 4.75 V to 5.9 V,and the ion migration number increases from 0.34 to0.54.After 320 cycles at a charge-discharge rate of 0.5 C,the full battery assembled with the modified polyvinylene carbonate gel electrolyte and NCM622 cathode,lithium metal anode showed a specific discharge capacity of 104.4 m Ah·g^-1,which was higher than Unmodified polyvinylene carbonate gel electrolyte(70.8 m Ah·g^-1).