Development And Application Of Electrolyte For Hard Carbon Electrode Of Sodium Ion Battery

With the further development of new energy vehicles,the price of lithium resources has increased year by year and the uneven distribution of lithium resources has become a key issue limiting the further development of lithium ion batteries.Sodium ion batteries have become a new type of energy storage secondary batteries.Research hotspots.Sodium-ion batteries have similar physical and chemical properties as lithium-ion batteries,but experiments have shown that the results obtained by completely using lithium-ion battery materials in sodium-ion batteries are not good.The current research focus of sodium-ion batteries is mainly on finding high-performance batteries Materials,sodium ion batteries have always had a problem of lacking a reliable negative electrode.HC（Hard Carbon）materials are more researched negative electrodes of sodium ion batteries in recent years,but as an energy storage battery,poor rate performance and cycle Performance restricts the application of HC materials in sodium ion batteries.These two problems boil down to an interface problem.In this paper,by optimizing the electrolyte composition of the sodium ion battery,we will find an electrolyte that highly matches the hard carbon electrode and improve the electrochemical performance of the hard carbon electrode in the sodium ion battery.The main research contents are as follows.Seven kinds of carbonate electrolytes were respectively configured using NaPF₆ and NaClO₄ as electrolyte salts,and seven kinds of electrolytes were used in sodium ion batteries respectively.The charging and discharging of seven kinds of electrolytes,cycle performance,and rate performance tests were carried out.It was found that sodium ion batteries with carbonate-based electrolytes generally have problems such as unstable cycling performance and low rate performance.After characterizing the pole piece,it was found that the surface of the pole piece after circulation had formed an SEI film compared to the original pole piece.The specific composition of SEI film was characterized by XPS test.The EIS test results show that as the cycle progresses,the interface impedance shows a trend of increasing first and then decreasing.This shows that the SEI film formed in the ether electrolyte is not in a stable form once formed.It went through a process of continuous growth,fragmentation,and stability.Three kinds of ether electrolytes are configured,namely 1M NaPF₆/DME,1M NaPF₆/Diglyme and 1M NaPF₆/Tegdme.The conductivity of the three ether electrolytes shows a decreasing trend.Chemical tests,the test results show that sodium ion batteries using ether electrolytes are far better in cycle performance and rate performance than batteries using carbonate electrolytes,in which batteries with 1M NaPF₆/DME as the electrolyte,The reversible capacity of the current density of 30mA g^-1is 235 mAh g^-1.At a current density of1000 mA g^-1,the capacity is 180 mAh g^-1.After 50 cycles,the capacity is 220.65 mAh g^-1,and the charge and discharge efficiency is stable,Above 99.9%,after EIS,scanning electron microscope and XPS tests,it has been shown that the ether electrolyte will form a relatively stable SEI film at the interface of the hard carbon material and the electrolyte more quickly,which is conducive to Na⁺transmission,making sodium ion batteries Has superior cycle performance and rate performance.