The Effects Of Electrolytes And Their Additives On The Electrochemical Performances Of LiNi_0.4Co_0.2Mn_0.4O₂ As Positive Electrode Material

Lithium-ion battery has attracted considerable attention because of its high working voltage,large specific energy,long service life,as well as the advantage of environmentally friendly.Lithium-ion battery was served as the crucial component for portable consumer electronics during the last two decades.To date,these batteries are being considered as the most promising energy storage system for electric vehicles?EV?and hybrid electric vehicles?HEV?application.The electrolyte affects the electrochemical performances and the safety performances of the lithium-ion battery to a large extent.LiNi_0.4Co_0.2Mn_0.4O₂ has the advantages of high working voltages,high specific discharge capacity,stable plateau,and so on,which attract people's extensively attention,and it is used as a cathode material of lithium-ion secondary batteries.This study investigated the effects of different electrolyte,different flame retardant additives of TMP and TTFP on the electrochemical performances?charge/discharge performances,cycle performances,rate capability and reversibility?of LiNi_0.4Co_0.2Mn_0.4O₂positive material by means of SEM,galvanostatic charge/discharge methods,cyclic voltammograms,and AC impedance spectroscopy.The first discharge specific capacity of LiNi_0.4Co_0.2Mn_0.4O₂ material in 1 mol/L LiPF₆-EC/DMC/DEC+1.5%VC electrolyte can reach 164.54 mAh/g,148.03 mAh/g and135.11 mAh/g,respectively,when the discharge ratio is 0.2 C,0.5 C and 1 C,and the capacity retention remains above 92%.after 50 times.Ac impedance and cyclic voltammograms data show that the LiNi_0.4Co_0.2Mn_0.4O₂ material in the electrolyte of 1mol/L LiPF₆-EC/DMC/DEC+1.5%VC displays better charge transfer activity and elevtrochemical reversiblility than that in the other three kinds of electrolyte.Through the study of the effects of the flame retardant additives of trimethyl phosphate?TMP?and three?2,2,2-three fluoroethyl?phosphate?TTFP?on the electrochemical performances of the LiNi_0.4Co_0.2Mn_0.4O₂ positive material,it can be found that the capacity fading of the battery will be speed up and the electrochemical reversibility will be decreased with the increase of the additive content of TMP and TTFP.However,the cycle performances of the battery will be impoved with the increase of the TTFP,and the capacity retention ratio can be maintained at 88.80%after recycling for 100 times with 10%TTFP in the electrolyte.