Research On The Low Temperature Performance Of NCM811 Material Electrolyte And The Modification Of NCM523 Material Cycle Performance

In the highly developed society of science and technology,people's daily life and work can not be separated from electronic products.Due to the advantages of low self-discharge and high energy density,Li-ion batteries play a leading role in the electronic products market.However,so far,the comprehensive performance of the lithium-ion battery can still not fully meet the needs of the application,mainly as follows:?1?The application range of lithium-ion battery electrolyte is narrow,especially at low temperature,the discharge capacity of lithium-ion battery is low or even unable to discharge,which seriously restricts the application range of lithium-ion battery;?2?The capacity and cycle performance of electrode materials for lithium-ion batteries are still difficult to meet the application requirements of high-power batteries.Therefore,in view of the problems mentioned above,the following three aspects of work on ternary positive materials are carried out in this paper:?1?The electrolyte of NCM811 material was modified by adding carboxylic acid ester BA?butyl acrylate?to the basic electrolyte.The results show that BA can improve the conductivity of the electrolyte and reduce its viscosity,thus improving the low-temperature discharge capacity of the battery.The discharge specific capacity of the battery was 91.50 mAh/g at a low temperature of-40 ?.Added BA can improve the low temperature performance of the battery.?2?The electrolytes with different BA contents were studied,modified reagent EC?ethyl carbonate?was added.The test results show that EC can improve the conductivity,discharge capacity at low temperature and cycle stability of the battery.The ionic conductivity of the electrolyte is 0.575 mS/cm at-40 ?,and the specific discharge capacity of the battery is 108.94 mAh/g,which reaches 65%of the discharge capacity at room temperature.The cell cycle capacity retention rate increased to 87.95%at room temperature of 25 ?.According to the analysis,EC can form a CEI film on the surface of the electrode to improve the low temperature performance and cycle stability of the battery.?3?The electrolyte containing BA16%+EC10%was used as a research object,and the modification reagent LiBF4 was added.The test results showed that the viscosity of the electrolyte was lowered,the conductivity was improved,and the low temperature performance of the battery was improved.The discharge specific capacity of the battery at-40? was 119.26 mAh/g.The results show that LiBF₄ can precipitate LiF on the surface of the electrode,protect the electrode,reduce the contact between the electrode and the electrolyte,prevent the electrolyte from reacting with the active material,and improve the transmission efficiency of lithium ions and reduce the impedance.Improve the low temperature performance of the battery.?4?NCM523 is coated with organic carbon used economical bagasse and starch.The results show that the surface of LiNi_0.5Co_0.2Mn_0.3O₂ coated with organic carbon does not change the surface morphology and crystal structure,but greatly improves the conductivity,rate and cycle performance of LiNi_0.5Co_0.2Mn_0.3O₂.The initial discharge specific capacity of the LiNi_0.5Co_0.2Mn_0.3O₂ material lithium ion battery without carbon coating was 147.8 mAh/g.After 2%starch and bagasse coated,the specific discharge capacity increased to 152.4 mAh/g and 153.3 mAh/g.A suitable coating amount can make the coated carbon layer more uniform to achieve better electrochemical performance.Reasonable organic carbon coated technology is an effective method to improve the electrochemical performance of LiNi_0.5Co_0.2Mn_0.3O₂based materials.