Preparation And Modification Of LiNi_0.5Mn_1.5O₄ Cathode Materials For 5 V Lithium-Ion Battery

In order to improve the cycling stability of LiNi_0.5Mn_1.5O₄?LNMO? cathode materials at elevated temperature, this study will focus on the preparation and surface modification of LNMO. The LNMO cathode material is prepared by Sol-Gel method, and the influence of diffrent coatings on structure, morphology and electrochemical performance of material is systematically investigated for LNMO. The crystal structure, surface morphology and electrochemical properties of the synthesized cathode materials have been characterized by scanning electron microscopy?SEM?, X-ray diffraction?XRD?, Fourier Transform Infrared Spectroscopy?FTIR?, thermogravimetry–differential thermal analysis?TG-DTA?,charge-discharge test, cyclic voltammetry?CV? and electrochemical impedance spectroscopy?EIS?.The LNMO cathode material was prepared by Sol-Gel method. The influence of different calcination time and chelating agent on the crystal structure, surface morphology and electrochemical performance of material is systematically investigated for LNMO. Prolonging holding time results in the increasing of dispersibility, the decreasing distribution range of particle size, the enhancement in crystallinity. The selection of chelating agent can give rise to the differences in the crystal structure, surface morphology and electrochemical performance of LNMO material. The product prepared by C₂H₄O₃ has smaller particle size,higher crystallinity and better cycling stability. The results show that the material prepared by C₂H₄O₃ as chelating agent, and calcinated at 850°C in air for 10 h has higher crystallinity and delivers larger initial discharge capacity. The LNMO electrode delivers an initial discharge capacity of 134.6 mAh·g^-1 at 1C rate, and its capacity retention reaches to 79.35% after 200 cycles. After analyzing the reason for capacity fading, the study will focus on the modification for the material with small particle.Al?NO₃?₃·5H₂O is used as the raw material to synthesize Al₂O₃-coated spinel LNMO material via a novel carbamide-assistant hydrothermal process. The effect of Al₂O₃ amount on the crystal structure, surface morphology and electrochemical performance of material issystematically investigated for LNMO. Compared with pristine sample, the coated ones show no change on crystal structure as well as microstructure. The capacity retentions delivered by the coated samples are enhanced remarkably compared to that of the pristine one, especially at elevated-temperature. It is proved that the 1% Al₂O₃-coated sample?the mass ratio of Al₂O₃ to LNMO? has not only improved capacity retention but acceptable initial capacity. The 1%Al₂O₃-coated LNMO electrode delivers an initial discharge capacity of 131.9 mAh·g^-1 at 1C rate, and the capacity retention reaches to 86.09% after 200 cycles at room-temperaturewith.At elevated temperature even at 55 ?, its capacity retention is 59.96% after 50 cycles.Cr₂O₃ was applied to modify the surface of LNMO cathode material via a novel carbamide-assistant hydrothermal process. The effect of Cr₂O₃ amount on physicochemical property and electrochemical performance of material is systematically investigated for LNMO. After coating with 0.75% Cr₂O₃, the initial specific discharge capacities decrease to133 mAh·g^-1 at 1C rate. Despite an increasing charge transfer resistance for the Cr₂O₃ coating,a better cycling ability have been obtained, especially at elevated temperature. Compared with the bare LNMO material, capacity retention of the 0.75% Cr₂O₃ coated sample at 55 ?increases from 17.65% to 59.68% after 50 cycles. In result, Cr₂O₃ is beneficial to improving eletrochemical performance of LNMO cathode material.The ZnO-coated LNMO powders with excellent electrochemical cyclability and structural stability were synthesized via a novel carbamide-assistant hydrothermal process.The electrochemical performance and structural stability of ZnO-coated LNMO electrodes at elevated temperature has been studied as function of the level of ZnO coating. The 1%ZnO-coated LNMO electrode delivers an initial discharge capacity of 132.3 mAh·g^-1 at 1C rate with excellent cycle ability at elevated temperature even at 55 ?. Meanwhile, its capacity retention at 55 ? is 59.96% after 50 cycles. The reason for the excellent cycling performance of ZnO-coated LNMO electrode is largely attributed to ZnO playing an important role to cut off the contact between the cathode material and electrolyte?...