Research Of Cerium Salt In Electrolytes And Separator For Nonaqueous Lithium-Oxygen Battery

Non-aqueous Li-O₂ batteries are considered to be the next-generation energy storage systems for electric vehicles due to their high theoretical specific energy(11000Wh kg^-1).In recent years,although there have been more and more reports about Li-O₂ batteries,there are still many problems that limit the further development of Li-O₂ batteries,in which decomposition and volatilization of electrolytes are important factors.During the discharge process of Li-O₂ battery,oxygen obtains an electron,and then reduced to super-oxygen radical with strong activity,which can react with electrolyte and air electrode to produce by-products.In this paper,the off-line UV experiment confirmed that the cerium ion has a superoxide radical scavenging effect.The Cerium?III?trifluoromethanesulfonate was added as an additive to tetraglyme?G4?with an electrochemical window of 5.28 V under oxygen atmosphere.At a current density of 500 mA g^-1 and fixed capacity of 1000 mAh g^-1,G4 electrolyte is only 45 cycles,and the cycles number of G4 electrolyte with Cerium?III?can up to 85,nearly twice times than G4 electrolyte;when current density increased to 1000 mA g^-1,with a fixed capacity of 1000 mAh g^-1,the cycle number of the G4 electrolyte dropped to 31,while the G4 with Cerium?III?cycle number is 61 cycles.In the case of the addition of Ce³⁺ions into the electrolyte,Ce³⁺ions will react with the superoxide radicals(O^2-)to form peroxyl radicals(O₂^2-)and Ce⁴⁺ions.The peroxyl radicals(O₂^2-)will combine with Li⁺ions to get the final discharge products.The higher overpotential in lithium-oxygen batteries is also one of the important factors causing the decomposition of electrolyte,in order to further improve the electrochemical performance of the electrolyte.In the second research system,cerium iodide is added as an additive to the electrolyte,in which cerium ions act as a superoxide radical scavenger and iodide ions act as redox mediators to reduce the overpotential during charging process.The anions and cations work together to slow down the decomposition of the electrolyte.When the current density is 500 mA g^-1,and the limited capacity is 1000 mAh g^-1,the G4 electrolyte added with cerium iodide can be circulated to 125 cycles compared to the 45 cycles of G4 and 85 cycles of the electrolyte with cerium?III?.Comparing the XPS C1s spectrum of the air electrode after 30 cycles,at 286.2,289.0,289.7 and290.2 eV,corresponding to ethers,carboxylates,carbonates,and carbonates relatively,the peak intensity of the G4 electrolyte with cerium iodide is weaker than the peak intensity of the G4 electrolyte,which demonstrates the addition of cerium iodide effectively can slow down the decomposition of the electrolyte and air electrodes.Although the addition of cerium iodide to the G4 electrolyte improves the stability of the electrolyte and slows down the decomposition of the electrolyte,the problem that the G4 electrolyte is easily burned and volatile.Therefore,we prepare PVDF-HFP-based polymer electrolytes and added cerium iodide to slow down the decomposition of PVDF-HFP caused by superoxide radicals and overpotentials.The infrared spectrum showes that the PVDF-HFP polymer electrolyte with cerium iodide has no peak at 1635cm^-1?C=C?soaked for 72 h in potassium peroxide solution,while PVDF-HFP polymer electrolyte soaked has a clear peak of C=C,indicating that the addition of cerium iodide inhibites the decomposition of PVDF-HFP.At a current density of 500 mA g^-1 and fixed capacity of 1000 mAh g^-1,the number of cycles of PVDF-HFP polymer electrolyte is 45,and the number of cycles of PVDF-HFP polymer electrolyte with cerium iodide reaches 96.Futhermore,the addition of cerium iodide increases the hydrophobic properties of PVDF-HFP,which provides important significance for the future development of lithium-air batteries.