Modification Of Li₄Ti₅O₁₂ Anode Material And LiMn_1.5Ni_0.5O₄Cathode Material For Lithium-ion Batteries

Li4Ti5O12(LTO) with a zero strain characteristic is considered to be one of the mostpromising anode materials for lithium-ion batteries, but its defect of lower conductivitylimits its practical application greatly. This paper attempts to use Na+which is the samemain group with Li+to dope effectively the8a Li. The effect of doping on crystal structureand electrochemical properties of Li4Ti5O12material was explored. Doped sample showeda smaller particle size, particle size distribution and good morphology. Their capacity andelectronic conductivity have been improved significantly. The first discharge capacitiesunder0.1C charge-discharge rate of Li4-xNaxTi5O12(x=0,0.05,0.1,0.15,0.2) are200.5,207.5,183.5,179.8,184.8mAh·g-1, respectively. After80cycles, the discharge capacitiesunder2C charge-discharge rate are109.8,135.3,139.1,111.3,139.4mAh·g-1. Especiallythe modified material with doping level x=0.1has the best structure and electrochemicalproperties.LiMn1.5Ni0.5O4(LMNO) has become one of the most promising lithium ion batterycathode materials due to the high discharge voltage platform at4.7V and high theoreticalcapacity. The fact that LiMn1.5Ni0.5O4has a higher structural stability than that of LiMn2O4was verified theoretically by first-principles calculations. Modified research for less stablecycle and poor rate discharge performance issues were done. Mo6+doping, FePO4andLi3xLa2/3-xTiO3(LLTO) surface coating were used to modify LiMn1.5Ni0.5O4. The resultindicates that the electrochemical properties of modified materials have been improved,and the discharge capacity and cycle stability have also been significantly increased.Especially, LiMn1.4Ni0.55Mo0.05O4(c),3wt.%LLTO coated LiMn1.5Ni0.5O4and1wt.%FePO4coated LiMn1.5Ni0.5O4have the maximum discharge capacity of139.1,134.3and140.3mAh·g-1, at different discharge rates (0.1-2C). The corresponding capacity retentionrate are90.5%,94.1%and102.9%, respectively. These modified LiMn1.5Ni0.5O4materialsexhibit high electron conductivity, lithium ion diffusion coefficient and excellentelectrochemical performance.Condering the intercalation kinetics experiment that the effect of temperature onLiMn1.5Ni0.5O4material lithium, it can be seen that the charge transfer resistance of theelectrode material decreased with the temperature increasing gradually. At the same time,the diffusion coefficient of lithium ion (DLi) increases significantly. The lithium iondiffusion apparent activation energy EaD(EaD:87.86KJ·mol-1) is higher than thecharge-transfer apparent activation energy Ea(Ea:15.94kJ·mol-1), showing the chang oftemperature may affect lithium ion diffusion during the LiMn1.5Ni0.5O4electrode reactiongreatly, so raising the temperature is not conducive to the improvement of electrochemical performance.According to the study of electrochemical performance for LiMn1.5Ni0.5O4/Li4Ti5O12full battery system, it was found that a full battery cycle performance which usingFePO4-coated LiMn1.5Ni0.5O4for positive electrode and Na+doped modified Li4Ti5O12asnegative one is significantly better than the full battery with same negative one and pureLiMn1.5Ni0.5O4as positive one. After80cycles (0.1mA), LMNO/LNTO capacity retentionof before and after the modification are31.4%and98.2%, respectively.