Preparation Of LiNi_0.5Mn_1.5O₄ As Cathode Material For Li-ion Battery And Studies Of Its Electrochemical Performance

In recent years,with the continuous breakthrough of high-pressure electrolyte performance,the development and utilization prospect of Li Ni_0.5Mn_1.5O₄ is more optimistic.However,if we want to further improve the discharge capacity and power density of Li Ni_0.5Mn_1.5O₄ material,it is necessary to improve the transfer rate of Li⁺and electrons within the material and between the interfaces under the premise of guaranteeing the service life of the battery.The nanoscale Li Ni_0.5Mn_1.5O₄ material has a high specific surface area,which is favorable for increasing the contact interface between the electrode and the electrolyte,shortens the migration path of Li⁺and electrons,and improves the rate performance of the battery.However,excessive contact interface will accelerate the progress of corrosion reaction and shorten the service life of the battery.The nano-spherical structure formed by the agglomerating of nano-primary particles of Li Ni_0.5Mn_1.5O₄ material combines the dynamic advantages of the nano-structured unit and the high stability of the micro-sized particles,and exhibits excellent physical and chemical properties.In addition,the nanocrystalline Li Ni_0.5Mn_1.5O₄ has low crystallinity and low electrochemical activity,which has limited improvement in tap density and battery safety performance of the material.In this paper,the nano-structured Li Ni_0.5Mn_1.5O₄ material was successfully prepared by co-precipitation method,and compared with the materials prepared by the traditional solid-phase method,and the influence of the morphology of the material on its electrochemical performance was studied.According to the results of electrochemical tests,the first discharge specific c apacity of Li Ni_0.5Mn_1.5O₄ material with nano-micro structure at 0.25 C is 122.1 m Ah g^-1,and the discharge capacity at 10C rate is 51.9 m Ah g^-1 at 0.5 C.The capacity retention rate after 100 cycles of C-rate was 93.91%,which was better than that of Li Ni_0.5Mn_1.5O₄ prepared by the conventional solid-phase method.The reason is that the nano-microstructure can effectively relieve the erosion of the electrode material by the electrolyte,and can improve the material's cycling stability performance,its internal distribution of pore structure is conducive to electrolyte infiltration,can improve the material utilization efficiency and rate performance.In addition,the effect of the solvent system composition?ethanol/water mixture ratio?on the morphology,particle size,crystal shape,and electrochemical performance of the co-precipitation method was studied,and it was found that as the ratio of ethanol/water mixture increased.The nano-micro balling rate of the structure material is gradually reduced,but its primary particle size and its crystallization performance are gradually increased,and the electrochemical performance of the material is also improved.When the ethanol/water mixing ratio is 1,the discharge specific capacity of Li Ni_0.5Mn_1.5O₄ material prepared by co-precipitation method is128.3 m Ah g^-1 at 0.25 C,and the discharge capacity is 86.9 m Ah g^-1 at 10 C rate.The higher performance of nano-structured Li Ni_0.5Mn_1.5O₄ is attributed to its higher particle size and higher crystallinity primary p articles with higher electrochemical activity and more stable crystal structure.Based on the above conclusions,the electrochemical performance of the electrode material is not only related to its morphology structure,but also closely related to its primary particle size and crystallization properties.For this purpose,we made the primary particles of Li Ni_0.5Mn_1.5O₄ directly into the micron level and studied its effect on the electrochemical properties of the material.For the solid-phase preparation of micro-scale Li Ni_0.5Mn_1.5O₄ particles randomly aggregated,non-uniform particle size distribution,low crystallinity and other defects,in the process of high-temperature calcined graphite,as a dispersant and crystal growth aids,The Li Ni_0.5Mn_1.5O₄ material with micron-level truncated octahedral structure was successfully prepared.After testing,the initial discharge specific capacity was 131.2m Ah g^-1 at 0.5 C,the capacity retention rate was 92.31%after 0.5 C cycle for 300cycles,and the discharge cap acity was as high as 79.1 m Ah g^-1 at 0.5 C charge 60 C discharge.The Li Ni_0.5Mn_1.5O₄ material,which is superior to the microsphere structure composed of nanometer or submicron-sized primary particles,can be adopt due to the higher electrochemical activit y of its single-crystal particles and a more stable crystal structure.In addition,the prepared micro-scale truncated octahedral Li Ni_0.5Mn_1.5O₄material was used as a reference material to study the overall performance of the battery in different charge and discharge modes,and found that:a small current charging stage can improve the efficiency of the use of materials.In addition,it has also been found that battery capacity decay occurs mainly in the later stages of the cycle.Based on the charge-discharge curve and its corresponding impedance spectroscopy,it can be inferred that the capacity loss in the latter cycle is mainly due to the accumulation,consumption,or the closs active material of Li⁺in the active material.Due to structural changes,partially deactivated lithium no longer participate in charge-discharge reactions,which in turn leads to a continuous decline in battery capacity.