Effect Of Different Electrolyte Systems On Electrochemical Properties Of LiNi_0.6Mn_0.2Co_0.2O₂ Electrode

In the next few years,the demand for lithium-ion batteries in the electric vehicle market,which is dominated by electric vehicles,and in the communications energy storage market will continue to increase.The performance requirements of lithium-ion power batteries generally focus on energy density,power density,cycle life and safety performance.It is generally believed that the capacity of lithium-ion batteries under high voltage will be improved to a certain extent,but the higher the voltage,the greater the safety risks.Finding a suitable ratio of conductive agent and electrolyte system is one of the economical and simple methods to solve the high voltage resistance of lithium-ion batteries.In this paper,the effects of conductive agent content,cutoff voltage and electrolyte system on the electrochemical performance of LiNi_0.6Mn_0.2Co_0.2O₂ electrode were studied step by means of constant current charge-discharge test,cyclic voltammetry,electrochemical impedance spectroscopy?EIS?,XRD and SEM.The electrode interface characteristics of LiNi_0.6Mn_0.2Co_0.2O₂ electrode for lithium-ion battery were studied by electrochemical impedance spectroscopy?EIS?.It is hoped that the cycle stability of the electrode would be further improved by changing the electrolyte system.The main contents and conclusions of this paper are as follows:?1?At room temperature,different contents of conductive agents were added to the electrode,which were 10%,20%,30%and 40%,respectively.The results of constant current charge-discharge test show that when the content of conductive agent in LiNi_0.6Mn_0.2Co_0.2O₂ electrode is 40%,The discharge specific capacity in the first cycle increased from 149.7 mAh g^-1 to 163.4 mAh g^-1,the Coulomb efficiency increased from79.5%to 83.7%in the first week,and the capacity retention increased from 81.4%to85.1%after 90 weeks of cycling.According to the results of EIS test,it is found that when the content of conductive agent in LiNi_0.6Mn_0.2Co_0.2O₂ electrode is 40%,a more stable SEI film can be formed on the electrode surface,which promotes the transmission process of lithium ion and improves the charge transfer ability.The cyclic stability of the electrode also increased.?2?The electrochemical tests were carried out at 4.3 V,4.5 V and 4.7 V for the battery.the results show that the higher the charging cutoff potential is,the greater the capacity loss of LiNi_0.6Mn_0.2Co_0.2O₂ electrode is.The lower the capacity retention rate.Although the Coulomb efficiency and capacity retention rate of the electrode at 4.3 V are the highest,the charge-discharge specific capacity is the lower.in contrast,the performance of the electrode at 4.5 V is more balanced.The discharge capacity in the first cycle can reach 176.4 mAh g^-1,and the capacity retention rate is still 91.6%after100 weeks of cycle..The results of EIS show that the SEI film formed on the surface of LiNi_0.6Mn_0.2Co_0.2O₂ electrode is stable,the charge transfer ability is good,and the electrochemical performance is balanced when the charge-discharge voltage range is3.4 to 4.5 V.?3?According to the experimental results of the first two chapters,the effect of electrolyte system on the electrochemical performance of LiNi_0.6Mn_0.2Co_0.2O₂ electrode was further investigated.The results of over-charge-discharge test show that the electrochemical performance of the electrode is better than 4.7 V at 4.5 V at high voltage.The first cycle Coulomb efficiency and capacity retention rate of the electrode can be improved by using HZ01-1 electrolyte at 4.5 V.the Coulomb efficiency in the first week is 82.6%,and the capacity retention rate is still 95.3%after 100 cycles.The increase of charge-discharge current density will lead to the decrease of reversible specific capacity of LiNi_0.6Mn_0.2Co_0.2O₂ electrode,but in HZ01-1 electrolyte,the attenuation of electrode capacity at high current is inhibited.The results of EIS fitting show that in HZ01-1 electrolyte,a more stable SEI film can be formed on the surface of the electrode,the charge transfer impedance is reduced,and the interface stability of the LiNi_0.6Mn_0.2Co_0.2O₂ electrode is better.