The Research Of Concentrated Electrolyte For Lithium Batteries Based On LiODFB And LiFSI

Lithium salt is a key factor affecting the electrolyte and electrode performance of lithium batteries.The development of a new type of lithium salt that satisfies its stability,high solubility in organic solvents,high ionic conductivity,ease of preparation,and non-toxic environmental protection,is of vital importance for prolonging the service life of lithium batteries and increasing the specific charge-discharge capacity.Lithium oxalate difluoroborate?LiODFB?and bisfluorosulfonyl imide?LiFSI?have many advantages,such as good electrochemical performance,low and high temperature performance,high decomposition temperature,high decomposition potential,and safety protection performance.The salt emerged as the electrolyte lithium salt that is the most promising alternative to commercial lithium hexafluorophosphate?LiPF₆?.At the same time,the concentration of lithium salt also directly affects the performance of lithium batteries.High-concentration Lithium-ion Lithium batteries can avoid the formation of lithium dendrites by providing sufficient lithium ions during the cycle,providing a new research idea for the development of lithium metal secondary batteries.In this paper,novel high-concentration electrolyte systems,4M LiODFB-DME and4M LiODFB-Li FSI/DEM,were proposed using the advantages of high-concentration electrolytes.The 4M Li ODFB-DME electrolyte was used for the first time on a lithium secondary battery,and a commercial LiPF₆ electrolyte was used as a comparative experiment to study the compatibility between the lithium metal negative electrode and the LiFePO₄ positive electrode,including improvement of the electrochemical performance of the positive electrode at room temperature and high temperature.Then we discussed the application of mixed lithium salt LiODFB-LiFSI in inhibiting corrosion of aluminum current collector and the performance of LiFePO₄ batteries.Through the assembly of Li/Cu,Li/Li/,Li/Al and Li/LiFePO₄ button batteries,electrochemical performance characterization methods such as constant current charge/discharge test,rate test,cyclic voltammetry,and impedance test were used to study new electrolytes.We used a scanning electron microscope?FEI Q600,USA?to characterize the lithium deposition morphology of the copper foil surface,the positive electrode material and the surface morphology of the aluminum foil.X-ray electron spectroscopy?K-Alpha,USA?was used to analyze the surface composition of the SEI membrane and analyze possible functional mechanisms.The thermal stability of the electrolyte was measured using a thermogravimetric analyzer?TGA/DSC3+,China?to further illustrate the difference in the electrochemical performance of the battery.Research indicates:?1?The new 4M LiODFB-DME electrolyte was used to deposit Li on the copper foil.After 1.5 hours,the surface showed a smooth solid particle morphology.No dendrites were observed.After 50 cycles,the Coulomb efficiency of Li/Cu button cell in4M LiODFB-DME electrolyte reaches 95.2%;Li/Li battery can be cycled at 1mA/cm²for more than 3000 hours;Li/Li FePO₄ battery shows at this high concentration electrolyte Good electrochemical performance can reach the same level as 1M LiPF₆electrolyte.At the same time,at a high temperature of 65°C,the Li/LiFePO₄ battery has a good capacity retention rate?92.5%?,which is much higher than the capacity retention rate of 1M LiPF₆ electrolyte?79.2%?.?2?Using 4M Li FSI+LiODFB-DME as an electrolyte,it was found that this high concentration of mixed electrolyte can effectively inhibit aluminum foil corrosion.The electrolyte and the positive electrode materials LiFePO₄ and Li?NiCoMn?O₂ have good compatibility and have excellent electrochemical reversibility.When Li/Li FePO₄battery was used,good electrochemical performance was exhibited.At a constant current density of 1C,the specific capacity retention rate was as high as 96.8%after 250cycles,and it also had a good rate performance.?3?The high concentration of LiODFB electrolyte is expected to replace LiPF₆electrolyte and promote the further development of lithium metal secondary batteries.High-concentration mixed lithium salt electrolyte can optimize single-salt electrolyte and improve LiFePO₄ based electrochemical performance.