Effect Of Ions Doping On Morphology And Electrochemical Performance Of LiNi_0.5Mn_1.5O₄

Spinel LiNi_0.5Mn_1.5O₄ cathode material is considered to be one of the most promising cathode materials for power lithium-ion batteries due to the advantages of high working voltage,high energy density,and good rate performance.However,the severe capacity attenuation has seriously limited its practical application.Ions doping is considered to be one of the most effective modification methods.Therefore,a carbonate precursor was prepared by co-precipitation-hydrothermal method,which was mixed with lithium source and then calcinated at high temperature to synthesize LiNi_0.5Mn_1.5O₄ material.Ethyl silicate and butyl titanate were used as Si source and Ti source,respectively.The glacial acetic acid assisted sol-gel method was used to achieve doping.The effects of different doping amounts of Si and Ti on the structure,morphology,electrochemical properties and surface interface of LiNi_0.5Mn_1.5O₄ materials were studied.The effects of different Si doping contents on the structure,morphology,electrochemical performance and surface interface of LiNi_0.5Mn_1.5O₄ materials were investigated.The results show that Si doping can inhibit the formation of Li_xNi_1-xO impurity,whereas excessive Si doping results in the appearance of Li₂SiO₃ secondary phase.Although Si doping does not change the particle morphology,it can reduce the particle size and improve the particle distribution uniformity.Appropriate Si doping amount can obviously improve the rate and cycle performances of material.Among them,LNMO-Si0.06 sample with Si doping amount of 6%shows a discharge specific capacity of132.1 m Ah g^-1 at 10 C rate,and a capacity retention rate of 91.5%after 200 cycles at 1C and 25°C,and 86.8%after 100 cycles at 55°C.XPS and SEM analysis results of cycled electrodes show that proper Si doping can effectively reduce electrolyte decomposition and other side reactions,resulting in thinner CEI/SEI layer on the surfaces of cathode and anode,which is beneficial to the electrochemical performance of material.The effects of different Ti doping contents on the structure,morphology,electrochemical performance and surface interface of LiNi_0.5Mn_1.5O₄ materials were systematically studied.The results show that Ti doping can also inhibit the formation of Li_xNi_1-xO impurity phase,and excessive Ti doping results in the appearance of Li₂TiO₃secondary phase.Although Ti doping can not change the particle morphology,the particle size gradually increases with the increase of Ti doping amounts.LNMO-T0.03 material doped with 3%Ti shows higher phase purity,moderate particle size,and uniform particle size distribution,thus leading to its optimal electrochemical performance.The discharge specific capacity at 10 C rate can reach 127.3 m Ah g^-1,and capacity retention rate can reach91.7%after 200 cycles at 1 C and 25°C,and 87.2%after 100 cycles at 55°C.Proper Ti doping amount can effectively alleviate electrolyte decomposition and other side reactions,thereby forming a SEI/CEI layer on the anode/cathode surface favorable to electrochemical performance.