Synthesis And Modification Of LiNi_0.5Mn_1.5O₄Cathode Material For Lithium Ion Batteries

With the increasing demand of batteries for portable electronic devicesand electric vehicle industry as well as aerospace industry, the developmentof high energy cathode materials for lithium ion batteries is a critical researchproject. The5V cathode material LiNi_0.5Mn_1.5O₄has a charging anddischarging platform close to5V vs. Li, thus could provide a higher energydensity. Furthermore, it can also provide more possibility for using anodematerials with high charging and discharging platform, such as Li4Ti5O12.Therefore LiNi_0.5Mn_1.5O₄is a good choice for the new generation oflithium-ion battery.In this paper, a spray drying method was used to prepare the powderprecursor for LiNi_0.5Mn_1.5O₄materials, the obtained precursor were thencalcined at high temperature to get the final LiNi_0.5Mn_1.5O₄products. Thecalcination process was optimized. The best condition for preparing theLiNi_0.5Mn_1.5O₄is calcining the precursor material at900℃for12h. Severalmethods were used to characterize the LiNi_0.5Mn_1.5O₄material preparedunder the best condition. XRD and FT-IR data indicate that the product isspinel LiNi_0.5Mn_1.5O₄belonging to Fd-3m space group. SEM images showthat the shape of the product is octahedral with partical size of1μm. CVmeasurement demonstrated that three couples of redox peaks were observedon CV curve, the redox peaks around4.7V corresponding to the redoxreaction of Ni⁴⁺/Ni³⁺and Ni³⁺/Ni²⁺respectively, the redox peaks around4.0Vcorresponding to Mn⁴⁺/Mn3+. LiNi_0.5Mn_1.5O₄shows a good cycle stabilityunder room temperature（20℃） with its first specific capacity of125.1mAh/g at1C rate which maintains95.28%after100cycle. However, its rateperformance need to be improved, the capacity at10C was only80mAh/g.Modifications on LiNi_0.5Mn_1.5O₄cathode material were carried out tofurther improve its electrochemical performance.A coprecipitation methodwas used to prepare FePO₄/LiNi_0.5Mn_1.5O₄and a milling method was used toprepare LATP/LiNi_0.5Mn_1.5O₄.A coprecipitation method was used to coat FePO₄nanopaticals（with0wt%,1wt%,3wt%,5wt%FePO₄）. XRD patterns indicate the crystal structureof LiNi_0.5Mn_1.5O₄was not affected by the treatment process.. Electrochemicaltests show that only the sample coated by1wt%FePO₄has a betterperformance than LiNi_0.5Mn_1.5O₄on cycle stability under room temperaturewith first cycle specific capacity of122.2mAh/g at1C rate, which maintained98.20%after100cycle. At55℃, the samples coated with1wt%and3wt%FePO₄has a better cycling performance than LiNi_0.5Mn_1.5O₄with first cyclespecific capacity at1C rate of122.8mAh/g and121.3mAh/g respectively,which maintains97.72%and92.42%after100cycle.A milling method was used to prepare LATP/LiNi_0.5Mn_1.5O₄composite.firstly, an annealing method was used to prepare the LATP nanoparticlematerial which has a good lithium ion conductivity of3.64×10-4S/cm. ThenLATP/LiNi_0.5Mn_1.5O₄composites were prepared by ball milling the mixtureof LATP and LiNi_0.5Mn_1.5O₄. The samples with LATP content of0wt%,1wt%,3wt%,5wt%,repectively, were obtained. Electrochemicalmeasurement show that the addition of LATP content improve the cyclingstability of LiNi_0.5Mn_1.5O₄at room temperature. The sample with1wt%LATPhas a better performance than pristine LiNi_0.5Mn_1.5O₄on cycle stability underhigh temperature with specific capacity of its first cycle is119.6mAh/g at arate1C which maintains94.90%after100cycle. This sample also has abetter performance than LiNi_0.5Mn_1.5O₄on rate performance under roomtemperature with specific capacity98mAh/g,18mAh/g more than that ofLiNi_0.5Mn_1.5O₄which is80mAh/g.