Application Of Mixed Lithium Salts And Concentrated Salt Strategy At High Temperature Electrolyte

With the popularity of various portable electronic devices and new energy electric vehicles,lithium ion batteries have played an important role in people's daily lives.However,lithium hexafluorophosphate has poor thermal stability,prone to hydrolysis at high temperature and the elution of transition metal ions from the surface of the positive electrode material make it difficult for lithium ion batteries to exhibit excellent performance at high temperature.From the perspective of the lithium salt of the electrolyte,this paper comprehensively considers the performance characteristics of different lithium salts,selects the characteristic solvent system,and develops mixed lithium salts electrolytes and concentrated salts electrolyte,which could broaden the high-temperature working range of the lithium ion battery and make the battery maintain excellent cycle stability at high temperature.For mixed lithium salts electrolyte systems,we prepared LiDFOB/LiPF₆ electrolyte and LiFSI/LiDFOB electrolyte to match NMC811 cathode material and LiFePO₄ cathode material,respectively.This paper used constant current charge and discharge test,cycle performance test,scanning electron microscope and X-ray photoelectron spectroscopy analysis,etc.These methods were used to study the effect of mixed salts electrolytes on the performance of lithium ion batteries at high temperature.It can be seen from the experimental results that when the LiPF₆:LiDFOB molar ratio is 4:1,the stability of the electrolyte is greatly improved and the capacity retention rate of the NCM811/Li battery is89.00%after 100 cycles at 60?.When the LiFSI:LiDFOB molar ratio is 4:1,the polarization of LiFePO₄/Li battery is the smallest,and the cycle performance and rate performance are significantly better than conventional electrolyte at high temperature.For concentrated salt electrolyte system,different concentrations of LiPF₆ electrolytes were prepared to match the Ni-rich cathode materials,the electrochemical performance of NCM811/Li battery at high temperature had been studied.The experimental results show that the special solvent structure of the concentrated salt electrolyte can form a dense and stable SEI film on the surface of NCM811 materials at high temperature and have a widely electrochemical window.The capacity retention rate of NCM811/Li batteries using 3.0 M LiPF₆ electrolyte at high temperature is 33.81%higher than that of conventional electrolyte,which greatly improves the cycling stability of NCM811/Li battery under high temperature.