Study On The Electrolyte Additives On The Electrochemical Performance Of High Nickel NCM811

With the continuous expansion of lithium-ion battery applications,people put forward higher requirements for its energy and density.A material of LiNi_0.8Co_0.1Mn_0.1O₂（NCM811）with high capacity and high energy density electrolyte system is one of the most promising materials for lithium ion battery applications.But cation mixing occurs easily during the deintercalation of lithium,which leads to its unstable structure and reduces the cycling performance and rate performance of the battery.The intense electrochemical reaction between the electrolyte and the electrode is one of the reasons for the unstable structure of the material.The performance of NCM811/Li batteriy is effectively improved by introducing additives into the NCM811 electrolyte systems.In this paper,lithium bis（oxalato）borate（LiBOB）,lithium diflfluoro（oxalate）borate（LiODFB）and tri（trimethylsilyl）borate（TMSB）are used as additives to modificate the solid-electrolyte-interface,which are add to common commercial electrolyte systems（1.0 mol L^-11 LiPF₆-EC/DEC（STD））to prepare electrolytes suitable for LNCM811/Li battery systems.Effects of STD,LiBOB and LiODFB as additives on electrolyte properties,electrode interface reactions,and battery electrochemical properties are studied,and preliminary explore the mechanism with action of these three additives on the formation of solid interface film（SEI）.The contents and conclusions of the study are as follows:（1）The effects of STD,LiBOB and LiODFB electrolyte systems on the electrochemical performance of NCM811/Li battery are investigated,respectively.The results show that the electrochemical performance of battery with 2 wt.%LiBOB and 2 wt.%LiODFB electrolyte systems are better than that with STD,0.5 wt.%,1 wt.%,3 wt.%LiBOB and STD,0.5 wt.%,1 wt.%,3 wt.%LiODFB electrolyte systems.Compared with STD,at 0.2 C rate,the capacity retention rate of LNCM811/Li battery with 2 wt.%LiBOB and 2 wt.%LiODFB electrolyte systems are increase by 9.8%and 34.5%after 50 cycles,respectively.At 0.5 C rate,the discharge specific capacity is increase by 12.8%and 26.7%,respectively.At 4 C rate,the discharge specific capacity is increase by 16.7%and 43%,respectively.（2）The effects of STD and TMSB electrolyte systems on the electrochemical performance of LNCM811/Li battery is studied,respectively.The results show that the electrochemical performance of 0.5 wt.%TMSB electrolyte systems are better than that of STD,1 wt.%,2 wt.%TMSB electrolyte systems.Compared with STD,after 50 cycles at 0.2C rate,the specific discharge capacity of the 0.5 wt.%TMSB electrolyte systems increased by17.2 mAh g^-1.After 100 cycles at a rate of 2 C,the specific discharge capacity of the 0.5 wt.%TMSB electrolyte system has more than doubled.At 4 C rate,the specific discharge capacity of 0.5 wt.%TMSB electrolyte system is increased by 38.5 mAh g^-1.In addition,at 55℃,the cycle performance of 0.5 wt.%TMSB electrolyte system is more stable than that of STD.To sum up,because the LiBOB,LiODFB and TMSB additives are preferentially oxidized than other electrolyte components,a protective film can be formed on the surface of the NCM811 electrode,which inhibit the decomposition of the electrolyte and protect the structure of the cathode material.Moreover,the addition of additives also improve the cation mixing of the surface structure of the NCM811 cathode material,and improve the cycling performance and rate performance of NCM811/Li battery,which are expected to promote the commercial application of the cathode battery systems.