Study On The Synthesis Of Bis(Fluorosulfuryl)imide And The Corrosion Behavior Of Its Electrolyte To Aluminum Foil

Lithium hexafluorophosphate?LiPF₆?based electrolyte is sensitive to water and easy to decompose and release corrosive gases,which is one of the main reasons limiting the development of lithium-ion batteries?LIBs?.It is an urgent task to develop an alternative lithium salt to LiPF₆.Among many new lithium salts,lithium bis?fluorosulfuryl?imide?LiFSI?has developed into one of the most concerned lithium salts due to its excellent properties.The problem of corrosion of aluminum current collector of positive electrode limits its application in LIBs.A great deal number of studies have shown that adding lithium salt such as lithium bis?oxalato?borate?LiBOB?,which can passivate aluminum foil,to LiFSI-based electrolyte can effectively inhibit aluminum foil corrosion at room temperature.However,the development of power LIBs requires that the electrolyte withstand the harsh environment above 45?,so it is necessary to study the corrosion behavior of LiFSI-based electrolyte on aluminum foil at high temperature.This thesis consists of three parts as follows:?1?Synthesis of LiFSI.Imido-bis?sulfuric acid?dichloride?HN?SO₂Cl?₂?was synthesized from NH₂SO₃H,SOCl₂ and ClSO₃H.Then,imido-bis?sulfuric acid?difluoride?HN?SO₂F?₂?was synthesized by the reaction between HN?SO₂Cl?₂ with SbF₃.In acetonitrile solvent,HN?SO₂F?₂ reacts with K₂CO₃ to obtain KFSI solutions.At last,LiFSI products with purity up to 98.8%were prepared by the ion exchange reaction between KFSI and LiClO₄ in acetonitrile.?2?Study on corrosion of aluminum foil by LiFSI-based electrolyte at 45?.Cyclic voltammetry?CV?,linear scanning voltammetry?LSV?and potentiostatic chronoamperometry were used to study the corrosion behavior of aluminum foil by the electrolyte and the effect of LiBOB salt on the corrosion of aluminum foil.X-ray photoelectron spectroscopy?XPS?and scanning electron microscope?SEM?were used to characterize the aluminum foil.It is found that the corrosion of aluminum foil at 45?is more serious than that at room temperature.This is because the aluminum foil reacts with the electrolyte to generate irregular and loose AlF₃material which has no protective effect on aluminum foil under the action of electrochemistry,resulting in the continuous consumption of aluminum metal and serious corrosion of aluminum foil.The calculation of density functional theory?DFT?also proves the existence of AlF₃ in corrosion products.Adding LiBOB into LiFSI-based electrolyte can change the interface reaction between aluminum foil and LiFSI-based electrolyte,and form a solid passivation film on the surface of aluminum foil,which is strong and protective,and the main components are B₂O₃ and LiF.?3?The optimum ratio of LiFSI,LiBOB and carbonate in the electrolyte was determined to keep good compatibility with aluminum foil and LiFePO₄ cathode at 45?.The optimal proportion of the electrolyte was determined by combining the basic physical and chemical properties of the electrolyte with the cycle performance and rate performance of the battery,and the simplex method.The composition of the electrolyte was LiFSI_0.53-LiBOB_0.35-EC/DEC/EMC?1.3:1.5:1.5,volume ratio?.The capacity of Li/LiFePO₄ half-cell is still 143.1mAh/g after 100 charges and discharges at 0.5 C rate,and the capacity retention rate is 94.9%.At last,a simple model for rapid evaluation of electrolyte is established.It provides a new idea for the evaluation of electrolyte in industry.