The Performance Study Of NaODFB And LiBOB As Additives For Lithium Ion Battery Electrolyte

Lithium ion battery as a new secondary power source has been attractedglobal attention and thus realized widely applications. However, the existingissues lie in the low initial coulombic efficiency and inferior high-temperatureperformance of graphite carbon as anode, as well as the instable capacity offull-charging LiCoO2cathode material.These influence the performance ofgraphite/LiCoO2battery. Use of electrolyte additives is one of the most effectivemethods for the improvement of electrolyte performance for Li-ion battery. Herewe have realized the improvement of the initial coulombic efficiency andmorderate-temperature cycle performance of graphite by adding NaODFB tocommon electrolyte. And we study its mechanism by EIS, SEM and FTIR test.Additionally, the heat-storage performance of Li/LiCoO2battery at morderatetemperature is obviously improvement by adding moderate amount of LiBOBadditive in electrolyte.The main results are listed as follows:1. The effect of NaODFB additive on cathode and anode and commonelectrolyte (1)The electrochemical window and conductivity of common electrolyte ofLi-ion battery can be improvemed by adding appropriate NaODFB additive.(2)The reversible charge-discharge capacity of natural graphite material canbe significally improved by adding small amount of NaODFB additive tocommon electrolyte. When0.01mol/L NaODFB additive is added, the cyclingperformance of Li/graphite battery is optimal. At room temperature, thedischarge capacity is374mAh/g and capacity retention rate is99.4%after100thcharge-discharge cycle of Li/graphite battery at0.1C rate. When0.05mol/LNaODFB additive is added, the cycle performance of Li/graphite battery is bestat morderate temperature. The discharge capacity is358.6mAh/g and capacityretention rate is83.9%after50th charge-discharge cycle of Li/graphite battery at55℃. Additionally, the rate performance of Li/graphite battery can be improvedby adding NaODFB.These improvement of performance is attributed to theformation of SEI which is smooth and uniform and advantageous to the lithiumion migration in the surface of graphite.(3) The compatibility of the NaODFB added electrolyte with LiCoO2isquite good. The initial coulombicic efficiency, room temperature cycleperformance and rate cycle performance of LiCoO2materials have been slightlyenhanced without negative effect.(4) The compatibility of the NaODFB added electrolyte withLiCo1/3Ni1/3Mn1/3O2is not very good. The cycle performance and rateperformance of LiCo1/3Ni1/3Mn1/3O2is significally decreased with the increase of NaODFB additives.2. The effect of LiBOB as the additive on electrochemical performance ofelectrolyte and LiCoO2material(1) The moderate amount of LiBOB additive although slightly reduces theconductivity of the electrolyte, but it can increase the electrolyte electrochemicalwindow.(2) The heat-storage performance of Li/LiCoO2battery at high temperaturecan be improved by adding moderate amount of LiBOB additive in electrolyte.By adding0.01mol/L LiBOB additive in the electrolyte,the discharge capacityof Li/LiCoO2battery nearly keeps unchanged when the charged Li/LiCoO2battery is kept in a80degree oven for12hours, in contrast, the dischargecapacity of Li/LiCoO2battery without additive quickly reduced to31.83%ofthe initial capacity.